About 50 people were temporarily evacuated from Tesoro Corp.'s Kapolei refinery Tuesday evening following the discovery of unacceptably high levels of hydrogen gas.

The incident, which occurred at about 6 p.m., forced about 50 people to vacate the refinery's hydrogen production unit for one hour, said Tesoro spokesman Nathan Hokama. The hydrogen unit, which was shut down, was expected to resume production yesterday.

Hokama said the problem was unrelated to lingering problems resulting from a power outage earlier this month. That rain-induced power failure forced a suspension in gasoline production at the plant, which is expected to last until mid-December.

Other recent incidents at the Tesoro refinery, which is the state's largest, include a June 2006 smoldering fire in a liquid asphalt storage tank. No one was injured; however, there was an evacuation of workers from the tank farm area at Campbell Industrial Park.

Tesoro's asphalt production was suspended for about a month following the incident.