Mine Gases
Air is a mixture of gases in the
following on the dry sample
|
Nitrogen
|
By Volume
|
79.0
|
By weight
|
76.8
|
|
Oxygen
|
By Volume
|
20.97
|
By weight
|
23.16
|
|
Carbon Dioxide
|
By Volume
|
0.03
|
By weight
|
0.04
|
|
Moisture is always present in the atmosphere, but
in varying proportions depending on weather and temperature,
but a rough average of 1% may be regarded as normal.
The breathing of oxygen is absolutely necessary to
human life and for ordinary combustion. The effects
of a decrease in oxygen percentage are as follows:-
|
Oxygen %
|
Nitrogen %
|
Effects
|
|
20.97
|
79.03
|
Breathing and combustion normal
|
|
19
|
81
|
Breathing almost normal, lamp or candle
flame loses 30% luminosity
|
|
17
|
83
|
Breathing almost normal, combustion is
difficult
|
|
15
|
85
|
Breathing nearly normal, flame extinguished
between 17 & 15% Oxygen
|
|
12
|
88
|
Breathing deepens, flame extinguished
between 17 & 15% Oxygen
|
|
10
|
90
|
Abnormal shortness of breath, face flushed
and darkened
|
|
5
|
95
|
Panting, unconsciousness and death
|
|
0
|
100
|
Convulsions and death in a very short
time
|
|
It will be readily understood from
the above figures why the Coal Mines Act, 1911, requires
that at least 19 per cent. of oxygen shall be present
in the atmosphere of all roads and workings that are
in use.
Exemption is made where ventilation is accidentally
interrupted, but no person is to work in less than
19 per cent. of oxygen unless engaged in restoring the
ventilation. Another exemption is granted in the case
of mines liable to spontaneous combustion, but only
by order of and subject to conditions laid down by the
Mines Department.
The gases most commonly found in mines are oxygen, nitrogen,
carbon dioxide, and methane. In connection with gob
fires, blasting operations, and explosions, carbon monoxide
is very common, while in these and cases hydrogen sulphide,
hydrogen, ethylene, nitrous oxide, etc., sometimes occur.
The chief noxious gases are the very poisonous carbon
monoxide and carbon dioxide. Hydrogen sulphide is extremely
poisonous, but rarely occurs in dangerous quantity.
These gases are also said to be deleterious, as they
arc more or loss destructive of life.
The Chief Inflammable Gas is methane, which constitutes
97 to 100 % of the inflammable constituent of firedamp.
The Damps
The word " Damp " originally
meant " Mist " or " Vapour," but
is now used as meaning " Gas," and prefixes
are attached to indicate the various gases according
to their peculiarities
Fire-damp is inflammable and consists chiefly of methane
(marsh gas).
Black-damp extinguishes flame and causes death by suffocation
It is composed of carbon dioxide and nitrogen. It is
also known as stythe or choke-damp.
White-damp is a subtle and extremely poisonous gas,
also known as carbon monoxide.
After-damp is the gas resulting from an explosion; it
nearly always contains dangerous amounts of carbon monoxide.
Stink-damp, or sulphuretted hydrogen, is hydrogen sulphide
and is a very poisonous gas with a pungent smell of
rotten eggs, but it is seldom found in dangerous quantities.
|