Introduction about mine gases

1. By:
Prof. Suraj Kumar
Mining Engineering Department
GEC Palanpur

2. 
General Properties
 Oxygen is a colorless, odorless, and tasteless gas with a specific
gravity of 1.1047. Its molecular weight is 32. A typical miner at
rest consumes about 0.005 litres of oxygen every second due to
respiration. Similarly, a miner exposed to moderate and extreme
workloads consumes 0.03 litres and 0.05 litres of oxygen every
second respectively due to his breathing.
 Mine safety laws in India require a greater than 19% for oxygen.
This means that any part of a given mine must have an oxygen
concentration of at least 19% in the mine air/atmosphere. In
former USSR, the TLV for oxygen was 20% while it is 19.5% in
the USA.
OXYGEN (O2)

3. 
Physiological Effects

4. 
 The percentage of oxygen present in an atmosphere
can be estimated by using the principle of
electrochemical method, paramagnetic method or
the flame safety lamp.
 In the electrochemical method, very small
concentrations of the gas are detected by its influence
on the output from an electrochemical cell.
 The MSA Oxygen Indicator Model 244, Auer Oxygen
Indicator Model P etc. are based on this principle
and use fuel cells as oxygen sensors.
Detection of Oxygen

5. 
General Properties
 Nitrogen is a colorless, odorless and tasteless gas. It is
slightly lighter than air with a specific gravity of 0.967. It is
usually inert and does not support life or ignition. It has
low solubility in water.
There are three major sources of nitrogen in mines:
 Production by the decomposition of organic substances
 Production from blasting using explosives (1 kg of
nitroglycerine releases 0.135 m3 of nitrogen)
 Production from the strata through cracks
NITROGEN (N2)

6. 
 Nitrogen has no known harmful effects on the
human system but a higher concentration of nitrogen
leads to deficiency of oxygen in the mine air. Thus,
increase in nitrogen concentration indirectly leads to
the physiological effects caused by a lack of oxygen
on humans.
Physiological Effects

7. 
General Properties
 Carbon dioxide is colorless, odorless and has a slightly acidic
taste (CO2 is sometimes called carbonic acid gas because with
water it forms carbonic acid). The specific gravity of carbon
dioxide is 1.519, which is almost one-and-a-half times that of
the specific gravity of air. That is why carbon dioxide is found
in low-lying areas in the mines. It is fairly soluble in water and
forms carbonic acid when dissolved in water.
 Carbon dioxide occurs both in coal and metal mines. It is
produced from a variety of sources including strata emissions,
oxidation of carbonaceous materials, internal combustion
engines, blasting, fires, explosions and respiration.
CARBON DIOXIDE (CO2

8. 
 Carbon dioxide dilutes oxygen in air and acts as a
stimulant to the respiratory and central nervous
system.
 Diffusion of gas in bloodstream is rapid and it affects
the rate and depth of breathing.
 As per Indian Standards (DGMS), the CO2
concentration should not be allowed to exceed 0.5 %.
Physiological Effects

9. 
Cont.

10. 
 The presence of CO2 is usually detected from oxygen depletion
indicated by the extinguishing of oil lamps at 17-17.5%. CO2 also turns
lime water milky and this property can be used in detection of CO2 in
mines. Optical methods like non-dispersive infrared gas analyzers can
also be used in finding out the concentration of CO2.
 Portable instruments are also used to estimate CO2 concentrations.
Hand held detectors based on the principle of colorimetric indication
are also used for finding out CO2 percentage. These detectors have
detector tubes which are filled with an indicating chemical substance.
When a sample of air is drawn through a detector tube, this substance
changes its colour over a length. This length is proportional to the
concentration of CO2. The concentration of gas can be read off on the
concentration scale printed on the tube.
 M.S.A. Universal Tester, Drager Multigas Detector and Auer Gas tester
are commonly used in detection and estimation of CO2.
Detection of Carbon dioxide

11. 
General Properties and Sources
 CO is a colorless and odorless gas with a specific gravity of
0.972.As can be seen, its specific gravity is almost equal to that of
air and therefore it exists at all levels in an underground opening.
It burns with a blue flame and is explosive in presence of air at
concentrations between 12.5% and 75%.
 CO is produced by the incomplete combustion of carbonaceous
materials. It is also produced by internal combustion engines,
blasting and spontaneous combustion in coalmines.
 It can also be generated as a component of water gas (mixture of
CO and H2), when water is applied to coal for controlling the fire.
That is why it is advisable not to apply water at the centre of coal
fire because it will lead to the formation of hydrogen and CO,
and because of the formation of hydrogen which is an explosive
gas, this fire will become more violent.
CARBON MONOXIDE or WHITEDAMP
(CO)

12. 
CO is considered as the most dangerous gas in mines. This is
because of the following reasons:
 It is highly toxic in nature.
 As it is colorless and tasteless, it is not noticed easily.
 As its specific gravity is almost equal to the specific
gravity of air, it exists at all the levels in an
underground opening. Hence the chances of its
inhalation are very high
Why CO is more Dangerous?

13. 
Physiological Effects
% of CO in air Symptoms or Effects
0.02 Headache, discomfort and possibility of collapse after 45
minutes at work or two hours at rest
0.12 Palpitations after 10 minutes at work or 30 minutes at rest
0.2 Unconsciousness after 10 minutes at work or 30 minutes at rest
0.5 – 1.0 Death after 10 – 15 minutes of work
 Haemoglobin present in human blood has 300 times more affinity towards CO than
O2.The new substance formed by the combination of CO and haemoglobin is
known as carboxy-haemoglobin. This is relatively stable and accumulates in the
bloodstream. This results in a reduction in the number of red cells for carrying
oxygen to vital parts of the body. Thus the physiological effects of CO arise because
of the reduction in oxygen supply to vital parts of the body. As per Indian
Standards (DGMS), the CO concentration should not be allowed to exceed 0.005 %.

14. 
 Modern CO detectors, like Hoolamite tubes and M.S.A.
ammonium-palladium-complex colorimetric detectors
use detector tubes containing suitable gels such as
alumina, silica gel, iodine pentoxide and fuming
sulphuric acid soaked in pumice stone, silica gel
impregnated with palladium sulphate and ammonium
molybdate etc.
 The CO is detected using the principle of:
1. the change in the color of the chemical present in the
detector tube
2. the change in the length of the color of the detector tube.
Detection of Carbon monoxide

15. 
MSA CO detector with detector tube

16. 
 Warm blooded birds like munia/canary or mouse are
also used for detecting CO as they are affected sooner
than human beings by CO. Only fresh birds are used in
this method as repetition of same bird may lead to the
acclimatization of the bird to the low percentages of CO.
There are no immediate signs of distress observed when
birds are exposed to 0.1% of CO. But at 0.15% of CO, a
bird shows distress (pronounced chirruping and loss of
liveliness) in 3 minutes. And at 0.3% of CO in air, the bird
shows almost immediate distress and falls off its perch
(when a bird perches on something such as a branch, it
lands on it and stands there) in 2-3 minutes.
Cont.

17. 
General Properties and Sources
 H2S is a gas with a smell similar to that of a rotten egg and has a
sweetish taste with a specific gravity of 1.175. It burns with a light blue
flame and is soluble in water. It is also known as Stink Damp. It is
combustible and is explosive over a wide range of its concentration
from 4.3 % to 45.5 %. It is more poisonous than CO.
 H2S is not very common in mines and usually occurs in firedamp and
gob fires in sulphurous coal. It is formed naturally by
bacterial/chemical decomposition of organic compounds and is often
detected near stagnant pools of water in underground mines.
 It may also occur in natural gas and petroleum reserves and migrate
through the strata in a weakly acidic water solution. In metal mines it is
produced by the action of acidic water on iron pyrites which can be
represented by the equation:
[FeS2 + 2H2O → Fe (OH)2 + H2S + S]
HYDROGEN SULPHIDE or STINK DAMP
(H2S)

18. 
 Hydrogen sulphide has a very low odor threshold, with
its smell being easily sensed by the human nose at
concentrations well below 1 part per million (ppm) in air.
Physiological Effects

19. 
 H2S is easily detected by its smell at very low concentrations of
up to 0.000075%. Another detection test for this gas is done by
exposing a filter paper soaked in lead acetate solution to an
atmosphere containing H2S gas. The filter paper turns brown and
then black if the concentration of the gas is sufficiently high.
 The M.S.A. H2S detector is an accurate instrument for detecting
H2S. It consists of a glass tube filled with white granules of
activated aluminium oxide coated with silver cyanide. When gas
containing H2S is drawn through the tube, the gas combines with
silver cyanide forming black silver sulphide which turns the
granules black. The percentage is calculated with the help of a
scale placed along the side of the tube which measures the length
up to which the change of col
 or has taken place.
Detection of H2S