Report finds series of errors caused deadly DuPont plant accident in La Porte

String of errors and missed warnings contributed to deaths of La Porte plant employees

HOUSTON – Board members of the U.S. Chemical Safety Board voted unanimously to approve safety recommendations identified by investigators after the deadly November 2014 incident at the DuPont plant in La Porte.

Families of the victims told Channel 2 they hoped DuPont would adopt the recommendations as quickly as possible.

"What happened to my brothers shouldn't have have happened. I don't want anyone to lose their dad, brother or grandpa over careless neglect. That's what i call it. It shouldn't have happened," said Lanette Soto, Robert and Gibby Tisnado's sister.

The U.S. Chemical Safety Board has released findings of an interim investigation into the leak of a toxic chemical at the DuPont manufacturing facility in La Porte. Four employees were killed in the incident on Nov. 15, 2014. 

The board's investigation found a series of mistakes that began five days earlier, eventually lead to the release of nearly 24,000 pounds of methyl mercaptan, a toxic chemical. 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," Vanessa Allen Sutherland, the safety board's chairperson, said. "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."


The CSB investigation found a chain of events, beginning on Nov. 10, 2014 triggered the toxic leak that happened the following Saturday morning.  On Monday, Nov. 10, a water dilution system was accidentally activated and that caused a storage tank to overload. Crews were forced 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 states that 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.

On Friday morning, a new group of workers began their shift. The CSB report states these workers didn't know about the earlier system shutdown and the clogs that remained. The new team met and took over the plan to clear the clogs. The plan was to use hot water on the outside piping to dissolve the clog. The investigation shows the crew realized methyl mercaptan would expand when heated and they needed to figure out how to remove dangerous vapors from the building. So valves were opened along the feed line and a system was set up to vent the methyl mercaptan. The report states this plan was never evaluated for potential hazards and no safety analysis was performed. There was also no written procedure created to track the progress of the plan.


Around 1:30 a.m. on Nov. 15, the CSB investigation states, 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 that supervisors did not initially connect the alarms they were hearing to the problem of the clogged feed line, when in fact, they were related and highly toxic and highly flammable chemicals were being 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," Dan Tillema, lead investigator with CSB, said.

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 states they had no idea they were rushing into.a toxic gas release. A fifth worker in the area was overcome by fumes but managed to get out of the building and recover.

A sixth worker who was not identified in the report, but who Channel 2 Investigates identifies as 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 who was 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. He was found dead, next to his brother Robert.  Investigators found Gilbert wearing a rescue breathing tank mask, but he had not connected it to the air bottle. Investigators wrote it appeared Gilbert was trying to help his brother, but was overcome by the toxic fumes.

The plant's Emergency Response Team was alerted. 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 found unresponsive.


The CSB found the design of the building where Lannate pesticide was manufactured 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 are trapped and concentrated in the building, posing a risk to employees.

Ventilation fans were classified as "critical process safety equipment" by DuPont, but 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 was 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 states 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 to the Nov. 15 incident, multiple alarms sounded, but the company's emergency response team was not notified and employees continued to work in the area.  Leaks of methyl mercaptan were detected on Nov. 13 and 14, but were never reported as releases or investigated as safety issues.


CSB board members made seven 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 and report the findings to employees and the CSB.  The report makes a similar recommendation for the building's air ventilation system to ensure a safe environment for workers.

A public meeting will be held Wednesday at 6 p.m. at the Hilton Americas in downtown Houston to discuss the findings and recommendations.

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 was 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; and
  • Improved Lannate operating procedures and training for all personnel.