Release of hydrogen and hydrogen sulphide in a refinery

A release occurred following the rupture of a pipe of 250 mm in diameter. 350 kg of a hydrogen-reach gases were released to the atmosphere in 11 minutes (80% of hydrogen, 5% of hydrogen sulphide (H2S) and 4% of water and hydrocarbons).
Although the ARIA report (see references) does not mention it, the unit affected was very probably the oil desulphurisation unit.
The mixture was both toxic and flammable. H2S detector and explosimeters alarms were triggered and the operating staff cut off the supply. The cloud dispersed but the area of irreversible effects for H2S has remained within the site.

According to the ARIA report (see references), the rupture could have been caused by the corrosion of a section of the line with a rather complex geometry (2 successive bends in 3 dimensions). Nothing is said regarding the cause of the corrosion, but it is known that H2S is a corrosive substance for metals.
ROOT CAUS could be attributed to a design error, which under-estimated the effect of a corrosive environment, and/or to non-optimal construction of that section of the pipe.

supply pipeline of hydroge nand hydrocarbons

According to the multi-annual site inspection plan, this area should have been inspected before the end of 2000 (i.e. 2 years later) but the operator had advanced the inspection to the end of the current year.

There were no injuries and limited environmental consequences. People could smell H2S outside the refinery.

The ARIA report does not mention any corrective action. An obvious lesson to be learnt was that the inspection of the various part of the site had to become more frequent, to be able to detect every type of degradation phenomena.