The cause of the fire that triggered the deadly
An estimated 28 to 34 tons of ammonium nitrate fertilizer exploded in two stages, separated by a fraction of a second, according to the federal
Although the investigation eliminated some potential causes of the disaster, ATF agent Robert Champion said, several possibilities remain:
- A failure in the plant’s 120-volt electrical system.
- A battery-powered golf cart parked near the origin of the fire.
Officials refused to comment on whether a West paramedic who was arrested weeks after the conflagration on suspicion of possessing bomb-making materials had been cleared of involvement. But the blaze and the resulting explosion remain a criminal investigation, they said.
At a news conference in the parking lot of West’s now badly damaged high school, Champion said several possible causes had been eliminated:
- That a fire earlier in the day had reignited. Champion said there had not been an earlier fire.
- The plant’s 480-volt electrical system for heavy machinery.
- The weather.
Kelly Kistner, lead investigator for the state fire marshal, said the conflagration raised the temperature of the ammonium nitrate, subjecting it to increased pressure, then some "impact" triggered the explosion. A spokeswoman for the office said that impact remained under investigation, but it could have come from a structure that collapsed because of the fire.
Fourteen people were killed in the blast, including 12 first responders who arrived nine minutes after the fire was reported, and just eight minutes before the explosion.
Although the investigation of the blast scene has been completed, the probe will continue. The spokeswoman for the fire marshal said it was not clear whether the actual cause of the fire will be determined, however.
[For the record, 7:47 p.m. May 16: An earlier version of this post identified fire investigator Kelly Kistner as Kistler.]