In a rubber and plastic manufacturing plant, 3,500 kg of gas (C1-C5; mainly propylene: H2/CH4 7.5%, C2 22.5%, C3 28%, C4 17%, C5+ 25%) were emitted into the air in an ethylene production unit. The leak occurred after the cleaning of a strainer in the 5th gas compression phase. One or more lid bolts were loosened, thus causing the strainer’s lid to open. The gas discharge was detected and the plant was shut down. Firefighters activated several valves to stop the leak. The sprinklers came on and the emergency services used a water nozzle to create a vapour-fluid mixture. Drains were filled with foam to block the release of gas. A fire and/or explosion could have occurred due to domino effects.

An assessment on the strainer showed that it was not cleaned regularly contrary to the guidelines in force. Some of the bolts that were significantly corroded/damaged were also unsuitable: several lengths, various types of metal. The analysis carried out by technicians on the production section who had carried out the maintenance was unsatisfactory. No clear references on the quality of the bolts and no process or instructions for the cleaning were available. Organisation of the production was unsatisfactory and use of the strainer as a “process filter” was inappropriate. The strainer had to be cleaned on a weekly, or even, daily basis, and the risk linked to no maintenance on the filter had not been identified.

The operator planned to no longer use strainers as filters in this situation and to improve the assessment of the maintenance and availability of references for the operators.