On January 15, 2022, at 4:51 a.m., 201 pounds of hot methylene diphenyl diisocyanate (MDI) were accidentally released, seriously injuring two workers at a facility in Louisiana.
The company's investigation of this event concluded that the accidental release occurred when a rupture disc activated prematurely. The design activation pressure was 30 pounds per square inch (psi), and process data indicated that this emergency pressure-relief system activated at about 13 psi.
The equipment protected by this rupture disc was typically operated under vacuum conditions. At the time of the incident, however, the equipment was operating at an elevated pressure due to a problem that had developed within the system used to create and maintain the low-pressure (vacuum) conditions. Although the operating pressure was elevated, it was within safe operating limits.
When the rupture disc activated, a 400-degree Fahrenheit mixture of liquid and vapor MDI discharged into 8-inch piping that was vertically orientated downward and ended about eight inches above the concrete floor. At the time of the incident, non-essential workers were not restricted from the area near the rupture disc discharge piping because the system was operating within the safe operating limits.
When the high-velocity, two-phase mixture exited the discharge piping, it hit the solid floor, spraying two contract maintenance workers installing a pump near the rupture disc’s discharge piping. The two maintenance workers were hospitalized with thermal burns from exposure to the hot fluid. Although Rubicon’s process hazard analysis had identified personnel exposure to hot MDI as a potential consequence of activating the rupture disc, the company had not mitigated the potential hazard of personnel working near the rupture disc discharge piping.
Source:CSB.gov
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