In a PVC plant, an MVC leak ignited causing a (UVCE-type) explosion. The plant comprised 2 production buildings, one housing a boiler room and maintenance workshop, the other the laboratory, offices and warehouse, along with a series of MVC tanks (four with 180-m³ capacity) and a warehouse annex. The buildings were all equipped with sprinklers. Building V-1 had 20 7.5-m3 capacity polymerisation reactors, each fitted with a window. During this Sunday’s daytime shift, the opaque window glass on Reactor 4 was replaced. The reactor was reloaded without verifying the seal. Three hours later, a leak was noticed around the window (D: 15 cm). A worker was retightening the bolts when the glass burst into pieces. His face slashed, the employee was evacuated to safety by 3 colleagues. The leak had become impossible to contain. Personnel were evacuated from the building. At 6:51 pm, 5 to 10 minutes after the window broke, the air/MVC mix exploded with tremendous force, obliterating the structural walls and roof on Building V1 and causing the collapse of interior walls and metal frame structures on adjacent buildings. Struck by flying debris and crushed by falling walls and roof, 6 workers were killed on the spot, and a 7th died the next day. The broken reactor pipes allowed nearly 170 tonnes of MVC to escape, ultimately igniting as a fireball. A section of building column was propelled onto a 115-m³ MVC tank, triggering a gas fire. The destroyed sprinkler network caused a pressure drop in the water supply networks of both the plant and public system, complicating emergency rescue efforts. In a 600-m radius, dwellings and 2 schools sustained damage (shattered panes, walls displaced). The organisation of rescue teams was seriously hampered by immediate media coverage of the explosion on radio and television: thousands of bystanders headed to the scene, preventing emergency backup crews from reaching the accident. Only the first responders and police were able to arrive quickly. Fire-fighters, disturbed by the thick black cloud of toxic smoke hovering over the ground, feared that the MVC fire would spread to the filled tanks and tanker cars. They successfully shut off the inlet valve on the leaking tank, thus making it possible to extinguish the blaze. The MVC supply to Building V1 was ultimately cut, leading to extinction of this building’s fire. Around 11 pm, fire-fighters had finally closed the sprinkler network valve. Pressure rose, but the warehouse fire could no longer be brought under control; it would burn for several days, and the release of toxic combustion products interfered with rescue efforts. Property damage was significant (internal: 25 million francs, external: 350,000 francs). The boiler room was inoperable, and the frozen installations sustained damage to a point of being taken offline. The site would never resume PVC production.