Chemical Agents of Opportunity for Terrorism: TICs & TIMs

Chemical Agents of Opportunity for Terrorism
Training Support Package
Participant Guide
Slide 6
Chemical Agents of Opportunity for Terrorism:
TICs & TIMs
Bhopal Disaster
• Gas plume drifted over shanty -
town exposing 250,000 people
• Temperature inversion reduced
plume dilution
• Extent of risk:
– Modeled mean MIC ambient
concentration: 27 ppm (range
0.12 -85.6 ppm)
– Median MIC concentration: 1.8
ppm
– 30 minute Acute Emergency
Guideline Level -3 (AEGL3) 0.40
ppm
http:// www.bhopal.org/whathappened.html
Module One – Toxic Industrial Gases as Terrorist Threats
6
Approximately 250,000 people were exposed to the MIC gas fume. A temperature
inversion in the local area reduced the extent of a plume dilution effect that would have
occurred under normal weather conditions. After the fact, modeling suggested a median
air concentration of MIC of 1.8 ppm. This exceeded the AEGL-3 of 0.40 ppm which was
the predicted airborne concentration above which people are likely to experience life
threatening health effects or death.
Temperature inversions occur when the temperature of the atmosphere increases with
height. During a temperature inversion, warm air traps cool air below, acting like a lid.
Pollutants below the inversion are trapped, allowing them to build up. In the Bhopal
case the temperature inversion limited the usual dilutional effect of the chemical plume
increasing the airborne concentration of the MIC.
AEGLs are “acute exposure guideline levels” which have been developed for a number
of chemicals. The modeled concentrations after this release were quite a bit above the
threshold for devastating health effects, consistent with the actual events.
The map on the slide depicts the modeled distribution of the methyl isocyanate plume
following this release. The darker shading indicates higher gas concentration. The extent
of heavy concentration represents the lack of dilutional effect from the temperature
inversion and low wind speed. Note the extension in all directions with more prominence
towards the south, also representing the effects of a low wind speed.
December 2008 Version 2.0 Page 130