Monday, August 9, 2010

TSA and Chlorine Dispersion Modeling

This weekend I ran into an interesting article over at It briefly describes some concerns that the Transportation Safety Administration (TSA) has with the current scientific model used to describe the dispersion of chlorine gas from a catastrophic release from a chlorine railcar. It seems that the chlorine cloud from the two most recent catastrophic releases of chlorine from rail cars did not come anywhere near following the dispersion model for the release. TSA is initiating a two phase study of chlorine gas dispersion to clarify these discrepancies.

Chlorine Gas Dispersion Model 

I had a rather detailed discussion (for a blog) of the current chlorine gas dispersion model in a blog post back in March of this year. I discussed the model description in the Chlorine Institute’s Pamphlet 74 that is the currently accepted standard description of the chlorine gas release from a large hole in a chlorine railcar. I summarized that model in a single paragraph this way:
“Now, having exposed the hype, it must be clearly understood that there will be a significant area under the exposure curve where people will die if they are not adequately protected against exposure. There is an even larger area where there will be serious medical consequences from exposure to the peak concentration levels as the toxic cloud passes through the area. Looking at the charts on pages 24 and 25 of Pamphlet 74 it looks like anyone inadequately protected in the cloud for up to a couple of miles away from the catastrophic release from a full railcar is at serious risk of being killed by the cloud. Inadequate protection in the cloud at distances of up to 15 miles from the release could have very serious medical consequences.”
A TSA document prepared as part of their solicitation for commercial services for the first part of this study describes the reality of the results in 2004 and 2005 this way:
“However, evidence available to TSA suggests that this may not have happened in the Graniteville and Macdona chlorine releases. Unexpectedly, the released material appears to have had most of its impact in the area close to the release point with little downwind effects.”
TSA Modeling Study TSA is the agency responsible for assessing and regulating the security of chlorine gas in transit; protecting against a terrorist attack, if you will. As such they need to have a clear understanding of the potential consequences of such a terrorist attack. Thus TSA is preparing to conduct a two-part study of the situation. The first part will be a detailed review of the two accidents where there was a catastrophic release of chlorine. TSA expects to hold a seminar type meeting to evaluate what happened at those two incidents. That seminar is currently being tentatively scheduled for January, 2011.

A contractor, yet to be selected, will be responsible for collecting the information and putting it into a presentation format for this seminar. The second phase will be a physical study conducted with the US Army Edgewood Chemical and Biological Center (ECBC). I have not yet seen any details about that portion of the study. It will be interesting to see what comes of these studies and how much TSA actually intends to share with the potentially affected public. The ISCD folks might want to join TSA in this study because it would also be expected to pertain to protecting high-risk chemical facilities that produce, store, or use large quantities of chlorine gas. The Chlorine Institute might also have an interest in this study.

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