Investigators have not ruled out arson as the main cause of the explosions at West Fertilizer that left 15 people dead, the Texas fire marshal said on May 16. State Fire Marshal Chris Connealy said investigators were unable to rule out three possible causes, including a spark from a golf cart, an electrical short or an intentionally set fire.
"The cause cannot be proven to an acceptable level," Connealy told reporters.
Investigators said the incident was actually two simultaneous blasts triggered by the fire. The blasts, which registered on seismographs as a magnitude 2.1 earthquake and were felt 50 miles away, caused damage to a 37-block area of the town.
In that weeks that followed the blasts, scores of investigators have been following up on leads. At least 60 have been on site each day, conducted more than 400 interviews and spent $1 million trying to determine how the fire started and what caused the explosion, authorities said.
In 2012, the Transportation Department's Pipeline and Hazardous Materials Safety Administration fined West Fertilizer $5,250 for storing anhydrous ammonia in tanks that lacked the proper warning labels. The agency originally recommended a $10,000 penalty, but it was reduced after the company took corrective action.
In 2006, the EPA fined it $2,300 and told the owners to correct problems that included a failure to file a risk management program plan on time. The Texas Commission on Environmental Quality also investigated a complaint about the lingering smell of ammonia around the plant the same year.
Investigators from the US Bureau of Alcohol, Tobacco, Firearms and Explosives and the State Fire Marshal's Office have been the lead agencies in the criminal and fire investigations.
The Dallas Morning News said Chemical Safety Board officials had limited and intermittent access to the plant as the law enforcement investigation took priority.
Investigators have said that 22 minutes after the initial report of a fire at the West facility, around 28 to 34 tons of ammonium nitrate stored inside a seed room at the plant exploded. An additional 120 tons stored elsewhere at the plant did not explode.
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