A sealed, unclassified electrical control enclosure, part of a listed and certified force-ventilated commercial hydrogen processing unit enclosure, exploded when the equipment manufacturer’s technician pressed the machine stop switch to complete factory commissioning procedure. The technician was forcefully hit by the flying metal panel holding the switch and sustained serious injuries requiring lengthy hospitalization and rehabilitation. Two were hospitalized. Two others were injured. Significant damage to the indoor facility also occurred.

An independent investigation found that drain lines from the external hydrogen vent stack drain trap and the electrical control enclosure cooler/condenser drain were interconnected into a single external sealed floor drain, in a manner not prescribed by the manufacturer’s installation instructions. Further, a new hole was drilled through the hydrogen processing enclosure to interconnect an internal hydrogen gas dryer drain trap to the external drain, contrary to certified product configuration and installation instructions. These interconnections inadvertently provided a path for low pressure hydrogen gas and water to enter the unclassified electrical enclosure during process cycles. Activation of the machine stop switch in the electrical enclosure provided the ignition source.