Monday, October 22, 2007

An Anhydrous Ammonia Attack Scenario

A recent accidental release of about 1,800 gallons of anhydrous ammonia at a farm supply store in an Oregon farm community has some interesting security implications. According to news reports a farm vehicle was loading ammonia from large tanks at the supply store when the driver pulled away from the loading site without disconnecting the hose. The valve on the farm vehicle was pulled off of the tank and the entire contents of the small tank were released. Two local schools were evacuated and the nearby residents were told to shelter-in-place. Only one person was transported to the hospital though many people experienced some breathing discomfort or burning sensations to their eyes or throats.


It was fortunate that the valve on the trailer broke off and not the valve on the tank. If the valve on the tank had failed, it would have been significantly more than 1,800 gallons of ammonia released and the results would probably have been more serious. While an explosive device may be a more effective weapon to attack storage tank, facilities might want to examine this as a possible mode of attack on their storage tanks. Let’s look at a possible scenario.


A delivery driver that has been suborned by a terrorist organization or a terrorist substituted for a legitimate driver, shows up with a scheduled delivery of a toxic chemical. The paperwork and load are verified and the tank truck is hooked up to a storage tank. During the off-loading process the driver re-enters the vehicle, starts the engine and drives off. The still connected hose pulls the bottom valve off of the storage tank and the entire contents spill and a toxic cloud begins to drift downwind. The driver/terrorist drives the truck off-site during the resulting confusion and escapes.


While the accident in Oregon demonstrates that it would not be a sure thing that the valve on the storage tank would be the first to fail, the failure of the valve on the truck or the hose breaking would provide nearly as good a result if done early enough in the unloading process.


The protections against this type of attack are relatively simple and very low cost. The first thing to do is to isolate the outsider (the driver) from the unloading process. The driver should be kept in a break room or office away from the vehicle and restricted areas of the facility. Secondly, keys to the vehicle should be surrendered to the unloader (a site employee) before the vehicle is hooked up to the unloading line. Finally hoses from trucks should never be hooked directly to the bottom valve of a tank. If the tank is not loaded through a line over the top of the tank (generally the preferable method), then there should be a significant length of piping between the hose connection and the bottom valve with at least one valve between the two.


This example illustrates the fact that security solutions do not have to be high tech or expensive. Identification of attack scenarios and then walking through those potential attacks frequently makes it easy to identify places where it is relatively easy to interrupt the chain of events that is necessary to execute a successful attack. Not all scenarios will be this easy to disrupt, but many of them will be.

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