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