COMPRESSED GASESDOE-HDBK-1015/2-93Hazards of Chemicals and GasesCH-05Rev. 0Page 18The industry recommends that free acetylene should not ordinarily be handled at pressuresgreater than 15 psig because, if handled at higher pressures without special equipment, it candecompose with explosive violence. Consequently, acetylene cylinders are packed with an inertporous material that is saturated with acetone. Acetylene charged into the cylinder dissolves inthe acetone and in solution will not decompose at or below the maximum authorized shippingpressure of 250 psig at 70 F.Compressed or liquified gases are also often described according to loosely-knit families towhich they belong through common origins, properties, or uses. The major families of gases areatmospheric gases, fuel gases, refrigerant gases, aerosol gases, and poison gases.Atmospheric gases comprise one family. Its most abundant member is nitrogen, constituting78 percent of air by volume; oxygen, constituting 21 percent of air by volume, is its second mostabundant member. Most of the remaining 1 percent of the atmosphere consists of a sub-familyof gases, the inert gases, that share the property of chemical inertness. Inert gases are chieflyargon, with minute quantities of helium, neon, krypton, xenon and radon. The last four arefrequently called the rare gases due to their scarcity. Hydrogen also occurs minutely in theatmosphere, as do a large variety of trace constituents, small amounts of carbon dioxide, andlarge amounts of water vapor.Another family of gases are the fuel gases. Fuel gases burned in air or with oxygen to produceheat make up a large family related through their major use. Its members are notably thehydrocarbons including liquefied petroleum (LP) gases, propane, butane, methane, and weldinggases such as acetylene and hydrogen.An opposite application relates members of another large family, the refrigerant gases. Arefrigerant gas liquifies easily under pressure and works by being compressed to a liquid whichthen absorbs large amounts of heat as it circulates through coils where it vaporizes back intogaseous form. Examples of refrigerant gases include ammonia and the fluorocarbons (freon).Aerosol propellant gases make up a family also related by use through the introduction ofpressure-packaged products used in the form of a spray or a foam. Propellant gases havemoderate vapor pressures at room temperatures (70 psig down to 35 psig, and even lower insome cases). It is usually agreed that a good propellant should also be nontoxic, chemicallystable, noncorrosive, and inexpensive. The fluorocarbons (freon) and nitrous oxide are the mostcommonly used propellant gases.Gases considered to be members of the poison gas family are generally those that the ICC hasclassified as poison gases to ensure public safety in interstate shipments. Two examples of thesegases are hydrogen cyanide and phosgene.
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