Case Review: Explosion Caused by Illegal Welding Work

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An explosion occurred on May 4, 1997, at 11:30 a.m., when illegal welding operations were carried out in the wastewater treatment workshop of a chemical plant in Chongqing. These illegal activities ignited flammable gases released in the wastewater treatment tanks, resulting in 12 deaths, 6 people suffering burns, and economic losses amounting to 1.5122 million yuan. I. Accident course and hazards On May 4, 1997, the team leader of the installation team at a chemical manufacturing plant in Chongqing assigned four people, including the supervisor of the pipefitters group, to carry out welding repairs in the sewage treatment workshop. Around 8:30, the team leader of the plumbing crew and others obtained materials such as oxygen and acetylene from the project team’s material handler, but without obtaining a fire permit, they went to the sewage treatment workshop to get ready; they arrived at the sewage workshop around 9 o’clock. The technician in the wastewater treatment plant, as instructed by the plant manager, told the team leader and others: \"You need to go through the necessary procedures before performing any welding work today.\" Then, the team leader of the plumbers went to the office in the sewage treatment workshop to make a phone call to the safety officer in order to obtain the necessary permits for working with fire. But the safety officer was not there; subsequently, the person in question contacted the deputy manager of the engineering company by phone and informed him about the lack of a fire permit. The deputy manager then ordered the team leader and others to move the items that were to be worked on to a safer distance for inspection, and promised to send temporary workers to help with moving them. After the foreman of the plumbing team finished making the phone call, the other workers had already started working on the panels of the sewage treatment tank; so the foreman joined them in their work, without waiting for the fire permit to be obtained or for temporary workers to be sent by the company. At around 11 a.m., after the team leader and others had welded two elbows to the sewage treatment panel, a welder was working above the sewage treatment diversion channel (next to the sewage treatment tank), preparing to spot-weld the flanges of the valves at that channel to the pipes (as a fixing step before welding). As soon as the welder made the first spot weld, the sparks ignited the flammable materials inside the diversion channel. Next, the team leader of the pipefitters and workers from the wastewater treatment plant used fire extinguishers to put out the fire. They then called the factory’s fire department; upon receiving the alert at 11:32, the fire department dispatched 4 fire trucks along with firefighters to the scene. These firefighters used 2 FQ8-type (50 L/s) foam nozzles to extinguish the fire, and two 19mm water nozzles to cool down the DVA paint tanks. Around 11:45 during the firefighting efforts, the flames ignited the flammable gases released from the sewage treatment tank, which was constructed of reinforced concrete; this caused the tank to explode. The floor panels broke apart, resulting in 12 firefighters and workers on site being killed by the explosion and falling debris, while 6 others were injured or burned. After the explosion, the fire continued to burn; the remaining personnel together with the fire crew from Sichuan Dye Factory who arrived to provide support (1 vehicle, 8 people) continued to fight the fire, and it was not until 12:10 that the fire was completely extinguished. II. Analysis of the accident causes 1. Immediate cause: (1) Workers from the construction team of the engineering company were carrying out work in the sewage treatment workshop; they carried out welding operations in violation of the factory’s regulations regarding hot work, which led to the ignition of flammable and explosive substances in the workshop’s drainage channels. During the firefighting efforts, the flames ignited the combustible gases present in the sewage treatment tanks, resulting in an explosion. This was the immediate cause of the accident. (Note: The diversion channels in the wastewater treatment plant contain industrial wastewater discharged from the chloroprene production line. The flammable and explosive substances included are vinyl acetylene, chloroprene, acetaldehyde, acetylene, etc. The explosion limits for vinyl acetylene, acetylene, and acetaldehyde are 1.7%-73.7%, 2.3%-81%, and 4%-57%, respectively.) The wastewater treatment tank in the wastewater treatment plant consists of two regulating tanks, each measuring 35m×4.5m×4.3m. Pool A had a large amount of wastewater discharged from it a week ago due to maintenance work; based on the conditions at the explosion site, it can be determined that the pool was filled with explosive mixtures of gases. (2) The engineering company failed to arrange its work in strict accordance with the factory’s regulations regarding hot work. On May 4, the installation team sent workers to the sewage treatment workshop, which is located in a zone where hot work is strictly prohibited, to carry out welding tasks. When the workers called their supervisor to inquire about the procedures required for performing hot work, the supervisor, despite being aware of the relevant regulations and the factory’s requirements, failed to fulfill his duties as required. The production team carried out hot work without going through the proper procedures, ignored the warnings from the sewage treatment workshop, and proceeded with the welding work in violation of regulations, which led to a fire and explosion. 2 Problems in management: (1) Due to lax management, inadequate inspections, poor implementation of procedures, lax approval processes for hot work operations, and a weak safety awareness among employees, violations of rules and regulations occur from time to time in this chemical plant. This ultimately led to the failure to comply with orders on May 4, resulting in a major accident. (2) The chemical plant fails to manage special operation personnel properly. (3) The wastewater treatment plant failed to effectively prevent unauthorized welding by personnel entering the plant.