The Department of Labor has fined a power plant operator and an engineering company for a toxic gas exposure that left two contractors dead last August in Beaver County.

Kevin Patrick Bachner, 34, and John Michael Gorchock, 42, both of Pittsburgh, died Aug. 29 at FirstEnergy’s Bruce Mansfield Power Station after inhaling the toxic gas hydrogen sulfide in a confined vault inside the plant. They were part of a maintenance crew working on a 24-inch pipe that carried water, hydrogen sulfide and ash slurry, according to citations issued by the Occupational Safety and Health Administration.

Both men were employees of Enerfab, a Cincinnati-based contractor performing maintenance at the plant for FirstEnergy. Three workers were injured in the event, which is the subject of a federal lawsuit.

In its citations, OSHA said that FirstEnergy failed to alert Enerfab of the dangers the workers faced in the vault, including “engulfment hazard” and “hazardous atmosphere hazards,” and that Enerfab and failed to provide “appropriate respiratory protection” for the workers.

FirstEnergy was fined $77,605. EnerFab was fined $129,340. The companies have until March 20 to appeal.

Scott Anderson, CEO of EnerFab, said his company would appeal the decision, though he declined to elaborate the company’s reasons for appealing. “We want to go through the process to review those (citations) further with (OSHA),” he said.

Stephanie Walton, spokeswoman for FirstEnergy, said in an email that the company is reviewing the citations “to determine the appropriate response and whether any additional steps should be taken to prevent this type of accident.”

 She said the company was conducting an internal review of the incident and that it has already implemented a number of added precautions to prevent a repeat of the event.

“Safety remains our top priority, and we are committed to fully understanding the cause of this accident to ensure our employees and contractors are working in the safest possible conditions,” she said.

Hydrogen sulfide, or H2S, is a “colorless, flammable, extremely hazardous gas with a ‘rotten egg’ smell,” according to OSHA. The agency notes that the gas “is heavier than air and can collect in low-lying and enclosed, poorly ventilated areas.”

Bruce Mansfield Power Station is the largest power plant in Pennsylvania, and first came online in 1976, according to the Pennsylvania Public Utility Commission.