A spokesman for a Washington nuclear power plant says a small amount of hydrogen gas ignited in a six-inch flame Thursday when workers cut into the pipe.
Columbia Generating Station declared an "unusual event," evacuated plant areas near the pipe for about 90 minutes, and notified the Nuclear Regulatory Commission.
Energy Northwest spokesman Mike Paoli says no one was injured in the one second-long "puff" of gas that had been trapped in the pipe in the plant's non-nuclear turbine building.
Paoli says there's was "no association whatsoever with the reactor building or radiation."
An "unusual event" describes a condition that could potentially compromise normal safety levels, the least serious of four NRC emergency classifications.