According to their permit application for the TWO tanks, it was Anhydrous Ammonia.
For the media’s claim regarding the plant undersold the hazard, I will direct all FReepers to read and consider this article:
Why You Don’t Use the DOT Emergency Response Guidebook for Incidents Involving Anhydrous Ammonia at a Fixed Facility! http://my.firefighternation.com/forum/topics/889755:Topic:2841048
If the plant followed all of the hazard guidelines as required by the EPA and OSHA, no one at the plant would have understood the hazards. Hell, the NFPA label indicates no explosive/fire hazard.
This is a darn good case of following and trusting regulations...and the regulations being wrong! The NFPA does recognize the hazard and the MSDA doesn’t list that hazard.
Ammonia tank under fire will lift its pressure relief valve. The ammonia will then vent to atmosphere. Initially it is 100% ammonia. As it mixes with air the concentration of ammonia will go to 0. Thus every release at some point will be within the explosive mixture range. If indoors with an open flame in the building, there is usually an explosion. Ammonia was used extensively in refrigeration units in farming and there is a detailed list of all the explosion out there. Outside, the flame has to be in just the right location or it doesn’t happen. Outdoor release main hazard is the large toxic cloud that ‘walks’ along the ground. (See desert tortoise videos of large ammonia releases). Most fatalities occur within 500 yards? Due to toxic inhalation.
If liquid released, it auto chills down and burn hazards from the intense cold are a problem.
The ammonia tanks are about the size of a truck (12,000 gal), not the size of a rail car (33,000 gal). They appear to be the long white vessels south of the building and only minimally involved.