Carbon Monoxide

Carbon monoxide or white damp is the most dangerous of alt gases which occur in mines. It is nearly always contained in the after-damp, following an explosion of coal dust or fire-damp, and also results From gob fires and shot-firing with certain explosives. It has been suggested that this gas is a normal constituent (in small amounts) of the return air of coal mines over 500 yards deep.

Properties

Carbon monoxide is slightly lighter than air and is colourless, odourless, and tasteless. The gas is inflammable and burns in air with a non-luminous flickering blue flame, but it does not support combustion. The flame of the safety lamp burns more brightly in air containing certain percentages of the gas, but no reliable test can be made with a lamp under about 12 %. Moreover, the gas is so deadly poisonous that death would ensue in a few seconds in much smaller percentages than could be discovered with a safety lamp. The blood very readily absorbs the gas, which is very slow to part with it even under the best conditions. It therefore accumulates in the blood at a speed depending upon the percentage of the gas present and the rate and extent of breathing. It has been found that if a person continues to breathe air containing more than o.2 %, death is only a matter of time. The limbs are affected very quickly, and then the more a man exerts himself to get out of it the sooner he is overcome. This is due to the fact that with increased exertion breathing is quicker and deeper, whilst the pulse is more rapid; consequently the carbon monoxide is absorbed more quickly under such conditions than at the normal rate of exertion. It is probable that if a man once unwittingly enters an atmosphere containing 0.2 % of the gas he will be overcome before he can escape. Blood absorbs carbon monoxide much more readily than it does oxygen and converts the oxyhaemoglobin (red blood corpuscles) into carboxyhaemoglobin, a stable pink compound. Consequently a person suffering from carbon-monoxide poisoning has a pink skin and a healthy appearance. When all the blood has absorbed as much of the gas as it is capable, it is said to be saturated, but death occurs at 8o % saturation. Under 0.2 % the absorption of the gas by the blood stops at certain percentages of saturation, and the smaller the percentage of the gas the smaller is the maximum absorption. For 0.2 % the maximum absorption is about 8o % saturation. At 0.2 %, therefore, death occurs in about two hours, and the greater the exertion or the greater the percentage of gas present, the sooner death occurs. The effect of the gas varies with the person breathing it, some being overcome more quickly than others; but anything over 0.1 % should be regarded as very dangerous, and as low as 0.01 % is indicative of danger.

PHYSIOLOGICAL EFFECTS OF CARBON MONOXIDE

% Carbon Monoxide in Air

Max. Absorption % saturation of blood

Effect on Man after prolonged breathing

Below 0.02%

-

No appreciably poisonous symptoms.

0.02%

20

slight giddiness, headache and breathlessness

0.08%

50

0.08 to 0.02%

50 to 80

The above symptoms still more severe, partial loss of consciousness, especially in exertion, and later collapse and unconsciousness.

0.2%

80

The above symptoms followed by death in one to two hours.

Over 0.2%

-

The greater the percentage the sooner death occurs, especially in exertion.

Treatment of Carbon Monoxide Poisoning

In all cases of carbon monoxide poisoning, oxygen should be breathed or caused to be breathed into the lungs as soon as possible. If oxygen is not immediately available, fresh air should be applied at once. If neither fresh air nor oxygen is immediately available, the patient should be removed as quickly as possible to fresh air and oxygen must be obtained at the earliest possible moment. If the patient is unconscious, artificial respiration must be applied the moment fresh air or oxygen is available. He should be then wrapped up warm and a stimulant should be given as soon as possible. The patient should be kept under close observation, as there is a danger of relapse into unconsciousness in this particular case of poisoning.

Detection of Carbon Monoxide in the Mine

The best practical method of detection is by means of warm-blooded animals such as linnets, canaries, and mice. These are affected more quickly than a man and therefore give warning early enough to allow of withdrawal from the affected atmosphere. These effects, however, vary even with two similar birds, though birds are affected rather more quickly than mice and mice more quickly than men. An important point to observe, however, is that a man working vigorously may be affected before a bird at rest. Therefore tests should be carried out very cautiously and with two or more birds.

The General Regulations require that at every mine there shall be provided and maintained two small birds or mice for testing for carbon monoxide.

The Estimation of Carbon Monoxide

The use of warm-blooded animals are a good method of testing for carbon monoxide in the hands of a colliery official.
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