On the day of the incident, the refuge alternative had been examined during the required pre-shift examination, and no defects were identified. Approximately two and one-half hours later, a scoop operator discovered debris scattered on the mine floor near the refuge alternative.

The refuge alternative manufacturer, state inspectors and MSHA examined the refuge alternative to determine the cause of the incident. The preliminary findings indicate there was a catastrophic failure of a brass high pressure fitting connected to an oxygen cylinder valve.

This catastrophic failure allowed a rapid release of oxygen, which pressurized the interior of the steel structure. The initial determination is that the pressure build-up inside the container forced open both the tent deployment door and the air-lock access door, ejecting a supply container and three 5-gallon water containers from the access door area onto a nearby rib.