Gas accumulation and stratification
Gasescan collect in pockets separate from the rest of the mine air. This isespecially true where mines lack adequate ventilation. Hot gases from a firewill rise to the back and remain there until the smoke has time to cool and mixwith the air. Therefore, expect the smoke near a fire to be denser at the back.The smoke will be more uniformly distributed in a drift once it moves away fromthe fire and is mixed with the mine air by ventilation flows and turbulence.
Asecond example of gas stratification is the distribution of methane in a coalmine. Pure methane has a relative density about one-half that of air and can beproduced in massive quantities in an underground coal mine. Such large amountsof methane will physically displace the other mine air. Because of its lowdensity, there may be pockets of methane that will tend to accumulate near theback.
Smalldifferences between the density of a gas and of air will not causestratification. For example, oxygen is ten percent more dense than air.However, the oxygen will not be more concentrated near the floor in a room or astope. Itremains thoroughly mixed with the rest of the mine air.
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