What is the minimum percentage of incombustible material required after rock dust application in non-return entries?

The minimum percentage of incombustible material required after rock dust application in non-return entries is set at eighty percent. This requirement is crucial because it ensures that the risk of fire and explosion in underground mining environments is minimized. Rock dust acts as a way to prevent the propagation of flames by increasing the inert material in the atmosphere, substantially reducing the chances of combustible dust igniting.

Maintaining an eighty percent threshold ensures that a sufficient amount of incombustible material is present to effectively suppress coal dust flames in the event of a fire. It is an industry standard aimed at enhancing safety protocols within mines. This requirement reflects compliance with safety regulations, which are designed to protect miners from the dangers associated with combustible dust and to promote safer working conditions.

The other percentage options provided fall below the established standard, which would fail to adequately limit the potential for fire hazards. Hence, adherence to the eighty percent requirement is critical for ensuring a safe mining environment.