The U.S. Department of Labor on Thursday said a DuPont facility in Texas could have prevented the deaths of four workers last year if the company had taken proper safety precautions.

Four DuPont workers were killed in November by a methyl mercaptan gas leak at a manufacturing facility in La Porte, Texas, according to a Labor Department statement.

The U.S. Occupational Health and Safety Administration has cited the Wilmington, Delaware-based chemical company with 11 safety violations and issued a fine of $99,000 in relation to the accident, the Labor Department said.

Methyl mercaptan is a colorless gas with a strong odor that can be found in pesticides, jet fuels and plastics, the Labor Department said. Exposure to high levels of the gas can depress the central nervous system and cause death by respiratory paralysis.

“The fatal incident occurred as one worker was overwhelmed when methyl mercaptan gas was unexpectedly released when she opened a drain on a methyl mercaptan vent line,” the Labor Department's statement reads. “Two co-workers who came to her aid were also overcome. None of the three wore protective respirators. A fourth co-worker — the brother of one of the fallen men — attempted a rescue, but was unsuccessful. All four people died in the building.”

David Michaels, assistant secretary of Labor for occupational safety and health, said DuPont “did not have proper safety procedures in place” to prevent the workers' deaths.

“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,” Mr. Michaels said in the statement.

DuPont said in a statement that it is reviewing OSHA's findings and cooperating with state and federal authorities. The company also said that it “has taken a series of actions to prevent this from ever happening again.”

“Safety is a core value and constant priority at DuPont,” the statement reads. “Our response to this tragedy reinforces our absolute focus on safety and enables us to learn from it so that we can find ways to be an even better company.”

DuPont has 15 days to contest OSHA's findings or request an informal conference with OSHA to discuss the incident, according to the Labor Department.