【Accident Case Analysis】13 Why can’t I open that valve?

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In April 2004, an explosion and fire broke out at a polyvinyl chloride (PVC) factory, resulting in 5 deaths and 3 severe injuries. The buildings in the area where the reactor was located, as well as a nearby warehouse, were largely destroyed. The thick smoke generated by the fire drifted over the residential areas, prompting the authorities to issue evacuation orders; the factory was never rebuilt afterward. The U.S. Chemical Safety and Hazard Investigation Board (CSB) has released a report and video on this accident to that end. The CSB’s investigation identified several root causes of the accident, including the failure to adequately account for potential human errors in the design and operation of the plant ； The corrective actions recommended following previous incidents were not tracked or implemented ； Relying solely on programs to prevent major accidents ； The emergency response procedures for large-scale leaks of flammable substances are inadequate, and so on. This issue of the warning light focuses on the specific events that led to this accident; as frontline operators or maintenance staff, it is possible to prevent such events from occurring. This factory has 24 polyvinyl chloride batch production reactors that are basically identical to each other. At the end of each batch process, water is used to clean the reactors, removing the toxic and flammable vapors contained within them; the water used for cleaning is then discharged into an open sewer located beneath the reactors. This accident originated when an operator wanted to drain water from a reactor that had already been cleaned. However, this operator went to another reactor – which was at that time in the reaction phase. The mixture inside the reactor contains flammable polyvinyl chloride, with a pressure estimated at 0.48 MPa. The operator was unable to open the pneumatic valve located at the bottom of the reactor – because when there is pressure inside the reactor, the safety interlock prevents the valve from being opened. It is believed that the operator connected nearby compressed air to the valve, forcing it to open, which caused the reaction mixture to be discharged into the building; eventually, the flammable vapors in those emissions were ignited. What can you do? ★If you try to operate a pneumatic or electric valve (to open or close) and it doesn’t respond, stop and think about it. Perhaps there is a good reason explaining why the valve does not operate; for example: •Maybe this is not the valve you intended to operate! •This valve may be under safety interlock protection and not allow any operation. •If the equipment needs to be isolated or locked down due to some maintenance work or other reasons, the valve may be locked or the power supply may be disconnected. ★If the valve does not operate as intended, under no circumstances should the actuator be connected to an air supply or any other type of power source in an attempt to force the valve to move. ★If the valve cannot be opened and there is a bypass, do not use the bypass to establish and maintain flow unless the reason why the valve will not open is fully understood. ★If a valve cannot be operated, contact the management and engineers to help determine the reason for its failure to function. Do not take any action until the cause is identified. ★If it is not possible to operate a device – for example, if a pump or mixer cannot be started or stopped, or if no other devices can be operated – it is still necessary to determine the reason using the same approach. Under no circumstances should the device be forced to operate. ★Please watch the video about this incident to understand all the root causes and lessons learned. “Do not force open any valve that will not open – find out the reason why it won’t open!