After a fatal chemical release on November 15, 2014 (see our previous blog for an initial analysis), the Chemical Safety Board (CSB) immediately sent an investigative team. The team spent seven months on-site. Prior to the release of the final report, the CSB has approved and released interim recommendations that will be addressed by the site as part of its restart.
Additional detail related to the causes of the incident was also released. As more information is obtained, the root cause analysis can be updated. The Cause Map, or visual root cause analysis, begins with the impacts to the organization’s goals. While multiple goals were impacted, in this update we’ll focus on the safety goal, which was impacted due to four fatalities.
Four workers died due to chemical asphyxiation. This occurred when methyl mercaptan was released and concentrated within a building. Two workers were in the building and were unable to get out. One of these workers made a distress call, to which four other workers responded. Two of the responding workers were also killed. (Details on the attempted rescue process, including personal protective equipment used, have not yet been released.) Although multiple gas detectors alarmed in the days prior to the incident, the building was not evacuated. The investigation found that the alarms were set above permissible exposure limits and did not provide effective warning to workers.
Methyl mercaptan was used at the facility to manufacture pesticide. Prior to the incident, water accessed the piping system. In the cold weather, the water and methyl mercaptan formed a solid, blocking the pipes. Just prior to the release, the blockage had been cleared. However, different workers, who were unaware the blockage had been cleared, opened valves in the system as previously instructed to deal with a pressure problem. Investigators found that the pressure relief system did not vent to a “safe” location but rather into the enclosed building. The CSB has recommended performing a site-wide pressure relief study to ensure compliance with codes and standards.
The building, which contained the methyl mercaptan piping, was enclosed and inadequately ventilated. The building had two ventilation fans, which were not operating. Even though these fans were designed PSM critical equipment (meaning their failure could result in high consequence event), an urgent work order written the month prior had not been fulfilled. Even with both fans operating, preliminary calculations performed as part of the investigation determined the ventilation would still not have been adequate. The CSB has recommended an evaluation of the building design and ventilation system.
Although the designs for processes involving methyl isocyanate were updated after the Bhopal incident, the processes involving methyl mercaptan were not. The investigation has found that there was a general issue with control of hazards, specifically because non-routine operations were not considered as part of hazard analyses. The CSB has recommended conducting and implementing a “comprehensive, inherently safer design review” as well as developing an expedited schedule for other “robust, more detailed” process hazard analyses (PHAs).
Other recommendations may follow in the CSB’s final report, but these interim recommendations are expected to be implemented prior to the site’s restart, in order to ensure that workers are protected from future similar events.
To view an updated Cause Map of the event, including the CSB’s interim recommendations, click “Download PDF” above. Click here to view information on the CSB’s ongoing investigation.