Fatalities in the Aracoma Alma Mine in West Virginia have focused again on conveyor belt related fires and the devastating impact it has on miners' safety in the United States.

Conveyor belts represent a high risk, because they have the ability to spread a fire over long distances.

Fires on belt conveyors are mostly ignited by mechanical failures, for instance in an idler bearing or by friction.

Except in the USA, fire safety requirements are similar for the largest hard coal mining countries China, India, Australia, South Africa, Russia and Poland. In Germany, for instance, such strict requirements were implemented more than 30 years ago. See also here. The tests in these and most other countries are:

• Drum Friction Test
  The drum friction test simulates a belt slipping over a jammed pulley, or a pulley rotating under a stationary conveyor belt. This measures whether the surface temperature remains under a required maximum after a specific time and under a specific tension. Generally a rubber conveyor belt can produce a pulley surface temperature of up to 500°C (930°F). The visual appearance of flame or glow is not permitted.

• Surface Resistance Test
  An electrostatic charge may build up on the conveyor belt surface and iginite a mixture of flammable gases and air. Therefore the surface resistance of the conveyor belt covers has to be below 300 MOhms.
  

• High-Energy Propane Burner Test
  Conveyor belts must not propagate fire. In order to determine whether a conveyor belt fulfills this requirement, it is ignited by a propane burner. After the ignition source has been removed, the flames must self-extinguish within a certain time frame or within a certain distance. A typical sample for this test is 2 m long at full width.

• Spirit Burner Test
  A small piece of the conveyor belt is held over a spirit burner flame. After a certain time the burner is removed. The duration of flame and glow has to be within a specified time limit.

Some countries have even more stringent requirements, for instance regarding the belt's toxicity, hygiene or cover roughness.
The exact specifications can be found in the relevant standards.

It is obvious that not every single belt can be tested as per the above procedures. Therefore a kind of finger print method was developed in Europe:

• The Limiting Oxygen Index (LOI)
  This method is an effective and inexpensive quality control. It determines the minimum concentration of oxygen that will support combustion of a specific belt sample. The result of the approved belt must comply with any supplied belt of the same type.

The requirement in the United States is quite simple:

• Bunsen burner test
  A small piece of a belt is held over a Bunsen burner flame and the duration of the belt's afterglow must be less that a specified maximum time.

This test, which was implemented as per the 1969 Federal Coal Mine Health and Safety Act, is similar to a standard that was in force in europe until the mid 1970's for underground conveyor belts (fire resistant, grade K or S). Later, these conveyor belts have only been allowed to be used in above ground applications. The German mining authority, as an exemple, stated that such conveyor belts could act as a fuse.

In December 1992, the US Department of Labor, Mine Safety and Health Administration (MSHA), proposed a new rule for conveyor belt test requirements (Federal Register, Vol. 57, No. 248) that would bring safety standards up to the international level.

This proposed rule was withdrawn in July 2002. The reasons given for withdrawal were that the number of conveyor belt fires had significantly declined and that improvements in belt monitoring were implemented.

A comprehensive description of international safety standards has been published here: http://www.msha.gov/Beltair/OtherSubmits/Kusel%20of%20Phoenix%20Conveyor%20Belts.pdf

In December 2007 the Final Report of the Technical Study Panel recommends the use of fireproof conveyor belt: http://www.msha.gov/BeltAir/BeltAirFinalReport122007.pdf