Hazards of Modern Firemanship
Firemen Today Must Know Properties of Many Cases and How to Cuard Against Toxic Results
THERE is no single group of individuals who must meet a wider group of gas hazards than firemen. The situations where these hazards may be encountered by firemen are too numerous to mention, but a few general cases may be cited: Mechanical refrigeration has brought with it certain hazards to life and property because the refrigerants employed are, as a rule, flammable or toxic; warehouses and stores contain many flammable liquids such as naphtha, solvents, paints and lacquers which are readily vaporized to form irrespirable atmospheres and flammable vapor-air mixtures; many manufacturing plants may be found with such compressed gases as ammonia, chlorine and sulfur dioxide; street manholes frequently contain poisonous and flammable fuel gases; and motion-picture theatres and hospitals present a hazard from film storage.
Frequent Calls for First Aid
In addition to these hazards frequently encountered by firemen during their regular line of duty, they are often called to give aid in accidents and emergencies which involve gas hazards; for example rescuing persons from underground tunnels, giving assistance where leakage of refrigerants such as ammonia and sulfur dioxide have taken place, rescuing persons overcome through the use of fumigating gases, and many other similar services.
The fireman of today must know the poisonous and flammable properties of gases and vapors, and be trained in the use of protective equipment. The hazards under discussion can be divided into four subjects which we will take up one by one: Products of combustion, atmospheres deficient in oxygen, refrigerants, and other gases.
Products of Combustion
Carbon dioxide is present in small amounts in normal air, and is produced by fires and by breathing. A man can breathe up to three or four per cent in air with no other effect than a marked increase in depth of breathing. At five per cent, breathing becomes laborous. Excess of ten per cent becomes dangerous to life.
Carbon monoxide is produced in the burning of carbon containing materials such as natural gas, coal, coke, wood, gasoline, explosives, etc., whenever the supply of air or oxygen is not sufficient for complete combustion. It is asphyxiating to breathe because in the lungs it combines chemically with the hemoglobin of the blood, reducing the capacity of the blood for transporting oxygen according to the amount of carbon monoxide absorbed. Four one hundredths of one per cent is about the maximum concentration that can be inhaled for one hour without appreciable effect. Concentrations of 0.1 to 0.15 per cent, if inhaled for an hour, cause unpleasant but not dangerous symptoms, but higher concentrations usually render the victim unconscious without warning. Carbon monoxide has no taste or odor. A person who breathes it may not be aware of its presence until he becomes greatly weakened or nauseated. He may even lose consciousness without receiving any warning. Firemen should, therefore, be equipped with the proper type of respiratory equipment for protection against this gas.
Atmospheres Deficient in Oxygen
Normal air contains about twentyone per cent oxygen. When the oxygen is reduced to below seventeen per cent, the flame of a miner’s safety lamp is extinguished. This indicates the practical limit beyond which a person should not enter a confined space without the proper respiratory protection. Although a flame is extinguished at about seventeen per cent, a man is not in serious danger until the oxygen falls; below, say, fourteen per cent. Atmospheres markedly deficient in oxygen are dangerous because they possess no warning properties and the action is so rapid that the symptoms of shortness of breath and dizziness are followed in a matter of seconds by collapse and unconsciousness. Such atmospheres should never be entered by firemen unless equipped with the proper respiratory protection devices.
Gases Used in Refrigeration
The two gases most widely used as refrigerants at the present time are ammonia and sulfur dioxide. Both gases are strongly irritating to the eyes and membranes of the nose and throat so that one has ample warning of their presence. These irritant refrigerants are indirectly fire hazards in that their liberation at time of fire would retard fire fighting operations.
Ammonia gas as used in refrigeration machinery, is liquefied under high pressure, and when a break occurs in the confining system, through accident or fire, the ammonia gas escapes. Refrigerating machinery is widely distributed at ice-making plants, breweries, cold-storage plants, hotels, meat and provision stores and elsewhere. When leakage occurs the use of proper type of gas masks enables workers to close valves to stop escape of ammonia or to conduct other operations in the presence of the gas. Ammonia is a powerful irritant upon the mucous membranes of the eyes, nose, throat, and lungs. When leakage of this gas occurs, it is necessary that city Fire Departments have adequate protection against this irritating gas, not only to cope with fires, but also to enter rooms into which the gas is leaking in order to shut off the valves of the container from which the gas is leaking.
Sulfur Dioxide Fumes
There is little danger from sulfur dioxide poisoning because the fumes are so irritating to the eyes and throat that the victim is compelled to seek fresh air at once. Most persons can detect sulphur dioxide in concentrations as little as three to five parts per million of air; 0.05 per cent of sulfur dioxide is acutely pungent and produces a sense of suffocation; concentrations greater than this are dangerous even for a short exposure. In addition to its use as a refrigerent, sulfur dioxide fumes may be encountered in sulfite paper mills, sulfuric acid plants, chemical plants and stores. Most persons can recognize the gas by its odor with which they have become familiar through the use of burning sulfur for fumigation purposes. Firemen should always wear protective devices where the gas is present.
Chlorine was the first poisonous gas used on a large scale in the world war. At ordinary temperatures, chlorine is a greenish-yellow gas. It is handled commercially in the form of liquid in steel cylinders or special tank cars, and used for treating city water to kill bacteria; for treating the water in indoor swimming pools; for bleaching cotton, paper and flour, for use in liquid soap manufacturing, and for manufacturing many other chemicals.
If exposed to fire, a cylinder containing liquid chlorine would very likely blow out a fusible metal plug and release the gas to add to the difficulties of fire-fighters as the suffocating action of the chlorine is intolerable even in very small amounts. The breathing of air containing only 0.004 to 0.006 per cent chlorine for a period of thirty minutes to one hour is dangerous to life. A few deep breaths of air containing 0.1 per cent chlorine is likely to prove fatal. Respiratory protective devices should always be used when dealing with atmospheres where chlorine is present.
Gas for Fumigation
Hydrocyanic acid gas is used in the fumigation of buildings for ridding them of vermin. It may be encountered by firemen either in their regular line of duty while fighting a fire in a building undergoing fumigation, or in the case of an emergency in rescuing persons overcome by the fumigating gas. This gas may be purchased in liquid form in cylinders or it may be generated on the premises from sodium cyanide and sulfuric acid. It is an exceedingly toxic gas and acts very quickly. A concentration as low as 0.01 per cent is dangerous for thirty minutes exposure. A concentration of 0.3 per cent is rapidly fatal. In immediately harmful concentrations, the odor (bitter almonds) is moderate and distinct, but it is not discomforting and is insufficient to prevent serious exposure. The warning odor of low concentrations is also insufficient to prevent harm from extended exposure. The concentration of the gas, therefore, cannot be accurately judged by the sense of smell and gas masks should always he used by firemen in entering a building where the gas is present.
Oxides of nitrogen are given off by the burning of cellulose nitrate x-ray films. Most of us remember the disastrous x-ray film fire occurring in the Cleveland, Ohio. Hospital C linic in 1929, resulting in the death of about 125 persons, caused by the poisonous gases carbon monoxide and nitrous fumes. Firemen should make periodic inspections to determine that x-ray films are properly stored.
Carbon tetrachloride has come into extensive use as a fire extinguisher for small and incipient fires and is very effective. It is sold under various trade names. There is danger from inhaling the gases formed by carbon tetrachloride when sprayed on heated materials. In addition to the high concentration of carbon tetrachloride fumes formed when this material is used on a fire, decomposition products are also formed which consists of phosgene, chlorine, and hydrochloric acid gas. Death may result by breathing these gases for even a short time. Of course the danger is greatest when the material is sprayed on a fire occurring in a closed or confined space.
Devices for Respiratory Protection
Three types of apparatus are commonly used, gas masks, hose masks, and self-contained oxygen breathing apparatus. The term “gas mask” is used to designate that type of appliance for protecting the respiratory organs, which removes the poisonous gases and fumes from air by means of a chemical filter. This filter is often used in combination with mechanical filters which remove dusts and smokes. A gas mask, cannot, therefore, be used in atmosphere deficient in oxygen. You cannot use a gas mask in an atmosphere carrying less than fourteen per cent oxygen. An oxygen deficiency might exist in unventilated places such as sewers, gasoline or oil tanks, closed vats, caves, old wells and abandoned mines, unventilated basements, before and following fires, and similar places.
In such atmospheres, a hose mask or self-contained oxygen breathing apparatus must be used. Neither does the gas mask afford complete protection against a very high concen tration of toxic or irritating gases such as may be found in closed tanks containing volatile liquids, or in small closed rooms where a considerable quantity of gas has been suddenly released.
Limitations of Mask
In general the gas mask is limited to concentrations not to exceed two or three per cent, depending on the kind of gas. the absorbent used, and the size of the canister. These limitations of gas masks, however, do not prevent their being used in most of the ordinary situations that come to the attention of the fireman.
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The hose mask consists of the regular gas mask with a face-piece attached to a long non-collapsible hose, through which the wearer inhales fresh air. The hose is firmly attached to a safety belt so that a drag on it does not displace the face-piece. The hose mask is not limited as regards the concentration or kind of irrespirable vapors or gas that surround the wearer; it protects against any atmosphere that the skin can endure. It is the simplest and safest type of respiratory protection available. If the hose is over twenty-five feet in length, a rotary blower is used to force air to the wearer.
The oxygen breathing apparatus differs from the gas mask or hose mask in that it carries a supply of pure oxygen for the wearer. This type of apparatus can never be displaced by a gas mask for use in atmospheres deficient in oxygen. The chief advantage of this type of apparatus is that it is completely independent of the atmospheres encountered and can be used in any atmosphere that the skin can endure. The wearer is completely free and can work any place, not being dependent on the length of the hose or an atmosphere with sufficient oxygen. It has the disadvantage of being a complicated piece of apparatus which, for its proper operation, requires frequent inspection and adjustment, also it is cumbersome and heavy. No one should ever attempt to use this particular type of apparatus unless thoroughly trained.