Pollution
Humain
Environnement
Economique

At around 4.00 pm, an employee in a chemical plant detected a hydrogen sulphide (H2S) leak from a transport pipe (NPS 50, pressure 5 bar) in a four-cable walkway. Upon receiving the alert, the operator decreased the pressure in the pipeline, opened the automatic sectional valves and informed the emergency services. However, the surveillance and contingency plan relating to the structure was not triggered.

Once the fire-fighters arrived, a fire extinguisher nozzle was implemented to neutralise the hydrogen sulphide vapours, a safety perimeter was established and the gas concentrations were measured. The accredited inspection department of the chemical facility arrived onsite at around 4.30 pm. The leaking transport pipe was isolated using metal plates and at around 6.30 pm a collar was fitted to seal the pipe. The entire structure was inerted using nitrogen at around 7.00 pm. The operating company planned to submit a repair proposal to the inspection authorities for classified facilities. The operator immediately drafted a press release after the incident

No casualties or environmental impact were reported. Differential aeration corrosion of the structure may have been the cause of the incident. The corrosion area was localised in a lower generator, at about 20 cm after the point where the pipeline resurfaced from the ground where the coal-tar pitch coating passively protecting the part of the pipeline below the ground is no longer present.

Further to the investigation carried out by inspection authorities for classified facilities, it was found that the use of a general anti-oxidant treatment of the pipe was recommended to the operator. A malfunctioning in the cathodic protection was also brought to his notice. Errors in interpreting the images by the company that carried out the non destructive X-ray inspection were also observed. Lastly, the drop in the pipeline pressure failed to trigger the safety alarms provided for in the site’s safety study. The inspection authorities concluded that the detection systems were ineffective given the low leak volume and that the alert was sounded only due to the adventitious presence of an employee.

Furthermore, the site of the incident had not previously been identified by the operator as a singular point, and was therefore not the subject of specific monitoring actions (risks related to land exits in flood-prone areas).