1.   The gas is ignited by an electrical spark.

2.   When the wires fell, they ignited the gas leaking from the main.

3.   Flames melted a lead pipe and ignited leaking gas causing the fire to spread along the passageway and up the stairwell to the second floor.

4.   A teen-age boy who was mowing the lawn may have ignited the gas with a spark from the lawn mower.

5.   Akzo installed wells and ignited the gas, and company engineers say the flares should subside as water fills the mine.

6.   Electrical equipment ignited gas that had migrated from a line pierced months earlier by a contractor laying underground cable.

7.   Even if a spark ignited the gas, proponents said, it would burn away rapidly and cause less damage than gasoline.

8.   He said investigators are not sure what ignited the gas.

9.   The accumulating gas was later ignited by an ignition source, possibly the pilot light on the water heater.

10.   A stray spark apparently ignited cooking gas that had leaked from tanks and collected in a basement restaurant, they said.