It appears that someone declared June 8, 2007 as the day of serious anhydrous ammonia spills from refrigeration systems across the country. Three separate cases of significant spills were reported today. Mount Sterling, KY, Wyalusing, PA and Milwaukie, OR had pitches in the last 24 hours. No one died, but several people were taken to the hospital, shops were evacuated, and residents were asked to shelter in place.
There were explosions associated with two of the incidents. There are reports that the ammonia leak at a Nestlé plant in Kentucky caused an explosion that toppled a wall at that plant; no injuries have been reported from the explosion or falling debris. The American Cold Storage facility in Oregon had an inexplicable explosion (so far) causing the ammonia leak. There were no reports of an explosion associated with the leak at the Cargill Taylor meat plant in Pennsylvania.
Anhydrous ammonia is preferred in many large cooling systems because it has better heat transfer characteristics and is cheaper than the refrigerant gases used in domestic refrigeration and cooling systems. The problem is that this material is very reactive and is classified as a toxic gas by inhalation. Fortunately, the gas is extremely irritating at a level well below the toxic level, so when a minor leak occurs, unprotected people evacuate the area quickly with little urgency. However, a catastrophic leak can affect people before they have a chance to get out. This is partly because many people are temporarily blinded by sub-lethal concentrations.
The food industry has long argued that it should not have to comply with the anhydrous ammonia handling restrictions required by various federal laws, as they do not actually handle anhydrous ammonia; it remains in a closed system. During the regulatory comment period, they complained that they were required to submit information under the new anti-terrorism chemical facility rules based on the 7,500-pound threshold detection quantity (STQ) listed in proposed Appendix A, Chemicals of Interest, to the 6 CFR part 27. Would cooling systems that have more than 7,500 pounds of anhydrous ammonia in the system make that food processing business one? Chemical installation? under the rules of this regulation.
According to EPA’s Risk Management Plan (RMP) guidance documents, 7,500 pounds of anhydrous ammonia released in 10 minutes from a pressurized system (clearly a catastrophic leak, not a faulty valve) will have a column with a dot Toxic end 3.2 miles downwind from leak site (Table 9, 1.5 m / s wind speed). That means anyone between the leak and 3.2 miles downwind could be exposed to dangerous concentrations of anhydrous ammonia.
Obviously, due to the lack of casualties, none of these three release events came close to 7,500 pounds at a 10 minute release rate required for a 3.2 mile long toxic column. There is nothing in any of the available articles that says anything about the release rate of these accidents, but based on the description, they did not appear to be catastrophic release events. But what about the explosion caused by the Kentucky launch?
Anhydrous ammonia is a highly reactive chemical, and even on its own it can form an explosive mixture when mixed with air in concentrations of 16 to 25% ammonia in air, although it would require a strong ignition source. Reacts to produce explosive by-products when mixed with chlorine, bromine, or iodine. Violent reactions occur with bleach or peroxides. It also forms explosive compounds with gold, silver, and mercury. Therefore, although explosions are not part of the normal operating conditions for refrigeration systems that use anhydrous ammonia as a refrigerant, an explosion after a major leak would not be totally unexpected.
Just maybe, DHS was correct in setting the STQ limit for anhydrous ammonia low enough that some refrigeration plant users could be labeled as chemical facilities.