Hydrogen relase from a metal treatment furnace

The event occurred at a pit furnace for metal component treatments. The hydrogen feed system for the furnace developed a leak, located on the hydrogen dryer inside a shack attached to a building.
The leak vented hydrogen at 200 psig (approximately 15 bar) into the shack. The hydrogen low-pressure alarm sounded. No furnace operators were present at the time. An estimated 10,000 standard cubic feet (25 kg) of hydrogen vented.

The hydrogen release was caused by a failure of an elastomeric pressure seal on the body of a particulate filter located in the hydrogen supply circuit of the pit furnace.

A month earlier the same incident happened and was identified as a simple seal failure. However, an independent engineering review after the present incident showed the cause to be system overpressure, caused by the failure of a regulator.

The INITIATING CAUSE was the damage to a seal, which started leaking. The reason for the damage was the malfunctioning of a pressure regulator, which caused overpressure to the low-pressure part of the hydrogen supply system.

The high-pressure part had been revamped and renovated, but the medium-low pressure part was still consisting in the original setting, including the high-to-low pressure interconnecting component.
Therefore, the ROOT CAUSE could be identified in shortcoming when re-designing the installation.

pit furnace, pressure regulator, gasket

Part of the hydrogen supply system had been renewed.

An employee noticed a visual alarm few seconds before the explosion, but could not communicate it.

3.5 to 7 kg of hydrogen estimated to have burned violently in the explosion.
No quantitative evidence that the cloud detonated, but from the damage observed, experience from other accidents and experiments detonation seems most likely.
The explosion was followed by a large horizontal jet fire lasting about 30 seconds.

The plant manager took the decision to have an independent engineering review after the second incident, as essential step to more long-range corrective actions.