DuPont has been cited by federal investigators for 11 violations related to a chemical leak at the company’s plant in LaPorte, Texas, that claimed the lives of four workers.

The Occupational Safety & Health Administration (OSHA) on May 14 said the tragedy would have been prevented had DuPont taken steps to protect the workers. The agency is proposing fines totaling $99,000 for the November 2014 deaths, which were caused by exposure to a leak of methyl mercaptan, an insectide ingredient.

An investigation by OSHA determined that one worker was overcome when “methyl mercaptan gas was unexpectedly released” after she opened a drain on a vent line. Two coworkers nearby, unaware of the leak, attempted to save her but were also consumed by the gas. The brother of one of the victims rushed to rescue the three but was also overcome by the gas.

“Four people lost their lives and their families lost loved ones because DuPont did not have proper safety procedures in place,” says OSHA chief David Michaels. “Had the company assessed the dangers involved, or trained their employees on what to do if the ventilation system stopped working, they might have had a chance.”

The accident occurred in a unit that manufactures methomyl, a carbamate insecticide DuPont markets under the trade name Lannate.

In a statement, DuPont says it is reviewing OSHA’s findings and has taken “a series of actions to prevent this from ever happening again.” The company says the unit remains shut down while it conducts “completely new process hazards analyses, acting on findings from our own investigation.”

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Methyl mercaptan, one of the ingredients used to make methomyl, is a colorless gas with a strong odor. DuPont has determined that more than 23,000 lb of methyl mercaptan was released during the Nov. 15, 2014, accident.

At dangerous levels of exposure, the gas depresses the central nervous system and affects the respiratory center, producing death by respiratory paralysis, according to OSHA.

DuPont was cited for one repeat violation, nine serious violations, and one other than serious OSHA violation. The repeat violation was assessed for not training employees on using the building’s ventilation system and other safety procedures, such as how to respond if the fans stopped working.

In July 2010, DuPont was cited for a similar violation after a fatal accident at a plant in West Virginia.