Once again, since there have been no reported terrorist incidents at chemical facilities reported in the press, we will look at chemical accidents and incidents that have been reported. This is not being done to review safety, but rather to look at such incidents to see what they can teach us about security and mitigation.
Mountaire Farms Ammonia Leak, Selbyville, DE
A faulty valve on a rooftop refrigeration unit resulted in the leakage of an unreported amount of anhydrous ammonia into the Mountaire Farms poultry processing plant. Thirty-one people needed medical attention and seventeen were transported to local hospitals for additional treatment. No lasting injuries were reported. The ammonia fumes entered the facility through the HVAC system and response personnel measured concentrations at 100 ppm. The facility has a history of reported ammonia leaks.
Food processing facilities are frequent users of anhydrous ammonia refrigeration units. They are also good targets for terrorist attack because of the perception of danger to the food supply. Facilities that have a published history of ammonia leaks and resulting injuries to their workers are also likely to draw the attention of home grown terrorists in search of easy targets. It would take a very small explosive device to remove a valve on a roof top system.
Ammonia sensors in the HVAC system could have prevented most of these injuries. Such a sensor could be tied into an emergency stop for the blowers and an alarm in the facility. Stopping the blowers would have reduced the amount of ammonia taken into the facility and the alarm would have started the evacuation process.
Ethanol Storage Tank Explosion, Harristown, IL
An apparent lighting strike resulted in the explosion of a 30,000-gallon ethanol storage tank. The lightning apparently ignited vapors in the tank headspace. The force of the explosion blew the top of the tank over 350 feet away. No injuries were reported and the only damage reported was to the storage tank. There is nothing in the news report to indicate how much liquid was in the tank.
Storage tanks of flammable liquids are only threats for fire or explosion if the headspace in the tank contains oxygen (air) and the flammable vapors. Inerting the headspace with a non-combustion supporting gas such as nitrogen or carbon dioxide will prevent a fire or explosion in the headspace. If this is done, the only hazard from fire or explosion would arise if the tank were to rupture or leak.
Chlorine Leak at Water Treatment Plant, Medford
A chlorine leak at the Big Butte Springs water treatment plant resulted in the evacuation of the plant and some nearby homes. No injuries were reported and people were allowed to return to their homes that afternoon. Investigation showed that the leak was small enough that the evacuation of nearby homes was not actually needed.
The facility did have an airborne chlorine detection unit in the area of the chlorinating operation. The sensor sounded the alarm and shut off the supply from the chlorine tank. This was almost certainly responsible for the lack of injuries and the small size of the leak.
Interestingly the local paper reported that the plant is preparing two switch from chlorine gas to the use of hypochlorite for their water treatment. While the switch over is costing $1.29 million the plant was facing upgrade costs (presumably for security) of $0.8 million so the net cost of the switch was just under $0.5 million. The switch over to hypochlorite does not do away with the risk of chlorine exposure, but does eliminate the security costs associated with using chlorine gas. There are no security regulations covering the use of hypochlorite.