Page 108 - Advances In Productive, Safe, and Responsible Coal Mining

92 Advances in Productive, Safe, and Responsible Coal Mining

accumulations of methane near the tailgate corner. Green arrows show typical posi-
tions where nitrogen may be injected through headgate seals to inertize the gob behind
the face. Similar back return arrangements are used in European longwalls. Europeans
commonly use single-entry gate roads and build a continuous seal “dam” along the
tailgate. To create a back return, a window is left in the dam to be sealed at a later time.

6.7 Mine fire and explosion prevention, refuge chambers

Fires and explosions have caused catastrophic accidents in coal as well as metal and
nonmetal underground mines. In coal mines, methane gas and spontaneous combus-
tion of coal are the most common causes for fires and explosions, with other ignition
sources, including open flames, faulty electrical equipment, and hot metal smears cau-
sed by worn cutter bits. Blasting used to be a frequent cause of coal mine explosions,
but the use of permissible explosives along with the mechanization of the cutting pro-
cess has made such explosions rare. In metal and nonmetal mines, frequent sources of
fires include diesel and electrical equipment, batteries, flame cutting and welding, and
spontaneous combustion of timber and trash.
The mine ventilation system must be capable of exhausting smoke and fire gases
away from escape routes for employees. Many modern mine ventilation modeling
programs give the user the option of placing a fire at any point inside the mine and
observing where the smoke travels and which escapeways may remain usable. Metal
and nonmetal mines are frequently equipped with underground refuge chambers
where miners whose escape is blocked can seek temporary shelter from fire and
smoke. Such refuge chambers have been used during numerous mine fires and have
allowed miners to wait safely until the fire hazards were cleared. In metal and non-
metal mines, fires typically burn out from lack of fuel after several hours.
In the wake of explosion disasters at the Sago Mine in the US State of West Virginia
and the Darby Mine in the US State of Kentucky that occurred in 2006, the US Con-
gress passed the Mine Improvement and New Emergency Response (MINER) Act
requiring, among other safety improvements, the installation of underground refuge
chambers in coal mines as well. Chambers must enable life support for all miners
potentially unable to escape, and must be kept within close reach of face areas. Since
faces in coal operations typically move 15–30m (50–100ft) per day, many chambers
are mobile and moved up with the face regularly. Fires in underground coal mines may
continue to burn for days, months and, in some cases, years due to the abundance of
fuel the coal provides. Missions to rescue miners from refuge chambers are often dif-
ficult if the mine ventilation system is compromised allowing methane to accumulate
near the fire area and creating explosion hazards. Planning and maintaining open,
accessible escapeways provides the best chance for miners to survive and escape a
coal mine fire or explosion.
If a coal mine is on fire, there is little chance of fighting the fire directly. Due to
ventilation, mine fires grow rapidly, in some cases leaving only minutes before the fire
grows out of control. Mitchell [9] states that fires that are not controlled within the first
2–4h will likely lead to sealing the fire area or the entire mine. Fires have a significant