Hazards of Chemicals and GasesDOE-HDBK-1015/2-93COMPRESSED GASESRev. 0CH-05Page 25The following discussion addresses some of the more commonly used gases, and describes thespecific chemical properties and characteristics that are important for accident prevention.HydrogenHydrogen (H ) is the lightest of all elements. Its presence cannot be detected by any of the2senses. It is flammable in oxygen or air, and has a flammable range of from 4.1 percent to74.2 percent by volume in air. A mixture of 10 to 65 percent hydrogen by volume in air willexplode if ignited. Pure hydrogen burns quietly in air with an almost invisible flame, and whenburned with pure oxygen, a very high temperature may be reached. Hydrogen will burn readilyin chlorine gas, and under proper conditions, will combine with nitrogen, forming ammonia.Some chemical reactions produce hydrogen as a byproduct. A lead-acid battery will producehydrogen when it is being charged. Metallic sodium and potassium are examples of somechemicals that react violently when exposed to water, producing hydrogen, which may flamespontaneously due to the heat of the reaction. Many electroplating processes produce hydrogen.Some chemicals used to remove scale from the water side of boilers give off hydrogen.Whatever the operation, it is important to know whether hydrogen will be produced, and if so,precautions must be taken to prevent its accumulation and ignition. The precautions to takeinclude adequate ventilation to prevent its accumulation and the elimination of possible sourcesof ignition. Hydrogen is classified as an asphyxiant.NitrogenNitrogen (N ) makes up more than 78 percent of the earth's atmosphere. It will not burn or2support combustion. It cannot be detected by any of the senses and it is not toxic. Although itis often referred to as an inert gas because it does not oxidize readily, it nevertheless forms manycompounds. It is frequently used to inert systems that contain, or have contained, flammableliquids or gases. Inerting a system means replacing the oxygen with an inert gas in order toreduce the possibility of fire or explosion.Nitrogen is fairly soluble in the blood, and a considerable amount will dissolve in the blood ofa person when the air pressure is increased, as in diving, caisson, and some tunnel work. If theseemployees are not properly decompressed, the dissolved nitrogen escapes from the blood in theform of small bubbles in the bloodstream causing intense pain and is often fatal. This disorderis commonly known as the bends.If a large amount of nitrogen were released into the air of an enclosed space, it could cause aserious oxygen deficiency. Nitrogen is an asphyxiant.
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