Pollution
Humain
Environnement
Economique

At a chemical facility, during a plant’s triennial maintenance shutdown, 2 subcontracted temp technicians were seriously burned by hot water mixed with lime sludge during repairs to a wastewater scrubber. The 78-m³ scrubber was turned off as of 2:30 am. At 3:15 am, the 25-mm valve at the base of this equipment and the two 25-mm side drains at the suction outlet of purified water racking pumps were opened. The 100-mm base slide valve could also be opened, though with difficulty. By 3:40 am, the lower threshold of the reactor level meter had been reached: 45 m³ were drained. At 6am that morning, water was still flowing through the side chains, and steam was escaping from both valves. At 8 am, flow was no longer visible. 15 min later, when technicians broke a seal on a third valve, flow resumed for another 10 min. Between 8:30 and 9:15, a technician and the foreman attempted to open the manhole located at the base of the scrubber. At 9:45, with the manhole only attached by 2 bolts, a large quantity of water and sludge rushed in, injuring the technician and spattering a second repairman working nearby. The foreman was unharmed. Clogging at the bottom of the scrubber was responsible for this accident: for several months, the 25-mm valve had no longer been used to drain sludge due to handling difficulties and/or a compromised seal once closed. A huge lime deposit thus formed in both the valve body and lower part of the scrubber, extending several cm thick and creating a plug. Only a small-diameter central chimney had remained unencumbered. During the manhole opening steps, this bottom plug broke and the 30 m³ of water still in the reactor that could not be drained spilled through the manhole. Since hot water-related risks had not been cited in the prevention and protection plan given to the subcontractor, technicians were not wearing clothing adapted to this particular risk. To reduce the probability such an accident recurs, several corrective actions were proposed upon completing the investigation, e.g.: technical adjustments to avoid clogging the scrubber and allow verifying its thorough drainage, a revised workplace layout, increased employee awareness of defective equipment, improved technician dress code when working with potential exposure to hot water.