Using Carbon Dioxide as a Tracer Gas

8/12/2019 Using Carbon Dioxide as a Tracer Gas

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Boelter & Yates, Inc. 2004

Situation

Procedure was needed to determine the

ventilation rate in air changes per hour(ACH) for representative boiler rooms and

an isolation test chamber.

Ventilation information was needed to

perform a retrospective exposure

assessment.


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Problem

Existing methods allow for the use of a variety of tracer

gases to be used.

Each has advantages and disadvantages.

Selected method highly portable

easily measured

non-toxic or very low toxicity

inexpensive

Tracer gas acceptable to school district personnel.


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Research Standard Test Method for Determining Air Change in a

Single Zone by Means of a Tracer Gas Dilution ASTM E

741 00 Tracer gases (examples)

CO2 PEL 5000 ppm

SF6 PEL 1000 ppm

CO PEL 50 ppm

Selection of test method

Concentration Decay

Constant Injection Constant Concentration


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Resolution

Selection of tracer gas

Carbon dioxide

Relatively high PEL

Inexpensive

Easy to obtain and measure

Acceptable to School personnel Selection of method

Concentration Decay Test Method Measures the decay rate of carbon dioxide over

time to calculate the air exchange rate. Regression Analysis

InC(t) = -At + C(0)


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Sample Time

20.5

.254

.52

11

40.25

Minimum Duration (hour)Air Change Rate (1/hr)

Minimum sample duration based on 10% uncertainty at the 95%confidence level in the detection of air change rate, a tracer gas

concentration measurement precision error of 5% of reading and

various air change rate. Using the regression method reduces the

minimum test duration due to more than 2 data points.


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Boiler Room Ventilation

Testing Using Tracer Gas

Representative Boiler Rooms

Elementary School - IN

Elementary School - IL

Middle School - IL


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Gas Injection and Distribution


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Direct Reading Equipment

TSI Q-Trak

Log Data


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School

Indiana

5500 ft3

Boiler Room Volume of gas needed

Calculated based on roomsize and target

concentration of 4000 ppmVtracer= Ctarget X Vzone 2 boilers

Input BTU/hr. - 117,000

Input BTU/hr. 156,000 Both boilers operating

during the testing

No mechanical ventilation


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Average CO2 Concentration vs Time Indiana Boiler Room - 2 Boilers Operating

March 26, 2003

0

500

10001500

2000

2500

3000

35004000

4500

1 7 13 19 25 31 37 43 49 55 61 67 73

Time in Minutes

Car

bonDioxide

Concentr

ationinPartsP

er

Million(PPM)

Trial 1 - AverageCO2 Concentration

(PPM) 5.2 Air

Changes Per Hour

Trial 2 - Average

CO2 Concentration

(PPM) 5.3 Air

Changes Per Hour

Trial 1 5.2 ACH Trial 2 5.3 ACH

Average 5.2 ACH


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Elementary School

Illinois

Measured Volume

24,322 ft3. 2 Boilers

Ventilation tracer

gas testingconducted with

boilers on and off.


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Ventilation Rate - Boilers Off

1.8 Air Changes Per Hour

March 27, 2003

0

1000

2000

3000

4000

0 18.75 37.5 56.25

Time in Minutes

Carbon DioxideConcentration(ppm)

Trial 1

Boilers Off - 1.8 ACH

Average CO2 Concen tration vs Time

March 27, 2003

0

1000

2000

3000

4000

5000

0

2

.2

5

4

.5

6

.7

5 9

1

1

.3

1

3

.5

1

5

.8

1

8

2

0

.3

2

2

.5

2

4

.8

2

7

2

9

.3

3

1

.5

Time in Minutes

Carbon

Dioxide

Concentration

(ppm

) Trial 2 - Average Carbon

Dioxide Concentrations

with 2 Boilers Operating

Trial 3 - Average Carbon

Dioxide Concentrations

with 2 Boilers Operating

Boilers On

Trial 2 3.5 ACH

Trial 3 3.9 ACH

Average 3.7 ACH

Elementary SchoolElementary School


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Average Carbon Dioxide Concentration (ppm) vs

Time

Middle SchoolMarch 21, 2003

0

1000

2000

3000

4000

5000

0 25 50 75

Time in Minutes

Carbon Dioxide

Concentration (ppm)

Boilers Off

1.2 ACH

Average CO2 Concentr ation vs Time

Boiler Room - 2 Boiler s

March 31, 2003

0

1000

2000

3000

4000

5000

1 11 21 31 41 51 61 71 81 91

Time in Minutes

CarbonDioxide

Concentration(PPM)

Boilers On (1 boiler on part

time): Trial 2 - Average CO2

Concentration 4.4 Air

Changes Per Hour,

GlenCrest School March 31,

2003

Boilers On: Trial 3 - Average

CO2 Concentration 5.3 Air

Changes Per Hour,

GlenCrest School March 31,2003

Boilers On

Trial 2 - 4.4 ACH

Trial 3 - 5.3 ACH

Average 4.9 ACH

Middle School


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Measured Range of Boiler Room

Ventilation

Summary Boilers Off

Range: 1.2 to 1.8 ACH

Boilers On

Range: 3.7 to 4.9 ACH


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Isolation Test Chamber

Approximately 20 x 20 x 9(3600 ft3)

Wood Frame

Polyethylene sheeting on

walls and floors

2 viewing windows Entrance airlock

Decontamination Shower (ifneeded)

HEPA fil tered exhaustmachines for ventilation


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HEPA Filtered Exhaust Machinesfor Chamber Ventilation System

Note: Using various configurations, both machines operated

as exhaust (tubing was attached to machines to exhaust

outside the building).


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Installation and Measurement of

Ventilation System

Various configurations to achieve

approximately 1, 3, 5 and 10 ACH

Carbon dioxide tracer gas used to

measure venti lation rate. Each rate tested twice to assure

repeatability.

Final ventilation rates were: 1.2, 2.9, 5.7,10.7 ACH.


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Carbon Dioxide Concentration (ppm) vs Time

B & Y Test Chamber5.7 Air Changes Per Hour

April 29, 2003

0

1000

2000

3000

4000

5000

6000

16:28

16:30

16:32

16:34

16:36

16:38

16:40

16:42

16:44

16:46

16:48

16:50

Time

C

arbonDioxide

Con

centration(ppm

)

Trial 1 - high

Trial 1 - low

Trial 2 - high

Trial 2 - low



Average 5.7


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Conclusions

Ventilation rates for representative boiler

rooms were between 1 and 5 ACH.

Using carbon dioxide as a tracer gas andfollowing ASTM E 741 00, Standard TestMethod for Determining Air Change in aSingle Zone by Means of a Tracer Gas

Dilution met the objectives and goals of theproject.


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Benefits Carbon Dioxide as a tracer gas

Inexpensive, reliable procedure for IHs to determineventilation rates.

Measuring Equipment is readily available

The method provides an additional tool forindustrial hygienists to better characterizeworkplace conditions during the initial stages ofan exposure assessment.

Ventilation information is critical to the ability toperform and validate mathematical modeling for

exposure estimation.


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+

+

+

+

+

= tV

VkQ

expCtV

VkQ

exp1VkQ

QCG

C(t)LL

L

IN

0

Well Mixed Room ModelWell Mixed Room Model -- ConstantConstant

Contaminant Emission RateContaminant Emission Rate

Initial concentrationC0

mg/m3

Loss Pathway (sinks)KL per min

Volume of RoomV m3

Exhaust air flowQ m3/min

Generation RateG mg/min

Concentration in incoming airCIN

mg/m3

Input Variables


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Predic ted Concentration at 0.01, 0.1, 1, 3, 4, 5 and 10

Air Changes Per Hour

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 3 6 912 15 18 21 24 27 30 33 36 39 42 45

0.01

ACH0.1ACH1 ACH

3 ACH

4 ACH

5 ACH

10ACH

Effect of Ventilation Rate on

Concentration of Contaminant


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Thank you!

Questions?

Speaker Contact Information:

Catherine E. Simmons, CIH

Boelter & Yates, Inc.

Park Ridge, [email protected]

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Using Carbon Dioxide as a Tracer Gas