Hydrogen fire in a sulphur recovery unit of a refinery

Three workers were working in the sulphur recovery unit (SRU), trying to restore the hydrogen flow. The workers were trying to isolate the cause of a flow problem: hydrogen was entering the regulators at 200 psi (14 bar), but the pressure was dropping to 18 to 20 psi (approximately 1.3 bar) after having passed through various components of the unit.

They closed a valve preceding the regulators and vented the bleed manifold before removing a flange located beyond the valve. One of the worker then re-opened the closed valve to check the flow. A hiss was heard, followed by a pop, and the area became engulfed in flames. The three workers suffered burns .

INITIATING CAUSE was the wrong operation during the search for a flow problem.
Nothing is known on the main problem which triggered the action.
The ROOT CAUSE could be identified in a combination of two FACTORS:
(1) the intervention of the repairing team appeared characterised by improvisation, in absence of a good script (procedures), and therefore somebody made some errors.
(2) it is very probable that the team did not have a full understanding of the pressure control system they were working on, and this call for a better technical knowledge and safety awareness, to be ensure by the management by effective training.

pressure regulator, valve, flange

Because of a problem on the hydrogen flow of the sulphur recovery unit (SRU), workers were looking for the cause of the problem. The OHSA report does not specify if the unit was shut down or operating.

DESCRIPTION OF THE PROCESS
A sulphur recovery unit (SRU) is used to recover sulphur-containing, poisonous acidic gas in oil refinery process.
The event occurred apparently on the so-called SCOT-component of the SRU. The SCOT process, integrated with the other component of the SRU (the Claus process) converts COS, CS2 and remaining SO2 by reacting with H2 in the catalytic reactor back to H2S. The hydrogenating catalysts used in SCOT contain nickel or tungsten on alumina support and the reaction takes place at 250-300°C.

Thee workers received burns