By ThinkReliability Staff

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.

By ThinkReliability Staff

In the early morning hours of November 15, 2014, a release of methyl mercaptan resulted in the deaths of four employees at a plant in Texas that manufactures pesticides. The investigation into the source of the leak is still ongoing, though persistent maintenance problems had been reported in the plant, which was shut down five days prior to the incident.

Even though the investigation has not been completed, there are some lessons learned that can be applied to this facility, and other facilities that handle chemicals, immediately.

Even “safer” chemicals are dangerous when not treated properly. The chemical released – methyl mercaptan – is stored as a safer alternative to methyl isocyanate (which was the chemical released in the Bhopal disaster). Although it’s “safer” than its alternatives, it is still lethal at concentrations above 150 parts per million. The company has stated that 23,000 pounds were released – in a room where complaints were made about insufficient ventilation. The workers were unable to escape – likely because they were quickly incapacitated by the levels of methyl mercaptan and did not have the necessary equipment to get out. (Only two air masks and oxygen tanks were found in the area where the employees were.)

A fast response is necessary for employee safety. Records show that 911 was not called for an hour after the employees were trapped. (One of the victims called his wife an hour prior to indicate there was an issue and he was attempting rescue.) The emergency industrial response group, which is trained to provide response in these sort of situations, was never called by the plant. Medical personnel could not access the employees because they were not trained in protective gear. Firefighters who responded did not have enough air to travel through the entire facility and did not have enough information on the layout to know where to go. It’s unclear whether a quicker response could have saved lives.

Providing timely, accurate information is necessary for public safety. The best way to determine the impact on the public is to measure the concentration of released chemicals at the fenceline (known as fenceline monitoring). Air monitoring was not performed for more than four hours after the release. Companies are not required to provide fenceline monitoring, although an Environmental Protection Agency (EPA) rule requiring monitoring systems for refineries is under review. (This rule would not have impacted this plant as it produced pesticides.) Until that monitoring, the only information available to the public was information provided by the company (which did not release until days later the amount of chemical released.) In Texas, companies are required to disclose the presence of chemicals, but not the amount. A reverse 911 system was used to inform residents that an odor would be present, but did not discuss the risks.

What can you do? Ensure that all chemicals at your facility are known and stored carefully. Develop a response plan that ensures that your employees can get out safely, that responders can get in safely (and are apprised of risks they may face), and that the public has the necessary information to keep them safe. Make sure these plans are trained on and posted readily. Depending on the risk of public impact from your business, involving emergency responders and the public in your drills may be desired.

To see a high level Cause Map of this incident, click on “Download PDF” above.