Explosion when venting hydrogen

After completion of a process using hydrogen an explosion occurred in the vicinity of the vent stack. Cold hydrogen gas was being vented into the atmosphere for about 45 minutes. The weather was unusually calm and the gas probably accumulated around the vent stack area and ignited.

The INITIATING CAUSE was the formation of a hydrogen-air flammable mixture at the exit of the vent stack, due to lack of wind able to disperse the hydrogen.

The fact that the safety design of the vent was based on expectation of enough wind, suggests a ROOT CAUSE related to its design.

vent stack

Possibley only some damage to stack vent exit

A venting system which does not foresee an ignition source at the vent stack exit is bases don the principle of hydrogen dispersion into the atmosphere without formation of explosive mixtures. In this case this theoretical model did not work. The report attributed this failure to the very calm weather. Wind was then a critical component of the dispersion assumption. Probably, also the hydrogen velocity at the stack exit played a role. Without an accurate computational flow dynamics model, is impossible to exclude formation of an explosive atmosphere in all speed and weather conditions (humidity, wind force and direction , etc.).