Pollution
Humain
Environnement
Economique

At 12:27 am, an employee attempted to replace a manometer placed on a tap downstream of a pump that was moving propylene from a storage capacity to the depropanizer (i.e. a tower that separates propane from the remainder of product contents) on the cracker of a refinery’s ethylene unit. The pump was set up at the periphery of the unit, on the edge of a cleared zone. Its discharge pressure was equal to 20 bar. The employee tried to unscrew the manometer on the tap using a wrench. During this effort, the tap broke around the connection on the pump discharge pipe. A spray of propylene reached the employee before being projected into the cleared zone. A gas cloud formed adjacent to the production unit and then very quickly ignited, accompanied by an explosion and fireball approx. 20 m in diameter. The fire was subsequently contained to a “blowpipe”, lasting several minutes before the propylene leak was stopped. Process calculations indicated an estimated flow rate of 16 tonnes/hr. The discharged quantity was roughly 1 tonne. The employee’s clothing ignited and he sustained 3rd degree burns, especially to the face, arms and legs, despite wearing clothing compliant with safety rules. Property damage was limited.

The investigation revealed that the victim had followed an appropriate procedure for manometer replacement, but the thickness of the tube used was not compliant with original specifications (measured at 2.6 mm vs. a specification of 3.7 mm). Introduction of a noncompliant connection was the direct cause of this accident, even though the investigation could not determine the circumstances under which the fault arose. An extensive inspection and repair programme was undertaken on the commonly used and high-risk taps, with all other taps being included in a periodic control plan. The implementation of a quality assurance system dedicated to construction works as well as all repairs and modifications was also approved.

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