A maintainer working at an open-cut coal mine had completed gouging a weld from an excavator travel motor guard when a bystander noticed small blue flames between the excavator track pads, directly below the hot work area.
Hot work stopped immediately and the flames burnt out. The entire work area was checked with a gas monitor and intermittent pockets of methane gas were detected under the excavator track pads. The machine was then relocated to a work area 400 m further up the ramp. Before work recommenced, this area was checked with a gas monitor and was found to be gas free.
How did it happen?
Intermittent pockets of methane gas issuing from the ground beneath the excavator track pads were ignited by sparks from hot work being performed above.