Chlorine Theft Scenarios

One of the things that a professional blogger does is to keep track of how people get to his site; it helps us work at keeping them coming. One of the tools that I use to do this is Google Analytics®, an on-line tool that lets me keep track of referring sites and search engines that people use to find my site. One of the things that it tells me is the key words people use in search engines that brings them to my writing. A key word phrase that has been creeping up the charts over the last couple of weeks has been “Chlorine Theft Scenarios”. That’s more than a little odd, since I can’t find any where that I have actually written on that specific topic, though I have looked at chlorine threat in passing on a number of occasions. So, I’ll correct that oversight now. Theft and Release COI Chlorine is one of the DHS Chemicals of Interest (COI) that falls under two separate categories; it is both a theft/diversion COI and a release COI. That means that facilities with large quantities of chlorine gas would be concerned about the consequences of an on-site release that would affect large civilian populations. Facilities with smaller quantities of chlorine gas do not present much of an off-site hazard as the dispersion of the chemical would reduce the potential health risk. Instead, DHS would be more concerned about a terrorist stealing the more portable containers of chlorine gas and then using them to release the gas at some other location where the dispersion area would be compact enough to keep the gas at a toxic concentration. The screening threshold quantity (STQ) for chlorine as a release-toxic COI is 2,500 lbs. There have been some complaints for the 2,500 lb STQ because this would theoretically allow a facility to have one-ton cylinder on site and remain below the threshold. In practice most facilities would at some point have a second cylinder of chlorine to switch over to once the first was emptied. Trying not to get the replacement cylinder on site until the primary cylinder contains less than 500 lbs would be a good theoretical procedure, but one that would periodically fail in actual practice. The STQ for chlorine as a theft-toxic COI is 500 lbs. This is a bit more problematic. The next smaller size standard shipping container for chlorine gas is the 150-lb cylinder. Even smaller lab-scale cylinders are available. A facility that utilizes the 150-lb cylinders could have three full cylinders on site and not be required to file a Top Screen; thus they would not fall under CFATS under the current rules. DHS recognized that the wide spread use of these cylinders in industrial water treatment and a number of chemical manufacturing processes would make it impractical to regulate at the less than 150-lb level. In the preamble to the final rule on Appendix A, 6 CFR part 27 (72 FR 65407) DHS noted that: “DHS believes that quantities less than 500 pounds would capture facilities that are unlikely to present significant consequences.” They further noted that: “Overall, DHS’s approach toward chlorine recognizes that chlorine is distinct from other WME precursors in terms of its broad utility and availability.” Stealing Chlorine Gas Now, a 150-lb cylinder is not a man-portable container in the classic meaning of the term, but it could be routinely handled with a pallet jack (think manually powered fork-lift). One would not expect these to be easy to steal. I have, however, reported on the theft of one of these cylinders in Houston, TX in 2007 and two similar thefts in California earlier that year. There is no telling how many other thefts may have happened, but never made it into the press. Chlorine Cylinders as Weapons The Chlorine Institute Pamphlet 74 provides estimates of the areas that would be affected by the release of chlorine gas from various storage/shipping containers. It estimates that a 150-lb cylinder would have a gas cloud at 20 ppm concentration (really dangerous but not probably not deadly) that would extend about 0.6 miles ( about 3200 feet) from the source of the leak with a cloud width of up to 0.2 miles (about 1000 feet). That dispersion is based on an open air release with a steady state wind speed. In an enclosed space like a mall the danger area would be smaller, but the concentration could be high enough to reach deadly levels in many areas of the building. Re-marked as a helium cylinder the material could be placed at a party goods store or balloon kiosk in the mall. The first time that it was used to fill a balloon the person operating the system would probably be overcome before they could shut the valve. The cylinder would be emptied before emergency response crews could respond with properly equipped personnel.

Alternatively, an electronic valve could be placed on the cylinder and it could be opened by a cell phone call or computer command. Again, remarking the cylinder as a helium cylinder could allow it to be placed at any number of places without undue suspicion. The discharge of the chlorine gas on a busy shopping day could cause hundreds of deaths and serious injuries as well as wide spread panic.