Specific and Non-Specific Hazards in Underground Mines

5 Hazards of Underground Mining

Gold mining at the Anglo Gold Ashanti Mine, South Africa
Gold mining at the Anglo Gold Ashanti Mine, South Africa. Getty Images/Graeme Williams

The Gleision Colliery tragedy reminds us of how dangerous mining jobs can be and how specifically hazardous underground mining remains.

Fire, flood, collapse, toxic atmospheric contaminant, and dust or gas explosion are the most critical hazards specifically linked to underground mining.

Blasting related hazards have to be added to that list. Although not specific to underground operations, their consequences could be exacerbated by the confined atmosphere and the workplace configuration.

Specific Hazards in Underground Mines

Accidents are always a combination of hazards and causes. Making the issue more comprehensible is the only reason for presenting the hereafter list of hazards. The collapse and flood of underground workings could be a consequence of a dust or gas explosion. Similarly, a fire could cause dust explosion and/or release toxic contaminants.

1. Fire

In the document “The prevention and control of fire and explosion in mines” issued by the Health and Safety Executive (HSE), the following potential sources of fire in underground mines are listed:

  • "Friction from:
  • - Defective bearings – conveyor idlers, drums, wheels/axles;
    - Conveyor belts rubbing against some fixed object, such as a roadway support or a tail end structure, or running in spillage;
    - Seized brakes on vehicles;

    Further reading on lightning propagation

    See also the section on blasting related hazards below.

    • Internal combustion engines – exhaust systems, air inlets, hot surfaces;
    • Spontaneous heating of coal in the waste or of broken coal in the roadside in high-risk seams;
    • Incendive sparks from cutting machinery picks;
    • Electrical and mechanical machinery and equipment;
    • Electrical sparking and hot surfaces from electrical equipment and distribution systems;
    • Short circuits and earth faults on electrical equipment and distribution systems;
    • Natural sources, for example, electrostatic discharges and lightning
    • Explosives and detonators
    • Compression of air or gasses;
    • The thermite reaction between light alloys and iron/steel (…)
    • Hot work – burning, welding, and grinding;
    • Smokers’ materials, e.g. cigarettes, lighters and matches.”

    2. Flood

    After the inrush in the Gleision Colliery on September 15, 2011, in the County of Wales, which killed four miners, the Health and Safety Executive (HSE) issued the HID 4-2011 safety bulletin focusing on Regulations 1979 (Precautions Against Inrushes). This regulation has been introduced in 1973 after the Lofthouse accident, Yorkshire, where seven miners were killed.

    3. Collapse

    Mine collapse might be caused by the following factors:

    Induced Seismicity

    Mines located in seismically active regions, such as the Andean region (also known to be one of the wealthiest metallic mining zones in the world), are particularly at risk. Especially dangerous in underground mining areas, mine-induced seismicity also causes slope instability in surface mining.

    Use of Explosives

    The use of explosives might cause earthquake-like events that collapse mine workings, and traps miners, as happened to the 33 miners stuck underground from August to October 2010 in a Chilean mine near the city of Copiapo, or kill them, flood the mine and damage structures on the surface.

    Dust or Gasses Explosion

    Please refer to Common Mining Accidents

    Timbering / Pillar Failure

    Webster’s dictionary gives this definition:

    “The operation of setting timber supports in mine workings or shafts to support the roof or the face of a tunnel during excavation and lining. The term "support" would cover the setting of timber, steel, concrete, or masonry supports”.

    You can get an idea about the traditional way to timber a mine by reviewing this video. The role of pillars or timbers is obviously key in underground operations.

     The instability of pillars induced by stress or other unfavorable causes may lead to horrendous cascading pillar failure mechanisms.

    4. Toxic Contaminant

    Considering that the atmosphere underground is limited and confined, the contaminants may include dust, aerosols, diesel fumes and particulates and fumes from blasting, as well as gasses released from the rock strata. Ventilation is key to extract or dilute to a harmless level the toxic contaminants.

    5. Blasting Related Hazards: A Common Threat To Surface And Underground Miners

    As reported by the National Institute for Occupational Safety and Health (NIOSH): “In underground mines, most explosive-related fatalities were caused by miners being too close to the blast (fly-rocks), followed by explosive fumes poisoning, misfires, and premature blasts". 

    Mine induced seismicity must be added to that list. 

    Fly-Rocks

    Workers struck by rocks, either because they are too close to the blast or because the rock is thrown much farther than expected, remains one of the main causes of accidents both in surface or underground mines.

    Explosives Fumes

    “Blasters at surface mines and construction operations have not been as concerned about blasting fumes as their counterparts in underground mines, believing that fumes would disperse in the open air. Surface blasters, however, must be aware that toxic fumes have the potential to create hazards in their operations” (Source: Dangers of Toxic Fumes from Blasting, Mainiero & al.)

    The explosive products used in surface and underground blasting operations produce a variable quantity of toxic gasses:

    Harmful concentrations of such gasses are more likely to appear in underground confined environments. An efficient, well designed and maintained ventilation system is key to preventing or mitigate this risk.

    Misfires

    "Misfire means the complete or partial failure of a blasting charge to explode as planned." (Definitions for Surface and Underground Metal and Nonmetal Mines, Department of Labor, Mine Safety and Health Administration (MSHA),30 CFR Parts 56 and 57, Sec. 56.2, Volume 69, Number 124, pages 38837-38843

    Premature Blast

    "The detonation of an explosive charge earlier than warranted. Premature explosions may be due to carelessness, accidental percussion, a faulty fuse, or degenerated explosives." Source: Dictionary of Mining, Mineral and Related Terms

    The explosive or pyrotechnical products that remain on the ground or in the muck pile might be triggered by any mechanical effect during the digging, milling or crushing stages of the mining process, causing injuries or fatalities to blasters or operators.

    • Nitrogen dioxide (NO2)
    • Nitric oxide (NO)
    • Carbon monoxide (CO)