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February 7th, 2010 admin No comments

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Anhydrous Ammonia Spill Day

It looks like someone declared June 8, 2007 to be the day for serious Anhydrous Ammonia spills from refrigeration systems across the country. There were three separate instances of significant spills reported today. Mount Sterling, KY, Wyalusing, PA, and Milwaukie, OR all had releases in the last 24 hours. No one was killed, but a number of people were taken to the 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 the ammonia leak at a Nestle Plant in Kentucky caused an explosion that blew down a wall at that plant; no injuries from the explosion or falling debris have been reported. The American Cold Storage facility in Oregon had an unexplained (as yet) explosion result in the ammonia leak. There were no reports of an explosion associated with the leak at Cargill Taylor Beef Plant in Pennsylvania.

Anhydrous Ammonia is favored in many large cooling systems because it has better heat transfer characteristics and is cheaper than the refrigerant gasses used in home cooling systems and refrigerators. The problem is that this material is very reactive and is classified as a Toxic by Inhalation gas. Fortunately, the gas is extremely irritating at well below the toxic level so that when a minor leak happens, unprotected people evacuate the area quickly with little urging. A catastrophic leak, however, can overcome people before they have a chance to get clear. This is partially because many people are temporarily blinded by less than lethal concentrations.

The food industry has long maintained that they should not have to comply with any handling restrictions on Anhydrous Ammonia required under various Federal laws, since they don?t actually handle Anhydrous Ammonia; it stays in a closed system. During the regulatory comment period they complained about being required to submit information under the new Chemical Facility Anti-terrorism standards based on the 7,500 pound Screening Threshold Quantity (STQ) listed in the proposed Appendix A, Chemicals of Interest, to 6 CFR part 27. Cooling systems having 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 the EPA Risk Management Plan (RMP) guidance documents, 7,500 lbs of Anhydrous Ammonia released in 10 minutes time from a pressurized system (clearly a catastrophic leak, not a faulty valve) will have a plume with a toxic end point 3.2 miles down wind from the site of the leak (Table 9, 1.5 m/s wind speed). That means that anyone between the leak and 3.2 miles downwind could be exposed to dangerous concentrations of Anhydrous Ammonia.

Rather obviously, from the lack of casualties, none of these three release events came any where near 7,500 lbs in 10 minute release rate required for a 3.2 mile long toxic plume. There is nothing in any of the available article that tells anything about the release rate for these accidents, but from the description they did not seem to be catastrophic release events. But what about the explosion caused by the release in Kentucky?

Anhydrous Ammonia is a very reactive chemical, and even by itself can form an explosive mixture when mixed with air at concentrations of 16 to 25% Ammonia in air, though it would require a strong ignition source. It reacts to produce explosive by-products when it mixes with Chlorine, Bromine or Iodine. Violent reactions occur with Bleach or Peroxides. It also forms explosive compounds with Gold, Silver and Mercury. So, while explosions are not part of the normal operating conditions of refrigeration systems using Anhydrous Ammonia as a refrigerant, an explosion after a significant leak would not be totally unexpected.

Just maybe, DHS was correct in setting the STQ limit for Anhydrous Ammonia at a low enough level so that some refrigeration plant users could be labeled as Chemical Facilities.

About the Author

Patrick J. Coyle has 15 years experience with the US Army, including a stint as a Physical Security NCO in Europe. He has also spent 12 years working as a Process Chemist is a specialty chemical manufacturing company.

Further information about the new regulations concerning protecting chemical plants from terrorist attack can be found at http://www.members.aol.com/ChemPlantSec/ChemPlantSecurity.htm