The Pryor Times

June 22, 2013

LEPC: The anatomy of an explosion

Staff Writer
Cydney Baron

— The Local Emergency Planning Committee was in problem-solving mode at the meeting Thursday.

While most of the country has forgotten about the explosion at a fertilizer plant in West, Texas, LEPC analyzed the technical aspects of the explosion.

Mark Stafford, Pryor Chemical Plant Health and Safety director, broke the event down and lent his expertise to a discussion of the investigation. After showing before and after pictures highlighting the devastation, he gave the committee a run-down of the facts confirmed so far.

“Some known facts about the case are, it was an ag distribution center with reportable quantities, failed to report/comply (with regulatory agencies) numerous times, there were two explosions — one occurring milliseconds prior to the main blast,” said Stafford. “Some conclusions can be made from the West explosion. There were four storage bins, two of which contained ammonium nitrate. Only one bin of ammonium nitrate exploded and that particular bin was located between two bins of wheat, an organic material.”

Ammonium nitrate is an oxidizer, meaning that in a fire it emits oxygen which makes fire burn with greater intensity. It is used to blast rocks, to make gravel and in fertilizer. Ammonium nitrate and diesel fuel were used to blow up the Murrah Building in Oklahoma City. The presence of wheat bins was significant as wheat dust can auto-combust if the dust is not eliminated. Anhydrous ammonia is similar to ammonium nitrate, but is stored as a pressurized gas (anhydrous means 'no water'). Ammonium nitrate is also used as fertilizer. Stafford explained that a sister plant of Pryor Chemical produces ammonium nitrate but the Pryor location does not. In regard to the importance of location, he said a plant, either manufacturing or distributing, should not be located near the general public. The explosion in West occurred quite close to a nursing home, elementary school and apartment building.

Stafford said at this point in the investigation, some possible causes and contributing factors have been eliminated including rekindling, spontaneous ignition, a 428 voltage system in plant, anhydrous ammonia, smoking and weather. He explained what has not been eliminated; a 120-volt electrical system in the plant and intentional detonation.

Weather, he said, was a contributing factor as the wind was over 30 miles per hour.

Many people, including emergency responders, were killed or injured in the blast. Stafford said it is crucial for emergency personnel, like the fire department, to have an understanding of the materials and processes taking place in a given plant; only then will they know how to correctly and safely respond to the situation.

Stafford reminded the group West wasn’t the first explosion of this kind. He discussed an explosion at a fertilizer plant, dealing with ammonium nitrate, in Pryor in 1973.  Stafford said the ammonium nitrate caught fire and parts of the structure were made of wood. He showed newspaper headlines from the incident. According to newspaper coverage of the event, the warehouse of the fertilizer plant was filled with 15,000 tons of fertilizer when it exploded and six people were injured. The newspaper said the explosion was felt 44 miles away and blew out many windows in downtown Pryor. 

After reviewing both, Stafford re-emphasized that Pryor Chemical does not makes pellets from ammonium nitrate and has no plans to do so. Pryor Chemical is working closely with Pryor Fire Department for the safety of both parties.

Mayes County Emergency Manage-ment, Pryor Fire Department and LEPC did a site inspection of Pryor Chemical, reviewing their emergency plan and looking for ways to improve.

The plant is considering a radar security system around the perimeter.

“Pryor Chemical is trained to Hazmat (hazardous materials) level. We are working on training opportunities with Pryor Fire Department,” said Stafford. “We’ve put a lot of money into the company and the community. We’re responsible stewards of the environment.”

The day of the meeting, an explosion at a chemical plant in Louisiana killed one and injured 75. Though news coverage of this explosion often includes discussion of the Texas plant, the two are very different. The Louisiana plant produces about 1.3 billion pounds of ethylene and 90 million pounds of polymer-grade propylene each year, according to the company's website.