Page 404 - Advanced Mine Ventilation

Prevention of Frictional Ignitions 373

3. Incorporating wet cutting on all mining machines and eventually design machines that assist
coal cutting with high pressure water.
4. Using larger cutting tools made of high-grade stainless steel to provide deep cutting without
frequent breakdowns.
5. Using high attack angle bits, such as radial or forward attack bits. The machine should be
originally designed to incorporate these bits. A retrofit is generally unsuccessful.
6. Bit tip material made of polycrystalline diamonds, which can be directly deposited on
tungsten carbide or bonded to it as a thin wafer.
The suggested steps will not only make mining safer but also more economic by
enhancing coal productivity and creating a source of extra revenue from coalbed
methane. Loss of production due to mandatory suspension of mining subsequent to
an ignition will also be minimized.

22.6 Frictional Ignitions Caused by Belt Conveyors

Belt conveyors are quickly replacing all old methods of coal transport. As mentioned
in Chapter 21, they create nearly 17% of mine fires but they are usually contained
quickly. An exception is the Wilberg Mine Fire [11], where 27 lives were lost due
to a belt fire.
Francart [12] reports an average of 5.7 incidents of belt fire per 1000 mines over the
period 1980 to 2005. A breakdown of belt conveyor ignition sources is shown in
Table 22.2.
Belt friction accounts for nearly 50 percent of all belt fires.
The belt drives and conveyor transfer points are the first primary ignition source for
many reasons. Electrical sources are likely to exist near the drives. Spillage of coal at
such location is also very likely. Belt slippage can cause the belt fabric to heat up and
ignite itself or the spilled coal underneath.

Table 22.2 Ignition Sources of Belt Fires

Ignition Source Number of Fires Percent
Friction at belt drive 11 18
Friction along belt 11 18
(Stuck) hot rollers 6 10
Electrical 8 13
Cutting and welding 5 8
Hydraulic fluid 2 3
Undetermined 18 30