In a chemical plant, 3 empty rail tanker parked on the unloading zone of unit 46 were replaced by 3 full tanker cars: 1 carrying methyl mercaptan (MM) and 2 with chlorine. At 3 am, the 2 chlorine cars were hitched to one another. A worker connected the MM car. 45 minutes later, 2 employees began unloading an MM car when a stationary connection pipe on an unloading line loosened its connection to a defective valve: 67 to 74 tonnes of gaseous MM, depending on the source, were released into the atmosphere. A technician tripped the fire alarm; the production manager notified employees and requested that the fire department be called. At 3:47, the MM detectors recorded a high gas concentration on the 2nd floor of building 46. In leaving the building, a technician saw that the production manager had fallen to the ground. Employees from other workshops equipped with self-breathing devices entered the premises and discovered the bodies of one of the 2 technicians and the production manager. Both were rushed to hospital, where they were pronounced dead. In-plant fire-fighters sprayed the MM tanker car from which the smoke had escaped. At 3:52, external fire-fighters made their way to the plant and 6 minutes later, 2 units accompanied by the police were at the scene. At 4:09 am, the toxic gas ignited, inflaming the car and producing a fireball 61 m high by 15 m wide. The tanker car exploded (BLEVE-type), releasing MM and its decomposition products into the atmosphere. The rescue team leader requested backup from other fire stations. A north-westerly breeze caused the toxic cloud to drift south-easterly in the direction of Grosse Ile, located in the middle of the Detroit River and connected to the continent by 2 bridges. Around 5 am, authorities issued the confinement order. After updating the situation, 2,000 residents were evacuated over a 10-hour period, out of precaution, within a perimeter encompassing several municipalities. Due to the smoke release, as of 6:30 am, American authorities followed by Canadian officials decided to close a portion of the Detroit River to traffic until 4:45 pm that afternoon. The body of the 2nd technician was found on the railway. The hose connecting the chlorine car to the plant was destroyed. All chlorine circuit valves were opened when the team arrived in the unloading zone; 12 of the 81 tonnes of chlorine contained in the car were released. At 12:47 pm, the leak was finally stopped. Residents were allowed to return home as of 3 pm. The final human toll listed: 3 deaths, 1 serious injury and 48 minor injuries (including 5 employees, 3 fire-fighters and 40 members of the public). The National Transportation Safety Board (NTSB) investigation indicated: erosion/corrosion caused the pipe to burst; operator procedures regarding the monitoring, control and maintenance of unloading station pipes failed to mention wearing individual protective gear (allowing technicians to leave the zone); servo-controlled valve closing had not been foreseen for eventual leaks.

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