RE: Gas flows4 Mar 2022 01:04
As the father of Baby in Dirty Dancing said, when I am wrong I say I am wrong!
I discovered an article on Safety Lamps which from school days taught me that Humphrey Davy invented it, and I cannot remember ever knowing how it actually works.
This paragraph defies my theory that gasses will separate according to their density.
It mentions air (Nitrogen, Oxygen, plus other stuff, depending on the environment of course. (CO,CO2,CH4 are amongst the principal ones I think, in no particular order).
Whether CO2 and CH4 at 400m are likely to mix is not mentioned but it looks possible or maybe even probable to produce the composition that Moagi refers to. Other inflammable gases omits CO2 I guess but Pure Methane suggests not a lot else , whatever it is? And my floating terminology does not look that far off.
"THE DANGEROUS MINE GASES OR “ DAMPS. ” DIFFUSION OF METHANE.
Methane is about one-half (0.53 times) as heavy as air. On account
of its lightness methane has a tendency to accumulate in the high
parts of workings and to gather in the cavities in the roof. How-
ever, it will diffuse or mix uniformly in air in spite of being lighter,
and when once mixed with air will not again separate. The rate at
which methane and air mix depends to some extent on how the gas
enters the air.
If the gas is given off in the upper part of a coal seam or from the
roof, it will usually take a longer time to mix with the air than if
given off in the lower part or the bottom of the seam.
The Bureau of Mines has analyzed many samples of gas collected
in different mines. The results show that under normal working con-
ditions the inflammable gas coming from the coal in a mine may be
considered pure methane. It is very rare that the proportion of other
inflammable gases is more than one or two hundredths of 1 per cent."
The safety lamp paragraph follows for those who are interested
"An explosive mixture of methane and air ignites if heated to a
temperature of about 700° C., or 1,300° F. If the flame of burning
methane is cooled below this temperature it goes out. When a safety
lamp is put into fire damp the gas passes into the lamp through
the gauze and takes fire at the lamp flame. But the flame of the
burning gas can not pass back through the gauze to ignite the fire
damp outside the lamp because contact with the gauze cools the
flame and puts it out. However, if the gas continues to burn inside
the lamp, the wires of the gauze may become so hot that they will
not cool the flame enough to put it out. Then the flame will pass
through the gauze and cause an explosion of fire damp outside. Such
an accident, however, rarely happens with a modem safety lamp"
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