CASTRO COUNTY, Texas — State investigators determined the cause of the South Fork Dairy fire was an accident that started with an engine fire in a manure vacuum truck, according to a report from the Associated Press.

The report did not determine what caused the engine fire but found there was “no intentional act to cause a failure.”

According to the AP, a worker driving the truck told investigators he noticed what he thought was steam coming from the engine. He tried to drive out of the barn when he realized it was a fire, but he could not make it out, the AP reported. The driver tried to put the fire out with two extinguishers but failed.

The AP said several other employees told investigators they rushed to help, but the fire spread too quickly. Investigators also found a second truck on the property that previously caught fire in the engine, the AP reported.

The State Fire Marshal’s Office previously said the April 10 explosion was a result of “flammable liquids expanding rapidly” after the fire started. previously reported Castro County officials estimated that 18,000 cattle died in the fire. The Animal Welfare Institute called it the deadliest fire involving cattle in nearly a decade. Castro County Judge Mandy Gfeller said in April the incident was “devastating and catastrophic.”

The disaster critically injured one employee who was trapped inside the facility when the explosion happened, but firefighters were able to get her out. She was flown to University Medical Center for treatment and released after spending more than a week in the hospital.

The State Fire Marsha’s Office said the investigation was closed.

The Associated Press contributed to this report.