What started as a mock plane crash meant to train firefighters took a dangerous turn when a huge fireball went up — and investigators now know what went wrong.

Instead of spraying water on the fire, the firefighters were shooting water tainted with flammable jet fuel.

jet fuel instead of water

The mock crash site was already on fire when crews arrived for the training exercise. (Image source: KING-TV)

jet fuel instead of water

When the firefighters started unknowingly spraying the fire with jet fuel laced water, it blew up. (Image source: KING-TV)

“When the firefighters put water on a fire that had been deliberately developed for training the fire got bigger instead of smaller,” Bob Calkins with the Washington State Patrol told KING-TV.

The Washington State Patrol’s investigation into the incident, which occurred Oct. 25 and resulted in minor burns for two firefighters, found that the training academy’s recycled water separator did not filter jet fuel from the water properly, according to KING.

Watch KING’s report about the incident:

The news station reported that the investigation is still underway to determine whether the incident was a result of a malfunction or an employee mishap.

(H/T Huffington Post)