Focus on Coal Mining: Safety Hazards, Health Hazards, and Mine Rescue

The tragedy of the January 2, 2006, Sago mine explosion in Tallmansville, West Virginia, reinforces the importance of recognizing the potential hazards in underground coal mining, and the need for systematic safety and health vigilance. CDC's National Institute for Occupational Safety and Health (NIOSH) conducts a strategic research program for preventing injuries, illnesses, and fatalities in mining. The products of that research form the basis for partnerships with industry, government, miners and their representatives, and other stakeholders to advance safety and health through recommendations, technical assistance, and new technologies.

Among potential hazards in mines are methane, a naturally occurring gas that can ignite and explode, and carbon monoxide, a toxic gas that can occur as a byproduct from combustion. Further information and resources on preventing the risk of death and injury from these potential hazards, as well as links to additional information on other facets of mine safety and health, appear below. While great strides have been made in recent decades to reduce risks in mining emergencies, the potential for injury, illness, and death remains in this inherently challenging industry. NIOSH is committed to working with its partners to further health and safety in the industry, to enhance mine emergency response operations and to train mine rescue teams and evacuating miners in partnership with state and federal agencies and mining companies.

Fire Response Preparedness for Underground Mines

Fire has long been a concern for underground mine workers. A mine fire can occur at any time and can result in a partial or total evacuation of mine personnel and the loss of lives. Fires can grow rapidly. Time is the critical element. Prompt detection, timely and accurate warnings to those potentially affected, and a proficient response by underground miners can have a tremendous impact on the social and economic consequence of a small underground fire. Fire preparedness and response have components of technology and people. These components can work synergistically to reduce the time it takes to bring the system back in balance.

Information Circular 9481: Fire Response Preparedness for Underground Mines
DHHS (NIOSH) Publication N0. 2006-105
 PDF only  2442 KB (25 pages)
Contains details and techniques for planning and conducting fire response activities in mines.

NIOSH Mining Safety and Health Topic: Emergency Management
Provides information about emergency response for mines. Includes history, emergency planning, evacuation and training exercises.

Facts About Methane

• Methane (chemical formula CH₄) is a colorless, odorless, flammable gas. When mixed with air, methane is explosive in concentrations between approximately 5 and 15%.
  
  
• Methane is non-toxic but it can be can be asphyxiating in high concentrations as it displaces the available oxygen.
  
  
• Methane gas occurs naturally in all coal mines, trapped in pores within the coal bed. It is released as the coal is broken up during the mining process. The amount of methane liberated by the coal depends on the geologic age and type of coal and the depth of the coal deposit. Natural gas used in household furnaces is composed mostly of methane.
  
  
• Methane is lighter than air and is often found near the mine roof (ceiling of the mine opening).
  
  
• Methane can be detected with hand-held or stationary instruments. Checks for methane are made by certified persons at regular intervals before and during the time while people are working underground.
  
  
• Federal safety standards ¹ mandate that, “when 1.0 percent or more methane is present in a working place or an intake air course […] electrically powered equipment in the affected area shall be de-energized, and other mechanized equipment shall be shut off.”
  
  
• A flammable mixture of methane and air can be ignited by electric arcs and sparks, open flames or by the heat of friction between the cutting bits of mining equipment and the mine rock immediately above or below the coal.

Facts About Carbon Monoxide

• Carbon Monoxide (chemical formula CO) is a toxic gas that is produced from the incomplete combustion or explosion of substances containing carbon such as coal, natural gas or gasoline. Large quantities of CO are generated during mine fires or explosions.
  
  
• CO is colorless, tasteless, odorless and slightly lighter than air. It is flammable and explosive in mixtures with air in concentrations between 12.5 and 74%. It is toxic because it blocks the ability of the hemoglobin in the blood to carry oxygen from the lungs to the muscles and other tissue in the human body.
  
  
• The NIOSH ² recommended exposure limit (REL) for CO is 35 ppm, measured as a time-weighted average (TWA) for up to a 10-hour workday during a 40-hour work week. The ceiling concentration (not to be exceeded during any part of the workday) is 200 ppm. CO in concentrations of 500 ppm or 0.05% can be fatal in 3 hours ³. Higher concentrations can lead to coma and death in minutes. Carbon monoxide is known as a “silent killer”.
  
  
• Carbon monoxide can be detected by hand-held sensors. Stationary sensors may also be installed at strategic points in mine airways.

Mine Ventilation

The purpose of mine ventilation is to dilute, render harmless, and carry away dangerous accumulations of explosive and toxic gases and dust from the working environment in underground mines.

Federal safety standards ¹ for ventilating underground coal mines mandate that “the air in areas where persons work or travel […] shall contain at least 19.5 percent oxygen and not more than 0.5 percent carbon dioxide, and the volume and velocity of the air current in these areas shall be sufficient to dilute, render harmless, and carry away flammable, explosive, noxious, and harmful gases, dusts, smoke, and fumes.”

Hazardous concentrations of methane underground can be controlled by dilution (ventilation), capture before entering the host air stream (e.g., methane drainage), or isolation (seals and stoppings).

Explosions can be prevented or mitigated by eliminating ignition sources, by minimizing methane concentrations and coal dust accumulations, and by using passive and active barriers to suppress propagating explosions.

In coal mines, methane explosions can cause subsequent, violent explosions of coal dust. To prevent such explosions, miners cover the floor, rib and roof surfaces of mine openings with large quantities of inert rock dust such as fine limestone dust. Rock dusting is mandated by and subject to federal safety standards.

Ventilation Controls: Stoppings, Seals, Regulators and Fans

Stoppings are permanent walls constructed of brick or other approved materials. They are built to separate and isolate different air courses in underground mines, such as the fresh (intake) air from the return air or from belt airways.

Seals are substantially constructed according to federal standards ¹. They are used to isolate worked-out areas of a mine that are no longer ventilated. Sealed areas cannot be entered by mine workers.

Miner finishing a stopping constructed from brick   Mine seal testing in the NIOSH Lake Lynn Experimental Mine

Regulators are used to adjust the quantity of air flowing to various sections of the mine.

Fans (both large, main mine fans at the surface and smaller, mobile, auxiliary fans underground) provide fresh air in mines and are usually operated by electric power.

Dual main mine fan installation

Mine Rescue and Emergency Response

Mine operators often rely on mine rescue teams to save miners during an underground emergency such as a fire, explosion, roof fall, or water inundation. In 2005, there were approximately 230 company- and State-sponsored mine rescue teams in the United States.

Mine rescue team training in smoke

Rescue team members often place their life in jeopardy to save fellow miners. It is essential that mine rescue team members be well trained, physically fit, provided with the latest in personal protective equipment, and fully understand the hazards that may await them during rescue and recovery operations. Mine rescue teams train regularly several times per year to practice rescue missions under realistic conditions. Mine rescue teams approach dangerous conditions in mines by careful and methodical exploration. They use self-contained breathing apparatus to protect themselves in toxic atmospheres. Team members are also trained to render emergency medical care.

As the teams explore the mine, they examine the atmosphere, mine roof conditions and all other potential hazards. They may have to re-establish essential ventilation controls to enable the team to proceed deeper into the mine. All progress and findings of the rescue team are communicated to the command center in charge of emergency management at the mine

Mine Communication Systems

Issues raised by recent coal mine disasters have highlighted the need for reliable communications between the miners inside the mine and the outside. Present, wire-based communications systems may fail due to exposure to fires, roof falls or explosions tearing down wires, power failure or battery failure.

View a brief review of mine communications concepts and technologies
This overview is based on information that has been previously published by NIOSH, the former U. S. Bureau of Mines and other sources, including information from manufacturers.

Miner Training, Escape and Barricading

Underground coal miners receive annual safety training including escape and emergency evacuation. They are also trained in using self-contained self-rescue (SCSR) devices that are readily available to every miner underground. Miners are trained to evacuate the mine along designated escape routes. If an escape is not possible, miners are trained to erect a barricade to isolate themselves from a contaminated mine atmosphere while they await rescue.

Miners training in the use of SCSR equipment

Other Resources

Emergency Management - NIOSH Mining Safety and Health Topic
Provides history, planning and evacuation resources for emergency management, as well as training materials including simulation software.

An Overview of Technology and Training Simulations for Mine Rescue Teams
 PDF only  307 KB (18 pages)
Contains details and techniques about highly realistic mine rescue simulation exercises conducted at NIOSH's Lake Lynn Laboratory from 1995 to 1999.

Methane Monitoring - NIOSH Mining Safety and Health Topic
Provides resources regarding the evaluation and use of methane monitoring equipment.

Explosions - NIOSH Mining Safety and Health Topic
Links to information about engineering controls to reduce the danger of explosions in mines, as well as measurement and analysis of explosive conditions in mines.

NIOSH Mine Safety and Health Research Program
For further information and resources from the NIOSH Mine Safety and Health Research Program

Sources:
¹ Code of Federal Regulations, Title 30, Part 75: Mandatory safety standards--underground coal mines

² NIOSH Pocket Guide to Chemical Hazards, Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, September 2005

³ Mine Gases. Safety Manual No. 2, U.S. Department of Labor, Mine Safety and Health Administration, 1994