Explosion in a facility for boilers maintenance

The explosion occurred during repair work on a boiler. A technician had previously descaled the device using hydrochloric acid, after which he performed the neutralisation step with soda and drained the passivated acid.
The significant scaling on the boiler required a second acid injection, followed by welding work, but this time the rest of the acid had not been drained from the boiler.
Hydrogen emitted by a metal + acid reaction was the cause of this accident. An employee wound up in hospital in a coma.
Labour inspection authorities noted that operating conditions were not respecting environmental protection requirements, i.e. failure to control discharge pH.
They also noted the absence of written procedures.

INITIATING cause was failure to perform an operative step
This caused the formation of hydrogen from the reaction of hydrochloric acid with metals, in presence of a hot source (welding).
Root cause (probably) found to be the absence of any written procedure.

Workshop for maintenance of boilers, hydochloric acid

The explosion occurred during repair work on a boiler.

An employee wound, in hospital in a coma.

Labour inspection authorities noted that operating conditions were not favourable towards environmental protection, i.e. failure to control discharge pH, absence of written procedures.