Explosion when working on a hydrogen cylinder

A process operator was working on a hydrogen tank in a mechanical workshop.
The goal of the onoging operation was the removal of the collar from a hydrogen cylinder. An electric crosscut saw was used to make two diagonal cuts in the collar of the cylinder before removal of the collar with a hammer and chisel.
An angle grinder was also occasionally used when a collar was proving difficult to remove.
The investigation found out that the purging of the cylinder had not been performed, or performed only partially, leaving high concentrations of hydrogen.
Sparks from the cutting process caused ignition of hydrogen present in container.

INITIATING cause: Rest hydrogen in cylinder while starting mechanical work
ROOT CAUSE: no purging, thus failing to execute correctly procedures, or shortcoming in procedure, and lack of risk management throughout the process.

Hydrogen cylinder, mechanical workshop

This is a case of wrong or ineffective purging. Failure in performing a proper purging, able to eliminate any possibility of ignition, is a recurrent event in industrial environment dealing with flammable gases. In this specific case, purging was carried out in different locations of the company, what caused lack of proper information and increased the risk of confusion on the status of the cylinders. Moreover, little attention had been given to the risks to which the workers were exposed when working with hydrogen cylinders.

:
The following measures were taken since the accident:
(1) All cylinders to be purged at this location and undergo batch control of purging,
(2) A physical barrier erected to stop the operator standing in line with the cylinder outlet.