Federal investigators said an electrical spark appeared to have triggered the explosion.
"We have no indication that would lead us to believe that this was a traditional criminal act," said ATF Special Agent Fred Milanowski during a press conference Wednesday. "No indication it was arson, no indication it was a sabotage, and no indication it was vandalism."
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Milanowski said believe the spark ignited a propylene leak, leading to the explosion. It's unclear what caused the leak.
"The likely ignition source was arcing within the electrical system within the building. Normal arcing within that building," said Milanowski.
He said the final report won't be complete for another 60 days.
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The ATF National Response Team spent more than 1,400 hours investigating the explosion site, according to Milanowski. The team consisted of fire investigators, explosion specialists, bomb technicians, fire protection engineers, forensic mappers and chemists and digital investigators.
The city of Houston said more than 450 homes and businesses were damaged. Two people died and a series of lawsuits have been filed against Watson Grinding.
After the ATF introduced its findings Friday, the attorneys of the family of one of victims, Frank Flores, added two more defendants in their wrongful death lawsuit.
"The newly added defendants are Western International Gas & Cylinders, Inc. and Matheson Tri-Gas, Inc. Plaintiffs allege these defendants were negligent in relation to their maintenance, supply and monitoring of the propylene equipment at Watson Grinding's facility in Houston, where the explosion occurred on January 24, 2020," attorney Mo Aziz stated. "Propylene distributors have a duty to ensure that storage and delivery equipment is free of leaks. We now know that there was a significant propylene leak before the explosion."
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