Fred Millar left a comment on my blog from last month about the DHS subway study being conducted in Boston. He wrote:
“How many major target city subway systems have in close proximity a non-re-routed freight line carrying chlorine gas and other TIH cargoes? You won't find this issue discussed on any transit rail website. Best defense: insert head in sand.”
While Fred and I agree that railcars of chlorine in major urban areas is a potential security (and safety) problem I have to disagree with Fred here that this would be a major mode of attack against subways. Where most transit and freight lines share space would be where the intra-city trains are above ground. Since they would be moving through the chlorine cloud at speed, they would be less affected than people living or working in the area of the release.
Where subways have a greater problem with TIH gasses like chlorine is when they are under ground. Since chlorine (and many other TIH chemicals) is heavier than air it would have a tendency to collect in subway tunnels. While trains moving through a limited chlorine cloud would still have the advantage of getting out of the cloud quickly, the lethal cloud would spread a longer distance underground because of the limited volume involved.
Actually, the ideal way to attack a subway (other than through the use of explosives or a shooter attack which are always the easiest attacks) would be to hijack a chlorine tank truck and stick the discharge hose into a subway vent. Of course, it would take only a limited number of gas detectors to protect the subway system and evacuation would be fairly straight forward.
No, a much better way to attack subways would be a few well placed explosives detonated when trains entered stations and a few well placed shooters on the stairs. Lots of ugly deaths, panic and terror; a much easier attack to pull off and the shooters could probably escape in the panic. Terrorists should always follow the KISS principle.
I spent 15 years in the US Army as an Infantry NCO. After getting out of the Army I started working in the chemical industry, getting my BSc Chemistry degree while working as a technician. I spent 12 years working as a process chemist in a specialty chemical company. I'm now working as a QA Manager in a specialty chemical manufacturing facility.