OSHA Addresses Hazards of Purging Hydrogen Gas-cooled Electric Generators

Published February 24, 2016

A new OSHA publication warns employers about the potential hazards workers face at electric power plants when purging electric generators cooled with hydrogen gas. A “safety and health information bulletin” dated Jan. 22 describes these hazards, which include flash fires and dangers related to working in confined spaces. According to OSHA, employers must ensure that hydrogen gas is purged completely before workers perform any type of maintenance on the generators.

“Work in the typical electric generator housing or bushing box usually involves permit-required confined space entry procedures including atmospheric checks for oxygen concentration and flammable gases such as hydrogen,” the bulletin reads. “If hydrogen gas remains in any area in a concentration from 4 percent to 75 percent (the lower and upper flammability limits) in air, then the atmosphere in that area is flammable. The wide flammability range increases susceptibility to flash fires in particular.”

Hydrogen gas can concentrate in overhead areas, making it harder to detect. With low minimum ignition energy, hydrogen gas can be ignited by something as small as an electrostatic spark from a worker’s movement. According to OSHA, all areas where workers are located should be monitored because hydrogen gas can cause asphyxiation if it is not completely purged.

The bulletin describes an incident in 2011 in which inadequate purging of hydrogen gas during repair of a turbine generator led to a worker’s death. The generator had been taken offline due to hydrogen contamination and a suspected leak. In a violation of written procedures, workers tested for hydrogen using fixed gas detectors instead of portable models, and did not detect the hydrogen that had accumulated at the roof of the generator housing. When another worker entered the confined space with an electric drop light and an electric fan, a flash fire erupted, and the worker was fatally burned.

OSHA recommends training workers on hydrogen gas purging procedures and the related hazards, and developing written procedures for working in confined spaces. The agency also recommends placing detectors in areas that may accumulate hydrogen gas, testing atmospheric conditions in permit spaces before allowing entry, and establishing ignition control procedures.

For more information, see the OSHA bulletin.