Final Report for Air Exchange Rate Analysis and Protocol

Final Report for Air Exchange Rate Analysis

and Protocol Development

Submitted to:

Air Force Center for Engineering and the Environment/AC Building 171 2261 Hughes Ave. Suite 155 Lackland AFB, TX 78236-9853

Prepared by:

Tetra Tech, Inc. 3746 Mt. Diablo Blvd., Suite 300 Lafayette, CA 94549 Tetra Tech, Inc. 301 Mentor Dr., Suite A Santa Barbara, CA 93110

February 2012

Tetra Tech, Inc. i

Table of Contents

1 INTRODUCTION...................................................................................................................1-1

2 SITE BACKGROUND INFORMATION ......................................................................................2-1

2.1 Site Background Information (Facility 1381, CCAFS) ................................................2-1

2.2 Site Background Information (Building 1416, former Kelly AFB) ...............................2-2

2.3 Site Background Information (Building 1130, Travis AFB) .........................................2-4

3 AIR EXCHANGE RATE STUDY FIELD INVESTIGATIONS ...........................................................3-1

3.1 Facility 1381, Cape Canaveral Air Force Station .......................................................3-1

3.1.1 Building Description and Indoor Volume Estimates .....................................3-1

3.1.2 Experimental Design ...................................................................................3-4

3.1.2.1 SF6 Tracer Gas Release ............................................................3-5

3.1.2.2 Helium Gas Release ..................................................................3-7

3.1.3 CCAFS Experiment 1 Implementation .........................................................3-7

3.1.4 CCAFS Experiment 2 Implementation .........................................................3-8

3.1.5 CCAFS Meteorology ...................................................................................3-8

3.2 Building 1416, Former Kelly Air Force Base ..............................................................3-9

3.2.1 Building Description and Indoor Volume Estimates .....................................3-9

3.2.2 Experimental Design ................................................................................. 3-10

3.2.2.1 SF6 Tracer Gas Release .......................................................... 3-11

3.2.2.2 Helium Gas Release ................................................................ 3-12

3.2.3 Kelly AFB Implementation ......................................................................... 3-13

3.2.4 Kelly AFB Meteorology .............................................................................. 3-13

3.3 Building 1130, Travis Air Force Base ...................................................................... 3-13

3.3.1 Building Description and Indoor Volume Estimates ................................... 3-14

3.3.2 Experimental Design ................................................................................. 3-17

3.3.2.1 SF6 Tracer Gas Release .......................................................... 3-18

3.3.2.2 Helium Gas Release ................................................................ 3-18

3.3.3 Travis AFB Implementation ....................................................................... 3-18

Final Report for Air Exchange Rate Analysis and Protocol Development

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3.3.4 Travis AFB Meteorology ............................................................................ 3-19

3.3.5 Variances from the Travis AFB Work Plan ................................................. 3-19

4 EXPERIMENTAL RESULTS ...................................................................................................4-1

4.1 Facility 1381, Cape Canaveral Air Force Station (CCAFS) .......................................4-1

4.2 Building 1416, Former Kelly Air Force Base ..............................................................4-8


5 AIR EXCHANGE RATE ANALYSIS .........................................................................................5-1

5.1 Facility 1381, Cape Canaveral Air Force Station .......................................................5-2

5.1.1 Analysis of He Release Methods for AER Predictions .................................5-2

5.1.2 Analysis of SF6 Release Methods for AER Predictions ................................5-6

5.1.3 Comparison of Results ................................................................................5-9

5.2 Building 1416, Former Kelly Air Force Base ............................................................ 5-10

5.2.1 Analysis of He Release Methods for Air Exchange Rate Predictions ......... 5-11

5.2.2 Analysis of SF6 Release Methods for AER Predictions .............................. 5-12

5.2.3 Comparison of Results .............................................................................. 5-19

5.2.3.1 Least Squares Tests ................................................................ 5-19

5.2.3.2 SUMMA Tests .......................................................................... 5-21


5.3.1 Analysis of He Release Methods for AER Predictions ............................... 5-22

5.3.2 Analysis of SF6 Release Methods for AER Predictions .............................. 5-23

5.3.3 Comparison of Results .............................................................................. 5-25

6 DISCUSSION AND CONCLUSIONS .........................................................................................6-1

6.1 Cape Canaveral Air Force Station ............................................................................6-1

6.2 Former Kelly Air Force Base .....................................................................................6-1

6.3 Travis Air Force Base ...............................................................................................6-2

6.4 Issues and their Resolutions .....................................................................................6-2

6.4.1 Use of MGD-2002 Field Helium Detector .....................................................6-3

6.4.2 Loss of Helium From Tedlar Bags ...............................................................6-3

6.4.3 Helium Shortage and Cost ..........................................................................6-3

6.5 Cost Comparison ......................................................................................................6-4

6.6 Overall Conclusions ..................................................................................................6-6

6.7 Further Method Development/Validation ...................................................................6-7

7 REFERENCES .....................................................................................................................7-1


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APPENDIX A PROTOCOL FOR AIR EXCHANGE RATE CALCULATIONS

APPENDIX B THEORY AND SOLUTION TO LEAST SQUARES METHODS FOR INSTANTANEOUS

HE RELEASES

APPENDIX C MODIFIED ASTM METHODS USED DURING PROJECT TO COMPARE AGAINST

LEAST SQUARE RESULTS

APPENDIX D MATLAB CODE


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List of Figures

Figure 2-1 Location of Facility 1381, Tower 303, and the Skid Strip weather sensors. .......2-1

Figure 2-2 Photograph of Facility 1381 at CCAFS looking east-northeast. .........................2-2

Figure 2-3 Location of Building 1416 at former Kelly AFB ..................................................2-3

Figure 2-4 View of East Side of Building 1416 at former Kelly AFB, ...................................2-4

Figure 2-5 Location of Building 1130 at Travis AFB ...........................................................2-5

Figure 2-6 View of southeast side of Building 1130 at Travis AFB......................................2-6

Figure 3-1 Floor Plan of Facility 1381 at CCAFS illustrating components of the AER experiments. .....................................................................................................3-2

Figure 3-2 Photographs of cracks in closed doors and building walls that may affect the AER ............................................................................................................3-3

Figure 3-3 Photograph of Room 4 looking northeast. HVAC ducting panel is visible in the upper left. ....................................................................................................3-4

Figure 3-4 Photograph of the SF6 cylinder, two-stage pressure regulator, and flow controller. ..........................................................................................................3-6

Figure 3-5 Photographs of MIRAN SapphIRe portable gas analyzer. .................................3-6

Figure 3-6 Floor Plan of Building 1416 illustrating components of the AER experiment. .......................................................................................................3-9

Figure 3-7 View of manifolded SF6 tubing with blue gas cylinder and rotameters positioned in empty red fire extinguisher fastener. .......................................... 3-10

Figure 3-8 View of SF6 analyzer and two collocated SUMMA canisters on the desk in the shop. ......................................................................................................... 3-12

Figure 3-9 View of SF6 analyzer, hand-held He detector, SF6 cylinder with two-stage regulator connected to variable flow meter and manifold, and two collocated SUMMA canisters .......................................................................... 3-14

Figure 3-10 Floor Plan of Building 1130 schematically illustrating components of the AER experiment. ............................................................................................. 3-15

Figure 3-11 View of the equipment room looking northeast; the front doors are to the right................................................................................................................. 3-16

Figure 3-12 View of equipment room look east toward front door and view of generator room vents from outside of Building 1130 looking north. ................. 3-16

Figure 4-1 Plot of logged SF6 concentrations measured on-site at CCAFS Facility 1381 and laboratory sample results. .................................................................4-5

Figure 4-2 Plot of logged SF6 concentrations at CCAFS Facility 1381 measured on-site and outdoor ambient temperatures. ............................................................4-6


vi Tetra Tech, Inc.

Figure 4-3 Plot of logged SF6 concentrations measured on-site at CCAFS Facility 1381 and barometric pressure. .........................................................................4-7

Figure 4-4 Plot of logged SF6 concentrations measured on-site at CCAFS Facility 1381 and wind speed. .......................................................................................4-8

Figure 4-5 Plot of logged SF6 concentrations measured on-site at former Kelly AFB Building 1416 and laboratory sample results. .................................................. 4-11

Figure 4-6 Plot of logged SF6 concentrations measured on-site at former Kelly AFB Building 1416 and outdoor ambient temperatures. .......................................... 4-13

Figure 4-7 Plot of logged SF6 concentrations measured on-site at former Kelly AFB Building 1416 and barometric pressure. .......................................................... 4-14

Figure 4-8 Plot of logged SF6 concentrations measured on-site at former Kelly AFB Building 1416 and wind speed. ....................................................................... 4-15

Figure 4-9 Plot of logged SF6 concentrations measured on-site at Travis AFB Building 1130 and laboratory sample results. .................................................. 4-18

Figure 4-10 Relationship between field measurements and laboratory results ................... 4-20

Figure 4-11 Plot of logged SF6 concentrations measured on-site at Travis AFB Building 1130 and outdoor ambient temperatures. .......................................... 4-22

Figure 4-12 Plot of logged SF6 concentrations measured on-site at Travis AFB Building 1130 and barometric pressure. .......................................................... 4-23

Figure 4-13 Plot of logged SF6 concentrations measured on-site at Travis AFB Building 1130 and wind speed. ....................................................................... 4-24

Figure 5-1 Relationship between tests conducted for air exchange rate analysis at CCAFS.. ...........................................................................................................5-2

Figure 5-2 Results of AER calculations at CCAFS using SUMMA approach and instantaneous helium releases. .........................................................................5-5

Figure 5-3 Predicted AERs from continuous SF6 releases into Facility 1381 at CCAFS. ............................................................................................................5-8

Figure 5-4 AER calculated based on SUMMA data and continuous release of SF6. ...........5-9

Figure 5-5 Relationship between air exchange rate tests for former Kelly AFB. ............... 5-11

Figure 5-6 Plots of distributions of air exchange rates at Building 1416, former Kelly AFB................................................................................................................. 5-15

Figure 5-7 Results of AER calculations using SUMMA approach and instantaneous He releases, Building 1416, former Kelly AFB. ................................................ 5-16

Figure 5-8 Time series of SF6 concentrations and air exchange rates for former Kelly AFB................................................................................................................. 5-17

Figure 5-9 Air exchange rates calculated by continuous SF6 release using SUMMA canisters, former Kelly AFB. ............................................................................ 5-18

Figure 5-10 Relationship between air exchange rate tests for Building 1130 at Travis AFB................................................................................................................. 5-22

Figure 5-11 Predicted AERs and SF6 concentration in Building 1130 at Travis AFB. ......... 5-24

Figure 5-12 AERs calculated based on SUMMA data and continuous release of SF6, Building 1130, Travis AFB.. ............................................................................. 5-25

Figure 5-13 Summary of air exchange rate test results for Travis AFB. .............................. 5-26

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List of Tables

Table 1-1 Summary Table for Three Buildings Used in Protocol Development .................1-2

Table 3-1 Summary Table of Indoor Volumes for Facility 1381 .........................................3-3

Table 3-2 Summary of Field Activities at Facility 1381, CCAFS ........................................3-5

Table 3-3 Helium Mass Released into Facility 1381 ..........................................................3-7

Table 3-4 Summary Table of Indoor Volumes for Building 1416 ..................................... 3-10

Table 3-5 Summary of Field Activities at Building 1416, Former Kelly AFB ..................... 3-11

Table 3-6 Helium Mass Released into Building 1416 at former Kelly AFB ....................... 3-12

Table 3-7 Summary Table of Indoor Volumes for Building 1130 ..................................... 3-17

Table 3-8 Summary of Field Activities, Building 1130, Travis AFB .................................. 3-17

Table 3-9 Helium Mass Released into Building 1130 at Travis AFB ................................ 3-18

Table 4-1 Helium Concentrations in Facility 1381 at CCAFS ............................................4-2

Table 4-2 SF6 Concentrations in Facility 1381 at CCAFS ..................................................4-3

Table 4-3 Discrete SF6 Concentrations in Facility 1381 at CCAFS ....................................4-4

Table 4-4 Helium Concentrations in Building 1416 at Former Kelly AFB ...........................4-9

Table 4-5 SF6 Concentrations in Building 1416 at Former Kelly AFB ................................4-9

Table 4-6 Discrete SF6 Concentrations in Building 1416 at Former Kelly AFB ................ 4-10

Table 4-7 Helium Concentrations in Building 1130 at Travis AFB ................................... 4-16

Table 4-8 Helium Concentrations in Building 1130 at Travis AFB as Measured at Multiple Times After Sample Collection ........................................................... 4-16

Table 4-9 SF6 Concentrations in Building 1130, Travis AFB ........................................... 4-17

Table 4-10 Discrete SF6 Concentrations in Building 1130 at Travis AFB ........................... 4-17

Table 5-1 Air Exchange Rate Results for He Tests Conducted at CCAFS using Least-Squares Methods ....................................................................................5-3

Table 5-2 Estimated Percentile Ranges of AERs Calculated using Instantaneous He Releases into Facility 1381 at CCAFS ..............................................................5-4

Table 5-3 Averaged AERs Calculated by Finite Difference Methods for Continuous SF6 Releases into Facility 1381 at CCAFS ........................................................5-9

Table 5-4 Summary of AER Results for Facility 1381 at CCAFS ..................................... 5-10

Table 5-5 Air Exchange Rate Results for He Tests Conducted at Former Kelly AFB using Least-Squares Methods......................................................................... 5-12

Table 5-6 Least Squares Air Exchange Rate Results for He Tests: Monte Carlo Analysis at Building 1416, Former Kelly AFB .................................................. 5-14


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Table 5-7 Air Exchange Rates, Day-1, Over Interval Shown ............................................ 5-20

Table 5-8 Summary of Air Exchange Rate Analysis for Former Kelly AFB ...................... 5-21

Table 5-9 Air Exchange Rate Results for He Tests Conducted at Building 1130 at Travis AFB ...................................................................................................... 5-23

Table 5-10 Summary of Air Exchange Rate Analysis for Building 1130, Travis AFB ......... 5-26

Table 6-1 Helium vs. SF6 Method Cost Comparison .........................................................6-5

Table 6-2 Helium vs. SF6 Method Cost Comparison .........................................................6-6

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1 INTRODUCTION

Tetra Tech, Inc. (Tetra Tech) was contracted by the United States Air Force (USAF),

Air Force Center for Engineering and the Environment (AFCEE) to conduct

experiments designed to validate an innovative and cost-effective methodology for

estimating the air exchange rate (AER) of a building. The methodology was

employed during vapor intrusion investigations conducted at four Air Force

installations in 2008 (Tetra Tech 2009a, b, c, d). The objective of this investigation

was to quantitatively validate the methodology against a standard American Society

for Testing and Materials (ASTM) method (ASTM E741-00). Research for this study

was conducted at (1) Cape Canaveral Air Force Station (CCAFS), Florida; (2)

former Kelly Air Force Base (AFB), Texas; and (3) Travis AFB, California.

The AER of a building is critical in determining whether vapor intrusion (VI) may

result in unacceptable concentrations of volatiles in indoor air. A building with

relatively high rates of VI may never develop high indoor air concentrations, as

vapors will be continually flushed out of the building and replaced with ambient air.

Conversely, a building with very low AER could be subject to significant buildup of

indoor air concentrations, even with a relatively low concentration source or low rate

of intrusion. Commonly used methods of measuring AERs tend to be somewhat

cumbersome and costly; however, during previous vapor intrusion investigations

conducted at CCAFS, Travis AFB, former Kelly AFB, and Vandenberg AFB, a

relatively simple and cost-effective method for determining AERs was developed

and used (Tetra Tech 2009a, b, c, d). The method consists of instantaneously

releasing a finite quantity of helium (He) inside a building and then measuring the

helium concentration in the air over time as it dissipates. A formula is then applied to

the results to calculate the building AER.

The purpose of the recent experiments conducted at CCAFS, Kelly AFB, and Travis

AFB, and discussed in this report, was to conduct side by side comparisons of the He

release methodology with an existing published method, with the objective of

validating the He method as a tool for use at other sites. A modified version of

ASTM Method E741-00 was used to obtain an independent estimate of the AERs at

three buildings while simultaneously deploying the helium methodology. The ASTM

method used involves the release of a tracer gas into a building at a constant, known

rate, and then measuring equilibrium concentrations in the building air. A formula is

then applied to calculate the AER.

An additional method using a single data point from a SUMMA canister sample was

also developed to allow for further testing comparisons, and this method is


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introduced later when it is used. However, this method is not documented in detail

and is only meant to allow further comparison due to its simplicity of execution.

Buildings selected for this study were Facility 1381 at CCAFS, Building 1416 at

former Kelly AFB, and Building 1130 at Travis AFB. These buildings were selected

for this study based on a variety of criteria including size (1,000 to 5,000 square

feet), use (commercial/industrial), and availability/access for the study. See Table

1-1 for a summary of the three buildings.

Table 1-1 Summary Table for Three Buildings Used in Protocol Development

Building 1381 CCAFS

FL 1461 Former Kelly AFB

TX 1430 Travis AFB

CA

Stories 1 1 1

Foundation Slab-on-grade Slab-on-grade Slab-on-grade

Effective volume for AER analysis

27,640 ft3 14,200 ft

3 9,900 ft

3

Amount of He released 2.9 kg (HVAC on); 1.8 kg (HVAC off)

3.24 kg (HVAC on) 2.21 kg (HVAC cycled

on and off)

Definitions:

ft3 – cubic feet

He - helium HVAC – heating, ventilation, and air conditioning in – inches kg – kilogram


2 SITE BACKGROUND INFORMATION

2.1 Site Background Information (Facility 1381, CCAFS)

Facility 1381 is an unoccupied building located on Armory Road approximately 0.5

mile southwest of the intersection of Central Control Road and Armory Road. The

building is located in a relatively remote area of CCAFS approximately 1.5 miles

southeast of the industrial area (Figure 2-1). The building is located in an

approximately 400-foot diameter cleared area surrounded by forested lands (Figure

2-2).

Figure 2-1 Location of Facility 1381, Tower 303, and the Skid Strip weather sensors (AERial photograph source: USGS Seamless Data Warehouse).



Figure 2-2 Photograph of Facility 1381 at CCAFS looking east-northeast.

From its construction in 1958 through 1968, Facility 1381 was operated as the

Guidance Azimuth Transfer Building. From 1968 until 1977, it served as the In-

Place Precision Cleaning Lab for Pan Am World Services (Pan Am). During Pan

Am’s operations, the building housed acid and solvent dip tanks that were used for

cleaning metal components. Trichloroethene (TCE) was used on-site during cleaning

operations. Stainless steel acid dip tanks containing “Fozdip” acid, oil, and water

were used on site to clean galvanized steel pipes (Tetra Tech 2007). From 1977 to

approximately 2006, the Site served as an Ordnance Support Facility for the U.S.

Coast Guard. The U.S. Coast Guard moved out of Facility 1381 in 2006. The

building is currently listed for demolition.

2.2 Site Background Information (Building 1416, former Kelly AFB)

Building 1416 is located at the north end of former Kelly AFB, San Antonio, Texas,

on North Frank Luke Drive, near the intersection with Growdon Road (Figure 2-3).

Building 1416 is located immediately southeast of an aircraft hangar in an industrial-

use area.



Figure 2-3 Location of Building 1416 at former Kelly AFB (AERial photograph source: USGS Seamless Data Warehouse).

Building 1416 is a single story, slab-on-grade building with sheet metal siding, a

pitched roof, and roll-up doors on the east and west ends (Figure 2-4).



Figure 2-4 View of East Side of Building 1416 at former Kelly AFB, showing front roll-up doors and front door leading into entry (open).

Construction of Building 1416 was completed in 1944 and it was used for paint and

dope storage by the San Antonio Air Service Command. The building was moved

from its original location to the present site in 1956 and it became a reclamation

facility shop in 1963 (U.S. Army Corps of Engineers [USACE] 1997). Currently,

Building 1416 is vacant.

2.3 Site Background Information (Building 1130, Travis AFB)

Building 1130 is located on the southeast side of the Travis AFB runways, off

Perimeter Road near the intersection with Carson Road (Figure 2-5). Building 1130

is located in an open space area in the East Industrial Operable Unit. Building 1130

was used as an ultra-high frequency (UHF) radio transmitter building and is

currently vacant and slated for demolition.



Figure 2-5 Location of Building 1130 at Travis AFB (Draft Groundwater Sampling and Analysis Program 2006–2007 Annual Report, CH2M Hill, 2007).



Figure 2-6 View of southeast (front) side of Building 1130 at Travis AFB, showing the front double doors leading into the main building and a single door into the generator room on the right.


3 AIR EXCHANGE RATE STUDY FIELD INVESTIGATIONS

3.1 Facility 1381, Cape Canaveral Air Force Station

The AER experiments at CCAFS were conducted from 06 through 08 December

2010. Two experiments were conducted at Facility 1381, one with the heating,

ventilation, and air conditioning (HVAC) system on and one with it turned off. The

following sections detail the field activities.

3.1.1 Building Description and Indoor Volume Estimates

Facility 1381 is a single story slab-on-grade structure. The floor plan and

components of the AER experiments are shown on Figure 3-1. The structural

integrity of the back portion of the building has been compromised by cracks in the

wall, which appear to be widening.

Additionally, the sets of double doors located on the northwest (front) and southeast

(rear) sides of the building do not close completely (Figure 3-2). Room 5 is an

addition to Facility 1381 and there are cracks between the walls and roof of this

room and the rest of the building (Figure 3-2). All these features may lead to an

increase in the flow rate of air into and out of the building. A HVAC system located

in a room in the northern corner of the building services the entire building. The

HVAC room has no internal connections to the rest of the building (i.e., doors or

passageways), other than the HVAC ducting. While the intake for the HVAC system

is located within the building (i.e., design specifications are for 100% re-circulated

air), the HVAC room has vents on the front doors and a fanned vent on the side of

the building.



Figure 3-1 Floor Plan of Facility 1381 at CCAFS illustrating components of the AER experiments.



Figure 3-2 Photographs of cracks in closed doors and building walls that may affect the AER: (A) front double doors, (B) rear double doors, and (C) Seam between Room 5 and original building.

Detailed measurements were taken of each room to determine the indoor volume

(Table 3-1). Each room contained various amounts of furniture and equipment that

filled space, and the large center room contains HVAC ducting (Figure 3-3) and

concrete trenches containing sub-floor utility lines creating void spaces that may or

may not be considered part of the indoor volume of the room. Therefore, the volume

estimates presented in Table 3-1 are considered to have a margin of error of ±10

percent.

Table 3-1 Summary Table of Indoor Volumes for Facility 1381

Room Length

(in) Width

(in) Height

(in) Volume

(ft3)

Indoor Air Sample Aliquot

(ml)

HVAC Room 235 214 178 5,180 NA

Room 1 296 233 144 5,747 150

Room 2 233 183 144 3,553 100

Bathroom 66 53 118 239 NA

Room 3 159 125 140 1,610 50

Room 4 575 242 144 11,596 300

Room 5 215 189 128 3,010 75

Room 6 226 121 119 1,883 50

Total Volume without HVAC Room 27,639 725

Definitions:

in – inches ml – milliliters ft

3 – cubic feet

NA – Not applicable, no air samples collected from the bathroom or HVAC room

A B C



Figure 3-3 Photograph of Room 4 looking northeast. HVAC ducting panel is visible in the upper left.

3.1.2 Experimental Design

Two separate comparison experiments were conducted at Facility 1381, one on 07

December 2010 with the HVAC system on, and the second on 08 December 2010

with the HVAC system off. The objective of this approach was to run the experiment

under two different AERs and thereby provide a more robust comparison of the two

methods.

The AER in Facility 1381 was measured simultaneously using the helium release

methodology and the ASTM E741-00 method during both experiments (HVAC on

and HVAC off). Sulfur hexafluoride (SF6) was used as the tracer gas for the ASTM

method. A Thermo Scientific MIRAN SapphIRe portable gas analyzer calibrated for

SF6 was used on-site to measure and log SF6 concentrations throughout the

experiments. A Radiodetection MGD-2002 hand-held helium (He) meter was used to

take field measurements of He concentrations in air samples collected at pre-

determined intervals after release of the He. Samples for off-site laboratory analysis

were sent to Air Toxics, Ltd., (Air Toxics), located in Folsom, California. Air Toxics

is a Department of Defense (DoD) Environmental Laboratory Accreditation Program

(ELAP) certified analytical laboratory. ASTM method D-1946 was used for analysis

of He and an Air Toxics standard operating procedure (ATL Applications No. 8),

which uses gas chromatography with an electron capture detector (GC/ECD), was

used for analysis of SF6.

The following sections provide details of the field experiments and Table 3-2

summarizes the field activities conducted during the period of the experiments.



Table 3-2 Summary of Field Activities at Facility 1381, CCAFS

06 December 2010

Arrive at Facility 1381 and set up components of AER experiments

Upon arrival, HVAC system was on but not operating due to the moderate outside temperatures. The thermostat was adjusted to cause the HVAC system to start up and the blower fan to operate.

Steady flow of SF6 tracer gas into building initiated at 1603

Continuous logging of SF6 concentrations in Room 4 initiated at 1604

07 December 2010

SF6 analyzer found to have turned off at 0246; logging re-started at 1022 (SF6 release was not interrupted)

Helium from six 111-cf cylinders released into building at 1126

Indoor air samples for on-site field meter and off-site laboratory analysis of He collected over course of 8 hours

Discrete indoor air samples collected for off-site analysis of SF6 at 1156 and 1926

SF6 analyzer carried through building periodically to collect readings from each room

SUMMA canister deployed in Room 4 next to SF6 analyzer at 1226 to collect 4-hour time-integrated sample for He and SF6 analysis

Final He sample collected at 1926

HVAC turned off at 1945; first experiment completed

08 December 2010

Helium from four 111-cf cylinders released into building at 0820

Indoor air samples for on-site field meter and off-site laboratory analysis of He collected over course of 8 hours

Discrete indoor air samples collected for off-site analysis of SF6 at 0920 and 1620.


SUMMA canister deployed in Room 4 next to SF6 analyzer at 1020 to collect 4-hour time-integrated sample for He and SF6 analysis

Final He sample collected at 1620

Second experiment completed

Site cleaned up and restored to condition as found

3.1.2.1 SF6 Tracer Gas Release

The release of SF6 tracer gas into Facility 1381 for the ASTM method was started on

the afternoon of 06 December 2010 and continued for the duration of both

experiments. Beginning the SF6 release on 06 December allowed time for the gas to

reach equilibrium in the building prior to the start of the first experiment on the

morning of 07 December.

In accordance with ASTM Method E741-00, a pre-determined release rate was

selected based on the building volume and a rough estimate of the expected AER.

For this investigation, the tracer gas was a 2.0 percent mixture of SF6 with pure

nitrogen as the balance gas. The release was started at 1603 on 06 December 2010.

The arrangement for SF6 tracer gas release consisted of a 28-cubic-foot (cf) cylinder,

a two-stage pressure regulator that allowed the pressure to be decreased to

approximately 23 pounds per square inch (psi), and a flow meter (rotameter) that

ensured a constant flow rate of 200 milliliters per minute (ml/min), which equates to

4 ml/min of SF6 tracer gas (Figure 3-4). A series of four manifolded, 1/4-inch

diameter Nylaflow tubing lengths were attached to the flow meter and run to four

locations throughout the building to promote homogenization of the tracer gas

throughout (Figure 3-1). The system was checked for leaks using the MIRAN gas

analyzer (Figure 3-5).



Figure 3-4 Photograph of (A) the SF6 cylinder, (B) two-stage pressure regulator, and (C) flow controller (rotameter).

Figure 3-5 Photographs of MIRAN SapphIRe portable gas analyzer.

Throughout the experiments, the SF6 gas analyzer logged the SF6 concentration at

10-minute intervals in the center of Room 4 at the location shown on Figure 3-1, on a

free standing shelf, approximately 5 feet off the floor (Figure 3-5). The instrument

was set to continually monitor the SF6 concentration and to log the minimum

maximum, and average concentrations during each 10-minute interval. Periodically,

field personnel took the analyzer to each room to measure the SF6 concentrations in

the individual rooms. Due to a malfunction with the power supply to the MIRAN,

the instrument shut down several times during the study period, which resulted in

gaps in the logged SF6 data, although the release of SF6 continued uninterrupted.

A B C

A B



3.1.2.2 Helium Gas Release

The He source for Experiment 1 was six 111-cf cylinders of at least 99 percent pure

He, which were placed at the locations shown on Figure 3-1. Only four cylinders

were used for Experiment 2, because the HVAC system had been turned off for this

experiment, and the AER was therefore expected to be lower. For each release, the

valves were fully opened simultaneously by the field crew and the tanks allowed to

empty into the building. Each cylinder emptied in approximately 1 minute. The

cylinders were weighed before and after release to estimate the mass of helium

released (Table 3-3).

Table 3-3 Helium Mass Released into Facility 1381

Tank Start Weight

(kg) End Weight

(kg) Difference

(kg)

12/7/2010 - HVAC On

1 31.67 31.14 0.53

2 33.74 33.25 0.49

3 33.73 33.25 0.48

4 29.54 29.04 0.50

5 30.35 29.88 0.47

6 29.40 28.92 0.48

Total He Released (HVAC On): 2.94

12/8/2010 - HVAC Off

7 28.74 28.30 0.44

8 31.33 30.89 0.44

9 39.51 39.06 0.45

10 33.93 33.46 0.47

Total He Released (HVAC Off): 1.80

Definitions:

He – helium HVAC – heating, ventiliation, and air conditioning kg – kilogram

3.1.3 CCAFS Experiment 1 Implementation

The first experiment was conducted on 07 December 2010, with the HVAC system

on. The HVAC system blower was running constantly during Experiment 1. The He

was released into the building at 1126. Composite indoor air samples were collected

in Tedlar bags for He analysis at 15, 30, 60, 120, 180, 240, 360, and 480 minutes (8

hours) after the release. In addition, indoor air samples were collected in Tedlar bags

for SF6 analysis at 30 and 480 minutes after release of the He. All of the composite

samples were collected by drawing pre-determined volumes of indoor air from

rooms throughout the building into a 60-ml disposable syringe and expelling them

into a Tedlar bag. In order to obtain a sample that was representative of the entire

building space, the volume of each sample aliquot was proportional to the volume of

the room from which it was collected (Table 3-1).



Samples for He analysis were collected in duplicate. One sample was submitted to

Air Toxics for laboratory for analysis. The second sample was analyzed on-site using

the MGD-2002 helium meter. Due to malfunctions with the instrument, the on-site

He measurements taken at Facility 1381 are considered suspect. Further, as a result

of the instrument malfunction, the planned discrete measurements from the

individual rooms were not collected.

Concentrations of SF6 were continuously logged with the portable SF6 gas analyzer

and discrete measurements were collected in each room approximately once per

hour. In addition, a time integrated indoor air sample for SF6 and He analysis was

collected from Room 4 in a 6-liter SUMMA canister placed at the location shown in

Figure 3-1. The SUMMA canister was equipped with a flow controller calibrated to

fill it in 4 hours, and was filled from 1226 to 1626 (1 hour to 5 hours after the He

release. The SUMMA tests were experimental and are not part of the protocol

developed from this investigation (Appendix A).

3.1.4 CCAFS Experiment 2 Implementation

The second experiment was conducted on 08 December 2010 with the HVAC

system turned off. The system was turned off the previous evening in order to allow

the SF6 concentration to adjust to the lower air exchange rate in time for Experiment

2 (Table 3-2). The He was released into the building at 0820. Indoor air samples

were collected in Tedlar bags for He analysis at 15, 30, 60, 120, 180, 240, 360, and

480 minutes after the release. In addition, indoor air samples were collected in Tedlar

bags for SF6 analysis at 60 and 480 minutes after release of the He. All of the

samples were collected as described for Experiment 1. The time-integrated 4-hr

sample collected with the SUMMA canister was collected between 1020 and 1420 (2

hours to 6 hours after the He release).

3.1.5 CCAFS Meteorology

Meteorological data for the study period was obtained from the 45th

Weather

Squadron, which gathers weather data from a variety of locations across CCAFS.

Data obtained for this study were collected from the southeast end of the Skid Strip

(the runway), and Tower 303, located approximately 1 mile southeast and southwest,

respectively, of Facility 1381 (Figure 2-1). Data collected included wind speed and

direction, ambient air temperature, and barometric pressure (Skid Strip sensor only).

The Skid Strip sensors are located on a tower approximately 33 feet (10 meters)

above the ground surface, and measurements were logged every hour. The

temperature sensor at Tower 303 is positioned at 6 feet above the ground while the

wind sensors are positioned 12 feet above the ground. Measurements at Tower 303

were logged every 5 minutes.

Tower 303 is located in a small clearing in the woods, while the Skid Strip sensors

are located in a large cleared area, at the downwind end of the runway. The

differences in the amount of surrounding trees and the relative heights of the sensors

result in higher wind speeds at the Skid Strip as compared to Tower 303.

Temperatures at the two locations were relatively consistent.



3.2 Building 1416, Former Kelly Air Force Base

The AER experiment at former Kelly AFB was conducted from 22 through 23

March 2011. The experiment was conducted with the HVAC system turned on,

although the air vents in the shop area of the building did not appear to work. Air

flow was noted in the entry and classroom. The following sections detail the field

activities.


Building 1416 is an approximately 2,400-square-foot, single story slab-on-grade

structure. The building consists of five areas: an entry way room, class room, shop,

restroom, and paint room (Figure 3-6). The paint room has a vaulted ceiling, while

the remaining rooms have drop ceilings. The paint room and the shop have an

uncovered concrete floor, while the entry, classroom, and restroom have linoleum

floors. The roll-up door located on the east (front) side of the building does not close

completely and sunlight can be seen coming in through small cracks. As shown on

Figure 3-6, the front door and the double doors leading from the shop area into the

paint room were closed during the experiment. The Paint Room was excuded from

the experiment.

Figure 3-6 Floor Plan of Building 1416 illustrating components of the AER experiment.



Figure 3-7 View of manifolded SF6 tubing with blue gas cylinder and rotameters positioned in empty red fire extinguisher fastener.

Detailed measurements were taken of each room in order to assess the indoor

volume. Indoor volume estimates are presented in Table 3-4 and are considered to

have a margin of error of ±10 percent.

Table 3-4 Summary Table of Indoor Volumes for Building 1416

Room Length

(in) Width

(in) Height

(in) Volume

(ft3)


(ml)

Classroom 271 179 114 3,200 100

Entry 198 138 114 1,800 75

Shop various various various 8,190 300

Restroom 115 138 114 1,050 25

Total volume of classroom, entry way, shop and restroom 14,240 500

Definitions:

ft3 – cubic feet

in – inches ml – milliliters


The experiment conducted at Building 1416 at former Kelly AFB consisted of the

same design components as the experiments conducted at CCAFS (see Section



3.1.2), with the exception that only one experiment (with the HVAC system turned

on) was conducted. The following sections provide details of the former Kelly AFB

field experiments and Table 3-5 summarizes the field activities conducted during the

period of the experiment.

Table 3-5 Summary of Field Activities at Building 1416, Former Kelly AFB

22 March 2011

Arrive at Building 1416 and set up components of AER experiments

Upon arrival, HVAC system was on but not operating due to the moderate outside temperatures. The thermostat was adjusted to cause the HVAC system to start up and the blower fan to operate.


Continuous logging of SF6 concentrations in the Shop initiated at 1526

23 March 2011

Helium from six 111-cf cylinders released into building at 0625

Indoor air samples for on-site field meter and off-site laboratory analysis of He collected over course of eight hours



2 collocated SUMMA canisters deployed in Shop next to SF6 analyzer at 0655 to collect 3.5-hour and 9-hour time-integrated samples for He and SF6 analyses

Final He sample collected at 1425 (8 hours after He release)

SF6 gas turned off at 1655



The release of SF6 tracer gas into Building 1416 for the ASTM method was started

on the afternoon of 22 March 2011 and continued for the duration of the experiment

through 23 March 2011. Beginning the SF6 release on 22 March allowed time for the

gas to reach equilibrium prior to the start of the experiment.

The SF6 tracer gas was released in the same way as it was for Facility 1381 at

CCAFS with the exception of using a 4.0 percent mixture of SF6 rather than 2.0

percent (Figure 3-6 and Figure 3-7). The 4.0 percent mixture resulted in an SF6

release rate of 8 ml/min. The higher release rate was selected because the AER was

expected to be higher. The system was checked for leaks using the MIRAN gas

analyzer.


10-minute intervals in the center of the Shop at the location shown on Figure 3-6, on

a desk, approximately 4 feet off the floor (Figure 3-8). The instrument was set to

continually monitor the SF6 concentration and to log the minimum, maximum, and

average concentrations during each 10-minute interval. Periodically, field personnel

took the analyzer to each room to measure the SF6 concentrations in the individual

rooms. The instrument functioned properly without interruption for the entire

duration of the experiment.



Figure 3-8 View of SF6 analyzer (grey with black and purple probe) and two collocated SUMMA canisters on the desk in the shop.


The He source for the former Kelly AFB experiment was six 111-cf cylinders of at

least 99 percent pure He, which were placed at the locations shown on Figure 3-6.

The valves were fully opened simultaneously by the field crew and the tanks allowed

to empty into the building. The cylinders emptied in approximately 90 seconds. The

cylinders were weighed before and after release to estimate the mass of helium

released (Table 3-6).

Table 3-6 Helium Mass Released into Building 1416 at former Kelly AFB

Tank Start Weight

(kg) End Weight

(kg) Difference

(kg)

1 27.76 27.20 0.56

2 35.80 35.28 0.52

3 34.50 33.96 0.54

4 24.86 24.34 0.52

5 29.88 29.35 0.53

6 25.24 24.67 0.57

Total He Released: 3.24

Definitions:

He – helium HVAC – heating, ventiliation, and air conditioning kg – kilogram



3.2.3 Kelly AFB Implementation

The experiment was conducted on 23 March 2011, with the HVAC system on. The

He was released into the building at 0625. Composite indoor air samples were

collected in Tedlar bags for He analysis at 15, 30, 60, 90, 120, 180, 240, 360, and

480 minutes (8 hours) after the release. In addition, indoor air samples were collected

in Tedlar bags for SF6 analysis at 30 and 240 minutes after release of the He. All of

the composite samples were collected by drawing pre-determined volumes of indoor

air from rooms throughout the building into a 60-ml disposable syringe and expelling

them into a Tedlar bag. In order to obtain a sample that was representative of the

entire building space, the volume of each sample aliquot was proportional to the

volume of the room from which it was collected (Table 3-4).


Air Toxics for laboratory analysis. The second sample was analyzed on-site using the

MGD-2002 helium meter. It was determined during the study that the MGD-2002

instrument, designed as a sensitive leak detection instrument, does not function

correctly when ambient He concentrations are high (i.e., inside a building following

release of the He tracer gas). Therefore, the on-site, room-to-room He measurements

taken at 1416 were not included in the data set used for analysis for this experiment.

However, the integrated samples collected in Tedlar bags and measured using the

helium meter outside the building yielded usable results.


and discrete measurements were collected in each room approximately once per

hour. In addition, two time-integrated indoor air samples for SF6 and He analysis

were collected from the Shop in two collocated 6-liter SUMMA canisters placed at

the location shown in Figure 3-6. The SUMMA canisters were equipped with flow

controllers calibrated to fill in 3.5 and 12 hours; however, the 12-hour canister was

closed after 9 hours due to low ambient He concentrations as measured from

integrated samples collected in Tedlar bags. The canisters were filled from 0655 to

1025 and 1555 (0.5 to 4 hours and 0.5 to 9.5 hours after the He release. The

SUMMA tests were experimental and are not part of the protocol developed from

this investigation (Appendix A).

3.2.4 Kelly AFB Meteorology

Meteorological data for the study period was obtained from Lackland AFB Weather

Squadron (802 OSS/OSW). Data obtained for this study were collected from the

Lackland Airfield, approximately 0.5 miles west of Building 1416 (Figure 2-3). Data

collected included wind speed and direction, ambient air temperature, and barometric

pressure. Measurements were logged every minute.

3.3 Building 1130, Travis Air Force Base

The AER experiments at Travis AFB were conducted from 12 through 13 July 2011.

The experiment was conducted with the HVAC system turned on. Following

completion of the planned experiment and collection of the last He sample, the

ceiling vents to the outside were sealed in order to evaluate what effects this action

would have on the SF6 gas concentrations in the building.



Figure 3-9 View of SF6 analyzer (on table), hand-held He detector (on black box on cooler), SF6 cylinder with two-stage regulator connected to variable flow meter and manifold, and two collocated SUMMA canisters; Tedlar bags and sealed sampling syringes can be seen in the foreground on the clipboard.


Building 1130 is an approximately 1,250 ft2, single story, slab-on-grade structure.

The interior consists of one main room and a small storage area (Figure 3-10). A

generator room is located on the northeast side of the building. Photographs of

Building 1130 are presented as Figure 3-11 and Figure 3-12.



Figure 3-10 Floor Plan of Building 1130 schematically illustrating components of the AER experiment.



Figure 3-11 View of the equipment room looking northeast; the front doors are to the right (out of view).

Figure 3-12 View of equipment room look east toward front door (A) and view of generator room vents from outside of Building 1130 looking north.

The generator room was not included in the experiment and indoor volume

calculations. However, air was flowing from the generator room into the equipment

room through a utility trench connecting the two. This opening allowed significant

A B



flow of air into the equipment room from the generator room, which has open vents,

and to the outside via three celing vents in the equipment room (Figure 3-12). The

open vents of the generator room can be seen from the outside on Figure 3-12A. The

effects on the AER are discussed in Section 5.

Detailed measurements were taken of each room in order to assess the indoor

volume. Indoor volume estimates are presented in Table 3-7 and are considered to

have a margin of error of ±10 percent.

Table 3-7 Summary Table of Indoor Volumes for Building 1130

Room Length

(in) Width

(in) Height

(in) Volume

(ft3)


(ml)

Equipment Room various various 117 8,800 450

Storage Room 162 103 117 1,100 50

Total Volume of Equipment Room and Storage Room 9,900 500

Definitions:

ft3 – cubic feet

in – inches ml – milliliters


The experiment conducted at Building 1130 at Travis AFB consisted of the same

design components as the experiments conducted at CCAFS and former Kelly AFB

(see Sections 3.1.2 and 3.2.2). The following sections provide details of the Travis

AFB field experiments and Table 3-8 summarizes the field activities conducted

during the period of the experiment.

Table 3-8 Summary of Field Activities, Building 1130, Travis AFB

12 July 2011

Arrive at Building 1130 and set up components of AER experiments

Upon arrival, HVAC system was on and cycling on and off throughout the duration of the experiments


Continuous logging of SF6 concentrations in the Equipment Room initiated at 1605

13 July 2011

Helium from four 125-cf cylinders released into building at 0700

Indoor air samples for off-site laboratory analysis of He collected over course of 2 hours to be sent to laboratory via air

Measurements using on-site field meter recorded over course of 4.5 hours


SF6 analyzer carried through building twice to collect readings from each room

2 collocated SUMMA canisters deployed in Equipment Room next to SF6 analyzer at 0730 to collect 1.75-hour and 4-hour time-integrated samples for He and SF6 analyses

Final laboratory He sample collected at 0900 (2 hours after He release)

Final on-site He measurement taken at 1130

SF6 gas turned off at 1345





The release of SF6 tracer gas into Building 1130 for the ASTM method was started

on the afternoon of 12 July 2011 and continued for the duration of the experiment

through 13 July 2011. Beginning the SF6 release on 12 July allowed time for the gas

to reach equilibrium prior to the start of the experiment.

The SF6 tracer gas was released in the same way as it was for Building 1416 at

former Kelly AFB with the exception of using a flow rate of 100 ml/min. The 4.0

percent mixture resulted in an SF6 release rate of 4 ml/min. The low release rate was

selected because of the small volume of the building. The system was checked for

leaks using the MIRAN gas analyzer and soapy water.


10-minute intervals in the center of the Equipment Room at the location shown on

Figure 3-10, on a desk, with the intake suspended approximately 4 feet off the floor

to coincide vertically with the intakes of the collocated SUMMA canisters (Figure

3-11 and Figure 3-9). The instrument was set to continually monitor the SF6

concentration and to log the minimum, maximum, and average concentrations during

each 10-minute interval. Periodically, field personnel took the analyzer to each room

to measure the SF6 concentrations in the individual rooms. The instrument

functioned properly without interruption for the entire duration of the experiment.


The He source for the Travis AFB experiment were four 125-cf cylinders of at least

99 percent pure He, which were placed at the locations shown on Figure 3-10. The

valves were fully opened simultaneously by the field crew and the tanks were

allowed to empty into the building. The cylinders emptied in approximately 40

seconds. The cylinders were weighed before and after release to estimate the mass of

helium released (Table 3-9).

Table 3-9 Helium Mass Released into Building 1130 at Travis AFB

Tank Start Weight

(kg) End Weight

(kg) Difference

(kg)

1 33.97 33.39 0.58

2 35.82 35.25 0.56

3 36.88 36.35 0.54

4 28.86 28.34 0.53

Total He Released: 2.21

3.3.3 Travis AFB Implementation

The experiment was conducted on 13 July 2011. The HVAC system was and the

blower cycled on and off periodically. The He was released into the building at 0700.

Composite indoor air samples were collected in Tedlar bags for He analysis at 15,

30, 45, 60, 90, and 120 minutes after the release. In addition, indoor air samples were

collected in Tedlar bags for SF6 analysis at 30 and 120 minutes after release of the



He. All of the composite samples were collected by drawing pre-determined volumes

of indoor air from rooms throughout the building into a 60-ml disposable syringe and

expelling them into a Tedlar bag. In order to obtain a sample that was representative

of the entire building space, the volume of each sample aliquot was proportional to

the volume of the room from which it was collected (Table 3-7).


Air Toxics for laboratory analysis. The second sample was analyzed on-site using the

MGD-2002 helium meter. Discrete He measurements were not taken inside Building

1130, because high ambient He concentrations (i.e., inside a building following

release of the He tracer gas) interfere with the instrument sensor, inhibiting its ability

to reliably measure concentrations. However, the integrated samples collected in

Tedlar bags and measured using the helium meter outside the building yielded usable

results.

An observation from the experiments conducted at all three study sites is that the

field He measurements were consistently higher than the laboratory results. Two

likely explanations are: (1) the field meter is calibrated differently and yields higher

concentrations than the laboratory method, or (2) He is lost from the Tedlar bags

between the time of collection and time of analysis. To test the latter possibility, the

two He samples collected at Travis AFB at 15 and 90 minutes after the He release

were analyzed three times by the laboratory; once upon receipt along with the other

samples, and again 24 hours and 48 hours after receipt of the samples.


and discrete measurements were collected only twice in each room due to the short

duration of the experiment. In addition, two time-integrated indoor air samples for

SF6 and He analysis were collected from the Equipment Room in two collocated

6-liter SUMMA canisters placed at the location shown in Figure 3-10. The SUMMA

canisters were equipped with flow controllers calibrated to fill in 4 and 12 hours;

however, the 4-hour canister was closed after 1.75 hours and the 12-hour canister

was closed after only 4 hours due to faster than anticipated He decay inside the

building and early low ambient He concentrations as measured from the integrated

samples collected in Tedlar bags. The canisters were filled from 0730 to 0915 and

1130 (0.5 to 2.25 hours and 0.5 to 4.5 hours after the He release).

3.3.4 Travis AFB Meteorology

Meteorological data for the study period was obtained from Travis AFB Weather

Squadron (60 OSS/OSW). Data obtained for this study were collected from Sensor

21L at the Travis AFB Airfield, located approximately 2.4 miles northeast of

Building 1130 (Figure 2-5). Data collected included wind speed and direction,

ambient air temperature, and barometric pressure. Measurements were logged every

minute.

3.3.5 Variances from the Travis AFB Work Plan

Following the He release, the readings from the hand-held He detector indicated that

He concentrations were decreasing at a significantly faster rate than anticipated



(indicating higher than anticipated AER). Therefore, a 45-minute sample was added

to the originally planned sampling schedule and the final sample collected was the

120 minute sample from only 2 hours after the He release, when the hand-held meter

measured concentrations below the laboratory detection limit of 500 ppm. Hand-held

measurements were taken until the meter no longer detected He, at 1130, or 4 hours

after the He release.

Although not in the original work plan, a second SUMMA canister, collocated with

the first, was deployed. This SUMMA canister was planned to be deployed for 8 to

12 hours; however, due to high AER, it was closed after only 4 hours. Also due to

the higher than anticipated AER of the building, the first SUMMA canister was

closed after only 1.75 hours, rather than the originally proposed 3.5 hours.

Discrete SF6 samples in Tedlar bags were scheduled to be collected at 30 minutes

and 4 hrs after He release, to bracket the 3.5-hour SUMMA sample; however, due to

the unexpectedly high He concentration decay, these were collected at 30 minutes

and 2 hours after the He release.


4 EXPERIMENTAL RESULTS

4.1 Facility 1381, Cape Canaveral Air Force Station (CCAFS)

The He concentrations in the composite Tedlar bag samples and the time integrated

SUMMA canister samples collected during Experiments 1 and 2 at Facility 1381 are

presented in Table 4-1. The corresponding SF6 concentration data are presented in

Table 4-2. On-site measurements of SF6 concentrations in the individual rooms are

presented in Table 4-3 and a plot of the logged SF6 concentrations is presented in

Figure 4-1.

The MIRAN gas analyzer was set to continuously monitor SF6 concentrations and to

log the measurements every 10 minutes. Figure 4-1 shows the maximum, minimum,

and average SF6 concentrations logged for each 10-minute period. The SF6 was

continuously released throughout the study period; however, the logging was

interrupted due to a malfunction with the power supply, as can be seen in Figure 4-1.

The discrete samples shown on Figure 4-1 were collected 30 minutes after release of

the He (12/7/2010), 60 minutes after release of the He (12/8/2010), and 8 hours after

release of the He (both days). It appears from Figure 4-1 that there is some “noise” in

the logged SF6 data. Some of the noise is likely the result of normal fluctuations in

AER related to people entering and exiting the building, and possibly meteorological

inputs. In addition, some of noise, particularly as observed in the plots of minimum

and maximum concentrations, is due to the instrument being moved from the regular

logging location (shown on Figure 3-1) to each of the individual rooms in the

building. As can be seen on Table 4-3, the SF6 concentrations in the individual

rooms was variable, and as the instrument was set to continuously log the

concentration data, when it was moved to other rooms this variability was captured

in the minimum and maximum data points, and it can be assumed also affected the

average concentration for the 10-minute logging period.



Table 4-1 Helium Concentrations in Facility 1381 at CCAFS

Sample ID Elapsed Time¹

(minutes) Collection

Time Field Result²

(ppmv)

Laboratory Result³ (ppmv)

HVAC On (07 December 2010)

1381-HON-15 15 11:41 15,100 10,000

1381-HON-30 30 11:56 12,275 8,500

1381-HON-60 60 12:26 8,650 6,100

1381-HON-90 90 12:56 6,500 3,800

1381-HON-120 120 13:26 4,700 3,000

1381-HON-180 180 14:26 2,150 1,400

1381-HON-240 240 15:26 1,200 980

1381-HON-360 360 17:26 550 530

1381-HON-480 480 19:26 275 ND

1381-HON-SUMMA 60 – 300 12:26 – 16:26 NA 3,100

HVAC Off (08 December 2010)

1381-HOFF-15 15 08:35 10,500 8,000

1381-HOFF-30 30 08:50 10,500 7,000

1381-HOFF-60 60 09:20 8,850 6,200

1381-HOFF-90 90 09:50 6,650 4,100

1381-HOFF-120 120 10:20 4,850 3,400

1381-HOFF-180 180 11:20 2,875 2,000

1381-HOFF-240 240 12:20 1,875 1,500

1381-HOFF-360 360 14:20 1,175 760

1381-HOFF-480 480 16:20 750 550

1381-HOFF-SUMMA 120 – 360 10:20 – 14:20 NA 2,200

Definitions:

HVAC – heating, ventilation and air conditioning system ppmv – part per million by volume Notes: 1 Elapsed time since release of He.

2 Instrument detection level for He was 25 ppmv

3 Laboratory detection level for He was 500 ppmv



Table 4-2 SF6 Concentrations in Facility 1381 at CCAFS


(minutes) Collection Time Laboratory Result

(ppbv)


1381-HON-30 30 11:56 280

1381-HON-480 480 19:26 600

1381-HON-SUMMA 60 – 300 12:26 – 16:26 330


1381-HOFF-60 60 09:20 820

1381-HOFF-480 480 16:20 810

1381-HOFF-SUMMA 120 – 360 10:20 – 14:20 650

Definitions:

HVAC – heating, ventilation and air conditioning system ppbv – part per billion by volume SF6 – sulfur hexafluoride Notes: 1 Elapsed time since release of He.

Laboratory detection level for SF6 was 0.2 ppbv before dilution Occupational Safety and Health Administration Permissible Exposure Limit for SF6 is 1,000,000 ppbv



Table 4-3 Discrete SF6 Concentrations in Facility 1381 (ppbv) at CCAFS

Time

Room

1 2 3 4 5 6


10:53 170 157 140 156 179 146

11:13 258 260 228 253 271 236

12:15 279 287 254 275 259 293

13:13 279 325 277 292 308 290

14:20 309 342 299 316 320 308

15:09 328 363 321 339 348 321

16:35 410 441 400 419 418 401

18:20 515 538 490 511 502 487


9:05 800 840 812 805 895 813

10:05 699 718 646 658 796 601

11:05 560 612 516 478 633 403

12:10 525 742 440 440 576 345

13:15 572 603 571 517 643 493

14:30 717 709 683 717 685 690

15:12 800 792 782 793 775 748

17:05 984 977 947 1,001 971 952

Definitions:

HVAC – heating, ventilation and air conditioning system ppbv – part per billion by volume SF6 – sulfur hexafluoride Notes:

Detection level for SF6 was 0.2 ppbv before dilution Occupational Safety and Health Administration Permissible Exposure Limit for SF6 is 1,000,000 ppbv Instrument detection level for SF6 was 10 ppbv



Figure 4-1 Plot of logged SF6 concentrations measured on-site at CCAFS Facility 1381 and laboratory sample results.

Plots of the logged SF6 concentrations with outside temperature, barometric pressure,

and wind speed are presented in Figure 4-2, Figure 4-3, and Figure 4-4 respectively.

As expected, there does not appear to be a correlation between outside temperature

and SF6 concentration (Figure 4-2). There may be a weak negative correlation

between barometric pressure and SF6 concentrations in the building (Figure 4-3),

although the gap in SF6 data during the early morning hours of 07 December make

this difficult to assess. There may also be a negative correlation between wind speed

and SF6 concentrations, with the drop in wind speed observed in the afternoons of

both days corresponding to the rise in SF6 concentration observed prior to the HVAC

system being turned off on 07 December, and at the end of the experiments on 08

December. Similarly, as the wind speeds increased slightly during the morning of 08

December, the SF6 concentrations decreased. This negative correlation is consistent

with increasing winds creating a “stack effect” and drawing air out of the building.



Figure 4-2 Plot of logged SF6 concentrations at CCAFS Facility 1381 measured on-site and outdoor ambient temperatures.



Figure 4-3 Plot of logged SF6 concentrations measured on-site at CCAFS Facility 1381 and barometric pressure.



Figure 4-4 Plot of logged SF6 concentrations measured on-site at CCAFS Facility 1381 and wind speed.


The He concentrations in the composite Tedlar bag samples and the time integrated

SUMMA canister samples collected during the experiments at Building 1416 are

presented in Table 4-4. The corresponding SF6 concentration data are presented in

Table 4-5. On-site measurements of SF6 concentrations in the individual rooms are


Figure 4-5.



Table 4-4 Helium Concentrations in Building 1416 at Former Kelly AFB



Time Field Result²

(ppmv) Laboratory Result³

(ppmv)

HVAC On (23 March 2011)

1416-HON-15 15 06:40 36,000 21,000

1416-HON-30 30 06:55 26,000 15,000

1416-HON-60 60 07:25 16,300 9,500

1416-HON-90 90 07:55 10,975 7,300

1416-HON-120 120 08:25 8,425 5,900

1416-HON-180 180 09:25 4,625 3,400

1416-HON-240 240 10:25 2,300 1,800

1416-HON-360 360 12:25 700 ND

1416-HON-480 480 14:25 75 ND

1416-SUMMA-3.5HR 30 – 240 06:55 – 10:25 NA 7,900

1416-SUMMA-9HR 30 – 570 06:55 – 15:55 NA 3,500

Definitions:

HVAC – heating, ventilation and air conditioning system NA – not applicable ppmv – part per million by volume Notes: 1 Elapsed time since release of He.



Table 4-5 SF6 Concentrations in Building 1416 at Former Kelly AFB



(ppbv)


1416-HON-30 30 06:55 1,900

1416-HON-240 240 10:25 2,200

1416-SUMMA-3.5HR 30 – 240 06:55 – 10:25 2,100

(2,000 lab duplicate)

1416-SUMMA-9HR 30 – 570 06:55 – 15:55 1,600

Definitions:

HVAC – heating, ventilation and air conditioning system ppbv – part per billion by volume SF6 – sulfur hexafluoride Notes: 1 Elapsed time since release of He.




Table 4-6 Discrete SF6 Concentrations in Building 1416 (ppbv) at Former Kelly AFB

Time

Room

Entry Classroom Shop Restroom


06:20 2,138 1,746 1,981 2,067

07:20 1,615 1,408 1,262 1,194

08:40 1,658 1,453 1,434 1,409

09:40 1,626 1,551 1,611 1,537

11:10 1,527 1,351 1,432 1,463

12:40 1,419 1,351 1,440 1,501

14:40 1,130 1,074 1,124 1,153

16:00 937 914 940 1,016

Definitions:

HVAC – heating, ventilation and air conditioning system ppbv – part per billion by volume SF6 – sulfur hexafluoride Notes:

Detection level for SF6 was 0.2 ppbv before dilution Occupational Safety and Health Administration Permissible Exposure Limit for SF6 is 1,000,000 ppbv Instrument detection level for SF6 was 10 ppbv



Figure 4-5 Plot of logged SF6 concentrations measured on-site at former Kelly AFB Building 1416 and laboratory sample results.

As during the CCAFS experiment, the MIRAN gas analyzer was set to continuously

monitor SF6 concentrations and to log the measurements every 10 minutes. Figure

4-5 shows the maximum, minimum, and average SF6 concentrations logged for each

10-minute period. The SF6 was continuously released throughout the study period,

with no interruptions. The discrete samples shown on Figure 4-5 were collected 30

minutes and 4 hours after release of the He. Again, there appears to be some “noise”

in the logged SF6 data due to normal environmentally induced fluctuations, as well

as fluctuations introduced by ingress and egress through the front door and moving

the SF6 analyzer from room to room to obtain discrete measurements. Concentrations

of SF6 logged by the on-site analyzer appear to be consistently lower than those from

the discrete and time-integrated samples collected for off-site laboratory analysis.

During the CCAFS experiments, there was a high degree of agreement between these

two data sets, suggesting that the instrument used for the former Kelly AFB

experiment may have been miscalibrated by the vendor. However, the relative

overall shape of the concentration curve is similar to the one documented during the

CCAFS experiments (see Figure 4-1), indicating that the relative readings are

representative of SF6 concentration fluctuations in Building 1416. The sudden drop

in SF6 concentrations immediately following the release of He was also noted after

the He releases during the CCAFS experiments, suggesting that the release of He



into the building space may displace a measurable amount of SF6 gas. Six cylinders

of He represent approximately 650 cubic feet of pure He, which represents

approximately 4.6 percent of the total indoor air volume of Building 1416; however,

this volume is not sufficient to account for the total drop in SF6 concentration. The

SF6 concentration is likely also affected by ingress and egress through the front door

beginning immediately prior to He release and continuing throughout the

experiment, with the greatest frequency occurring during the initial stages of the

experiment, when the sampling frequency is highest.


and wind speed are presented in Figure 4-6, Figure 4-7, and Figure 4-8 respectively.

There may be a weak inverse correlation between outside temperature and SF6

concentration (Figure 4-6). It is important to note that the first hours of the SF6

concentration curve show SF6 concentrations in Building 1416 as they are still

building up towards equilibrium conditions and therefore cannot be used to evaluate

correlative relationships between the curves. There appears to be no correlation

between barometric pressure and SF6 concentrations in the building (Figure 4-7).

There may be a negative correlation between wind speed and SF6 concentrations.

This negative correlation is consistent with increasing winds creating a “stack effect”

and drawing air out of the building.



Figure 4-6 Plot of logged SF6 concentrations measured on-site at former Kelly AFB Building 1416 and outdoor ambient temperatures.



Figure 4-7 Plot of logged SF6 concentrations measured on-site at former Kelly AFB Building 1416 and barometric pressure.



Figure 4-8 Plot of logged SF6 concentrations measured on-site at former Kelly AFB Building 1416 and wind speed.


The He and SF6 concentrations collected during the experiments at Building 1130

are presented in Table 4-7 through Table 4-10. The laboratory analytical results for

He analyzed upon receipt and then two additional times at 24 hours and 48 hours

following receipt of the samples are presented along with the corresponding field

measurements in Table 4-8. The corresponding SF6 concentration data are presented

in Table 4-9. On-site measurements of SF6 concentrations in the individual rooms are


Figure 4-9. After the final He sample was collected, the ceiling vents in the

equipment room were temporarily sealed in order to observe the effect on SF6

concentrations. As expected, the concentration increased after sealing the vents, and

then decreased again after unsealing them (Figure 4-9).



Table 4-7 Helium Concentrations in Building 1130 at Travis AFB



Time Field Result²

(ppmv) Laboratory Result³

(ppmv)

HVAC On (13 July 2011)

1130-HON-15 15 7:15 11,900 9,700

1130-HON-30 30 7:30 4,425 2,100

1130-HON-45 45 7:45 2,850 1,400

1130-HON-60 60 8:00 2,100 1,100

1130-HON-90 90 8:30 750 610

1130-HON-100a 100 8:40 600 —

1130-HON-120 120 9:00 400 ND

1130-HON-150a 150 9:30 225 —

1130-HON-180a 180 10:00 125 —

1130-HON-210a 210 10:30 50 —

1130-HON-240a 240 11:00 25 —

1130-HON-270a 270 11:30 0 —

Definitions:

HVAC – heating, ventilation and air conditioning system NA – not applicable ND – not detected above the laboratory detection limit ppmv – part per million by volume Notes: 1 Elapsed time since release of He.



a Sample collected for field measurement only

Table 4-8 Helium Concentrations in Building 1130 at Travis AFB as Measured at Multiple Times After Sample

Collection

Sample ID

Sample Collection

Time Field/Laboratory Analysis Time

Elapsed Time Since Sample Collection

(hours)

Field/Laboratory Result

1

(ppmv)

1130-HON-15

7/13/11

7:15

7/13/11 7:15 0 (field) 11,900

1130-HON-15 7/14/11 22:18 39 (lab) 9,700

1130-HON-15 7/15/11 19:45 60.5 (lab) 8,600

1130-HON-15 7/16/11 19:44 84.5 (lab) 7,000

1130-HON-90

7/13/11

8:30

7/13/11 8:30 0 (field) 750

1130-HON-90 7/14/11 22:27 39 (lab) 610

1130-HON-90 7/15/11 19:53 60.5 (lab) 530

1130-HON-90 7/16/11 19:22 84.5 (lab) ND

Definitions:

HVAC – heating, ventilation and air conditioning system ND – not detected above the laboratory detection limit ppmv – part per million by volume Notes: 1Field Instrument detection level for He was 25 ppmv and laboratory detection level for He was 500 ppmv



Table 4-9 SF6 Concentrations in Building 1130, Travis AFB



(ppbv)


1130-HON-30 30 7:30 130 (120 lab duplicate)

1130-HON-120 120 9:30 950

1130-SUMMA-1.75HR 30 – 135 9:15 530

1130-SUMMA-4HR 30 – 270 11:30 680

Definitions:

HVAC – heating, ventilation and air conditioning system ppbv – part per billion by volume SF6 – sulfur hexaflouride Notes: 1 Elapsed time since release of He.


Table 4-10 Discrete SF6 Concentrations in Building 1130 (ppbv) at Travis AFB

Time

Room

Equipment Room Storage Room


06:40 410 440

09:47 430 460

Definitions:

HVAC – heating, ventilation and air conditioning system ppbv – part per billion by volume SF6 – sulfur hexaflouride Notes:

Occupational Safety and Health Administration Permissible Exposure Limit for SF6 is 1,000,000 ppbv Instrument detection level for SF6 was 10 ppbv



Figure 4-9 Plot of logged SF6 concentrations measured on-site at Travis AFB Building 1130 and laboratory sample results.

As shown in Table 4-7, field-measured He concentrations decreased from 11,900 to

2,100 ppm within the first hour of the experiment. This represents more than an 80

percent drop, which suggested early on during the experiment that the AER within

Building 1130 was higher than anticipated, prompting field personnel to collect

additional He samples at 45 and 100 minutes after He release and to close the

SUMMA canisters earlier than planned. The fixed laboratory results confirmed the

rapid drop in He concentrations, although the laboratory results were generally lower

than the field measurements, as was the case during the CCAFS and former Kelly

AFB experiments.

The difference in He concentrations observed between the field measurements and

the corresponding laboratory analyses are shown on Table 4-8, along with the

additional laboratory results from sample reanalyses conducted at approximately 24

and 48 hours after the initial analysis. As shown in Table 4-8, concentrations of He

continued to decrease after the laboratory received the samples, suggesting that the

difference in He concentrations between field and laboratory measurements was not

an artifact of the field He meter, but instead was the result of He loss through the

Tedlar bag (Figure 4-10).



a) At Building 1130, Travis AFB

0

2000

4000

6000

8000

10000

12000

14000

0 20 40 60 80 100

He

Co

nce

ntr

atio

n (

pp

mv)

Time Elapsed Since Sample Collection (hours)

1130-HON-15

Field Measurement

Lab Measurement

0

100

200

300

400

500

600

700

800

0 10 20 30 40 50 60 70

He

Co

nce

ntr

atio

n (

pp

mv)

Time Elapsed Since Sample Collection (hours)

1130-HON-90

Field Measurement

Lab Measurement



b) At All Three Facilities Examined

Figure 4-10 Relationship between field measurements and laboratory results

A review of all field and analytical He data from the CCAFS, former Kelly AFB, and

Travis AFB experiments revealed that the difference in He concentrations between

the field-measured results and the laboratory analyses remained relatively consistent

with average relative percent differences (RPDs) ranging from 34 percent at CCAFS

to 49 percent at Travis AFB. It was originally suspected that low ambient barometric

pressure during air transport would promote greater diffusion of He out of the Tedlar

bags. However, the samples collected for the Travis AFB experiment were

transported via ground and showed the greatest loss of He between sample collection

in the field and laboratory analysis, suggesting that air transport of samples likely

does not increase the loss of He from the Tedlar bags.

As during the CCAFS and former Kelly AFB experiments, the MIRAN gas analyzer

was set to continuously monitor SF6 concentrations and to log the measurements

every 10 minutes. Figure 4-9 shows the maximum, minimum, and average SF6

concentrations logged for each 10-minute period. The SF6 was continuously released

throughout the study period, with no interruptions. The discrete samples shown on

Figure 4-9 were collected 30 minutes and 2 hours after release of the He. Again,

there appears to be some “noise” in the logged SF6 data due to normal

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000

Fie

ld R

esu

lts,

pp

mv

Laboratory Results, ppmv

CCAFS (HVAC on)

CCAFS (HVAC off)

Kelly AFB

Travis AFB

1:1 Line



environmentally induced fluctuations, as well as fluctuations introduced by ingress

and egress through the front door. Concentrations of SF6 logged by the on-site

analyzer appear to be consistently lower than those from the discrete and time-

integrated samples collected for off-site laboratory analysis, with the exception of the

30-minute discrete sample (Figure 4-9).

As at CCAFS and former Kelly AFB, a sudden drop in SF6 concentrations was

observed immediately following the release of He, which could not be entirely

attributed to displacement by the released helium.


and wind speed are presented in Figure 4-11, Figure 4-12, and Figure 4-13

respectively. There does not appear to be a correlation between outside temperature

and SF6 concentration, as shown by the relatively stable SF6 concentrations

throughout the night despite outside temperature fluctuations of 11 degrees

Fahrenheit (Figure 4-11). There appears to be no correlation between barometric

pressure and SF6 concentrations in the building, as expected based on the relatively

open nature of the building due to the generator vents and utility trenches; it would

not be expected in such a situation for a differential pressure to exist between the

inside and the outside of the building (Figure 4-12). No correlation between wind

speed and SF6 concentrations was observed, although this may be due to the short

observation period and other factors effecting the SF6 (e.g., egress and ingress,

sealing and unsealing the vents). .



Figure 4-11 Plot of logged SF6 concentrations measured on-site at Travis AFB Building 1130 and outdoor ambient temperatures.



Figure 4-12 Plot of logged SF6 concentrations measured on-site at Travis AFB Building 1130 and barometric pressure.



Figure 4-13 Plot of logged SF6 concentrations measured on-site at Travis AFB Building 1130 and wind speed.


5 AIR EXCHANGE RATE ANALYSIS

Analyses of the AER data for each of the three buildings investigated for this study

are presented in the following sections. For each site, the information presented

includes:

Analysis of He release methods: For these methods, He was released

instantaneously and AERs were calculated based on the decay in He

concentrations and using three least-squares (LS) methods.

Analysis of ASTM methods: For these methods SF6 was released

continuously at a known rate, and AERs were calculated. These tests were

conducted simultaneously with the He tests. A modification was made to the

ASTM method for this project to allow the ASTM methods to be excecuted

under conditions that were not at steady-state (not at equilibrium). This was

useful because data collected during the project clearly showed the SF6 tracer

concentrations were not at steady-state during the tests.

Comparison of He-release results and SF6-release results.

Additional information is presented on a site by site basis as warranted based on the

data collected. As discussed previously, at each building, the AER was calculated

using instantaneously released He and continuously released SF6. Multiple

approaches were used for calculating AERs for both the He and SF6 methods (e.g.,

different mathematical equations, different statistical treatment, or different time

intevals). In the following discussion, the term “test” is used to refer to a single AER

calculation. For example, for a single building with a single He release, three “tests”

can be conducted by calculating the AER using the three LS equations.

The three LS methods are documented in Appendix B. The three methods are all

similar to each other, and differ primarily in that for LS method #1 (LS-1), the initial

well-mixed He concentration (C0) is used in the equations to calculate AER, while

for method #2 (LS-2) and method #3 (LS-3), C0 is not required to calculate the AER,

although it can be estimated from the sample data. For LS-1, C0 is calculated in one

of two ways: either by directly calculating the difference in weights of the He

cylinders before and after He release, or using the vendor provided volume of the

cylinders.

The LS methods provide three similar approaches to evaluating helium concentration

decay data in order to calculate an AER. Methods LS-2 and LS-3 offer the nominal

advantage over LS-1 of not requiring knowledge of C0; however, C0 is easily



obtained from vendor provided information or weighing the cylinders before and

after release. None of the LS methods are considered more reliable than the others,

rather application of all three methods to a single data set results in three estimates of

AER and thereby provides a range of reasonable values.

5.1 Facility 1381, Cape Canaveral Air Force Station

Figure 5-1 illustrates the temporal relationships between the AER tests conducted at

Facility 1381, including the operation of the HVAC, and the beginning and end of

SF6 release.

Figure 5-1 Relationship between tests conducted for air exchange rate analysis at CCAFS. Test #1 and test #2 used He as the tracer for least-squares analysis. Test #3 used SF6 as the tracer for a continuous release.

5.1.1 Analysis of He Release Methods for AER Predictions

Table 5-1 shows the AERs calculated for Facility 1381 using the three LS methods.

Test results are shown in Table 5-1 for the following conditions:

The HVAC system is on.

The HVAC system is off.

C0 is estimated based on the calculated weight of the released He.

C0 is estimated based on the volume of the He cylinders.



Both field results and lab results of He measurements were used as input data

to each method to compare results.

The AERs calculated using the LS methods with the HVAC on ranged from 12.7/day

to 17.5/day, while with the HVAC off they ranged from 8.7/day to 11.4/day. Lower

AERs are expected with the HVAC system turned off.

Table 5-1 Air Exchange Rate Results for He Tests (Instantaneous Release)

Conducted at CCAFS using Least-Squares Methods1

Field Results Laboratory Results

Method LS-1

Method LS-2

Method LS-3

Method LS-1

Method LS-2

Method LS-3

AER, 1/day

C02,

% AER, 1/day

AER, 1/day

AER, 1/day

C02, %

AER, 1/day

AER, 1/day

HVAC ON #1

Initial Concentration by Weight

14.2 1.9

13.7 12.7

17.2 1.9

13.9 12.8 Initial Concentration by Volume

14.4 2.0 17.5 2.0

HVAC OFF #2


9.1 1.2

9.0 8.8

10.8 1.2


9.8 1.4 11.4 1.4

Definitions:

LS – least-squares AER – air exchange rate HVAC – heating, ventilation, and air conditioning C0 – initial He concentration (calculated) Notes: 1 The three least-squares methods for calculating AERs are explained in Appendix B.

2 C0 is required for method LS-1 only, and not the other two methods.

A Monte Carlo method was developed and applied to the LS methods, and example

results are shown in Table 5-2. In the table, results are shown when the HVAC

system is on (5-2a) and when the HVAC system is off (5-2b). The percentiles shown

are 5%, 50% (median), and 95%. Other percentiles could have been chosen as well.

Note that the difference between the 5% and 95% is relatively small, a good

indicator of the accuracy of the estimates.



Table 5-2 Estimated Percentile Ranges of AERs Calculated using Instantaneous He Releases into Facility 1381 at CCAFS

(a) HVAC On

AERs (1/day)

Percentile LS-1 LS-2 LS-3

5% 15.1 11.9 11.6

50% 17.3 14.3 12.7

95% 19.0 16.0 14.2

(b) HVAC Off

AERs (1/day)

Percentile LS-1 LS-2 LS-3

5% 9.2 7.9 7.7

50% 10.7 9.6 8.7

95% 12.3 10.9 9.5

Definitions:

LS – least-squares AER – air exchange rate HVAC – heating, ventilation, and air conditioning

In addition to the three least-squares approaches, a method was developed to

calculate AER that combined instantaneous release of He and laboratory analysis of

a time-integrated sample collected in a SUMMA canister. Features of this method

include:

It is straightforward like the LS methods, and requires the same He tracer gas

release.

Fewer He samples are needed. Theoretically, only one is required (the time-

integrated concentration).

The method can be used to estimate AERs averaged over 12 hours or more.

This method was only used for comparisons with the LS methods, and it is not

documented in detail.

Two applications of this method were completed for the time intervals shown in

Figure 5-1. Test #1 was performed with the HVAC on, and test #2 with the HVAC

off. The results for both tests are shown graphically in Figure 5-2. Figure 5-2(a)

shows the result of test #1, where the SUMMA was activated one hour after the He

release and continued for four hours. The time-integrated He concentration for that

period was 3,100 ppmv. The AER corresponding to this time interval was 16.95/day,

which is in the range of AERs calculated using the LS methods (Table 5-1).



a) December 7, 2010, Test #1 with the He Tracer (HVAC On)

b) December 8, 2010, Test #2 with the He Tracer (HVAC Off)

Figure 5-2 Results of AER calculations at CCAFS using SUMMA approach and instantaneous helium releases. The curves show the expected time-integrated He concentration for the specified period. By finding the measured He concentration on the curve, the AER can be read off the x-axis.



For test #2, the SUMMA was activated two hours after the He release and continued

for four hours. The time-integrated He concentration for this period was 2,200 ppmv,

which corresponds to an AER of 11.15/day, which is also in the range of AERs

calculated using the LS methods (Table 5-1).

5.1.2 Analysis of SF6 Release Methods for AER Predictions

The SF6 tests, which are being compared to the He tests, all use continuous releases

of SF6. The start and stop times are shown in Figure 5-1. Figure 5-3(a) shows the

time series of measured SF6 concentrations, and shows where data are missing. To

eliminate the impacts of data oscillations, the mean SF6 concentrations were

converted to seven-point running averages, and the AERs were calculated with the

running average data. Shown in Figure 5-3(b) are the AERs calculated over each of

five time intervals, which in some cases show noise. The running average approach

removed much of the noise, and provides (in most instances) one-hour average

values. For each of the five intervals, the average of each AER was calculated, and

the results are shown in Table 5-3. Note that for each interval the four methods of

calculating AER are very consistent with each other. The higher AERs are associated

with the HVAC on, as anticipated.

The next AER test performed (test #3) used the SUMMA canister to develop an

integrated concentration over the test duration, and these results were used jointly

with the continuous SF6 discharge to calculate AER. The methodology for

developing the modified ASTM method is described in Appendix C.

Test #3 was conducted with the HVAC on, and within the period when the first He

release test was being performed. The results of the tests are shown in Figure 5-4.

The solid sloping line represents the relationship between the AER and the

concentration in the SUMMA canister (which was opened 1 hour after the He was

released and was closed 4 hours later). The SF6 concentration does not have to be at

a constant concentration while the SUMMA canister is open. Rather, the SUMMA

canister yields a time-integrated concentration, and the calculated AER is assumed to

be an average concentration over the sample period. The time-integrated

concentration in the SUMMA at the completion of the test was 330 ppbv. Using that

concentration, the AER is calculated to be 19.1/day. In general the AERs are high

enough that the results typically depend only on the prior 10 to 12 hours before the

tests begin. For example, with an AER of 10/day, the concentration remaining after

12 hours from an instantaneous release is less than 1%.



(a) SF6 Time Series (Plot shows average SF6 concentrations and seven-point running averages)

Figure 5-3 Predicted AERs from continuous SF6 releases into Facility 1381 at CCAFS. (The seven point running average was intended to lessen or remove spikes in the AER calculations. However, some spikes still remain because of several remaining rapid changes in SF6 concentrations.)



(b) AER by Forward and Central Finite Difference Methods using Trapezoid Integration Method (Plot shows AERs based on data in Figure 5-3(a))

Figure 5-3 (continued) Predicted AERs from continuous SF6 releases into Facility 1381 at CCAFS. (The seven point running average was intended to lessen or remove spikes in the AER calculations. However, some spikes still remain because of several remaining rapid changes in SF6 concentrations.)



Table 5-3 Averaged AERs Calculated by Finite Difference Methods for Continuous SF6 Releases into Facility 1381 at CCAFS

Interval Average AER by FFD, 1/day

Average AER by CFD, 1/day

Average AER by FFD using running

averages, 1/day

Average AER by CFD using running

averages, 1/day

1 19.431 19.123 19.062 19.129

2 20.958 21.171 20.216 19.915

3 9.657 9.572 9.710 9.618

4 6.599 6.345 6.387 6.399

5 9.736 9.227 9.208 9.311

Definitions:

AER – air exchange rate CFD – central finite difference FFD – forward finite difference Note: 1

Too few data to make calculations.

Figure 5-4 AER calculated based on SUMMA data and continuous release of SF6 (Test #3, HVAC on).

5.1.3 Comparison of Results

Table 5-4 summarizes the results of the He-based methods (methods developed for

this work) and the SF6 methods (ASTM method E741-00 with some modifications to

the equations). Comparison of the results from the two methods indicate good

agreement, particularly in the context of all the sources of error in the calculations

(i.e., inaccuracies in building volume estimates, analytical variability). With the

HVAC system on, AERs calculated using the He-based method ranged from



12.8/day to 17.5/day, while AERs calculated using the SF6-based method ranged

from 9.6/day to 20.2/day. AERs calculated with the HVAC off ranged from 8.7/day

to 11.4/day with the He-based method and from 6.4/day to 9.3/day with the SF6-

based method. The greater variability in results for the SF6-based method is in part

due to the fact that AERs were calculated for discrete time intervals (Figure 5-3(a))

while the AERs calculated using the He-based method are for the entire He decay

period. These results suggest that the He test methods are robust and are as accurate

as the SF6 tests. The same conclusions apply when the HVAC is off.

Table 5-4 Summary of AER Results for Facility 1381 at CCAFS

(all AER values are in units of day-1

)

Methods HVAC On HVAC Off

He Tests (instantaneous releases)

LS-1 17.2–17.5 10.8–11.4

LS-2 13.9 9.4

LS-3 12.8 8.7

SUMMA-1a 17.0 NC

SUMMA-2a NC 11.2

SF6 Tests (continuous releases)

FD with Running Averages

Interval 1a 19.1 NC

Interval 2a 19.9–20.2 NC

Interval 3a 9.6–9.7 NC

Interval 4a NC 6.4

Interval 5a NC 9.2–9.3

SUMMA-3 b

19.1 NC

Definitions:

AER – air exchange rate FD – finite difference He – helium HVAC – heating, ventilation, and air conditioning LS – least-squares NC – not calculated SF6 – sulfur hexafluoride Notes: aThese tests were performed with either the HVAC on or off.

b For the SUMMA-3 result, the exchange rate is 19.1/day over both periods.

cThis test was not done because SF6 data were collected over the period when the HVAC was operating and also

over the subsequent period when the HVAC was not operating.


The AER analyses for Building 1416 are presented in the following sections. Figure

5-5 illustrates the temporal relationships between the AER tests conducted at

Building 1416. Also shown is when the instantaneous He release occurred, and the

beginning and end of the SF6 release.



Figure 5-5 Relationship between air exchange rate tests for former Kelly AFB.

5.2.1 Analysis of He Release Methods for Air Exchange Rate Predictions

Table 5-5 shows the results of AER predictions using the three LS methods. The

theory behind each method is documented in Appendix B. Test results are shown for

the following conditions:

The HVAC system is operating throughout the test period.

For method #1 (LS-1), the initial concentration is calculated in one of two

ways: either by directly calculating the difference in weights of the He

cylinders before and after He release, or from the vendor provided volumes of

the cylinders.

Both field results and lab results of He measurements were used as input data

to each method so that results could be compared.



Table 5-5 Air Exchange Rate Results for He Tests (Instantaneous Releases)

Conducted at Former Kelly AFB using Least-Squares Methods¹

Kelly AFB

Field Results Lab Results

Method LS-1

Method LS-2

Method LS-3

Method LS-1

Method LS-2

Method LS-3

AER, 1/day

C0², %

AER, 1/day

AER, 1/day

AER, 1/day

C0², %

AER, 1/day

AER, 1/day

HVAC ON


18.8 4.9

18.2 17.7

22.6 4.9


18.6 4.7 22.3 4.7

Definitions:

LS – least-squares AER – air exchange rate HVAC – heating, ventilation, and air conditioning C0 – initial He concentration (calculated from data available) Notes 1

The three least-squares methods for calculating AERs are explained in Appendix B. 2 C0 is only required for method LS-1.

In all, 8 different estimates of AERs were generated using the LS methods. The

Monte Carlo method discussed in Section 5.1.1was applied to the LS methods, and

example results are shown in Table 5-6. The percentiles shown are 5%, 50%

(median), and 95%. Other percentiles could have been chosen as well, as the

complete distributions are shown in Figure 5-6. Note that the difference between 5%

and 95% is relatively small, a good indicator of the accuracy of the estimates.

As at CCAFS, in addition to the three least-squares approaches, the method using a

single sample collected in a SUMMA canister was used. Two applications of the

SUMMA method were completed for the time intervals shown in Figure 5-5 (6:55 to

10:25 and 6:55 to 15:55). The results for both tests are shown graphically in Figure

5-7. Figure 5-7(a) shows the results of Test #1, where the SUMMA was activated 30

minutes after the He release and continued for 3.5 hours. The time-integrated He

concentration for that period was 7,900 ppmv. The AER corresponding to this time

interval was 24.6/day. This is close to the AER calculated using LS-1 (22.6/day).

For Test #2, the SUMMA was also activated 30 minutes after the He release and

continued for 9 hours. The time-integrated He concentration for this time period was

3,500 ppmv (see Figure 5-7(b), which corresponds to an AER of 23/day, only

slightly different from 22.6/day calculated by LS-1 using lab data.


The SF6 tests all use continuous releases. The start and stop times were shown in

Figure 5-5. Figure 5-8(a) shows the time series of measured SF6 concentrations and

running averages. Shown in Figure 5-8(b) are the AERs calculated over each time

interval.



The next AER test performed used the SUMMA canister to develop an integrated

concentration over the test duration, and these results were used jointly with the

continuous SF6 discharge to calculate AER.



Table 5-6 Least Squares Air Exchange Rate Results for He Tests: Monte Carlo Analysis at Building 1416, Former Kelly AFB

HVAC ON Percentile

Field Data Lab Data

AERs (1/day) AERs (1/day)

LS-1 LS-2 LS-3 LS-1 LS-2 LS-3


5% 18.2 17.22 17.12 21.48 14.48 13.34

50% 18.83 18.24 17.72 22.58 16.61 14.78

95% 19.43 19.14 18.35 23.81 18.35 16.08

Initial Concentration by Volume

5% 18.03 17.19 17.12 21.07 14.59 13.47

50% 18.65 18.21 17.70 22.29 16.50 14.82

95% 19.20 19.19 18.36 23.45 18.45 16.11

Definitions:

AER – air exchange rate C0 – Initial He concentration He – helium HVAC – heating, ventilation and air conditioning system LS – least squares method



Figure 5-6 Plots of distributions of air exchange rates at Building 1416, former Kelly AFB.



a) Test #1

b) Test #2

Figure 5-7 Results of AER calculations using SUMMA approach and instantaneous He releases, Building 1416, former Kelly AFB.



Figure 5-8 Time series of SF6 concentrations and air exchange rates for former Kelly AFB.

The results of the tests are shown in Figure 5-9(a), Figure 5-9(b), and Figure 5-9(c).

The solid sloping line represents the relationship between the AER and the

concentration in the SUMMA. In Figure 5-9(a) the SUMMA was activated 30

minutes after the He was released, and continued for 3.5 hours. The time-integrated

SF6 concentration in the SUMMA at the completion of the test was 2,100 ppbv and

2,000 ppbv for the duplicate. Using those concentrations, the AERs are calculated to

be 13.7/day and 14.4/day, respectively. For test #2, the SUMMA was also activated

30 minutes after the He release and continued for 9 hours. The time-integrated SF6

concentration at the completion of the test was 1,600 ppbv. The AER was calculated

to be 18/day. In general the AERs are high enough so that the results typically

depend only on the prior 10–12 hours before the tests began.



a) Test #1 (3.5 hour period)

b) Test #1 (using duplicate SF6 sample)

Figure 5-9 Air exchange rates calculated by continuous SF6 release using SUMMA canisters, former Kelly AFB.



c) Test #2 (9 hour duration)

Figure 5-9 (continued) Air exchange rates calculated by continuous SF6 release using SUMMA canisters, former Kelly AFB.


Table 5-7 and Table 5-8 summarize the results of the He-based methods and the SF6-

based methods.

5.2.3.1 Least Squares Tests

By examining Table 5-7 and cross-comparing results from the 13 different tests, the

results are generally consistent with only a few exceptions. These are briefly

described below. Tests #3 and #4, using lab data, show that methods LS-1 produces

higher air exchange rates (~22.2/day) than LS-2 or LS-3 (14.7/day to 16.5/day). One

hypothesis for this is that He is being lost from the Tedlar bags between the time of

sample collection and the time of sample analysis. Since method LS-1 uses a well-

mixed initial He concentration (C0) and if He were lost from the first sample, the

LS-1 method would tend to predict a higher air exchange rate. Methods LS-2 and

LS-3 are less affected because C0 is not imposed as for LS-1.

This hypothesis is supported by the fact that results from tests #1 and #2 (also LS

tests), which use field data, do not show this differential between the results of LS-1

and the remaining two LS tests.



Table 5-7 Air Exchange Rates, Day

-1, Over Interval Shown



Table 5-8 Summary of Air Exchange Rate Analysis for Former Kelly AFB

Tracer Range (day-1

) Average (day-1

)

Results for Short Duration Tests (3–4 hours), March 23, 2011

He LS 14.7–22.6 17.9

SUMMA 24.6 24.6

SF6 SUMMA 13.7–14.4 14.1

Finite Difference 16.6–18.6 17.6

Results of Long Duration Tests (8–9 hours)

He LS 17.7–18.8 18.1

SUMMA 22.9 22.9

SF6 SUMMA 18.0 18.0

Finite Difference 17.6–17.7 17.6

Definitions:

He – helium LS – least squares method SF6 – sulfur hexafluoride

5.2.3.2 SUMMA Tests

While the SUMMA tests are not a part of the final protocol document, they were

developed for this project as an independent and simple way to calculate air

exchange rates. One inconsistency with these tests where SF6 was the tracer was test

#7. Lower air exchange rates were calculated than for all other methods.

Overall, the He based methods compared well with the SF6 based method.


The AER analysis for Building 1130 is presented in the following sections. Figure

5-10 illustrates the temporal relationships between the AER tests conducted at

Building 1130. Information includes tracer release information and duration of tests.

The SF6 release began at 16:05 on 12 July 2011, well before the He tests began at

07:00 on 13 July 2011. SUMMA tests using SF6 as the tracer began 30 minutes after

He release.



Figure 5-10 Relationship between air exchange rate tests for Building 1130 at Travis AFB.

5.3.1 Analysis of He Release Methods for AER Predictions

Table 5-9 summarizes the He tests from each of the three methods and for field and

lab results. In general, the calculated AERs were larger than at the previous

buildings. A major contributing reason was an open conduit to the generator room

and open vents from the generator room to the outside air (shown in Figure 3-12),

which allowed for significant flow of outdoor air into the building. Differences in

AERs were also noted between field results and lab results, which may have been

related to loss of He from the Tedlar bags between the time of sample collection and

the time of analysis at the lab (Section 4.3).



Table 5-9 Air Exchange Rate Results for He Tests (Instantaneous Release)

Conducted at Building 1130 at Travis AFB

Method

Field Results Lab Results

AER, 1/day C0, % AER, 1/day C0, %

LS-1 50.8 4.76 86.7 4.76

LS-2 42.0 1.6 63.4 1.7

LS-3 36.6 1.0 47.1 0.9

Definitions:

AER – air exchange rate C0 – Initial He concentration (calculated using weight change of He canisters) He – helium LS – least squares method

Differences were also noted between the three least squares methods with LS-1

yielding the highest AERs.


The SF6 release occurred for nearly a day as shown in Figure 5-11a, and the AERs

were calculated over this time period using modified ASTM methods. The modified

ASTM method is described in Appendix C. The AER averaged about 61 to 63/day

(Figure 5-11(b)), about 15 percent higher than the LS-1 result (50.3/day) obtained

using the He data. The lowest AER shown in the figure is about 20/day, and occurred

when the vents in the generator room were closed.



a) SF6 time series (The averaged data are seven-point running averages).

b) AER by forward and central finite difference methods using trapezoid integration method.

Figure 5-11 Predicted AERs and SF6 concentration in Building 1130 at Travis AFB.

The AER analyses using the SUMMA method are shown in Figure 5-12. Both tests

use SF6 as the tracer, with the SUMMA canisters open for different periods of time

(1.75 hours and 4.0 hours). The calculated AERs were 27/day and 31/day. These are

lower than estimates using other methods. Since these methods are integrated over

periods of time, the high and low AERs are averaged out. The other methods used

the field measurements, while the SUMMA canisters were analyzed at the

laboratory.



Figure 5-12 AERs calculated based on SUMMA data and continuous release of SF6, Building 1130, Travis AFB. Two SUMMA tests were performed. The first test began 30 minutes after the He release and lasted 1.75 hours. The second SUMMA test also began 30 minutes after the He release and lasted four hours.


A summary of the results is shown in Table 5-10 and in Figure 5-13.

The AERs for Building 1130 at Travis AFB were the highest encountered at any of

the buildings investigated. Using lab data the LS results ranged from 47.1/day to

86.7/day. Using field data the results were lower: 36.6/day to 50.8/day. The lower

AER calculated using the field data versus the laboratory data was observed at all

three buildings, and is suspected to be related to loss of He from the Tedlar bags

from time of collection to time of analysis at the laboratory.

Several SF6 tests were completed, and average AER values were within range of the

LS results. Also two SUMMA tests were completed, with AERs of 27/day to 40/day.

While the predicted AERs exhibited more variability than the results from Facility

1381 and Building 1416, values still agreed by a factor of two.



Table 5-10 Summary of Air Exchange Rate Analysis for Building 1130, Travis AFB

Test Method

Tracer and AER (1/day)

He SF6

LS-1–LS-3 (lab data) 47.1–86.7 Not applicable

LS-1–LS-3 (field data) 36.6–50.8 Not applicable

Continuous SF6 Release, (modified ASTM)

Not applicable 63 (average of all data)

20 (minimum that occurred with vents closed)

SUMMA Concentration was ND;

no estimate made 27–39

Definitions:

AER – air exchange rate He – helium LS – least squares method ND – non-detect SF6 – sulfur hexaflouride

Figure 5-13 Summary of air exchange rate test results for Travis AFB.


6 DISCUSSION AND CONCLUSIONS

6.1 Cape Canaveral Air Force Station

From the comparative AER tests completed at CCAFS, the following conclusions

can be reached regarding the two types of tests (He and SF6):

The tests generate comparable results.

Less field equipment is needed for the He tests, reducing costs and reducing

the possibility of equipment failure.

The weight of the He released can be accurately estimated, and this is a useful

feature of the He tests. This information is directly used in the AER tests to

eliminate a source of uncertainty.

It is straightforward to implement an uncertainty analysis of results for the He

methods, so that confidence intervals of results can be estimated. For the SF6

methods, such an analysis is more difficult to implement, and was not

attempted during this work.

Safety issues are of less concern for He. SF6 concentration limits to protect

human health exist, although it is likely not to be an issue for well-designed

tests.

SF6 is a greenhouse gas with a high global warming potential, and is being

phased out as a tracer gas.

These conclusions tend to favor the use of He tests over SF6 tests. However, SF6

continuous release tests may be superior to the He instantaneous tests in the duration

of the tests. Typically He tests last only a fraction of the day, while SF6 tests can

continue for a day or more. It may be desirable for the He test to last longer in order

to get a more accurate estimate of daily AER.

6.2 Former Kelly Air Force Base

The major conclusion from the field investigations at former Kelly AFB are:

Qualitatively, the results of the tests were generally self-consistent.

As at CCAFS, the AERs calculated from the SF6 and He release methods were

similar.

All of the data analysis methods were successfully completed indicating that

the methods and data input are robust.



6.3 Travis Air Force Base

The AERs for Building 1130 at Travis AFB were the highest encountered at any of

the buildings investigated. Using lab data the LS results ranged from 47.1/day to

86.7/day. Using field data the results were less: 36.6/day to 50.8/day. The difference

in results based on field data vs. lab data appears to be related to loss of He from the

sample containers during transport to the laboratory.

Several SF6 tests were completed and average AER values were within the range of

LS results obtained from the He tests. Also, two SUMMA tests were completed,

calculated AERs ranged from 27/day to 39/day. While the calculated AERs exhibited

more variability than for previous sites, the values generally agreed by a factor of

two.

Overall, the results from Travis AFB are consistent with results from CCAFS and

Former Kelly AFB, and indicate that the instantaneous He release method yields

similar results to the ASTM method.

6.4 Issues and their Resolutions

All AER methods that were developed were tested to ensure their validity. All

methods successfully completed the performance tests. The three least squares

methods were the primary methods developed for use in the protocol (Appendix A).

In totality the following methods were developed:

LS-1 with specified initial concentration (least squares method #1);

LS-2 with initial concentration not used (least squares method #2);

LS-3 with unknown initial concentration (least squares method #3);

Modified ASTM method;

Use of SUMMA canister to estimate time-integrated value of AER; and

A Monte Carlo Method to capture uncertainties in LS estimates.

As stated previously, only the three LS methods are used in the protocol developed

in Appendix A. The remaining methods were used to cross-check with the three LS

methods. The LS methods were successfully compared against the the other

methods. Results were generally within 20%, although for Building 1130 on Travis

AFB, results differed by up to a factor of 2.

Methods LS-1 through LS-3 provide three similar approaches to calculating an AER

based on He tracer gas concentration decay data. The primary difference between the

methods is that LS-1 requires knowledge of the initial helium concentration (C0),

while LS-2 and LS-3 do not; however, C0 is easily obtained from vendor provided

information or by weighing the cylinders before and after release of the helium.

Therefore, none of the three LS methods are considered superior to the others, rather,

they provide three approaches to calculating an AER from the decay in

instantatenously released tracer gas concentrations. It is recommended that when



estimating a building AER using the He concentration decay methodology, all three

LS methods be applied to the data to provide a range of reasonable AER values.

Use of a single, time-integrated He sample concentration collected in a SUMMA

canister may offer some advantages in terms of simplicity; however, this approach

has not been fully developed and tested.

6.4.1 Use of MGD-2002 Field Helium Detector

One of the objectives of the study was to evaluate whether AERs could be calculated

simply by making direct measurements of He concentrations in the building air using

the MGD-2002 helium detector, without the interim step of collecting samples in

Tedlar bags. In principle, it should be possible to directly measure He concentrations

by analyzing the building air with a field meter and appling the LS methods to the

concentration data. However, it was determined during this study that the MGD-

2002 does not function correctly if the ambient He concentrations are similar to the

concentrations one is trying to measure (which is necessarily the case when

measuring tracer gas concentrations inside a building). The ambient concentrations

apparently interfere with the internal sensor and result in erroneous measurements.

Tetra Tech unsuccessfully attempted to identify an alternative direct reading field

instrument.

The MGD-2002 can be readily used to measure He concentrations in the field;

however, it is necessary to collect samples of indoor air in Tedlar bags (or other

sample container) and then take the sample to a location with low ambient He

concentrations (e.g., outside the test building) to measure the concentration using the

MGD-2002.

6.4.2 Loss of Helium From Tedlar Bags

As discussed in Sections 4.3 and 6.3, a loss of He from Tedlar sample bags was

observed from time of collection to time of analysis at the off-site laboratory, which

introduces some error into the calculated AERs. This error could be mitigated by

using different sample containers, such as SUMMA canisters or metalized laminate

bags; however, these containers are more costly than Tedlar bags, and the AERs

calculated using He data from Tedlar bags analyzed at the off-site laboratory

compared well with the other methods. Therefore, it appears to be a nominal effect

and is likely less important than other sources of error, such as imprecision in

building volume measurements or vendor reported He volumes.

6.4.3 Helium Shortage and Cost

It has been widely reported that He supplies are being depleted and that it may

become more expensive and less readily available in the future. Thus, use of He as a

tracer gas may become less desirable. Although no other tracer gases were tested for

this study, in principle, it is possible to implement the AER measurement

methodologies using any tracer gas that meets the following criteria:

Readily available at a cost-effective price;



Easily measured in the laboratory and/or in the field at parts-per-million

concentrations;

Non-toxic; and

Nonflammable.

In addition, it is preferable that the gas be colorless and odorless to avoid disturbance

to building occupants.

Carbon dioxide (CO2), meets all of the criteria above and may offer a suitable

alternative to He for AER measurement. The disadvantage to using CO2 is that it is

present in ambient air at a concentration of approximatley 390 ppm; therefore, if it is

used as a tracer gas, the measured concentrations would need to be adjusted to

account for the ambient concentration, although this should be simple. However,

CO2 may offer an advantage over He. Experiments conducted at Travis AFB in 2009

indicate that He released into a building becomes well mixed with the building air

within the first 2 hours after release; however, there is some vertical stratification of

the He (higher concentrations near the ceiling) immediately after release (Tetra Tech

2009c). While He is much lighter than air, CO2 has a similar density to air and

therefore may mix more quickly with the building air.

6.5 Cost Comparison

The results of this study have demonstrated that the instantaneous He release method

yields similar estimates of AER as the modified ASTM method. The He

methodology developed during this study provides two primary advantages over the

ASTM method using SF6. First, SF6 is a powerful greenhouse gas that is being

phased out and will become increasingly difficult to obtain for AER measurement

applications, while He is readily available. Second, the He methodology is simpler

and less costly to implement.

There are a variety of options for implementing both methods that will impact the

total cost; for example, field analysis only, laboratory analysis only, or field and

laboratory analysis. Due to the wide range in AERs at different buildings, it is

advisable to use field meters when conducting either test so that the approach (e.g.

number of samples collected or SF6 flow rate) can be adjusted in response to site

specific conditions. Therefore, for cost comparison purposes, two scenarios are

compared below: (1) implementing the methods using both field and laboratory

analysis (Table 6-1) and (2) using field measurements only (Table 6-2). For both

scenarios, unit costs and labor rates are estimates based on experience implementing

the methods during this study. Actual costs will vary based on location and other

factors. During this study, multiple SF6 samples were collected at each site;

however, in practice, only one is required to calculate an AER. Therefore, for the

first cost comparison scenario (Table 6-1), it is assumed that only one, time-

integrated sample would be collected for SF6 analysis.

It can been seen from Tables 6-1 and 6-2 that the cost of the He methodology is

significantly lower for both scenarios. The primary factors driving the higher



expense of the SF6 method are the cost of the SF6 gas and the regulator and rotameter

required to release it at a known, steady rate, and the cost of the portable SF6

analyzer. It can also be seen that the difference in cost is less for scenario 1 vs.

scenario 2 due to the cost of analyzing multiple samples for He.

Table 6-1 Helium vs. SF6 Method Cost Comparison (Field and Laboratory Analysis)

Item Unit Cost Unit

SF6 Method He Method

Quantity Extended

Cost Quantity Extended

Cost

Labor

Field Technician $75.00 hr 12 $900 8 $600

Equipment/ODCs

SF6 gas cylinder (28-cf) $600.00 ea 1 $600 0 $0

SF6 gas cylinder two-stage regulator $436.00 ea 1 $436 0 $0

Rotameter (flow-meter) $364.00 ea 1 $364 0 $0

He gas cylinder (110-cf) $75.00 ea 0 $0 6 $450

Scale (to weigh He cylinders) $25.00 ea 0 $0 1 $25

Nylon tubing $2.00 ft 200 $400 0 $0

Fittings/ferrules $15.00 ls 1 $15 0 $0

Portable SF6 analyzer (Miran SapphIRe) $212.50 day 3 $638 0 $0

Portable He detector (MGD 2002) $70.81 day 0 $0 2 $142

6-L Summa canister $45.00 ea 1 $45 0 $0

Summa canister flow controller $25.00 ea 1 $25 0 $0

Tedlar bag with syringe/tubing $15.00 ea 0 $0 11 $165

Incidentals* $100.00 ls 1 $100 0 $0

SUBTOTAL $2,623 $782

Subcontractor (Analytical)

SF6 sample analysis $150.00 ea 1 $150 0 $0

He sample analysis $60.00 ea 0 $0 10 $600

SUBTOTAL $150 $600

TOTAL $3,673 $1,982

Definitions:

AER – air exchange rate He – helium SF6 – sulfur hexafluoride ls – lump sum ea – each cf – cubic feet ODC – other direct cost L – liter



Table 6-2 Helium vs. SF6 Method Cost Comparison (Field Analysis Only)

Item Unit Cost Unit

SF6 Method He Method

Quantity Extended

Cost Quantity Extended

Cost

Labor

Field Technician $75.00 hr 12 $900 8 $600

Equipment/ODCs

SF6 gas cylinder (28-cf) $600.00 ea 1 $600 0 $0

SF6 gas cylinder two-stage regulator $436.00 ea 1 $436 0 $0

Rotameter (flow-meter) $364.00 ea 1 $364 0 $0

He gas cylinder (110-cf) $75.00 ea 0 $0 6 $450

Scale (to weigh He cylinders) $25.00 ea 0 $0 1 $25

Nylon tubing $2.00 ft 200 $400 0 $0

Fittings/ferrules $15.00 ls 1 $15 0 $0

Portable SF6 analyzer (Miran SapphIRe) $212.50 day 3 $638 0 $0

Portable He detector (MGD 2002) $70.81 day 0 $0 2 $142

Tedlar bag with syringe/tubing $15.00 ea 0 $0 1 $15

Incidentals $100.00 ls 1 $100 0 $0

SUBTOTAL $2,623 $782

TOTAL $3,453 $1,232

Definitions:

AER – air exchange rate He – helium SF6 – sulfur hexafluoride ls – lump sum ea – each cf – cubic feet ODC – other direct cost L – liter

6.6 Overall Conclusions

The primary objective of this project was to develop cost-effective, simple methods

for determining AERs. Simplified methods to determine AERs were developed from

a combination of field investigations and least-squares algorithms.

The AERs calculated for the three test buildings (Facility 1381, Building 1416, and

Building 1130) using instantaneous He release and the LS methods compared well

with the AERs calculated using the modified ASTM method with SF6 tracer gas. The

resuls of this study demonstrate that the He release methodology provides a cost-

effective, easy to implement method of measuring building specific AERs.

The three LS methods help to determine the uncertainty in AER predictions. While a

Monte Carlo method was developed for test analysis, it is not included in the

protocol (Appendix A).



6.7 Further Method Development/Validation

A number of ideas have evolved from the project that could further generalize the

protocol. They include:

Development of software to implement the air exchange methods. The

software would include methods to set up the field tests as well (such as

estimating the He release needed).

Further testing and implementation of the SUMMA techniques for both

continuous and instantaneous releases. These techniques may be the simplest

and least expensive of all the techniques developed in the report. However,

further testing of the technique is needed.

Inclusion of the modified ASTM method developed for this project. The

method can calculate AERs over short periods of time, and then can be

averaged over any time period desired, within the limits of the test duration.

Development of a cost framework for the alternative methods presented so

that comparative costs can be estimated prior to method implementation.

The methods implemented here are for buildings typically less than 30,000 ft3.

It may be worthwhile to expand the scope to larger buildings. New algorithms

may need to be developed for larger buildings, or the existing algorithm

modified.

Development of a method to calculate air exchange within office buildings

inside aircraft hangers, or adaptation of the present method to those

conditions.

Application of computation fluid dynamics codes to better characterize air

exchange in complex buildings, and to investigate how AER predictions

compare against buildings such as those examined during this project.





7 REFERENCES

CH2M Hill. (2007) Draft Groundwater Sampling and Analysis Program 2006–2007

Annual Report.

Johnson, P.C., and R.A. Ettinger. (1991) Heuristic model for predicting the intrusion

rate of contaminant vapors into buildings. Environmental Science & Technology Vol.

25, p 1445–1452.

Mills, William B., S. Liu, M.C. Rigby, and D. Brenner. (2007) Time-Variable

Simulation of Soil Vapor Intrusion into a Building with a Combined Crawl Space

and Basement. Environmental Science & Technology Vol. 41, No. 14., p 4993–5001

Tetra Tech, Inc. (2007) Corrective Measures Implementation Report, Volume I,

Revision 0 – Ordnance Support Facility (Facility 1381), Solid Waste Management

Unit C021, Cape Canaveral Air Force Station, FL.

Tetra Tech, Inc. (2009a) Investigation and Validation of Multiple Lines of Evidence

to Assess Vapor Intrusion at Cape Canaveral Air Force Station, FL for US Air Force

School of Aerospace Medicine (USAFSAM/OE) at Brooks City-Base, TX.

Tetra Tech, Inc. (2009b) Investigation and Validation of Multiple Lines of Evidence

to Assess Vapor Intrusion at Kelly Air Force Base, TX for US Air Force School of

Aerospace Medicine (USAFSAM/OE) at Brooks City-Base, TX.

Tetra Tech, Inc. (2009c) Investigation and Validation of Multiple Lines of Evidence

to Assess Vapor Intrusion at Travis Air Force Base, CA for US Air Force School of

Aerospace Medicine (USAFSAM/OE) at Brooks City-Base, TX.

Tetra Tech, Inc. (2009d) Investigation and Validation of Multiple Lines of Evidence

to Assess Vapor Intrusion at Vandenberg Air Force Base, CA for US Air Force

School of Aerospace Medicine (USAFSAM/OE) at Brooks City-Base, TX.




Tetra Tech, Inc. A-1

APPENDIX A PROTOCOL FOR ESTIMATING AIR EXCHANGE RATE

USING CONCENTRATION DECAY OF INSTANTANEOUSLY

RELEASED HELIUM TRACER GAS

A.1 Scope and Limitations This protocol covers the methodology used for estimating the air exchange rate (AER) of a building, or portion (zone) of a building, by evaluating the concentration decay rate of instantaneously released helium (He) tracer gas. Three mathematical methods to estimate AERs from field-collected data are developed from basic principles in Appendix B. The major assumption that guides these methods is that the He tracer gas is released instantaneously such that it becomes well-mixed in the building before sampling begins (typically 15 to 30 minutes after release). In addition, for Method #1, the value of Co (initial well-mixed concentration) is assumed to be accurately calculated from the initial mass of He released and the estimated volume of the building or building zone. The air exchange rate is calculated by a least-square method that minimizes the root mean square error, and in that sense the method produces a ‘best’ result.

The results from this protocol pertain only to those conditions of weather and building operation (e.g., heating, ventilation, and air conditioning [HVAC] system status) that prevail during the measurements. It is assumed that the He concentration within the test building can be characterized by a single value throughout the building. This test method has been evaluated and validated against an established method described in American Society for Testing and Materials (ASTM) Method E741-00 modified for this project. The method was validated using test buildings with volumes up to approximately 30,000 cubic-feet (cf).

As mentioned above, this methodology may be applied to individual portions or zones of a building, but in these applications, it is important to carefully isolate the zone volume being tested.

A.2 Glossary of Terms The following terminology is used in the sections that describe the air exchange rate equations.

AER = air exchange rate (exchanges per minute or per day)


A-2 Tetra Tech, Inc.

Ca, air = moles of air per cubic meter of AER (41.4)

CHe(0), C0 = well-mixed He concentration immediately following release of He gas

CHe(ti) = concentration of He inside the building at time ti after an initial release of He (percent by volume)

ln = natural log

N, NP = number of measurements

Σ = sum of mathematical terms

t = time measured starting from He release (minutes)

ti, = time of ith measurement of He (minutes)

A.3 Field Methodology This test method uses measurements of the decay in concentration of He that is instantaneously released as a tracer gas inside a building. The concentration measurements, which can be obtained on-site using a hand-held helium detector or by laboratory analysis of air samples, are used in calculations to estimate the air exchange rate (AER) of the building. Although three mathematical methods are presented to calculate the AER, both rely on a single field implementation method for gathering the necessary data.

A.3.1 Initial Preparations and Setup of Test

A.3.1.1 Determine Building Volume Once the test building has been selected, the building (or zone) volume must be estimated. The volume can best be estimated by direct measurement of length, width, and height of each room. The room volumes are then added together to attain the total test building/zone volume. For complex or large buildings, see ASTM Method 741-00 for alternative methods of estimating building volumes.

A.3.1.2 Procedure, Required Equipment and Supplies The required equipment and supplies are discussed below and summarized in Table A-1. The following equipment and materials are required to properly conduct the test: (1) appropriate number of helium cylinders or containers; (2) air sample containers and a means to collect samples of indoor air. Tedlar® bags are acceptable for this application, although samples should be analyzed as soon as possible after collection as He will diffuse out of the bag. Aluminized polyethylene sample bags are largely impermeable to He and are therefore technically superior but relatively expensive compared to Tedlar® bags. Collection of air samples into the bags is easily accomplished using an appropriate sized (50 to 100 milliliter [ml]) disposable



syringe equipped with a three-way Luer valve and Tygon® tubing connecting the valve to the sample bag (Figure A-1).

Helium concentrations can be measured on-site or samples of the building air can be submitted to a laboratory for off-site analysis. Off-site laboratory analysis of air samples offers better quality control and may be more precise; however, on-site measurement eliminates concern regarding loss of He from the sample, and is more cost-effective than off-site analysis. A hand-held helium detector is recommended for on-site analysis. The detection range of the helium detector must include trace to percent by volume levels in order to adequately characterize the concentration decay curve. A Radiodetection MGD-2002 hand-held helium meter works well for this application (Figure A-2), although it must be kept at a location outside the investigated building zone (i.e. outside areas of high He concentration) in order to maintain proper zero calibration as samples are analyzed throughout the experiment.

If Method #1 is to be used to calculate the AER (Section A.4), a scale for weighing He cylinders before and after release of the He is recommended to estimate the mass released into the building, although the mass can also be estimated based on the vendor supplied volume. The scale should be capable of weighing the He cylinders with a precision of ±0.05 pound (lbs) or 1 ounce. A typical 125 cf cylinder weighs 65 to 80 lbs and may contain a pound of He. A number of readily available fishing scales are suitable (Figure A-3). A scale is not needed if only Methods #2 and #3 (Section A.4) are used to calculate the AER; however, it is recommended to calculate the AER using all three methods.

For purposes of this test method, balloon grade He gas (97 percent purity) is considered adequate. The Helium gas should be supplied in easily manageable cylinders, which can be strategically placed throughout the building and opened simultaneously to maximize fast mixing. Typical 110 to 125 cf, commercially available He cylinders are suitable. Generally, it is recommended that a volume of He gas equivalent to at least 1 percent of the total building volume be released, although this number should be increased to up to 5 percent in buildings where the AER is expected to be high. Figure A-5 can be used to estimate an appropriate starting concentration of helium. Building conditions such as air leakage sites, pressure differences induced by wind and temperature, mechanical system operation, and occupant behavior should all be factored into a qualitative estimate of whether a high AER is anticipated, in order to estimate an appropriate amount of helium for release.



Table A-1 Equipment List

Helium cylinders Air sample containers (e.g. Tedlar bags) Syringe, pump, or other sampling device Tubing, valves, and connectors for sample collection Hand-held helium detector Scale to weigh cylinders Chain-of-Custody forms Ear plugs

A.3.1.3 Set Up Field Test Following selection of the test building, measurement of indoor volume, preliminary estimation of the building’s AER, and acquisition of all requisite equipment and materials, the test can be set up. The building HVAC, doors, windows, etc. should be in the desired settings/position before initiating the test. The He cylinders should be weighed and the initial weights documented. Care should be taken when maneuvering and weighing the cylinders to avoid injuries from lifting or accidentally dropping them. The He cylinders should be strategically placed throughout the building to maximize quick homogenization of the released He into the indoor building volume. The He detector must be properly zeroed in accordance with the manufacturer’s guidance and should remain outside the test building in order to retain proper zero calibration throughout the test. Finally, the sampling apparatus (e.g., sample bag, syringe, 3-way valve, and tubing) should be assembled and set aside for immediate use following release of the He into the building.

If the building is occupied, it will be necessary to brief the occupants on the testing. Typically, occupants will want to know what and why the tests are being conducted, and whether breathing the helium is dangerous. Helium is non-toxic, and the only danger from the gas would be displacement of air; however, this is not a concern at the concentrations expected using this protocol (less than 5 percent). Occupants should be provided with hearing protection (ear plugs) or asked to leave the building during the helium release due to the loud noise.

A.3.2 Conducting the Test

A.3.2.1 Release Helium and Collect Samples Once preparations are complete, the He cylinders are opened simultaneously; a 125 cf cylinder can be expected to completely empty in approximately 30 to 60 seconds. It is important to wear hearing protection during the time of release as the escaping gas is very loud. The time of release is noted and samples are collected at 15, 30, 60, 90, 120 minutes after release, and then every two hours thereafter, or until He concentrations decrease to levels below approximately 5 percent of the initial concentration reading taken at 15 minutes.



Samples are collected by integrating sample aliquots from each room throughout the building into a single sample bag (it is not necessary to sample small rooms such as closets or restrooms) (Figure A-4). The aliquot volume should be proportional to the volume of the room from which the sample is collected, with the objective of obtaining a sample that is representative of the average He concentration in the building or building zone at the sample time (Table A-2). For larger rooms, multiple sample aliquots can be collected from different locations in the room in order to better integrate He concentrations throughout the room. Care should be taken to ensure consistent sampling such that the aliquots are collected from the same location in a room each time, and that the same sample aliquot volumes and total sample volumes are collected each time. Additional sample times can be added if it becomes apparent that the decay of He inside the building is occurring at a faster rate than anticipated.

Table A-2 Example Sample Aliquot Distribution

Room Length

(in) Width

(in) Height

(in) Volume

(cf)

Percent Building Volume


(ml)

Percent Sample Volume

Room 1 296 233 144 5,747 21% 150 21% Room 2 233 183 144 3,553 13% 100 14% Bathroom 66 53 118 239 1% NA NA Room 3 159 125 140 1,610 6% 50 7% Room 4 575 242 144 11,596 42% 300 41% Room 5 215 189 128 3,010 11% 75 10% Room 6 226 121 119 1,883 7% 50 7% Total Volume 27,638 100% 725 100% Definitions: cf – cubic feet in – inches ml – milliliters NA – Not applicable, no air samples collected from the bathroom or HVAC room

A.3.2.2 Analyze/Submit Samples and Document Data Collection If measuring He concentrations on-site, each sample should be taken outside the test area immediately after collection and the He concentration measured using the hand-held detector. Each result is documented and a decay curve can then be plotted in real-time, on-site, as the experiment progresses, allowing for adjustments to the sampling schedule, if warranted. If the samples are to be sent to an off-site laboratory for analysis, the containers should be labeled and an identification number assigned to the samples that allow the results to be associated with the collection time, location, etc.

Samples to be analyzed on-site can be collected in the same sample bag as long as the bag is completely evacuated between samples. If samples are to be analyzed off-site, each sample must be collected in a separate sample bag, labeled, and recorded on a chain-of-custody form and shipped to the laboratory. Tedlar sample bags filled



to approximately two thirds or less of their total capacity can be air-shipped without bursting, although loss of He may occur during transport. The recommended analytical method is ASTM D-1946.

Meteorological data for the test area can be obtained from on-line sources or local weather stations, or a barometer, thermometer, etc. can be used on site to document these conditions as part of the data set. If any of these meteorological conditions or other building conditions such as mechanical system operation or occupant behavior change in the future, the AER may change as well. Because the AER calculated from this test method integrates the conditions throughout the sampling period, it is important to note whether building conditions change during the test (e.g., HVAC system turning on/off, opening/closing of windows, etc.). If multiple air exchange rate tests are performed, it is preferable that these conditions remain constant during each test, and only change between tests.

A.4 Calculation of Air Exchange Rate Three mathematical methods for calculating the AER based on the data collected as described above are presented here. The background theory and derivation of each of the three equations are presented in Appendix B. The equations and example solutions are presented below. As can be seen from the examples, the AER calculated using each method varies slightly. Therefore, it is recommended to calculate the AER using all three methods to obtain a range of estimated AERs.

A.4.1 Example Data Solutions to each of the equations are provided using the example data in Table A-3 below.

Table A-3 t, min CHe

15 0.8 30 0.7 60 0.62 90 0.41

120 0.34 180 0.2 240 0.15 360 0.076 480 0.055

Definitions: t – time in minutes from release of helium CHe – concentration of helium in percent (%)

A.4.1.1 Additional Initial Data for Method 1 Volume of the building: 783 cubic meters (m3)

Mass of He Released: 1,800 grams (g)



Molecular weight of He: 4 grams per mole (g/mole)

Ca, air: 41.40 mole/m3

( ) 2He 10airCa,building theof Volume/

He ofweight MolecularReleased He Mass(0)C ×⋅

= (1)

CHe(0) = Initial He concentration at time t0 = 1.3882 %

A.4.2 Method 1 First, the data presented in Table A-4 are calculated from the Table A-3 data by using the equation

=

(0)C)(tCln)A(t

He

iHei (2)

where

)A(ti = combination of mathematical terms given on right hand side of Equation (2)

Table A-4 t A(ti)

15 -0.55 30 -0.686 60 -0.807 90 -1.22

120 -1.408 180 -1.939 240 -2.226 360 -2.906 480 -3.23

Definitions: t – time in minutes from release of helium

The AER is then calculated using the equation:

∑

∑

=

=

⋅−= NP

1i

2i

NP

1iii

t

t)A(tAER (3)

AER (minutes-1) = 0.00803

AER (day-1) = 11.575



The conversion factor from minutes to days is 1,440 minutes/day.

A.4.3 Method 2 For Method 2, the following equation is applied to the data presented in Table A-3:

∑

∑

=

=

−

−

−= NP

2i

21i

NP

2i1i

1He

iHe

)t(t

)t(t)(tC)(tCln

AER (4)


AER (day-1) = 9.386

A.4.4 Method 3 For Method 3, the following equation is applied to the data presentwd in Table A-3:

2i

2i

iiii

ΝΣt)t(ΣtΝΣy)t)(Σy(ΣAER

−−

−= (5)

where

iy = ln CHe(ti)

N = number of measurements


AER (day-1) = 8.6802

A.5 Procedure to Estimate Air Exchange Rate Test Duration The labeled curves in Figure A-5 represent the time in hours from helium release until concentrations are below a reporting level of 0.05 percent for different AERs. Estimate the expected AER based on observed building conditions. Choose the desired test duration from the curves (3 to 8 hours recommended) then determine the recommended C0 from the horizontal axis. The appropriate number of He cylinders can be determined based on the building volume and the volume of each cylinder.



Figure A-1 Tedlar bag, syringe, and 3-way Luer valve assembly.

Figure A-2 Radiodetection MGD-2002 hand-held helium meter connected to Tedlar® sample

bag.



Figure A-3 Standard 125-cf He cylinder on fishing scale.

Figure A-4 Sample collection



Figure A-5 Time (hours) to reach reporting level for different combinations of CO and AER.

Tetra Tech, Inc. B-1

APPENDIX B THEORY AND SOLUTION TO THREE LEAST SQUARES

METHODS FOR AIR EXCHANGE RATE CALCULATIONS

FROM INSTANTANEOUS HE RELEASES

B.1 Background Theory It is assumed that helium (He) is released quickly (within a minute or two), and mixes completely with the air in the building, as illustrated in the sketch below.

where

Q = the air inflow rate (same as the outflow rate), at steady-state, L3T-1

CHe(t) = concentration of He inside the building at time t after an initial release of He, percent

V = volume of building that mixes with the released He, L3

The governing equation for the time variability of He in the building is given by:

QCdt

VdCHe

He ⋅−= (1a)

subject to:

C0(0)CHe = (1b)

The air exchange rate, AER, is defined as:


B-2 Tetra Tech, Inc.

Q/VAER = (1c)

Equation (1a) can be written:

HeHe CAER

dtdC

⋅−= (1d)

The solution to equations (1d) and (1b) is given by:

t)AERexp(C0(t)CHe ⋅−⋅= (2a)

In the section below, three methods are developed to estimate air exchange rate. All three methods start with the same approach and assumptions described in this section. Method 1 (Section B.2.1) requires knowing or calculating CO and is scaled using least-squares, as are the other methods. The other two methods (Section B.2.2 and Section B.2.3) do not require knowledge of CO. If an accurate estimate of CO can be obtained independently of the modeling framework, then Method 1 may produce the most accurate estimates. In Method 2, CO is eliminated from consideration in the mathematical equation and that can be an advantage if CO is not known with certainty. For the third method CO is calculated as part of the mathematical algorithm. Generally all three methods produce results that are similar to each other. The three methods, then, provide a defensible range of predicted air exchange rates.

B.2 Solutions to Each Least-Squares Technique

B.2.1 Solution for Air Exchange Rate: Method 1 The air exchange rate is found using a least-squares technique. To do this, Equation (2a) is linearized in terms of AER:

=⋅−

C0)(tClntAER iHe

i (3a)

Using least squares, minimize:

∑=

−−=N

1i

2ii )t*AER)A(t(mse (3b)

where

=

C0)(tCln)A(t iHe

i (3c)

)A(ti is a combination of mathematical terms with no specific meaning.

To minimize (3b), set 0*AER

mse=

∂∂ . Without showing steps:



∑

∑

−

=

⋅−= N

1i

2i

N

1iii

t

t)A(tAER* (4a)

(The asterisk denotes the optimal value.)

( ) 210*airCa,buildingtheofVolume/HeofweightMolecular

1000TracerMassC0 ⋅

⋅= (4b)

where

airCa, = 41.4 moles-m-3 (moles of air per cubic meter of air)

it = time since initial release when measurement i was made

• Volume of building: m3

• Mass of tracer (He): kg

• Molecular weight of He: 4 gm·mole-1 An alternative to method #1 can be obtained by slightly re-arranging Equation (3b) before minimizing by first dividing by ti. The resulting formula is:

( )

∑=

−=

N

1i i

He

tco

cln

N1AER*

it

(4c)

where

N = number of observations

This equation is not used in this report, however, due to its similarity to the other methods.

B.2.2 Solution for Air Exchange Rate: Method #2 Method #1 required an accurate estimate of C0, which in turn requires an accurate estimate of the mass of helium released. However, if there are large uncertainties regarding the accuracy of the estimate of C0, C0 can be eliminated by using:

)texp(-aerC0)(tC iiHe ⋅⋅= (5a)

)texp(-aerC0)(tC jjHe ⋅⋅= (5b)



−=−⋅⇒

)(tC)(tCln)t(tAER

jHe

iHeji

Using least-squares the estimate for AER becomes:

∑

∑

=

=

−

−

−= N

2i

21i

N

2i1i

1He

iHe

)t(t

)t(t)(tC)(tCln

AER (6a)

Note that t1 could be replaced by t2 (or t3,--) to obtain alternative estimates of AERs.

The estimate of C0 can now be made from Equation (5a) or Equation (5b) by finding C0 for each ti, and averaging results:

( )

( )∑= ⋅−

=N

1i i

He

tAERexpC

N1C0 it (6b)

B.2.3 Solution for Air Exchange Rate: Method #3 Start with taking the natural logarithm of (2a):

ln CHe(t) − ln CO = −AER ∙ t (7a)

From this, develop a statistical model with an error term:

iii εtβαy +⋅=− (7b)

where

iy = ln CHe(ti)

α = ln C0

β = -AER

iε = error term

The sum of squares of the errors is:

∑∑==

−−=N

i

N

i 1

2i

**i

1

2i )tβα(yε

To minimize the sum of squares of errors invoke the following:



0αε *

2i =

∂

∂∑ (8a)

0βε *

2i =

∂

∂∑ (8b)

On solving these two equations, the optimal estimates for air exchange rate ( *β− ) and for ln C0 (α *) become:

*2

i2

i

iiii* βΝΣt)t(Σ

tΝΣy)t)(Σy(ΣAER −=−−

−= (9a)

and

)tβy(expC0 ** −= (9b)

where

NΣyy i=

(9c)

NΣtt i=

(9d)

N = Number of observations

B.3 Example Applications

B.3.1 Initial Data ti minutes CHe(ti),%

15 0.8 30 0.7 60 0.62 90 0.41

120 0.34 180 0.2 240 0.15 360 0.076 480 0.055

B.3.2 Additional Initial Data for Method 1 Volume of the building: 783 m3

Mass of He Released: 1.8 kg



Molecular weight of He: 4 gm-mole-1

Ca, air: 41.40 mole-m-3

( ) 210*airCa,building theof Volume/ Heofweight Molecular

1000MassTracerC0 ⋅

⋅=

(9)

C0 = 1.3882 %

B.3.3 Method 1

By using Equation (3c):

=

C0)(tCln)A(t iHe

i

ti, minutes A(ti) 15 -0.55 30 -0.686 60 -0.807 90 -1.22

120 -1.408 180 -1.939 240 -2.226 360 -2.906 480 -3.23

By using Equation (4a): ∑

∑

=

=

⋅−= N

1i

2i

N

1iii

t

t)A(tAER*

AER, minutes-1 = 0.00803

AER, day-1 = 11.575

The conversion factor from minutes to days = 1440.

B.3.4 Method 2

By using Equation (6a): ∑

∑

=

=

−

−

−= N

2i

21i

N

2i1i

1He

iHe

)t(t

)t(t)(tC)(tCln

AER


AER, day-1 = 9.386

If t2 were used in place of t1 in equation (6a), the AER would be 9.178.



The estimate of C0 is made by equation (6b): ( )∑

=

=

N

iN 1 i

iHe

)t*exp(-AERtC10C

C0, % = 0.8383

B.3.5 Method 3

By using Equation (9a): *2

i2

i

iiii* βΝΣt)t(Σ

tΝΣy)t)(Σy(ΣAER −=−−

−=


AER, day-1 = 8.6802

and by using Equation (9b): )NΣtA

NΣy(expC0 i*i* ER+=

C0*, % = 0.7559

This prediction of C0* is lower than expected because the measured concentration at 15 minutes is 0.8%. However, because each of the methods used minimizes errors, but does not eliminate them, such small discrepancies are possible.

To facilitate detectable concentrations (C%) being obtained throughout the period of collection, Figure B-1 can provide guidance. The AER range can be estimated prior to the air exchange rate test to help decide how long the test would last with a given initial concentration C0(%). The initial estimate of AER can be from the data generated in this report. Figure B-1 is divided into two panels: (a) which shows AERs as high as 50/day, and panel (b) focuses on AERs less than10/day. For example, consider an estimated AER of 10/day. If we want an AER test that lasts for about 10 hours, set C0=3% (approximately).



(a)

(b)

Figure B-1 Time (hours) required to reach reporting level for combinations of C0 and AER.

Tetra Tech, Inc. C-1

APPENDIX C MODIFIED ASTM METHODS USED DURING PROJECT TO

COMPARE AGAINST LEAST SQUARES RESULTS

C.1 Modified ASTM Methods Using Finite Differences Finite difference methods were developed to compare against the least-squares methods. The following methods were developed and tested:

• Forward finite difference (FFD) methods for continuous and instantaneous tracer releases

• Central finite difference (CFD) methods for continuous and instantaneous tracer releases

C.2 Solutions to Each Method

C.2.1 Finite Difference Techniques for Instantaneous Releases For instantaneous releases, the two formulations are (derivation not shown):

FFD,ΔC

)C(C)AER(tii

i1ii ⋅

−−= +

(Forward finite difference) (1a)

CFD,)Δ(ΔC)C(C-)AER(ti1-ii

1-i1ii +⋅

−= +

(Central finite difference) (1b)

where )t(tΔ i1ii −= + and )t(tΔ 1-iit-i −=

C.2.2 Continuous Release Formulations For continuous release, the two formulations are:

FFD,CV

FΔC

)C(C)(tAibii

i1ii

⋅+

⋅−

−=

•

+ER (Forward finite difference) (2a)

( ) CFD,CV

FΔΔ

)C(C-)(tAERibi1-i

1-i1ii ⋅

++−

=

•

+

iC � (Central finite difference)

(2b)


C-2 Tetra Tech, Inc.

Often the interval Δi between two sampling times is approximately 10 minutes. Because of this short interval, the air exchange rates can exhibit oscillations. To dampen the oscillations and to generate longer-term averages (such as hourly air exchange rates), a moving average air exchange rate can be calculated. A seven-point moving average, with 10 minute sampling intervals, produces one-hour air exchange rates for example.

Tetra Tech, Inc. D-1

APPENDIX D MATLAB CODE

D

Matlab code is provided in this section for each of the three methods of calculating AERs using instantaneous releases of He. Matlab is a commercially available code and was used for the analyses presented in this report. However, Matlab does not have to be used, and a simpler method is provided at the end of Appendix B. To create the Matlab code for one of the three methods, create a Matlab function and input the required data.

D.1 Method LS-1: function[AER_min AER_day Conc C0 ] = LeastSquareMethod1(C0, C, T_minutes)

convertMinDay = 60*24;

dp = length(T_minutes);

[r c] = size(T_minutes);

if (r>1)

T_minutes = T_minutes';

end

[r c] = size(C);

if (c>1)

C = C';

end

SumT = 0;


D-2 Tetra Tech, Inc.

SumAT = 0;

A=zeros(1,dp);

for i = 1 :dp

A(i) = log(C (i)/C0);

SumT = SumT + T_minutes (i)^2;

SumAT = SumAT + A(i) * T_minutes (i);

end

AER_min = -SumAT /SumT ;

AER_day = AER_min * convertMinDay;

Conc = C0 * exp(- AER_min * (T_minutes));

D.2 Method LS-2: function[AER_min AER_day Conc C0] = LeastSquareMethod2(C0, C, T_minutes)


dp = length(T_minutes );


if (r>1)


end

[r c] = size(C);

if (c>1)

C = C';

end

SumT = 0;


Tetra Tech, Inc. D-3

SumAT = 0;

for i = 1:dp

delta= T_minutes (i)-T_minutes(1);

SumAT = SumAT + log(C(i)/C(1)) * delta;

SumT = SumT + delta^2;

end

AER_min = -SumAT /SumT ;


Conc = C(1) * exp(- AER_min * T_minutes (2:dp));

Conc = [C(1) Conc];

C0_m2= C'./(exp(- AER_min* T_minutes));

C0 = mean(C0_m2);

D.3 Method LS-3: function[AER_min AER_day Conc C0] = LeastSquareMethod3(C0, C, T_minutes)



if (r>1)


end

[r c] = size(C);

if (c>1)

C = C';

end


D-4 Tetra Tech, Inc.

y = log(C);

X = [ones(length(y),1) T_minutes'];

b2 = regress(y, X);

AER_min = -b2(2);


C0 = exp(b2(1));

Conc = C0 * exp(-AER_min.* T_minutes);

Documents

Final Report for Air Exchange Rate Analysis and Protocol