General Description Of War Gases | Chapter 7

General - This group comprises a number of poisonous gases and substances which, although not used for offensive purposes, are frequently met with under war conditions. Some of these are toxic gases, such as carbon monoxide and the nitrous fumes which are generated from burning explosives, while others are substances, used for the production of screening smokes, which may be dangerous to handle. In addition reference is made to the atmospheric dangers encountered in fire fighting.

63. Carbon monoxide.

Carbon monoxide is a colourless, odourless gas, extremely insidious because of its entirely non-irritating character, and the consequent impossibility of recognizing its presence in the atmosphere by the senses. It always accompanies any process of incomplete combustion of carbonaceous material, and is therefore commonly met under normal conditions of everyday life. It burns with the characteristic blue flame so often seen flickering over a coke or smouldering coal fire.

Occurrence.-Carbon monoxide is always present in dangerous amounts in the exhaust gases of internal combustion. engines, coke stoves or smouldering fires, while varying quantities of it are present in all types of illuminating gas; it also forms the deadly constituent in the so,-called "after-damp" in collieries.

In war, carbon monoxide may be met with in dangerous quantities under the following conditions :

(a) Mining operations.-Whenever a blasting charge is exploded, as in mines or camouflets, the resulting gases contain large quantities of carbon monoxide, which are liable to find their way to adjacent galleries, trenches or dug-outs; moreover, pockets of gas may occur which may be tapped when new galleries are being driven in the vicinity. Carbon monoxide is also produced in large quantities when the timbering of mine galleries catches fire.

(b) Heavy gun fire.-A high explosive shell penetrating the soil, and bursting in close proximity to confined living quarters such as dug-outs, may liberate sufficient carbon monoxide to poison the occupants.

(c) Gun emplacements, pill-boxes and ships' turrets. Carbon monoxide gas may accumulate rapidly in gun emplacements, pill-boxes or turrets of ships, especially when firing into the wind, owing to the blow-back of muzzle gases or when the breech of the gun is opened; in the case of ships' turrets, if the air-blast in the barrel be defective, high concentrations of the gas may accumulate within the turret.

(d) Underwater explosions. - At sea, following underwater explosions, large quantities of carbon monoxide may be trapped within the hull of the ship and may gain access to inner, inhabited compartments.

(e) Interior of "tanks." - If ventilation be defective, dangerous concentrations of carbon monoxide may be found in tanks from leakage of engine exhaust gases and from blow-backs from the guns.

(f) Burning buildings. - A considerable generation of carbon monoxide gas results from the burning of material in closed spaces, owing to an insufficiency of oxygen.

(g) Coke and charcoal fires. - Frequent cases of carbon monoxide poisoning have occurred through the use of coke or charcoal braziers or stoves in insufficiently ventilated billets.

(h) Internal combustion engines. - The exhaust gases of internal combustion engines contain from 1 to 10 per cent. or more of carbon monoxide; the use of such engines in confined spaces without adequate safeguards may be followed by serious results.

(i) Fractured gas mains. - The leakage of coal gas into closed spaces, such as billets, following fracture of a gas main (e.g. after a bombardment) may result in serious poisoning.

64. Mode of action of carbon monoxide.

Carbon monoxide owes its poisonous properties to the fact that it combines with haemoglobin to form a dissociable compound just as oxygen does, and that its affinity for the haemoglobin is about 300 times that of oxygen. But for this property of combining with haemoglobin carbon monoxide would be a physiologically inert gas like nitrogen or hydrogen.

When air containing carbon monoxide is breathed, the relative amounts of oxygen and carbon monoxide present in the atmosphere determine the proportion in which carboxy-haemoglobin is found in the blood. When the amount of oxygen is 300 times that of carbon monoxide, half of the haemoglobin can combine with the carbon monoxide and half with the oxygen; this is about the degree of blood saturation at which unconsciousness occurs.

As the concentration of the gas in the air rises, the saturation of the haemoglobin with carbon monoxide increases, and the oxygen carrying capacity of the blood progressively diminishes until symptoms, of anoxaemia (oxygen want, in this instance without cyanosis) make their appearance. In this sense the gas is cumulative in action.

Moreover, the rate of absorption of carbon monoxide is very much accelerated by muscular exertion or by mental excitement, which causes an increase in the breathing and circulation rates. This results in a more rapid diminution of the available oxygen content of the blood, with a corresponding increase in the severity of the symptoms of oxygen want.

The resulting effects are due to anoxaemia alone, and their severity is determined by the degree of oxygen want. There are no pathological changes in the lungs such as follow the action of asphyxiant gases, nor are the red blood corpuscles injured;, when freed from their combination with carbon monoxide, the corpuscles are as capable of resuming their normal function as oxygen carriers as they were before exposure to the gas.

Death occurs when saturation of the haemoglobin reaches about 70 to 75 per cent., but lower degrees of saturation of the blood may prove fatal if exposure to the poisonous atmosphere is prolonged. The colour of the blood and tissues, post-mortem, may be bright red.

65. Symptoms of carbon monoxide poisoning.

The great danger in carbon monoxide poisoning is that, owing to the non-irritant properties and the cumulative action of the gas, it may not be realized, until too late, that there is any danger present in the atmosphere. The first symptoms may be a loss of power in the limbs, so that although the danger may then be appreciated, escape may be difficult or impossible.

Where the proportion of carbon monoxide to oxygen is high, loss of consciousness may be very rapid, with practically no warning. More commonly, however, the onset of symptoms is gradual and insidious, and may be ushered in by a feeling of weakness, giddiness, vomiting and indistinct vision ; this is followed by breathlessness, palpitation and a loss of power in the limbs, and the least exertion at this stage may cause collapse.

The loss of muscular power and the confused cerebration often preclude a man from withdrawing from danger even though he is dimly aware that safety is only a few yards distant. Not infrequently there is a stage of acute. mental excitement, which may simulate alcoholic intoxication or even mania. This is more common in the milder cases. Apathy and a sense of complete helplessness supervene, followed by unconsciousness, with or without convulsions; the victim becomes comatose, with stertorous breathing, a low tension pulse and subnormal temperature, and death results if he be left in the poisoned atmosphere.

The colour of the face in cases of carbon monoxide poisoning may vary with the rapidity of the onset or the degree of anoxaemia. A leaden tint is often seen after profound coma, while in other cases the face may be pale and moist with perspiration; often however, the cheeks are pink and the lips of a vivid carmine tint. Individual susceptibility to the gas varies, and experience has shown that acute or chronic alcoholism, or the presence of cardiac or respiratory disorders, accentuate the severity of carbon monoxide poisoning.

Recovery from the initial symptoms may be followed by some degree. of mental confusion and slow cerebration which may persist for varying periods, while headaches, often of a severe or migrainous type are characteristic. Among the after-effects of severe poisoning may be mentioned cardio-vascular disorders, especially tachycardia and dyspnoea which may continue for months. There is a predisposition to pneumonia, usually as a sequel to a long exposure to the gas, while disturbances of the central nervous system may occur occasionally ranging from a simple neuritis to paresis and even mental derangement, usually of temporary duration, though sometimes lasting as the result of cellular damage to the brain caused by protracted anoxaemia.

66. Protection against carbon monoxide.

The respirator does not afford any protection against carbon monoxide. If it is necessary to enter an atmosphere in which the gas is present or suspected, it is essential that a special carbon monoxide respirator* (*Carbon monoxide respirators must be used with great care since oxygen deficiency is generally associated with the presence of carbon monoxide, and these respirators give no protection against this danger.) be used (e.g. mask with filter consisting of catalysts which oxidize the carbon monoxide to the dioxide) or some form of self-contained oxygen breathing apparatus such as the "Proto" or "Salvus" set, or, in the case of H.M. ships, the Davis S E apparatus which is more familiar to the personnel.

In the absence of special oxygen sets, a useful apparatus can be readily extemporized by means of an ordinary respirator facepiece to which is attached a suitable length of non-collapsible tubing of 1.5 inch diameter, the far end of which is left out in the open. Such an apparatus can only, be worn for short periods, owing to the absence of an inlet valve and the rapid accumulation of carbon dioxide in the tubing; the insertion of a valve however, at the inlet end of the facepiece valve holder will enable a !an to remain in a contaminated atmosphere almost indefinitely. Such an apparatus (with special valve) is already standardized in HAM. Navy, and is known as "B.A. Pattern 230."

Small animals, such as mice or canaries, can serve as valuable indicators of the presence of carbon monoxide gas, as, owing to their rapid metabolism, they show signs of carbon monoxide poisoning before man is affected.

67. Test for the detection of carbon monoxide in blood.

The simplest method of detecting carbon monoxide haemoglobin in the blood of persons who have been exposed to the risk of poisoning by carbon monoxide is to dilute the suspected blood considerably with water and to compare the tint with that of normal blood similarly diluted.

The method is as follows: Dilute a sample of the suspected blood in a test tube (of internal diameter of about 1.5 cm.) to 0.5 per cent. with distilled water to which a trace of ammonia has been added (e.g. 0-1 c.c. blood diluted to 20 c.c.) ; this will give a perfectly clear solution. Dilute similarly a sample of normal blood.

Compare the tints of the two test tubes by transmitted daylight, when it will be seen that the tint of the suspected blood, if carbon monoxide be present, is definitely more pink than the yellowish-red of the dilute normal blood.

This test is purely qualitative; the actual saturation in any suspected specimen can be determined either by the carmine method or by means of the reversion spectroscope.

68. Treatment of carbon monoxide poisoning.

The majority of cases of carbon monoxide poisoning recover with prompt treatment, although a relapse, or even sudden death, may occur where exposure to the gas has been prolonged.

The time required for recovery depends, however, on how long the victim has been exposed to the poisonous atmosphere. Unconsciousness may last for as long as 48 hours after regaining pure air, and yet the person may recover; but the longer unconsciousness lasts the less is the chance of recovery.

Treatment consists in the prompt administration of oxygen, or preferably oxygen or even air combined with 5 to 7 per cent. of carbon dioxide, and aided, if necessary, by artificial respiration.

Pure oxygen can displace the carbon monoxide far more rapidly than ordinary air, while the carbon dioxide stimulates the respiratory centre and induces deeper breathing, thus facilitating the elimination of carbon monoxide from the circulation. It is hardly necessary to add that the expired air must not be re-breathed by the patient, and with this in view a suitable apparatus should be used such as the B.L.B. or Haldane oxygen apparatus, which may be set to deliver 8 to 10 litres a minute, or one of the types of apparatus which allow the administration of a mixture of carbon dioxide with either oxygen or air.

A characteristic effect of carbon monoxide poisoning is a lowering of the body temperature, due to a disturbance of the heat regulating centreto a reduction in the normal oxidative processes. Even in mild gases patients may complain bitterly of cold, and it is necessary that this symptom be combated by means of hot coffee, blankets, hot-water bottles and other familiar measures. Rest, too, is imperative in order to avoid increase in the oxygen requirements of the body and to reduce the demands on the ill-nourished heart.

In serious cases a slow intravenous injection of 5 c.c. of 25 per cent. coramine solution is valuable, while blood transfusion has been found of great value in desperate cases. Venesection is quite valueless.

During convalescence, especially after severe or prolonged anoxaemia, particular care should be taken that no great strain be thrown on the heart owing to the risk of acute dilation.

69. Nitrous fumes.

When nitro-explosives are incompletely detonated or subjected to slow combustion, especially in confined spaces, considerable quantities of "nitrous fumes" are given off consisting of a mixture of oxides of nitrogen.

These fumes, which have an orange-yellow or reddish-brown colour, are very soluble in water, and react readily with moisture and oxygen to form nitric and nitrous acids. In damp surroundings, therefore, the concentration of these gases in the atmosphere will be lowered, but even though small amounts in the air are mildly irritating to the eyes and the respiratory tract, they are not sufficiently so to serve as a warning of a highly dangerous atmosphere.

Occurrence.- Under war conditions, nitrous gases may be met with in mining or tunnelling operations when detonation of the blasting charge is incomplete in gun pits, armoured cars, and tanks, and in magazines of ships when propellant charges are set on fire. In industry, dangerous concentrations may be evolved when nitric acid is heated, or when it comes in contact with organic material, such as wooden floors, after accidental spilling.

Although no serious cases of poisoning by these gases were recorded on land in the Great War, this may have been partly due to the fact that when nitrous fumes are formed in large quantities in mining operations, carbon monoxide, with its more rapid action, is also generated in lethal proportions. Another possible factor was the moist condition of the surroundings, which may have helped to reduce the concentration of nitrous gases; present in the atmosphere, with a resulting diminution in their effects on personnel relative to those of carbon monoxide.

At sea, the virulence of the nitrous gases was well illustrated in the Great War by the death-rolls which followed the sinking of H.M. Ships "Russell" and "Britannia," when a large proportion of the officers and men who had been exposed to the fumes of burning cordite succumbed to their effects.

70. Mode of action of nitrous fumes.

The action of nitrous fumes on the lungs closely resembles that of phosgene. They are particularly dangerous because they do not produce any marked sensory irritation, and men may therefore fail to realize the serious danger which may follow their inhalation.

When inhaled, the nitrous fumes come into contact with the moisture ever present in the respiratory tract, and form nitric and nitrous acids; this produces a local caustic effect, to which is superadded a general systemic action due to absorption of the alkaline nitrites formed by the interaction of the acids with the alkaline secretions. in the presence of the local action gives rise to an intense congestion of the lungs and the production of an acute inflammatory condition and pulmonary oedema. This usually. overshadows the general systemic effect of the alkaline nitrites, which, however contribute to the clinical picture through their enfeebling action on the circulation and the possible diminution, through the formation of methaemoglobin, of the oxygen carrying capacity of the blood.

With the nitrous fumes, as with phosgene, the initial symptoms of coughing and irritation are generally transitory, and a period of quiescence precedes the onset of the acute symptoms. This apparently delayed action may vary in duration from two to 24 hours or more according to the conditions of exposure. The usual duration of the period is between 10 and 24 hours after exposure. Once this period is over, the clinical signs develop rapidly, and the whole course be run in a few hours.

71. Symptoms of poisoning by nitrous fumes.

The initial symptoms, on exposure, are slight irritation of the eyes, nose and throat, accompanied perhaps by a little cough - symptoms which are seldom marked and which quickly subside during the latent period which follows. The termination of this latent period which may be precipitated by physical exertion, is marked by the onset of acute clinical signs and symptoms such as a dry, hacking and painful cough, a sense of constriction in the chest, and distressing breathlessness.

In mild cases, this may be a prelude to a bronchitis which is limited to the upper bronchi and is accompanied by a profuse muco-purulent expectoration. In more severe cases, however, a condition of acute bronchial spasm may set in, with pulmonary congestion and cyanosis, rapidly followed by a pulmonary oedema which may be haemorrhagic in character. Restlessness is extreme, and in fatal cases consciousness is retained almost to the end, the patient struggling vainly for breath while, with bloodstained fluid trickling from his mouth and nostrils, he drowns slowly in the fluid exuded in his lungs.

72. Protection against nitrous fumes.

The ordinary charcoal respirator affords limited protection against nitrous fumes, but none against the carbon monoxide which is nearly always generated simultaneously. It is essential, therefore, that an oxygen or air breathing apparatus (such as the "Proto" " Salvus," "DS.E.A." or the Naval B.A. Pattern 230) be worn in such atmospheres whenever possible, and reliance should not be placed on a respirator save in emergency.

Nitrous fumes may be readily demonstrated by means of test papers which have been previously dipped in a solution of starch and potassium iodide and slightly acidified; a blue coloration develops on them when they are exposed to the gases.

73. Treatment of poisoning by nitrous fumes.

The general principles of treatment in cases of poisoning by nitrous gases follow the same lines as those already outlined for cases of phosgene poisoning, stress being laid on the importance of enforcing complete physical rest from the time of exposure and on the early administration of oxygen as soon as cyanosis develops.

Venesection gives better results when practised early, even before the onset of pulmonary oedema, in subjects with a full bounding pulse, but it is generally contra-indicated where the pulse is soft and thready.

It should be remembered that a severe and often fatal broncho-,pneumonia is a complication in some cases of lung irritant poisoning.

Convalescence is apt to be prolonged, and the experience of the Great War showed that the combined action of carbon monoxide and the nitrous fumes had a harmful effect on the heart, necessitating careful surveillance and graduated exercises.

74. Screening smokes.

Smoke may be used for screening important positions or the movements of troops; it may also be employed to mask a gas cloud, or to extend its flanks so as to conceal its actual frontage. Such screening smokes may be generated from solids dispersed from shell or bombs, or from liquids sprayed from aircraft or land vehicles.

Screening smokes are irritating when inhaled in close proximity to their source, but they are not toxic in the concentrations that render them effective as screens; under ordinary conditions troops can operate in them without wearing respirators, while in higher concentrations they may be irritant yet without producing toxic effects.

A dangerous and possibly asphyxiating concentration, however, may arise if a smoke shell burst at, or close to, the entrance of a dug-out, while proximity to a bursting phosphorus smoke shell may result in very severe burns from flying particles of burning phosphorus.

Apart from these possibilities, the chief danger associated with the use of screening smokes arises through accidental contact with the chemicals used in their production. These chemicals are all corrosive or dangerous to handle, and accidental contamination of the eye or splashes on the skin with the liquids will result in severe ulceration or burns. With a view to preventing such accidents, it is essential that operators should wear protective goggles or respirators, thick gloves and special clothing.

Should contamination with the liquid chemicals occur, first aid treatment must be undertaken immediately. If the eye be affected prompt and copious lavage with water, or with sodium bicarbonate solution in warm water, may mitigate the resulting effects. Splashes on the skin should be treated with excess of water in order to dilute rapidly and wash away the corrosive liquid, while any article of clothing contaminated by the chemical should be discarded at once.

The respirator gives efficient protection against all the screening smokes, and clothing is not affected by exposure to them in the concentration met with in the open.

75. Phosphorus.

At ordinary temperatures this substance is a solid which can be handled safely, in water, but when dried in air it bums fiercely with the production of a dense white smoke.

Phosphorus may also be used by an enemy as an incendiary filling bombs or in shell, and flying fragments or melted particles of the burning chemical may be embedded in the skin of persons close to the bursting missile. These fragments continue to bum on the skin unless smothered; first aid treatment should therefore consist in the immersion of the affected part in water, or, in the absence of enough water, in the application of a thick pad soaked in water.

As the melting point of phosphorus is 44.4⁰ C. (112⁰ F.), the particles embedded in the skin can be removed, under water, by means of forceps or a gauze sponge, care being taken that none of the fragments be overlooked. The resulting burns should be treated as thermal burns, but they are apt to be slow in healing. Owing to the ready solubility of phosphorus in oils and fats no oily or greasy dressings should be used until it is certain that all the fragments have been removed.

A form of first aid advocated by American writers is the immersion of the affected part in, or the covering of the area with, thick pads soaked in a 1 or 2 per cent. solution of copper sulphate. The action is to coat the particles of phosphorus with an inert compound by chemical action, and so to arrest the burning and enable removal to be carried out.

In addition to its direct effects on personnel, phosphorus may also affect animals grazing on land contaminated by phosphorus bombs or shell. Many such animals have developed symptoms of acute phosphorus poisoning, as shown by restlessness, intense thirst, abdominal swelling and nasal discharge. Post-mortem examination reveals fatty degeneration of the liver and acute congestion, or even necrotic patches, in the kidneys and in the small intestine.

76. Chlorosulphonic acid (C.S.A.).

This is a fuming, highly corrosive liquid which, on contact with quicklime, gives off a thick white cloud closely resembling a dense mist. At close quarters this is sufficiently irritating to eyes and throat to necessitate the wearing of a respirator, but at a distance of 200 yards or more from the source of emission this can easily be dispensed with.

Owing to its highly corrosive nature, C.S.A. requires great care in handling; moreover in contact with water C.S.A. generates intense heat and acid may be scattered in all directions. It is necessary, therefore, that goggles or respirators and suitable protective clothing (such as oilskin or rubber coats, gauntlets and rubber boots) be worn by personnel when filling generators or otherwise working with the liquid.

Contamination of the eye with the liquid should be treated immediately with large quantities of water, followed by lavage with a 3 per cent. sodium bicarbonate solution; a few drops of castor oil and a light pad over the eye will assist in allaying the irritation.

Splashes on the skin should be flooded with water to remove the contaminant, and sodium bicarbonate solution should be applied locally thereafter. Drying should be effected by mopping up excess moisture gently with swabs of absorbent wool, and not by rubbing.

77. Oleum.

Oleum is a brownish-yellow corrosive liquid consisting of sulphuric acid with a percentage of sulphur trioxide. When exposed to air it gives off dense white fumes with a somewhat sulphurous smell .

As with C.S.A., protective goggles or respirator and suitable protective clothing. are necessary when handling this liquid, and accidental splashes should be treated immediately with an excess of water to wash off the acid, followed by the local application of sodium bicarbonate solution.

78. Titanium tetrachloride (F.M.).

This is a yellow, non-inflammable and corrosive fluid which, on contact with damp air, gives

off a heavy dense white cloud. This property is made use of by aircraft for the production of vertical smoke curtains extending down to the ground or sea level. The smoke consists of fine particles of free hydrochloric acid and titanium oxychloride, and its efficiency depends largely on the moisture present in the air.

The smoke is unpleasant to breathe, but it is not toxic; the wearing of goggles or a respirator, however, may be necessary when entering a smoke curtain if the spray is still falling, owing to the danger of drops entering the eye. The usual precautions must be taken when handling e liquid, and accidental contantination of the eyes or of the skin should be treated immediately by free lavage with water, followed by application f sodium bicarbonate solution.

79. Stannic chloride (K.J.).

Stannic chloride is a fuming, straw-coloured, corrosive liquid which produces a heavy white cloud on contact with air, and is therefore sometimes utilised by aircraft for the production of vertical smoke curtains.

The dangers attending the handling of it and the treatment necessitated by accidental splashes are similar to those associated with titanium tetrachloride.

80. Dangers associated with fire fighting.

(a) Noxious Products of combustion. - It is common knowledge that fire fighting, especially when practised inside buildings or in confined spaces, often entails risk, either because of noxious gases or through a deficiency of oxygen; hence the various protective devices used by firemen such as respirators and oxygen breathing apparatus.

In all fires in confined spaces the nature and concentration of the toxic gases produced vary with the rate of combustion and with the character of the burning material. Thus, a slow rate of combustion results in a heavy concentration of carbon monoxide and carbon dioxide, in addition to an oxygen deficiency, while burning cordite (as in a magazine) gives rise, in addition to the evolution of nitrous fumes.

When chemical extinguishers are used to quell fires in confined spaces additional toxic gases may be produced, causing further danger to unprotected men.

The unfailing presence of carbon dioxide hastens the onset and increases the severity of any toxic symptoms that may result. Carbon dioxide is more than a simple asphyxiant in that, at comparatively low concentrations, it causes increased breathing and thereby increases the quantity or dose inhaled of any noxious gas that may be present. In concentrations above 10 per cent. it produces unconsciousness and death.

The utility of the ordinary anti-gas respirator in fire fighting is strictly limited, and is confined to the arrest of particular products of combustion and of such gases as can be dealt with by the charcoal in the container. This does not include either carbon monoxide or carbon dioxide. Further. as the respirator cannot compensate for any oxygen deficiency that may arise, it is essential that, when fighting fires inside confined spaces where a free dilution of the atmosphere or a free escape for the noxious gases generated is not possible, an oxygen or air breathing apparatus should be worn.

Reference has already been made at the beginning of this chapter to the toxic properties and mode of action of carbon monoxide and of the nitrous gases. A short description is appended below of the toxic effects of two fire extinguishers in common use, followed by a brief study of the conditions under which a deficiency of oxygen may be met with.

(b) Chemical fire extinguishers.

The following are two types in common use, sold under various trade names -

(1) Carbon tetrachloride.- This is a volatile liquid, boiling at 76.7⁰ C. (170.1⁰ F.) which is extensively employed as a dry-cleaning agent and as a popular and effective fire extinguisher.

When carbon tetrachloride is sprayed on a fire or on a heated surface the chief decomposition products, in addition to the unchanged chemical, are phosgene, hydrochloric acid and chlorine. The production of phosgene is more marked when the liquid comes in contact with heated rusty iron and when large quantities of the extinguisher are used in the presence of moisture.

Although the thermal decomposition products are more or less irritant to breathe, this irritancy may not be such as to compel men, faced with dangerous emergency, to leave a burning room. In these circumstances a very real danger arises from the continued inhalation of vaporized carbon tetrachloride or its products of decomposition.

Recent experience has shown that exposure to the fumes of carbon tetrachloride in a confined space such as a garage or between decks may give rise to serious illness, often delayed in its onset, of renal and hepatic origin. The illness may be ushered in by pyrexia, general malaise and abdominal pain - a commonplace clinical picture which may lead to errors in diagnosis.

Personal idiosyncrasy plays a part in the character, as well as in the severity, of the resulting symptoms; but, as a rule, signs of impaired kidney function are always present, and may vary from a trivial rise in blood pressure to an acute uraemia. Evidence of liver damage may also be seen in the jaundice, the slow pulse, the abdominal pain and haemorrhage from stomach and bowel so characteristic of the toxic jaundice caused by the organic halogens.

(2) Methyl bromide.- Another type of fire extinguisher contains methyl bromide as its chief constituent. This is a gas at ordinary temperatures, but it is readily liquefied at 0⁰ C., to a clear, colourless extremely volatile liquid which boils at 4.5⁰ C. (40. 1⁰ F). The gas is almost odourless.

Methyl bromide is toxic, and its thermal decomposition products are practically irrespirable. The liability of this extinguisher to produce poisoning, however, is chiefly determined by the rapid rate of volatility of the undecomposed chemical, which is much higher than that of carbon tetrachloride. The rapid vaporization of methyl bromide in confined spaces may easily result in such a high concentration that a toxic dose inhaled before the danger is appreciated.

In high concentration methyl bromide has a profound effect on the central nervous system, producing unconsciousness and giving rise to epileptiform seizures and paralysis, both motor and sensory.

In less severe cases vertigo, visual troubles and general weakness are the usual symptoms, and it does not appear that the dose need be large to produce such symptoms.

81. Dangers of oxygen deficiency.

Oxygen deficiency occurs as the result of fires in confined spaces, and the presence of carbon monoxide and carbon dioxide add to the danger.

There are many situations, however, other than actual fires in closed compartments, where a reduction of the oxygen percentage in the atmosphere may occur. Apart from such occasions as high altitude flying or climbing (where the deficiency is of partial pressure and not of composition, though the effect is the same), oxygen deficiency may be met with, both in peace time and under war conditions, in the following circumstances:-

(a) In the air of wells, disused mine galleries, underground shafts and tunnels, etc. Through the oxidation of organic and mineral matter in soil, the composition of the air in such spaces may be seriously, and sometimes totally, deficient in oxygen on first entry. Even after thorough ventilation a constant watch on the purity of the atmosphere in the space must be maintained, as a fall in the barometric pressure tends to fill the confined area with residual nitrogen welling out of the surrounding strata.

(b) In air-tight compartments such as double-bottoms and "blisters" ships. When these compartments are sealed for any length of time, the whole of the oxygen in the enclosed air may be used up by the ordinary process of rusting of iron or steel bulkheads or through oxidation of the linseed paint commonly used in these spaces.

(c) In badly ventilated compartments, such as ships' holds or coal bunkers, in which oxidizable or oxygen absorbing substances, such as grain, fruit, potatoes or coal, are stored.

82. Symptoms of anoxaemia.

In healthy adults, the percentage of oxygen in the air breathed must be reduced by about a third before any symptoms, such as hurried breathing, become obvious, unless heavy muscular work is being und taken. If exposure to such an atmosphere be maintained, or if the concentration of oxygen be reduced still further, a chain of symptoms follows which is insidious in its onset and which is typical of anoxaemia from whatever cause it may arise, namely: headache, visual disturbance and mental dullness, loss of muscular power and of co-ordination, dyspnoea and weakened cardiac action; the power of judgment may be seriously impaired, while loss of memory is of common occurrence. With extreme reduction in the oxygen percentage in the atmosphere, a condition of acute anoxaemia results in immediate loss of consciousness.

83. Treatment of anoxaemia.

Immediate removal to fresh air is imperative, and, if the breath has stopped, artificial respiration should be resorted to at once. This should be supplemented, if possible, by the administration of oxygen, the addition of 5 to 7 per cent. of carbon dioxide to the oxygen will greatly enhance the value of the latter by stimulating the respiration.

84. Protection against oxygen deficiency.

The precautions which may be taken may be summarized as follows:

(a) Test the suspected atmosphere by means of a lighted candle oil lamp, after excluding the possible presence of. explosive combustible gases. A flame is much more sensitive than the human body to any variation in the oxygen percentage of the air, and will be extinguished with a fall of 3 to 4 per cent. in the oxygen content ordinary barometric pressure.

In this connection it may be useful to remember that a state of negative pressure may exist in an air-tight compartment owing to the reduction of its oxygen content, and that on opening the space the initial rush of pure air may dilute the atmosphere of the space in the immediate neighbourhood of the opening. This dilution may be sufficient to all a candle to burn at the entrance, but may not affect the possibly dangerous character of the air in remote parts of the same compartment.

(b) Thorough ventilation of all suspected spaces or compartments including all remote corners.

(c) The invariable use of a life-line attached to the body of the first person to enter the space and of any unprotected rescuing personnel, the other end of the line being held by observers outside.

(d) The employment of the only sure safeguard both against the presence of noxious gases and the absence of a sufficiency of oxygen, namely any type of self-contained oxygen breathing apparatus, such as the "Proto," or the "Salvus," or the Naval Breathing Apparatus, Pattern 230, or a valved air pipe drawing its supply from pure atmospheric air at a distance.

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