Federal labor regulators have cited four employers for safety violations related to an explosion that injured workers at a Louisiana chemical plant.

The U.S. Department of Labor’s Occupational Safety and Health Administration announced 11 serious violations Thursday. The agency proposed a total of $139,000 in penalties for the four companies that have employees stationed at the Westlake Chemical facility in Sulphur.

A flash fire and subsequent explosion seriously harmed six workers on Sept. 27. Infractions included not performing equipment inspections, allowing dangerous work in confined spaces and exposing workers to harmful chemicals, OSHA said in a news release.

Westlake Chemical had three violations with proposed penalties of about $30,400. Sulphur-based Wastewater Specialties had two violations with proposed penalties of about $24,800.

Two Texas-based companies were also cited: Turn2 Specialty Companies had four violations with proposed penalties of about $58,000 and Leak Sealers Inc. had two violations with proposed penalties of about $26,100.

“Employers are responsible for ensuring employees have a safe workplace by having the correct confined space permits and a plan in place to inspect equipment to prevent serious injuries,” said Roderic Chube, an OSHA area director in Baton Rouge.

A similar explosion at a nearby Westlake Chemical plant on Jan. 26 injured six employees and shook the Lake Charles area. It wasn’t addressed in the citations Thursday.

At least 23 workers are suing the company for broken bones, burns and other wounds, according to The Times-Picayune/The New Orleans Advocate. Westlake has declined to discuss the explosions and didn’t immediately respond to the news outlet’s request for comment about the safety violations.