Hydrogen Retort Explosion

At the workshop of a linear accelerator site, a hydrogen retort used for brazing exploded due to the ignition of a flammable mixture of hydrogen and air.

The explosion propelled the retort shell to the roof of the brazing area and then back to the floor. It causes two injuries.

The INITIATING CAUSE was the accidental formation and ignition of a flammable air-hydrogen mixture in the retort.
The post-accident inspection did not identify any mechanical or physical malfunctioning of the equipment. The preparatory procedure foresaw (1) to vacuum-pump the retort, (2) to fill it with nitrogen at pressure, and (3) to allow injection of hydrogen. It was guaranteeing a high level of safety.
The ROOT CAUSE of the explosion was identified in the failure of the operator to effectively evacuate the retort and backfill with nitrogen, combined with a hydrogen purge far short of the specified value.

brazing retort, vacum pump

One employee experienced hearing loss in one ear and a shoulder injury from being blown into a cabinet.
A second employee was checked by Medical and authorized to return to work.

The failure to apply the appropriate procedure suggested the need for either additional administrative controls and/or periodic refresher training.