Monday, August 21, 2017

Chlorine Incident Kills Two

This weekend there was an unusual incident in Mississippi where an auto accident involved a rural water treatment works. It resulted in the breach of a chlorine gas cylinder and the death of the two occupants of the car. As is usual, the details about the accident are sketchy, but with the help of Google Maps® and some industry knowledge, we can ferret out some lessons.

The Facility

The news article reports that two people were in a stolen car driving down a rural road when the “car slammed into the utility station, rupturing a large tank of chlorine”. In rural America, the only kind of ‘utility station’ that houses chlorine gas is a local drinking water pumping station. Searching Google Maps we can find that utility station here, on the west side of the road.

Looking at it on Street View®, we see a large, white, horizontal tank within a chain-link fenced enclosure. There is a small box-like structure, a pipe, a well-pump and an electric service pole with a nearby electrical panel.

I suspect that the reporter thought that the large white tank was a chlorine tank, but that is certainly not the case. First off, that tank is way too large; it would contain multiple years’ worth of chlorine gas for a facility this size. Second, chlorine gas is delivered in portable cylinders. For a facility of this size, that is typically a 50-pound cylinder that looks somewhat like a welding-gas cylinder. Two such cylinders will be found in the white box to the right of the tank; the one in current use and the backup for when the first is emptied. By the way, that large tank is a water tank, providing the pumping station with surge capacity.

The Accident

Looking at the map, I would guess that the car was proceeding north on Palmer Creek Drive, probably at a high-rate of speed. Instead of making the curve to the right, it continued straight and hit the large water tank. As part of the collision either the chlorine control box, or more likely the chlorine gas line from the box to the water system was damaged, releasing a small yellowish green cloud of chlorine into the atmosphere. It is not clear (and will not be until the autopsies are complete) if the chlorine gas, the injuries from the collision of a combination of the two caused the deaths of the occupants of the car.

There were chlorine gas related injuries to ‘several responding deputies and at least one fire fighter’. The Street View data is from 2013 and I cannot see any chlorine gas warning signs. It is quite possible that deputies responding to the accident did not know about the chlorine gas at the facility and approached the scene too closely. Fortunately, the small cloud would have dispersed enough to leave it a less-than-deadly concentration that they walked into, so the injuries were reportedly fairly minor.

Local residents were instructed to shelter-in-place in an abundance of caution. Again, with the small amount chlorine gas present, there was almost certainly no more danger at nearby residences than would be found in sniffing at the top of an open household bleach container.


Since the incident happened on Saturday night it was almost certainly a joy-riding accident. If it had happened twelve hours later, there would have been a very remote chance of it being an attack. There is a church located next to the treatment works it would have been remotely possible that the incident was an inept attempt to gas the congregation.

It would have been fairly easy to accomplish that type of attack by entering the facility with a pair of bolt cutters and a pipe wrench. But, again, releasing the chlorine gas at the facility would have resulted in a less than deadly gas cloud at the church, even if the breeze was blowing in the correct direction.

Of course, an even more effective attack could have been executed by removing the gas cylinders from the facility and then piping the connection into any sort of facility air-handling equipment that the attackers desired. Depending on the size of the facility, a lethal concentration of chlorine gas could possibly be introduced fast enough to cause some deaths. A large number of serious injuries and panic could certainly be an expected result.

There are no requirements under either the EPA water facility security regulations or the DHS Chemical Facility Anti-Terrorism Standards for physical security of the chlorine tanks at facilities of this sort; the facilities are just too small to make regulations cost effective. As is fairly typical, the padlocked gate on the chain-link fence and a padlock on the chlorine control box are the only security measures in place. Even if video surveillance or intrusion detection devices were in place, the response time to such rural locations is long enough to allow perpetrators to successfully leave the facility.


Laurie Thomas said...

Patrick - very interesting incident. Thank you for bringing this to our attention. It looks like it has nation-wide applicability.

Anonymous said...

Patrick, water treatment and supply facilities are exempt from CFATS...

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