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1 Definition of "gas" in chemical warfare

2. A brief historical review of the use of gas in the Great War

3. Aspects in which the use of gas is likely to differ in a future war

4. Objects to be achieved by the use of gas

5. Concentration and period of exposure thereto

6. Factors governing the use of gas

7. Classification of gases .

Group 1 -Vesicants

Group 2 - Lethal gases which may produce disablement or death

Group 3 - gases used as harrassing agents

Group 4 - gases frequently encountered in war conditions though not used directly as chemical warfare agents

1. Definition of "gas" in chemical warfare.

(1) War gases

In chemical warfare the term "gas" is applied to any substance, whether solid, liquid, or vapour, which is used for its poisonous, irritant, or blistering effects.

Gases may be liberated in the air as vapour or smoke; or may be brought into contact, in liquid form, with personnel, material, or ground.

(2) Persistent and non-persistent gases.

For military purposes war gases are described as "persistent" or "non-persistent.-

Non-persistent gases are those which, when released into the air, disperse quickly, leaving no liquid contamination.

Persistent gases are liquids which evaporate slowly. They will give off vapour, or remain dangerous until the liquid has dried both on and below the surface on which they are placed, or until steps have been taken to render them ineffective.

(3) Toxic smokes.

Toxic smokes are poisonous or irritant smokes, generated in the form of clouds of solid particles of arsenical compounds, so small as to be invisible to the naked eye.

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2. A brief historical review of the use of gas in the Great War.

Chemical warfare in the modern sense was first introduced by the Germans in April, 1915, on the Western Front, chlorine gas being used by them in successive attacks until May of the same year, when tear gases also were used. These attacks found the Allies not only unprepared, but also inexperienced in the effects that chlorine produced on its victims. The casualties sustained during this period of ignorance and unprepared- ness cannot be estimated accurately, but they were very heavy, and improvised means of protection had to be adopted at once.

The first official respirator (a cotton pad soaked in hyposulphite of soda, glycerine and sodium carbonate) was issued in May, 1915, and-after that date defence, on the whole, kept ahead of attack- so much so that the use of phosgene gas by the Germans in December, 1915, found the Allies relatively well protected against its effects.

With a view to overcoming this protection the Germans introduced the arsenicals (or nasal irritants) and mustard gas. The former were intended to penetrate the box respirator which was then in use by the Allies, while the latter, having a very faint smell and causing no immediate irritation, might be expected to take effect before the need for putting on the respirator was realized. Comparative failure attended the use of the arsenicals ; mustard gas, on the other hand, was highly successful, or, in addition to its insidious latency, the gas was free to attack an parts of the body not protected by the gas mask and had, in addition, the great offensive value of persistency.

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3. Aspects in which the use of gas is likely to differ in a future war.

In view of the efficiency of the modem respirator, the ease with which it can be adjusted, and the knowledge of chemical warfare instilled into troops in their anti-gas training, it is probable that the old wartime lethal agents, such as chlorine or phosgene, will be less extensively used in a future war against armies in the field.

It is with mustard gas, however, that novelty in use is to be anticipated. The action of this gas in the late war was confined, in the great majority of mustard gas casualties, to that of the vapour given off by ground contaminated by shells, though there were a good many cases of actual blistering in addition. If gas is used at all in a future war it is likely that mustard gas will be extensively used from aircraft by sprays directly on personnel exposed in the open, or by bombs on areas which it is desired to deny the enemy. Gross liquid contamination from bombs may be used on dumps of ammunition, stores, aerodromes, dockyards, etc., with a view to rendering material dangerous to handle.

A future war may witness the introduction of another powerful vesicant, namely, "lewisite." An area shelled with lewisite lacks the insidious dangers of one similarly contaminated with mustard gas, as in concentrations which are so low as to be harmless the vapour of lewisite has a powerful smell and irritates the respiratory tract.

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4. Objects to be achieved by the use of gas.

Gas may be used with one or more of the following objects in view

(a) To produce casualties by using it directly against personnel.

(b) To produce casualties by contaminating stores and material, thus rendering them dangerous to handle.

(c) To harass troops by compelling them to wear respirators for prolonged periods, and thus to reduce their mobility, efficiency and endurance, and, possibly, lower their morale.

(d) To deny ground by rendering it dangerous to occupy.

(e) To contaminate food and similar stores.

(f) To lower the morale of the civil population and induce a will to compromise or surrender by causing widespread discomfort, anxiety and disablement.

The type of gas used will vary with the object in view. Lethal gases such as phosgene will cause serious casualties among troops, even though they be equipped with efficient respirators, unless their training against gas is of a high order. Similarly, mustard gas used in shell or from aircraft will cause numerous casualties, in spite of respirators and other protective equipment if training in their use is defective. Even against troops fully equipped and trained, mustard gas will act as a powerful harassing agent, although casualties in large numbers may be avoided.

The arsenical irritants and lachrymators, when used against personnel equipped with respirators and trained in their use, should not produce casualties, but they may cause considerable impairment in efficiency through their harassing action.

5. Concentration, and period of exposure thereto.

It is evident that the higher the concentration of the gas, the shorter will be the period of exposure required to produce casualties among personnel exposed to it; and the converse holds good.

High concentrations can be obtained by liberating the gas in confined or sheltered areas, or, under conditions of open warfare, by the expenditure of an enormous quantity of gas. In the latter case, however, the element of surprise is essential if adequate results are to be obtained on trained personnel, especially when highly irritant gases are used, as it is obvious that the dosage, and consequent effect, will depend on a combination of concentration and length of exposure.

It should also be borne in mind that, with persistent liquids, a high temperature will tend to produce. a high concentration of vapour at the cost of persistence, whereas a low temperature will act in the reverse direction.

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6. Factors governing the use of gas.

The effective use of gas may be markedly influenced by meteorological conditions as well as by topographical features in the area affected.

it is obvious that a strong wind will rapidly dilute and disperse all concentrations of non-persistent gases, while in the case of a persistent gas the rate of evaporation of the liquid will be increased, thus tending to clear the area more rapidly. With a low wind velocity, on the other 'hand, a high local concentration may be obtained with both types of gases, and the persistency of such liquids as mustard gas will be markedly lengthened in the absence of other adverse factors.

Temperature plays an important role, both by influencing the diffusion of the gas by convection currents and by affecting the persistence of such liquids as mustard gas; hence warm, sunny weather is inimical to the most effective use of gas. Very cold weather, however, also has its disadvantages, as it reduces very markedly the immediate value of persistent gases - in the case of mustard gas, for example, evaporation will be very greatly reduced as this liquid freezes at comparatively high winter temperatures (about 440 F. for the crude product). Mustard gas in the frozen state, however, is not by any means inert, as contact with it under these conditions will still produce a bum. If the frozen mustard gas contamination is carried (e.g. on boots) to warmer surroundings it will soon liberate effective vapour concentrations.

Conditions of excessive moisture are also unfavourable to the effective use of persistent gases, as rain tends slowly to destroy them or to wash them away.

The most favourable meteorological conditions for the employment of the two main types of gases are the following:

(1) Non-persistent gases.

(a) A low wind velocity.

(b) Clear nights, (cloudy days and nights are slightly less favourable, while clear, sunny days are the least favourable).

(2) Persistent gases.

(a) A low wind velocity.

(b) A moderate temperature.

(c) Absence of heavy rain.

Generally speaking, a clear, still night offers the most favourable conditions for the use of non-persistent gas. At such times the absence of air movements causes the gas to dissipate very slowly with the result that a high concentration is maintained for a long time.

In the case of persistent gases, a high ground temperature is usually the most important consideration, since this will induce rapid evaporation of the gas and the formation of a high local concentration of the vapour.

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7. Classification of gases.

Chemical warfare agents have been subjected to various classifications according to our knowledge of their physical or their physiological properties. In the first year of their use in the Great War, when both the deadly chlorine and the comparatively innocuous "tear" gases were employed, a broad classification into "Lethal" and "Harassing" types was adopted. Later, when mustard gas was introduced, a new and tactically important distinction between "Persistent" and "non-persistent" gases was recognized, and, from a military point of view, this classification is not likely to be abandoned.

From the medical standpoint, however, these physical characteristics of gases were not helpful in assessing the nature of the injuries inflicted on the human body through their agency; hence a physiological grouping was introduced which tabulated the various gases according to their main action on the body. This action may, to a large extent, be regarded as specific, as chemical warfare agents usually produce their most marked effects on some particular structure of the body, especially when they are present in low concentrations. Thus we have "Pulmonary" and "sensory" irritants, where the main effects are produced on the lungs and sensory nerve endings of the upper respiratory tract respectively ; the "lachrymators," which affect chiefly the eyes; the "vesicants" or blistering gases, by which any part of the body surface may be attacked; the "paralysants," which act directly on the nervous system, etc.

Such a classification is by no means rigid, for some of the gases really possess the characters of more than one of the groups, but it has the great merit of convenience from a medical standpoint. With a view, however, to combining both tactical object and physiological effect, the following classification may be adopted:

Group I - Vesicants.

Group II - Lethal:

(a) lung irritants

(b) paralysants ;

(c) arseniuretted hydrogen.

Group III - Harassing:

(a) lachrymators ;

(b) sensory irritants

Group IV-Accidental: gases not used as weapons.

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VESICANTS or "blister gases," such as mustard gas (H.) and lewisite. These are substances which, whether in the liquid, solid or vapour state will damage any part of the body with which they come in contact. Typical effects of the vapour are acute conjunctivitis, inflammation of the mucous membranes lining the respiratory tract, and burning of the skin varying from erythema to vesication. The effect of the liquid on the skin is severe vesication.

When death occurs after the inhalation of mustard gas, it usually supervenes on a septic bronchitis with broncho-pneumonia, while as a result of very extensive vesication death may follow from secondary shock or from sepsis.

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(a) LUNG IRRITANTS or "choking" gases.--- These gases, which include chlorine, chloropicrin (P.S.), Phosgene (C.G.) and di-phosgene, are essentially lung irritants exerting their main action on the deeper, as well as the upper, respiratory passages. They are used primarily as lethal agents, and, in the absence of an efficient respirator, their action usually results in the production of a pulmonary oedema which may be fatal.

(b) PARALYSANTS, such as hydrocyanic acid and hydrogen sulphide. Although these highly toxic gases did not prove a success in the late war, they are included here because of their potential danger if used in different circumstances. In high concentration, both these gases can produce death rapidly through paralysis of the respiratory centre.

(c) ARSENIURETTED HYDROGEN.- This gas exerts its poisonous action only after absorption through the lungs into the body. It causes destruction of the red corpuscles in the blood, haemoglobinuria, jaundice and anaemia associated with damage to the kidneys and liver.

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GROUP III.-GASES USED PRIMARILY AS HARASSING AGENTS.- Such gases cannot be relied on to produce casualties, but they cause acute though temporary distress and compel the wearing of a respirator.

(a) LACHRYMATORS or "teargases," such as ethyliodoacetate (K.S.K.), bromo-benzyl-cyanide (B.B.C.), and chloro-acetophenone (C.A.P.). Even low concentrations of the gases given off by these compounds will immediately irritate the eyes, causing profuse lachrymation and intense spasm of the eyelids - symptoms, however, which disappear on leaving the contaminated area. In very high concentrations they may act as lung irritants.

(b) NASAL IRRITANTS or "nose gases." These are organic arsenical compounds such as diphenyl-amine~chloroarsine (D.M.) and diphenyl-cyanoarsine (D.C.). These solid arsenicals, when suitably dispersed, produce clouds of minute particles which, if inhaled even in exceedingly low concentration, will produce symptoms of acute physical distress. These symptoms are intense pain in the nose and chest, with lachrymation, salivation and even vomiting. The symptoms, however, although alarming at the time, usually subside within an hour after removal from the gassed area.

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GROUP IV-GASES FREQUENTLY ENCOUNTERED IN WAR CONDITIONS, though not used directly as chemical warfare agents:-

(a) CARBON MONOXIDE. - This dangerous gas is frequently met with in the course of mining and tunnelling operations, in the interior of burning buildings, in "tanks---"pill-boxes" and gun emplacements which are badly ventilated, and, generally, wherever combustion occurs in the absence of an adequate supply of oxygen. Typical instances occur in confined spaces following the burst of a high explosive shell or the employment of slow-combustion stoves, charcoal braziers or internal combustion engines in such spaces. It is present in ordinary illuminating gas, leakage of which may cause serious poisoning. The gas produces its insidious effects through its well-known interference with the respiratory functions of the blood. Ordinary respirators give no protection.

(b) NITROUS FUMES.- These gases are given off by burning cordite, or when detonation of nitro-explosives is incomplete. They act as powerful and very insidious lung irritants, with delayed symptoms resembling those of phosgene poisoning, and it is important to remember that they are often accompanied by carbon monoxide. Respirators generally afford partial protection against nitrous fumes, but none against carbon monoxide.

(c) SCREENING SMOKES.-Various chemicals are used in warfare to produce smoke for screening movements of troops or the emission of gas. Such substances as Phosphorus (W.P.), chlorosulphonic acid (C.S.A.), titanium tetrachloride (F.M.), and a number of the chlorinated-hydrocarbon series are utilized for this object, while phosphorus may also be used in shell, bomb or grenade for incendiary purposes. These smokes are nontoxic in the open field, but serious effects may follow the bursting of such projectiles at close quarters.

(d) FUMES which may be encountered in FIRE-FIGHTING. - In addition to the risk of encountering carbon monoxide, and possibly nitrous fumes, when fighting fires in confined spaces in wartime, danger may also arise from the toxic gases evolved by fire-extinguishing chemicals. Apart from its possible toxicity, such an atmosphere may be seriously deficient in oxygen.

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