Chain of Errors Led to Fatal Chem Leak
Thursday, October 1, 2015 @ 04:10 PM gHale
A series of mistakes that began five days earlier led to the release of nearly 24,000 pounds of methyl mercaptan, a toxic chemical that killed four workers and injured three others at the DuPont manufacturing facility in La Porte, TX.
The U.S. Chemical Safety Board (CSB) released findings of the interim investigation into the leak of the toxic chemical at the DuPont facility. Four employees died in the Nov. 15, 2014 incident.
Board members of the U.S. Chemical Safety Board voted unanimously this week to approve safety recommendations identified by investigators after the deadly incident.
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Crystal Wise, Wade Baker, Robert Tisnado and his brother Gilbert Tisnado all died of asphyxia and exposure while dealing with the leak.
“Our investigation has uncovered lapses, weaknesses or failures in the company’s safety planning and procedures — safety management systems that could have and should have prevented the accident and this loss of life,” said Vanessa Allen Sutherland, the safety board’s chairperson. “We believe these recommendations lay out what DuPont should do to protect its workers and the public. We hope these improvements at La Porte will serve as a first step to fully restore DuPont’s global reputation for safety.”
Timeline to an Incident
Nov. 10: A water dilution system accidentally activated on that Monday and caused a storage tank to overload. Crews had to shut down the system used to manufacture an insecticide produced at the plant. They tried to restart the system two days later, but discovered a clog.
As they tried to clear that clog, the investigation revealed, about 2,000 pounds of water accidentally ended up in a storage tank containing methyl mercaptan.
The report said normally, a mixture of methyl mercaptan and water would not create a problem. However, temperatures were unusually cold that day (around 40 degrees) and had been consistently below 55 degrees in the days preceding.
The low temperature caused the mixture to form a separate blockage in the system’s methyl mercaptan feed. Crews came up with a plan to clear the clog and get the chemical flowing again.
Nov. 12: Workers tried to restart the system, but found the piping blocked caused by a slurry in the pipeline. Operators flushed hot water through the piping.
Nov. 13: The blockage cleared, but workers found a valve was left open during the operation that should have prevented hot water from flowing into other piping. With the valve open water flowed into the methyl mercaptan feedline which led to a storage tank . About 2,000 pounds of water escaped into the feedline and into the tank. Water mixing with the methyl mercaptan caused another blockage, called a hydrate.
Nov. 14: On that Friday morning, the plan was to use hot water on the outside piping to dissolve the clog. The investigation showed the crew realized methyl mercaptan would expand when heated and they needed to figure out how to remove dangerous vapors from the building. So they opened valves along the feed line and a system was set up to vent the methyl mercaptan. The report said this plan never ended up evaluated for potential hazards and no one performed a safety analysis. There was also no written procedure created to track the progress of the plan. At 6 p.m. the night shift took over and they continued the work.
Nov. 15: Around 1:30 a.m. on that Saturday, the CSB investigation said, the team working to clear the clog in the methyl mercaptan feed line realized the plan was not working. They regrouped in the control room to figure out how to go forward. But they left two valves open that were part of their plan to clear the clog and remove the vapors. An hour later, at around 2:45 a.m., the report states, the flow of methyl mercaptan in the feed line suddenly resumed, but no one noticed.
The sudden flow sent the toxic chemical pumping into the venting system, building enormous pressure and sounding alarms. The CSB report found supervisors did not initially connect the alarms they were hearing to the problem of the clogged feed line. The problem was they were related and highly toxic and highly flammable chemicals released into the room.
“Two rooftop ventilation fans were not working, despite an urgent work order written nearly a month earlier. But we found that even working fans probably would not have prevented the fatalities within the room due to the large amount of toxic gas released,” said Dan Tillema, lead investigator with CSB.
A supervisor and an operator rushed into the room, unaware of the toxic fumes. The operator made an urgent distress call for help, but when the control room tried to get more information, there was no response. Three other operators rushed to the area to help, but the report said they had no idea they were rushing into a toxic gas release. Fumes overcame a fifth worker in the area who managed to get out of the building and recover.
A sixth worker not identified in the report, but later found to be Gilbert Tisnado, realized what was happening and prepared to enter the building to rescue his brother Robert, another employee who was not responding. On his way to the leak site, the report states Gilbert Tisnado found another worker overcome by the fumes. Tisnado rescued that worker by using an air bottle to help him breathe. The report states Gilbert Tisnado continued to the building where the leak was occurring. Emergency personnel found him dead, next to his brother Robert. Investigators found Gilbert wearing a rescue breathing tank mask, but he did not connect it to the air bottle. Investigators wrote it appeared Gilbert was trying to help his brother, but ended up overcome by the toxic fumes.
The plant’s Emergency Response Team (ERT) received an alert. But the report found the team showed up, unaware they were responding to a toxic leak and they didn’t have the right equipment to make rescues. About an hour and a half after the first distress call, the ERT had the right equipment and entered the site. But, by the time they arrived, the four employees missing were unresponsive.
The CSB found the design of the building where DuPont made Lannate pesticide contributed to the deadly incident. Investigators wrote that processing equipment housed in an enclosed manufacturing building exposed workers to highly toxic chemical and asphyxiation hazards that DuPont had not identified or controlled. The report states vapors from chemical leaks end up trapped and concentrated in the building, posing a risk to employees.
Ventilation fans ended up classified as “critical process safety equipment” by DuPont. Two fans designed to keep exposure levels low were not working at the time of the leak. The ventilation fan in the area where methyl mercaptan released was not operating, despite an “urgent” maintenance work order submitted on Oct. 20, weeks before the fatal leak. Even though the fan was out of order, CSB investigators wrote the company took no additional precautions to protect workers in case of an emergency. Regardless of the condition of the fans, the CSB team found the leak was so massive, even operable fans would not have prevented the deaths.
The CSB report said DuPont’s system for detecting methyl mercaptan did not do enough to warn workers or the public about a toxic exposure. Investigators found the trigger point for alarms at the plant was set well above what OSHA set as a recommended level. In the hours before the Nov. 15 incident, multiple alarms sounded, but the company’s emergency response team did not get a notification and employees continued to work in the area. Leaks of methyl mercaptan ended up detected Nov. 13 and 14, but never reported as releases or investigated as safety issues.
CSB board members made safety recommendations in the report. Among the recommendations:
• DuPont should complete a comprehensive engineering analysis of the manufacturing building where the chemical leak occurred
• Assess safer design options
• Report the findings to employees and the CSB
The CSB report makes a similar recommendation for the building’s air ventilation system to ensure a safe environment for workers.
The Occupational Safety and Health Administration previously fined the company $99,000 and an additional $273,000 for safety violations at the La Porte plant following the fatal incident and put the company in its “Severe Violator Enforcement Program.”
In July, DuPont told the CSB it remained committed to addressing safety issues identified in the investigation. The company also stated its commitment to implementing CSB safety recommendations and said the unit involved in the November 2014 incident will not restart until the safety actions are complete.
“DuPont representatives have engaged extensively with representatives of the CSB to discuss the agency’s findings and recommendations. We remain committed to cooperating with the agency throughout its investigation. DuPont is actively addressing the CSB recommendations as well as those identified from our own incident investigation,” said James O’Connor, La Porte plant manager. “We value the CSB’s perspective, and we are taking their recommendations seriously. The La Porte plant is shut down and will remain so until DuPont has executed a comprehensive and integrated plan to safely resume operations.
“While DuPont respectfully disagrees with aspects of the report and some of the CSB’s findings, we are coordinating with the CSB as we implement the following actions:
• Improved process hazard analyses
• Engineering analysis of the Lannate building and exhaust ventilation system, and implementing safety improvements
• Equipment modifications and redesign, including relief systems, detectors and alarms
• Improved Lannate operating procedures and training for all personnel