SHIPPINGPORT, Pa. — Authorities say two contractors who inhaled toxic fumes at a Pennsylvania power plant that killed two other workers have been released from the hospital.

Enerfab Corp. chief executive officer Scott Anderson says the employees were discharged from the hospital Friday. He says a 43-year-old worker still hospitalized “continues to show signs of improvement.” There was no word on the status of a fourth injured worker.

Police said the contractors were in a “confined, well-type” area at the Bruce Mansfield Power Station in Beaver County when hydrogen sulfide gas was released early Wednesday. Police said 34-year-old Kevin Bachner and 42-year-old John Gorchock were unable to reach safety and were killed.

The accident at FirstEnergy’s largest coal-fired plant in Shippingport, about 35 miles (56 kilometers) northwest of Pittsburgh, remains under investigation.