More than eight years after the tragedy, DuPont Insecticide Plant admitted that their negligence led to the employees' deaths.
According to the U.S. Attorney's Office, the plant and Kenneth Sandel, who was the unit operations leader at the time, plead guilty to the incident.
SEE ALSO: DuPont and former employee charged in 2014 fatal La Porte incident
On Nov. 15, 2015, DuPont released about 24,000 pounds of methyl mercaptan, a highly toxic and flammable gas.
The fatal accident occurred after an employee inadvertently left open a piping valve which caused a slushy material to block the flow of liquid MeSH into the Lannate process.
To melt it, DuPont day shift employees began applying hot water to the outside of the blocked piping and opened other valves to vent MeSH gas into a waste gas system. However, the MeSH piping was still blocked at the end of the day.
Sandel was responsible for ensuring shift supervisors, operators, and engineers understood and complied with safety, health, and environmental regulations. But according to the U.S. Attorney's Office, Sandel, and other employees failed to provide sufficient instructions to the oncoming shift on how to clear the remaining blockage safely.
In addition to the deaths of the four employees, the chemical released also injured other employees and traveled into surrounding areas.
SEE ALSO: 911 recordings released following deadly DuPont chemical leak
On top of the $16 million penalty, the company must also serve two years of probation, giving the U.S. Probation Office full access to all of its operating locations.
A judge also ordered Sandel to serve a one-year probation.
The company will also make a $4 million community service payment to the National Fish and Wildlife Foundation to address the harm caused by the projects that benefit air quality and around areas of Galveston Bay.