More details about the accident that killed four Marines at Camp Pendleton in California on Wednesday have been released.

The deceased military members, all of whom had combat experience, were tasked with the disposal of unexploded ordnance at the camp. The were killed while clearing the Zulu artillery range, although there was apparently no live-fire training happening at the time of the accident.

According to the LA Times, "The Zulu area is used for firing explosive munitions such as grenades, mortars, artillery and rockets and for dropping munitions from aircraft."

The four men, ranging from age 27 to 32, are Staff Sgt. Mathew Marsh, Gunnery Sgt. Gregory Mullins, Sgt. Miguel Ortiz, and Staff Sgt. Eric Summers. All four had served in Iraq and received a Combat Action Ribbon at some point.

The duties of a bomb removal technician are classified as some of the most dangerous in the Marine Corps. It is one of the only positions that members of the Marine Corps are allowed to quit whenever they want to.

The investigation into the incident is still ongoing.