On December 20, 2021, at approximately 9:30 a.m., a release of molten polymer caught fire, seriously injuring an employee in a company in Virginia. In December 2021, the company planned to perform maintenance work on a rupture disc used to protect one of its molten polymer positive displacement pumps from potential high-pressure conditions. On December 18, an operator prepared the equipment for maintenance. The preparation involved turning the pump off, locking and tagging its electrical switch, and closing, tagging, and locking the pump’s inlet and outlet isolation valves. The keys for the three locks were put into a lock box.
On December 20, 2021, the day of the incident, a different company operator issued safe and hot work permits to two maintenance workers to perform the rupture disc maintenance. Each of the two maintenance workers applied their personal lock to the lock box. The work involved using a propane torch to heat the external surface of the equipment and melt the polymer inside so that the rupture disc could be removed. One of the maintenance employees removed the bolts from the rupture disc holder, while the second worker acted as a “standby” and observed the work. Both workers wore the standard personal protective equipment (PPE) used at the plant, plus a face shield and an aluminized jacket. When the maintenance worker used the propane torch before removing the last bolt, the rupture disc and the bolt were forcefully ejected, spraying the employee with hot (500 degrees Fahrenheit) molten polymer. The propane torch ignited the molten polymer, starting a fire.
The standby worker pulled the emergency alarm and used the plant radio system to call for help. Emergency responders extinguished the fire and transported the injured maintenance worker to a nearby hospital with a burn center. The worker was admitted for treatment of his injuries, which included third-degree burns. The most severe injuries were to the workers’ legs. The worker’s denim jeans did not offer the same level of protection as his aluminized jacket.The company reported that approximately 50 pounds of molten polymer were released. The polymer primarily consisted of nylon 6 and some caprolactam.
The company's investigation found that the pump’s outlet valve had been incorrectly locked in the open position when it should have been closed (Figure below). On the day of the incident, the employees saw that the inlet and outlet valves had been tagged and locked. However, they did not verify that the valves were closed.
Simplified equipment drawing, highlighting the open outlet valve (left image)
In response to the incident, the company upgraded the PPE requirements to include aluminized clothing for line opening work on its molten polymer equipment.
Probable Cause
Based on the company's investigation, the CSB determined that the probable cause of the incident was not effectively isolating and draining the piping before having workers disassemble the rupture disc. As a result, after most of the rupture disc’s flange bolts were removed, the pressurized piping caused molten polymer to spray out of the rupture disc’s holder. The molten polymer ignited, leading to a fire that seriously injured one employee. Not verifying that the equipment was effectively isolated contributed to the incident. If any employee or supervisor had verified that the locked valves were closed, the incident could have been prevented. Not wearing aluminized pants with the aluminized jacket contributed to the severity of the incident.
Source:CSB.gov
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