Four workers were killed and another injured Saturday morning after responding to a leak of a hazardous gas at the DuPont Chemical Refinery in La Porte, Texas.

The leak of methyl mercaptan, which is mixed with odorless natural gas to give it a rotten-egg smell, appears to have started with the malfunction of a valve on a container of the gas in an operating unit that produces fertilizer additives.

According to an article in the Houston Chronicle, production operator Robert Tisnado was near the end of a shift early Saturday morning when he heard a female worker call for help at the operations building. Tisnado, along with crew supervisor Wade Baker, rushed in without masks and were overcome by a cloud of the gas.

Tisnado’s brother, Gilbert, put on a mask and went in to help the three after losing radio contact. He was overcome when he removed his mask to place it on his younger brother, though it was too late.

The 600-acre DuPont plant employs 800 workers and produces a wide range of products, including pesticides and plastics. In the past five years, the refinery has been fined six times and received dozens of citations from the Texas Commission on Environmental Quality.

In 2012, the plant was fined $91,125 for a failure to limit residual emissions of effluents, including methomyl and chlorine. In 2007, the Occupational Safety and Health Administration levied a small fine for unsafe handling of hazardous chemicals. Violations of the Clean Water Act also resulted in fines of $91,000 and $26,000 for the DuPont facility.

The U.S. Chemical Safety Board sent an 8-member team to the facility to investigate Saturday’s deadly leak. The federal agency is charged with examining industrial chemical accidents that result in fatalities, serious injuries or substantial property damage.

A lawsuit was filed Monday against DuPont on behalf of Jasmine Rae Wise, whose mother Crystle Wise was among the workers killed in the accident.

Refinery workers can be at-risk for many different types of chemical exposure injuries. If you or a loved one were hurt while working in a plant, contact our law firm Schechter, Shaffer & Harris, L.L.P., Accident & Injury Lawyers today to get legal help.