It seems that someone declared June 8, 2007 as the day of serious spills of anhydrous ammonia from refrigeration systems across the country. There were three separate instances of significant spills reported today. Mount Sterling, KY, Wyalusing, PA and Milwaukie, OR had releases in the last 24 hours. No one was killed, but several people were taken to hospital, businesses were evacuated and residents were told to shelter in place.
There were explosions associated with two of the incidents. There are reports that an ammonia leak at a Nestlé plant in Kentucky caused an explosion that brought down 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 unexplained (so far) explosion resulting in ammonia leak. There were no reports of an explosion associated with the leak at the Cargill Taylor Beef Plant in Pennsylvania.
Anhydrous ammonia is preferred in many large refrigeration systems because it has better heat transfer characteristics and is cheaper than refrigerant gases used in domestic refrigeration systems and refrigerators. The problem is that this material is very reactive and is classified as Toxic Gas by Inhalation. Fortunately, the gas is extremely irritating at a level far below toxic, so when a minor leak occurs, unprotected people quickly evacuate the area with little urgency. However, a catastrophic leak can overwhelm people before they have a chance to come clean. This is partly because many people are temporarily blinded by less than lethal concentrations.
The food industry has long maintained that it should not have to comply with any anhydrous ammonia handling restrictions required by various federal laws, as they do not actually handle anhydrous ammonia; remains in a closed system. During the regulatory comment period, they complained that they were required to report under the new anti-terrorism chemical facility standards based on the 7,500-pound detection threshold quantity (STQ) listed in proposed Appendix A, Chemicals. of interest, from 6 CFR part 27. Refrigeration systems that have more than 7,500 pounds of anhydrous ammonia in the system would make that food processing company a ?chemical facility? 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 plume 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 the 7,500-pound 10-minute release rate required for a 3.2-mile-long toxic plume. There is nothing in any of the available articles that says anything about the release rate of these accidents, but from the description, they do not appear to be catastrophic release events. But what about the explosion caused by the launch in Kentucky?
Anhydrous ammonia is a highly reactive chemical, and even by itself can form an explosive mixture when mixed with air at concentrations of 16-25% ammonia in air, although a strong ignition source would be required. Reacts to produce explosive byproducts when mixed with chlorine, bromine, or iodine. Violent reactions occur with bleach or peroxides. It also forms explosive compounds with Gold, Silver and Mercury. Thus, while explosions are not part of the normal operating conditions for refrigeration systems using anhydrous ammonia as a refrigerant, an explosion after a significant leak would not be totally unexpected.
Perhaps DHS was correct in setting the STQ limit for anhydrous ammonia low enough that some refrigeration plant users could be labeled chemical facilities.