An explosion on a hydrogenation reactor of a pharmaceutical products plant

The explosion occurred while starting up for the first time a hydrogenation reactor.
The reactor was being commissioned, by performing tightness tests under hydrogen atmosphere at very high pressure. The rupture of one of the seals caused a hydrogen release followed by the auto ignition of a 30 litre air/hydrogen mixture. Five employees were injured. Material damage was confined to the immediate perimeter of the reactor. The hydrogen detectors controlling the closing of the H2 supply valve had not yet been installed. Nevertheless, their absence was not critical thanks to the prompt reaction taken by employees. The preliminary tests carried out under nitrogen were insufficient.

The INITIATING cause was the failing of a seal under hydrogen pressure during a tightness test. The root cause was the ill-designed or ill-performed commissioning procedure. The previous tightness under nitrogen were performed or designed in a way that did not identify the release event which occurred under hydrogen. The cause classification could be shortcoming in operation.

Hydrogenation reactor, seals

The reactor had been installed for the first time, and the incident occurred during the commissioning tests.

Five employees experienced burns, suffered from ear pain due to the overpressure and were hospitalised. Among them, two employees were hospitalised for over 48 hours (humming sound in the ears).
Material damage was limited to the area around the reactor.

The fire brigade established a safety perimeter, closed the valve feeding the compressor. By using several permanent extinguishers they kept cooled the components and a trailer present on site.
The fire was quickly under control.
https://www.feuerwehr-neusaess.de/einsatzbericht/brand-wasserstoff-tankstelle/

As a rule, tightness tests have to performed with non-flammable gas, but have as well to consider the difference in behaviour between the gases. Helium could be a better replacement for hydrogen than nitrogen, it is however more expensive.