Equipment, explosives, or machinery that have been tested and approved by regulatory agencies for use in hazardous mine atmospheres. These items are designed so they will not ignite firedamp or coal dust under normal operating conditions. An electrical device earns this rating by containing any internal sparks within a flameproof enclosure, while approved explosives are formulated to produce a cooler, shorter-duration flame.
Heard on the job
You can't take that commercial drill into the return airway because it isn't permissible.
Insider tip
In the United States, the MSHA approval plate must be physically attached and legible, or the equipment immediately loses its permissible status.