damp
A gaseous product, formed in coal mines, old wells, pits, etc.
damp: deadly gas trapped in underground workings
In mining, damp is a general term for any gaseous product accumulating in coal mines, metal mines, wells, and other underground excavations. It is not moisture or dampness as the word suggests in common speech, but rather toxic or asphyxiant gas that pools in low areas and dead ends where air circulation fails. The term persists in mining vocabulary despite its confusing name, a legacy of centuries when the nature of these gases was not fully understood.
The most dangerous form is firedamp, which is primarily methane (CHâ‚„) mixed with nitrogen and carbon dioxide. Firedamp forms explosive mixtures with air between 5 and 15 percent concentration and has killed thousands of miners through explosion and suffocation. Blackdamp is carbon dioxide or nitrogen that displaces oxygen; it extinguishes flame and causes loss of consciousness. Afterdamp, the residual gas left in a mine after an explosion, typically contains carbon monoxide and is similarly lethal. Whitedamp, another name for carbon monoxide alone, burns with a blue flame.
Before mechanical ventilation became standard, miners carried canaries or other small birds into the mine. When the bird stopped singing or died, the miners knew toxic damp had reached lethal concentrations and had to retreat. Safety lamps with open flames were developed to detect firedamp: the flame shape and color changed in its presence, giving miners seconds to escape before explosion risk became critical. Modern mining uses gas monitors with electronic sensors rather than these biological and chemical indicators.
Damp concentrates in the lowest points of a mine, in sealed chambers, and along the return airway where it has traveled with air currents and settled. Prevention depends entirely on maintaining adequate ventilation through the entire working section. A single blocked passage or failed fan can allow damp to pool to dangerous levels within hours. The term remains in use among mining engineers and safety personnel despite its antiquated ring, particularly in British and European mining practice.