Release from a hydrogen compressor in a refinery

A hydrogen leak occurred on a makeup gas line of a gas oil hydrotreater unit of a refinery.
The release location was a 1-inch gate valve, which later was found 10% open and with no bull plug. The bull plug was found lying on the ground below the gate valve.
Approximately 133 pounds (60 kg) of makeup hydrogen with a purity of ~97% was released and dispersed without igniting.

When the leak was discovered, the hydrotreater unit shutdown procedures were implemented, and emergency response was requested. Both refinery and the county response teams responded. The shutdown was completed after approximately 1/2 hour. The procedure consisted in depressurising the unit and purging it with nitrogen, to allow the safe closing of the leaking valve and the re-installation of the missing bull plug.

The post-event investigation determined the likely INITIATING CAUSE of the hydrogen leak was that the gate valve had not been completely closed before the start of the operation of the hydrotreater unit.
A possible scenario for the loss of the valve bull plug was the expansion and contraction during hot and cold cycling of the unit combined with vibration from a nearby reciprocal compressor during the 18 months of operation.
The ROOT CAUSE was shortcoming in maintenance and/or inadequate control of the start of the normal operation.

gate valve, pipe, hydrogen compressor

The gas oil hydrotreater unit involved in this incident had been recommissioned 18 months earlier after a company ownership change occurred and had undergone recent maintenance and testing prior to activation for operation.
The unit, including the affected valve, had operated at pressure value of 350 psi (24 bar) for at least 36 hours, before the leak started.

No injuries, no damage to the gas oil hydrotreater unit, no adverse environmental consequences, no offsite impacts, nor any significant threat to human health.