Offsite Consequence Analysis (OCA) Hazard Assessments...Kazarians & Associates, Inc. Worst-Case Scenario Release quantity shall be the greater of the following: – The greatest amount

Offsite Consequence Analysis (OCA) Hazard Assessments

Presented byMichael Tia

Presented atLEPC Region 1 Meeting

February 10, 2016

Kazarians, & Associates, Inc.

Kazarians & Associates, Inc.

Topics1. Basics of accidental releases2. Dispersion plumes and atmospheric

conditions3. Incidents involving accidental releases4. Regulatory requirements5. Dispersion models


PurposeDetermine the offsite impacts in the event of a hazardous materials release and provide information for emergency response

California Accidental Release Prevention Program (CalARP), Title 19, Division 2, Chapter 4.5, Article 4

Risk Management Programs for Chemical Accidental Release Prevention, 40 CFR Part 68, Subpart B.


Release Phases

Liquid

Vapor

Two-phase

Aerosol


Example of Types of releases

Catastrophic vessel failure Leak in pipe or vessel Liquid spill and evaporation High momentum jet release Two phase jet (e.g., liquid rainout) Lighter than air plume Heavier than air plume


Typical Vessel Leak Scenarios

Image taken from Understanding Atmospheric Dispersion of Accidental Release, CCPS, 1995


Hazardous Release Event Tree We want to model at

least the worst case scenario.

Image taken from Guidelines for Chemical Process Quantitative Risk Analysis, CCPS, 1989


Liquid Pools

Boiling liquid– Pool remains at boiling point and total mass evaporation

rate is equal to heat flux/heat of vaporization

Evaporation of a volatile liquid– Heat loss of boiling or rapid evaporation can be great

enough to cause autocooling– Pool temperature decreases below liquid boiling point

Evaporation of a relatively non-volatile liquid– Evaporation driven by convection


Example of Evaporation and Dispersion from Liquid Pool

Image taken from Guidelines for use of Vapor Cloud Dispersion Models, CCPS, 1987


Gaussian Plume Distribution

Image taken from EPA

Release point will have the highest concentration

Concentration reduces further downstream due to mixing, but radius of cloud expands


Dispersion and Atmospheric ConditionsDispersion is dependent on wind and weather conditions Stability class Wind speed and direction Ambient temperature Surface friction


Pasquill Stability Classes

Image taken from Understanding Atmospheric Dispersion of Accidental Release, CCPS, 1995


Dispersion Plumes

Image taken from Handbook of Chemical Hazard Analysis Procedures, Federal EMA

Image taken from Guidelines for Chemical Process Quantitative Risk Analysis, CCPS, 1989


Liquid Pool and VCECaribbean Petroleum Tank Terminal Explosion (CAPECO) – October 23, 20091. Liquid overfill of

gasoline tank resulting in liquid pool

2. Aerosolized gasoline forming a vapor cloud

3. Damaged homes/businesses up to 1.25 miles

Image taken from the Chemical Safety Board (CSB)


Vapor Release – Buoyant PlumeMillard Refrigerated Services Ammonia Release

1. Vapor release of ammonia

2. Between 250 to 450 ppm of ammonia detected 0.25 miles away



Vapor Release – Non-Buoyant Plume

1. DPC Enterprises in Festus, Missouri

2. Vapor release of chlorine from unloading hose

3. 4 feet high yellowish-green fog covered the area 3.5 hours after the release, when HAZMAT personnel entered the release area.



RMP Program Levels

Program 1– One Worst-Case release scenario for each toxic

and flammable substance above TQ Program 2 & 3

– One Worst-Case release scenario to represent all toxics and one to represent all flammables above TQ

– One alternative release scenario for each regulated substance


Brief Regulatory Requirements

Worst-Case release scenario Alternative release scenario Offsite Impacts to population Offsite Impacts to environment Updated once per five-years Five-year Accident History


Worst-Case Scenario Release quantity shall be the greater of the following:

– The greatest amount held in a single vessel– The greatest amount in a pipe

Wind speed/atmospheric stability class – 1.5 m/s and F Ambient temperature/humidity – highest daily maximum

in the previous three years and average humidity. Height of release – ground level (0 feet) Surface roughness – urban or rural Temperature of release – Other than gases liquefied by

refrigeration, highest daily maximum temperature for the previous three years or at process temperature


Worst-Case Scenario

Wind direction cannot always be easily estimated – Worst case is provided in the highest

concentration that would be expected at a given radial distance from a release point.

– We are looking for calm, low wind speed conditions where turbulent mixing rates are low.


Alternative-Case Scenario One alternative release scenario for each regulated toxic and

flammable substance More likely to occur than the worst-case Will reach an endpoint offsite, unless no such scenario exists May use methodology in RMP OCA Guidance or any available

air dispersion modeling techniques Passive mitigations may be considered Select scenarios from either the 5-year accident history or

PHA


Toxic Endpoint

Appendix A of RMP Regulation


Flammable Endpoints

Endpoints vary according to the scenarios studied:– Worst-case

• Explosion – overpressure of 1 psi

– Alternative-case • Explosion – overpressure of 1 psi• Radiant heat/exposure time – 5 kw/m2 for 40 seconds• Lower flammability limit – provided by NFPA or other

generally recognized sources.


Explosion Overpressure Damage Estimates

Lee’s Loss Prevention in the Process Industries, Vol. 1

Overpressure (psig) Expected Damage0.15 Typical pressure for glass failure0.7 Minor damage to house structures1 Partial demolition of house structures

2.0-3.0 Non-reinforced concrete or cinder block walls shattered2.4-12.2 Range for 1-90% eardrum rupture among exposed populations

5 Wooded utility poles snapped7 Loaded train cars overturned

10 Probable total building destruction14.5-29.0 Range for 1-99% fatalities among exposed populations due to direct blast effects

Sheet1

Overpressure (psig)Expected Damage

0.15Typical pressure for glass failure

0.7Minor damage to house structures

1Partial demolition of house structures

2.0-3.0Non-reinforced concrete or cinder block walls shattered

2.4-12.2Range for 1-90% eardrum rupture among exposed populations

5Wooded utility poles snapped

7Loaded train cars overturned

10Probable total building destruction

14.5-29.0Range for 1-99% fatalities among exposed populations due to direct blast effects


Modeling Methods

EPA’s Offsite Consequence Analysis Guidance

EPA models such as RMP*Comp, ALOHA, Degadis

Other commercially available computer models such as SLAB, Phast


EPA’s RMP*Comp and Offsite Consequence Analysis Guidance

ProsFree

Simple to use

Compliant with the rule

ConsConservative results

Few site-specific factors considered

Best resolution 0.1 mile

Taken from Risk Management Program Guidance for Offsite Consequence Analysis, USEPA


Example of Dispersion Analysis Results


Other EPA models such as ALOHA

ProsFree/little cost

Simple to use

ConsConservative results

May not include chemical specific data

May not address all consequences


Commercially available models such as Phast

ProsMay address a variety of scenarios

May consider many site-specific factors

ConsMay be expensive

May require a high level of expertise


Identifying Offsite Impacts

Public Receptors– Residential– Schools– Hospitals– Prisons– Public Recreational

areas– Commercial or

industrial areas

Environmental Receptors– National or state parks,

forest, or monuments– Designated wildlife

sanctuaries, preserves, refuges

– Federal wilderness areas


Identifying Offsite Impacts

MARPLOT Local street maps U.S. Geological Survey maps Publically available search engines (yahoo,

google, yelp) California Department of social services

(www.ccld.ca.gov)


Summary

Offsite Consequence Analysis results are meant to err on the side of conservatism to account for worst-case conditions

Different models exists with their own pros and cons


Questions?

Offsite Consequence Analysis (OCA) Hazard AssessmentsTopicsPurposeRelease PhasesExample of Types of releasesTypical Vessel Leak ScenariosHazardous Release Event TreeLiquid PoolsExample of Evaporation and Dispersion from Liquid PoolGaussian Plume DistributionDispersion and Atmospheric ConditionsPasquill Stability ClassesDispersion PlumesLiquid Pool and VCEVapor Release – Buoyant PlumeVapor Release – Non-Buoyant PlumeRMP Program LevelsBrief Regulatory RequirementsWorst-Case ScenarioWorst-Case ScenarioAlternative-Case ScenarioToxic EndpointFlammable EndpointsExplosion Overpressure Damage EstimatesModeling MethodsEPA’s RMP*Comp and Offsite Consequence Analysis GuidanceExample of Dispersion Analysis ResultsOther EPA models such as ALOHACommercially available models such as PhastIdentifying Offsite ImpactsIdentifying Offsite ImpactsSummarySlide Number 33

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Offsite Consequence Analysis (OCA) Hazard Assessments...Kazarians & Associates, Inc. Worst-Case Scenario Release quantity shall be the greater of the following: – The greatest amount