An unloading operation of a tank car containing liquefied propylene (C3H6, an extremely flammable, colourless and explosive product) ended around 3:30 p.m. at a chemical platform. A technician attempted to degas the unloading arm, when someone came to ask him for the sequential switching key. The technician disconnected the arms and placed them back onto their support, thereby freeing up access to the room containing the key. On the railcar, he placed the cap on the gas valve and disconnected the liquid-side filter. He tapped the filter on the ground to remove the residues and then noticed a large deposit on the ground, a sign of a product leak. Being aware of the hazard, the technician quickly exited the area with the filter in hand. He then was struck by a cold jet of propylene. He removed his clothes and headed toward the safety shower. The explosimeters sounded and triggered deluge spraying throughout the unloading area. The technician was then assisted by the emergency services who had been called by the individual who had witnessed the scene. The technician had been burnt. The unloading station was shut down pending a new hazard assessment.
The technician had no recollection of the action leading up to the accident or the contact that caused the valve to accidentally open. Several elements point to the origin of the accident or its deterioration:
- quarter-turn valve and control lever more susceptible to accidental opening than the recommended globe valves;
- the valve’s safety lock was not engaged;
- presence of propylene that had not been degassed in the connection between the bottom valve and the valve;
- the technician was in the “firing line” of the valve’s opening;
- to disconnect the tank, the technician was unassisted by his work buddy, contrary to the procedure. Their manager had called upon the work buddy to speed up the unloading of a tanker lorry so that the driver did not have to come back the next day;
- use of standard PPE.
The plant operator implemented the following corrective actions:
- systematic degassing of the connection between the bottom valve and the valve;
- review of the specifications for propylene railcars including an acceptable unloading configuration;
- installation of a seal on the lock before disconnecting the arm;
- news flash on the technician’s position in relation to the railcar’s valve;
- search for PPE specific to liquefied propylene.