BAKER ENGINEERING AND RISK CONSULTANTS, INC.

©2010 Baker Engineering and Risk Consultants, Inc.

Shelter in Place Design for Toxic and

Flammable Hazards: Case Study

Anay P. Raibagkar

2017 CSCE Annual Conference

Key Items

Industrial Hazards

Shelter in Place (SIP)

Dispersion Modeling: Dispersion of Toxic Cloud

Building Leak Tightness: Tracer Gas Test

Occupant vulnerability from Toxic Hazards

Recommendations

Industrial Hazards

Explosion

Fire

Bhopal Disaster

Largest Industrial accident in the history

Over 500,000 people were exposed to methyl

isocyanate (MIC)

The official immediate death toll was 2,259

Occurred on the night of 2–3 December 1984 at

the Union Carbide India Limited (UCIL) pesticide

plant in Bhopal

Gas Dispersion

Case Study

SIP: Control Room Building

The control room building must be able to provide a

safe shelter for at least 60-mins in case of a toxic

release

Toxic Hazards: Hydrogen Sulfide

Evaluate building’s leak tightness – Tracer Gas

Testing

Calculate toxic concentration inside the building

from dispersion results and leak tightness

Provide recommendations on leak tightness

Key Issues

Building: Shelter In Place

Toxic

Release

1

Toxic

Release

2

Toxic

Release

3

• Multiple toxic release

locations (one or more

types of toxics)

• Several possible wind

directions with different

probabilities

• Angle of Release: Several

Possibilities

• Building has different

leakage characteristics at

different wind speeds

• CFD techniques can be

used but input data is

difficult

Hydrogen Sulfide Limits

Ref: http://enviromed.ca/index.php?id_cms=26&controller=cms

Dispersion Modeling

Toxic Cloud

Building

Dispersion modeling must consider

- Different weather conditions and wind speeds

- Potential release sources

Tracer Gas Test

Tracer gas test is used to determine building’s

leak tightness

Leak Tightness is typically defined in terms of Air

Changes Per Hour (ACH)

1 ACH means building will replace its entire

volume of air in one hour with air leaking from

outside

Test involves the release of Carbon Dioxide into

the building and observe the decay of its

concentration over time

Tracer Gas Test - Result

What is a good SIP?

Wind is Bad! Makes Building Leaky

Toxic Concentration Calculation

0

50

100

150

200

250

0 10 20 30 40 50 60

Co

nce

ntr

atio

n (

pp

m)

Time (min)

Building Conc.

SIP Conc.

AEGL-2 Limt (27ppm)

0.1% OccupancyVulnerability (132ppm)

Toxic concentration inside the building is a function of

- External concentration (obtained from dispersion

modeling)

- ACH from tracer gas test

-Assume perfect and instantaneous mixing (uniform

Recommendations and Results

Relationship between infiltration rate and duration for which the SIP can be considered

“safe”

Recommendations and Results

Conclusions

Effectiveness of a building envelope against

toxic hazards is critical in designing a good

shelter in place building

Design must rely on dispersion modeling under

various weather conditions

Building’s leak tightness must be evaluated on a

case by case basis

After retrofits have been installed, ACH should

be confirmed with another test

Questions?

Thank You