On October 1, 2020, at approximately 9:00 a.m., approximately 554 pounds of chlorine gas were accidentally released. Exposure to the toxic chlorine vapors seriously injured one employee. At the time of the incident, four (4) workers (two unit employees and two contractors) were trying to stop a chlorine leak (described as a fugitive emission) from a drain valve in the company’s methyl diisocyanate production plant. Because a chlorine leak was detected, the unit assumed that at least one of the drain valve’s connections in its flanges or bonnet was loose.
The four (4) workers held valid safe work permits to retighten the bolts using hand tools. However, the leak persisted after the bolts were retightened by hand. One of the contractors then tried to retighten the bolts with an impact wrench, a power tool that delivers short bursts of high torque. The vibrations from the impact wrench caused the connections on the drain valve’s bonnet to fail catastrophically, forcefully disconnecting the top half of the drain valve (closing element, stem, and handle) from the bottom half (body and seat) and releasing the toxic chlorine vapors.