JACKSONVILLE, Fla. -- A federal agency that investigated the deadly T2 Laboratories explosion that killed four and injured 32 in Jacksonville says it was likely caused by an inadequate cooling system and a reactor relief system incapable of relieving pressure from a runaway reaction.

The U.S. Chemical Safety Board released a 68-page report on Tuesday of its investigation into the Dec. 19, 2007, explosion -- a blast so powerful it was heard 15 miles away.

Employees were making a gasoline additive when a chemical reaction went out of control, raising the pressure inside the reactor, causing a massive explosion and chemical fire.

About 10 minutes before the explosion, the operator realized the reaction was overheating and notified one of the owners, but it was too late to get it under control.

The powerful blast and subsequent chemical fire killed a co-owner of T2 and three of its employees. It totally destroyed the company, which has ceased business. The explosion badly damaged neighboring businesses in an industrial area off Alta Drive. Debris from the reactor was found as far as a mile away.

Among the findings, investigators said the company's owners did not fully understand the dangers posed by the chemical reaction they were dealing with.

"The owners had these warning signs -- they had these near misses," said Robert Hall, supervisor of investigations for the CSB. "The response was not to further investigate the hazard and try find out why this occurred, but just begin making another batch."

The CSB said there currently are no rules for how to handle the chemicals T2 was using.

Among the report's recommendations is for chemical engineering students to get a better understand the potentially powerful chemical reactions they work with.

"It's reasonable for people to scratch their heads and say, 'How come this was allowed to happen?'" Hall said.

Before briefing the public, CSB investigators met with the families of the victims. Several lawsuits are pending in the case.