Mine tragedy prompts cautions against CO, CH4
NIOSH urges vigilance in similar industries
The tragedy of the Jan. 2 Sago mine explosion in Tallmansville, WV, reinforces the importance of recognizing the potential hazards in underground coal mining, and the need for systematic safety and health vigilance.
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. While recent decades have seen great strides to reduce risks in mining emergencies, the potential for injury, illness, and death remains in this inherently challenging industry.
Following the Sago disaster, the Centers for Disease Control and Prevention's National Institute for Occupational Safety and Health (NIOSH) issued new reminders to the industry about the need for enhanced mine emergency response operations and training for mine rescue teams.
Methane: Monitor for explosion risks
Methane (CH4) is a colorless, odorless, flammable gas that when mixed with air is explosive in concentrations between about 5% and 15%. Methane is non-toxic but it can be asphyxiating in high concentrations as it displaces 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 while people are working underground.
Federal safety standards mandate that "when 1% 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.
CO: Present around combustion
Mines are not the only place carbon monoxide (CO) is present. 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 hemoglobin in the blood to carry oxygen from the lungs to the muscles and other tissue in the human body.
The NIOSH-recommended exposure limit (REL) for CO is 35 ppm, measured as a time-weighted average 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 three hours. Higher concentrations can lead to coma and death in minutes. Carbon monoxide, the cause of death from faulty home heating, as well as in areas of fire or combustion, is known as a "silent killer" because it is undetectable without special sensors.
For more information on mine safety, visit www.cdc.gov/niosh or www.osha.gov.
The tragedy of the Jan. 2 Sago mine explosion in Tallmansville, WV, reinforces the importance of recognizing the potential hazards in underground coal mining, and the need for systematic safety and health vigilance.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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