Five teenagers from Thomas Jefferson High School in Auburn wanted to celebrate the end of the school year around an Alki Beach fire pit Monday evening.

Instead, the teens finished the night in area hospitals after sustaining varying degrees of burns to their upper bodies and faces after someone added an undisclosed “accelerant” to the fire, according to a release from the Seattle Fire Department.

According to the release, at 8:50 p.m., Monday, Southwest Precinct officers and the fire department arrived at the fire pits in response to a report of injuries to teenagers involving possible accelerants. As medics began treating the five injured teens, witnesses told police that while the kids had been standing around watching the fire pit and celebrating the end of the school year, one of the teens started to add some sort of accelerant to it, setting off the explosion.

According to the release, an SFD medic unit transported two boys to Harborview Medical Center with serious burns. Private ambulances transported two other boys and one girl to area hospitals with less-serious burns.

As of Tuesday afternoon, investigators were still trying to determine exactly what the “accelerant” and container were.

The Arson Bomb Squad is handling the followup investigation.