The Respiration of Injurious Atmospheres

In practice it is not easy to attain the concentrations of carbon monoxide necessary to produce fatal results. The experiments of Haldane have shown that the walls of ordinary dwelling rooms are quite permeable to the gas. This fact, together with the gradual movement of air, even through ill-ventilated rooms, as a rule prevents dangerous concentration of carbon monoxide being main tained, even where there is a slight escape of gas.

High Atmosphere Pressure.

Where men work under water at considerable depth, it is necessary to supply them with air at a pressure as great as, or greater than, the combined pressure of the atmosphere and of the water under which they are working. Unless the pressure be very high this in itself has no injurious effects and men may go confidently and quickly into such pressures ; great care, however, must be exercised in emerging from a high atmospheric pressure into a normal one. The danger is due to the nitrogen dissolved in the blood. The quantity of this gas held in solution in the blood depends upon the pressure of oxygen to which the body is exposed. Normally, each litre of blood holds about 15 cu.cm. of nitrogen; at depths of 33 ft. under water the pressure of air in the diving apparatus would be two atmospheres, in which case each litre of blood would hold 3o cu.cm. of gas in solution. As the gas is not removed by the for mation of any chemical compounds with other materials in the body, when the pressure is lowered it forms minute bubbles of nitrogen in the plasma. These bubbles when carried to the capillaries form emboli. Indeed, the danger is not confined to the blood, for if the worker be long enough exposed to the high pressure, all juices which permeate all the tissues of the body become charged with abnormally large quantities of nitrogen which, when the pressure is reduced, renders itself evident by the formation of small bubbles. These appear in many situations in the body, notably in nerve cells in the brain and elsewhere. Such bubbles are the cause of the condition known as "bends" asso ciated with pain and paralysis, which may be even fatal.

Chlorine.

The inhalation of chlorine in concentration of more than one part per million of air for an indefinite period is dangerous ; for half-an-hour the maximum allowable is four parts per milion, 40 to 6o even for short periods is dangerous. Chlorine is typical of a number of gases which produce inflammation of the lungs, death being due not directly to the gas, but to asphyxia. It is of particular historic interest as being the first gas used on a large scale as a lethal weapon in war; clouds of the gas being liberated from cylinders in the German lines were carried by the favourable wind over to the lines of the Allied armies, where it produced the most devastating effect. More potent asphyxiants than chlorine, but much less used in commerce, are phosgene and chloropicrin. Other gases which act similarly are sulphuretted hydrogen, sulphur dioxide, nitrous acid and acid fumes.

Other Gases Having Deleterious

Effects.—Hydrocyanic or Prussic Acid is much used for the fumigation of passenger steam ers in port ; for while poisonous to practically all forms of animal life, including vermin, it does not attack paint work. It is in visible and though it has a distinctive odour, the nose rapidly be comes deadened to the smell, so that persons may easily walk into stronger concentrations of the gas, being deceived by his nose into the idea that he is walking out of it. When the ship is

opened up after fumigation particular care must be taken that fatal concentrations of the gas do not remain in pockets. Canaries are much more sensitive to HCN than men, and may be used to detect the gas.

Aniline, Nitrobenzine and other bodies which contain NH2, NO, and groups, are met with in the dye industry and in the manufacture of explosives; their action is to appropriate the haemoglobin of the blood, turning it temporarily into methaemo globin. (See ANOXAEMIA.) The following table gives an idea of their toxicity.

Sulphides of Arsenic, Phosphorus and Hydrogen.- Arsene sometimes contaminates the air in the vicinity of storage batteries, for the charging of which impure sulphuric acid is being used. Thus in submarines whole crews may be affected. The poison is a cumulative one; small quantities inhaled accumulate in the body until a toxic concentration is reached. Phosphine is evolved when water acts on calcium phosphide and is used as an illuminating gas, in buoys, etc. Hydrogen sulphide may con taminate the air in chemical works, but is more frequently the cause of accident in sewers, where sewer gas may accumulate in pockets. Toxicity : Dichlordiethylsulphide--the so-called "mustard gas" or "Yper ite"—was by far the most devastating gas used in the World War. It owed its potency largely to the fact that it was extremely inde structible, contaminating the ground and giving off small quanti ties of vapour which, if breathed for long periods of time, pro duced an inflammation of the respiratory passages which was either itself fatal or was liable to doom the lung to subsequent infection by bacteria. This gas also caused intense inflammation of the eyes and blistering of the skin.

Toxic Smokes such as dichlorarsine and dicyanarsine which when inhaled caused intense irritation of the nose and throat, leading to uncontrollable fits of sneezing and coughing, were also used as shell fillings in the World War.

Respirators.—Both in war and in industry the entry of poison ous gases into the respiratory system is prevented by the use of respirators. These are of two general types: I. The oxygen breathing set consists of an air-tight mask (a) connected to a cylinder supplying oxygen; and (b) containing a cartridge of soda-lime or some other absorbent of carbon diox ide. The whole apparatus is self-contained, so that the subject has not and need not have access to the outer air. This form of ap paratus is particularly useful in atmospheres containing carbon monoxide, e.g., the air in mine galleries after an explosion, and is indispensable to rescue parties.

2. In various forms of respira tors the mask is attached to a canister containing some chemi cal absorbent. The outer air is inhaled during inspiration, but on its way this air is filtered through the absorbent and so rid of the poisonous principle. The expired air passes out from the mask through a valve. Naturally the absorbent employed depends upon the nature of the poison to be met.