More than 20,000 Big Island households lost power late Wednesday afternoon when the Puna Geothermal Ventures Plant in Pahoa went offline.
The Hawaii Electric Light Company says there was a fault on one of the transmission lines, which then released steam as part of a built-in safety system.
Hazmat and fire teams responded to the scene.
Hawaii County Civil Defense says only trace amounts of hydrogen sulfide and or other byproducts of the geothermal process were released in the steam.
Puna Geothermal says crews measured 19 parts of hydrogen sulfide to one billion, which they say is 18 parts per billion above normal.
They say the last time something like this happened was November 2011.
Puna Geothermal provides about 30 percent of the Big Island's electricity to HELCO.
HELCO says power was restored within 15 minutes, shortly after 4 p.m.
Civil Defense says there is no danger to the public.