The release of a small amount of residual gas that briefly suspended some activity at the Columbia Generating Station has been declared an "unusual event."

During work for the plant's ongoing refueling outage Thursday, a small amount of hydrogen gas was released from a pipe and ignited -- a less-than-one-second "puff," according to a news release from Energy Northwest.

The work was being performed in Columbia's main turbine building, which is a non-nuclear area of the plant. There were no injuries or damage to equipment, Energy Northwest reported.

During normal operations, the pipe is filled with water and some hydrogen, which is used to cool the generator. Workers were cutting the pipe, which had been closed and purged, when a small amount of residual, trapped gas escaped the pipe. The immediate area was evacuated and an "unusual event" declared.

An "unusual event" is a classification describing a condition at a commercial nuclear power plant or its surroundings that could potentially compromise the normal level of plant safety, or that warrants increased awareness by plant staff.

Notification was made to the Nuclear Regulatory Commission shortly after the incident, according to Energy Northwest.

Outage work resumed in the area following a safety inspection by Columbia officials.

Columbia powered down Saturday leading up to its biennial refueling outage, which started Wednesday, and is scheduled to be completed by mid-June.