Compressed Gas Hazards at Fires
Bursting of Cylinders When Exposed to High Temperatures, as Well as Releasing of Inflammable Gases, Make Such Fires Extremely Dangerous
MANY gases are stored under high pressure in metal cylinders, and some of them are encountered in almost every industry. The nature of the gas as well as the method of storing, and the quantities on hand, are of great importance from the standpoint of life hazards to members of the department operating at fires.
A few of the more commonly encountered gases found in metal cylinders under high pressure include acetylene, ammonia, carbon dioxide, chlorine, ethane, hydrogen, hydrogen sulphide, oxygen, propane, and sulphur dioxide. There are many others which are met with to a lesser degree, but the particular hazards included in the above also include other gases similarly retained.
Although the modern method of storing gases in metal cylinders under high pressure requires a wheel or disk which will let go under pressure lower than the bursting pressure of the cylinder, nevertheless many cases are encountered where the cylinders themselves give way under the tremendous pressure created by the heating of the cylinder and its contents. For this reason fire departments should be prepared to encounter the worst conditions.
Some gases are highly poisonous and may cause death upon inhaling; others are inflammable and produce explosive mixtures when brought in contact with air in proper proportions; others while not extremely poisonous, produce conditions in the atmosphere where they are released such as to seriously interfere with the work of the fire department.
The gases listed above will be reviewed in an endeavor to indicate what the fire department may expect from gases in metal cylinders, and stored under high pressure.
This is a colorless gas of disagreeable odor, caused by the presence of hydrogen-sulphide. It is highly inflammable, burning with a bright smoky flame.
It is used for illumination; and burned with oxygen it produces a very hot flame commonly used in cutting and welding of metal (oxy-acetylene welding). It may be used direct from generators or from tanks in which it is stored under pressure, and dissolved in acetone.
Acetylene is highly inflammable, as noted above, and forms explosive mixtures with air in a very wide range (about 2.5 per cent to 55 per cent). It has a tendency to decompose into its element with the development of great heat, the resulting expansion of the gases producing great explosive effect. It ignites spontaneously in the presence of chlorine. It may be exploded by a primer or under certain conditions by shock alone, or by an incandescent wire. It is exceedingly hazardous.
Ammonia is a colorless gas with a very pungent odor. If inhaled in its pure state in large quantities, suffocation and death may ensue.
It is encountered at fires in refrigerating plants, breweries ice factories, hotels, restaurants, wool washing establishments and dry houses, ice cream factories, candy factories and other establishments wherein low temperatures are necessary in manufacturing processes. When smoke at such fires becomes impregnated with ammonia fumes, it is highly irritating and extremely dangerous. Its chief danger is sudden death from edema of the lungs or rapid swelling of the glottis. The glottis is a valve which is lined with mucous membranes. When a person swallows, this valve closes over the windpipe to keep food from entering the lungs. When an irritating fume is inhaled, the mucous membrane, or covering membrance of this valve, may swell suddenly and shut off the wind pipe, thus causing asphyxiation.
Ammonia gas is not combustible at ordinary temperatures and a flame is extinguished if plunged into it. If, however, ammonia is mixed with oxygen, the mixed gases may ignite and burn with a pale yellow flame. Ammonia mixed with oil such as used in ammonia compressors, may produce an inflammable or explosive vapor.
Authorities also declare that ammonia gas is explosive when mixed in proper proportions with air. They point out as examples such explosions as occurred in the Morris Packing Company plant several years ago when a score of firemen were killed by walls being blown out on them.
This gas is usually stored in steel cylinders, and unless equipped with proper safety devices the cylinders may burst upon being heated. Ammonia, like other gases, expands upon being heated, and such expansion produces proportionate increase in pressure within the cylinder. If the cylinder is not sufficiently strong to withstand the pressure, it may burst, releasing the gas and doing other damage.
In order to protect men at fires in plants at which ammonia is present several precautions are necessary: Thorough ventilation, plentiful use of water, protection of men with smoke helmets, (especially in a gas filled room, and it ammonia gas is present in great density, only men with self-contained breathing apparatus and rubber suits should be permitted to enter.)
If there is an ammonia discharge pipe leading to the atmosphere and within control of members of the department, gas should be released. On the other hand, if there is mixing chamber wherein water may be discharged from hose lines through apparatus to absorb ammonia, this should be used as a precautionary measure. Such operation prevents escape of free ammonia to the air, and thus provides additional safeguard to the men operating in the immediate neighborhood of the fire.
Water streams absorb tremendous quantities of ammonia, and they also cool ammonia tanks, piping and cylinders, reducing the pressure therein and thus checking the possibility of explosion.
Carbon dioxide is a gas which is produced by the burning of ordinary combustible materials such as wood, cloth etc. It is also used extensively for fire fighting, both in its natural state, and as an agent for discharging liquids from other extinguishers as well as for filling the foam bubbles in foam extinguishing systems.
It is carbon dioxide that is generated in the soda and acid extinguisher when the soda water and acid unite.
The gas is ordinarily found in steel cylinders and under a pressure of around 1,200 pounds per square inch.
The pressure in the carbon dioxide cylinder is increased when the cylinders arc exposed to fire. They thus produce a severe hazard due to the possibility of bursting. However, carbon dioxide gas when freed in the presence of a fire, actually extinguishes the fire, it is heavier than air.
Carbon dioxide, when present in moderate proportions will not endanger the lives of men operating at a fire, but if present in large proportions it dilutes the air and thus may make it nonsupporting of life. However, if there is sufficient carbon dioxide in the air to endanger the men operating in an enclosure, there will be more than sufficient to extinguish the fire.
Chlorine is a greenish-yellow gas of very pungent odor, and is about two and a half times as heavy as air. It is used in many chemical products and is frequently thrown off by these substances when exposed to fire. Thus, even if chlorine is not tound in its free state at a fire, it may be present due to action of the fire on other materials into which it enters in the process of manufacture.
It is widely employed in textile and paper bleaching factories. Also in purification of water, synthetic dye manufacture, as a military poison gas, and in many industrial chemicals and explosives. Mixed with hydrogen or acetylene it explodes in the sunlight.
Chlorine in liquid form is shipped in either steel cylinders, ton drums, or tank cars of 15 tons capacity. The cylinders and ton drums are provided with fusible plugs.
Chlorine is a powerful respiratory irritant, and in sufficiently high concentration can cause death by action on the lung tissues.
However, in concentrations far below injurious ones, it gives warning of its presence by sight and smell. It is most harmful when inhaled in a confined space in which it is present in high concentration, provoking instant spasm of the glottis, nose, throat and bronchial tubes. When fatal results are produced, death is generally caused by smothering or asphyxiation, that is by inability to breathe because of edema of the lungs and closure of the bronchial tubes.
The following instructions on handling chlorine may prove of use:
Keep to the windward side of the leak.
If leakage is extensive, promptly warn all persons in the path of the fumes to move to a safer location.
If water is available, use it freely on the escaping liquid. This forms chlorine hydrate instantly, from which the evaporation of gas is slow.
If water is not available, dig a trench to draw off the liquid to a lower spot. The pool formed can then be treated later with water. Loose earth should be thrown on the liquid at once to retard evaporation.
If tanks are punctured above the liquid, only gas wall escape, and this will cool off the contents so that the leakage will be slow. If leakage is below the liquid level, it will continue until top of liquid reaches the opening and then slow down to a gas leakage.
Leakage in a severe fire should not be serious, as the gas will be carried upward and dissipated with the products of combustion.
In treating a person affected by chlorine gas the manufacturers of this gas recommend the following:
- Remove at once to open air and away from all gas fumes.
- Place patient flat on back with head slightly elevated.
- Give 1/2 teaspoon essence of peppermint or moderate dose of bromo seltzer or whiskey.
This will relieve the tendency to cough and soothe the inflamed membrance. allowing a passage of air and promoting the action of respiratory organs.
- The persons affected should resist as much as possible the impulse to cough.
While serious after-effects are not always to be expected, a physician should always be called.
This is a gas commonly used in refrigerating systems, and is a gas possessing the appearance of water when in liquified form. The gas itself is slightly heavier than air. It has an odor somewhat like ether.
It is shipped in steel cylinders. The hazards of the gas are due to its explosibility when mixed with air in proportions from 3.3 to 10.6 per cent. Its ignition temperature is about 960° F.
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When cylinders are exposed to fire, they are apt to let loose unless kept cool with water streams. Ethane is made by distilling liquified natural gas. It is considered extremely dangerous from the explosion standpoint.
Hydrogen is a gas which is extremely light; it is colorless, odorless, and tasteless. It weighs about one sixteenth that of air. It burns with a pale blue flame, producing water with a greater relative heating effect than any other combustible material. The temperature of the flame is about 3,600° F. It is used extensively in hardening of oils and fats, notably soap, edible and cooking fats. It is also used as a compressed gas for cxy-hydrogen cutting and welding in metal work, etc. Balloons are commonly inflated with it. It is a very inflammable gas with a wide explosive range (9.5 to 66.5 per cent). It is found in steel cylinders under high pressure.
If hydrogen leaks through a small opening of a cylinder, the temperature of the gas remaining in the cylinder is increased by this process and ignition or explosion may result. It is not poisonous to inhale.
This is a gas often present in various industrial plants as well as in mines and tunnels, and is an extremely poisonous gas. Acute poisoning of men can he produced by low concentration of this gas, and may result in respiratory paralysis followed by heat failure and death.
It is encountered in various stages of the manufacture of sulphuric acid, and in the distillation of petroleum, particularly those oils known as high-sulphur crudes; also about some gas wells, gas plants and smelters. It is a colorless gas, which, in low concentration, has the distinct odor of decayed eggs and in mines has been termed “stink damp.” It burns with a bluish flame, forming sulphur dioxide and water. In seven parts of air a mixture is formed which when ignited explodes with violence. Wherever hydrogen sulphide exists, the possibility of poisoning is present. Its toxicity is comparable to hydrocyanic acid gas (prussic acid).
When asphyxia from this gas is complete it results in almost immediate unconsciousness, and frequently death follows before rescue can be accomplished or even attempted. In cases where rescue can he accomplished the victim recovers almost immediately.
Hydrogen sulphide in low concentration produces symptoms of headaches, sleeplessness, dulness, dizziness and weariness. Pains in the eyes, followed by conjunctivitis is fairly constant. Further poisoning produces depression, stupor, unconsciousness and death. Treatment of acute cases consists in immediate removal from exposure to the gas and the immediate administration of artificial respiration. The breathing of oxygen is advisable when possible.
Where hydrogen sulphide gas may exist, good ventilation results in a decrease in the number of accidents. The canister type of mask, hose mask, and oxygen breathing apparatus are of value in protecting the men in case of emergency.
In operating at fires where hydrogen sulphide is encountered the first precaution is to provide thorough ventilation of the structure. It is heavier than air, and where ventilation is being provided for the gas only, with no presence of fire, ventilation should be provided at low points in the building. On the other hand, where fire is burning, ordinary ventilation starting at the top of the building first is satisfactory.
Oxygen is a colorless, tasteless gas and when liquified produces a slightly bluish liquid. It constitutes four fifths of the air. It weighs more than air. It is shipped in steel drums, cylinders or “gas bottle.” With hydrogen or acetylene it is used for the production of exceedingly hot flames for cutting and welding metals, including platinum. It is also used for resuscitation in asphyxia and stimulation in various diseases. It is occasionally used in combustion to promote better utilization of fuel.
While it is non-explosive, it presents a danger because it intensifies practically all fires. Even steel will burn in the presence of oxygen.
It may be found in establishments where oxy-acetylene welding is done, as well as in laboratories, hospitals, etc. it is non-poisonous and hence constitutes no danger from this angle to men operating at a fire where cylinders of oxygen are present. On the other hand, there is always a possibility of the oxygen cylinders under high pressure bursting due to increased pressure on exposure to heat.
This is a gas which can be liquified at a temperature of approximately 60° below zero Fahrenheit, and when so condensed forms a colorless liquid. It has an odor like ether. It is about 56 per cent heavier than air, and is used as a fuel for lighting, heating, welding and other purposes. Some of the names under which it is found on the market are Fuelite, Nu-gas, Thermolene and in Pyrofax.
It is shipped in steel cylinders, and when discharged into surrounding atmosphere it presents a hazard similar to gasoline. Its ignition temperature with air is 870 degrees F. (gasoline has an ignition temperature of 536° F.) and it is explosive when mixed with air in the proportions of 2.3 to 7.3 per cent by volume of the mixture.
Sulphur dioxide is a non-flamable, suffocating gas. It is, in high intensity, corrosive and poisonous. It is about one and a half times as heavy as air.
It is shipped in iron pressure tanks, and may be found in establishments where artificial refrigeration is carried on. It may also be looked for in concerns engaged in bleaching straw, feathers and silk; and is used as a preservative for beer, wine and meat. It is also employed in the cellulose and paper industries.
As sulphur dioxide is one of the products of combustion of sulphur, this gas does not support combustion and hence serves as a fire extinguishing agent. As an example, when sulphur candles are burned in a furnace, all openings in the flue being closed except the top and the point at which the fumes enter, sulphur dioxide discharged by the burning candles (provided there is sufficient draught up the chimney to carry the gas upward) will usually extinguish the chimney fire. Although heavier than air, as noted above, it is readily drawn upward by the draught created by the fire in the chimney.
Many of the small household refrigerating machines now use sulphur dioxide gas as the refrigerating agent, so that it may be encountered in residential fires as well as in industrial fires.
Practically all fires involving the above, and other compressed gases, the use of water in large quantities is highly beneficial. In the specific cases of ammonia, the water absorbs large quantities of the ammonia from the air; with chlorine, the ammonia forms a hydrate of chlorine from which the gas is released slowly.
But the chief benefit of using water on fires involving gases under high pressure in cylinders is the chilling effect of the water, and the consequent reduction in pressure within the containers. If the temperature of the containers can be kept at normal, or below, the chance of the letting go is negligible. For that reason departments should make every effort to protect exposed tanks with streams of sufficient size to insure cooling of the tanks.
Where poisonous, or corrosive gases are encountered at a fire, and the fire is within the building, thorough ventilation is absolutely necessary in order to protect the men as well as to enable the companies to work at an effective range.
Gases which are heavier than air can best be removed from a building by low ventilation, unless fire is burning and creating draft which tend to draw the gas upward.
Gases lighter than air can best be released from building by high ventilation, that is opening the roof, or upper windows of a building.
But for fires burning vigorously within the building and involving cylinders of gases, ventilation should be performed in the normal manner of opening up top and bottom of building and as many windows on the various floors as is deemed necessary.
Officers in charge of companies must be on the alert for explosion incidental to the addition of gases which are released by bursting cylinders, or cylinders on which the safety seal lets go.
Many gases are highly inflammable and create tremendous blasts when ignited in the presence of air. Others such as oxygen, increase the intensity of the fire by providing the necessary oxygen for quick and complete combustion.
To sum up prompt and thorough ventilation, use of water streams, and safeguarding men against exposure to gases are absolutely necessary in handling fires in establishments wherein gases in cylinders are encountered in large numbers.