COMPRESSED GASESDOE-HDBK-1015/2-93Hazards of Chemicals and GasesCH-05Rev. 0Page 20Proper storage and handling of containers avoids many possible incidents. Hazards resultingfrom the rupture of a cylinder or other vessel containing gas at high pressure are protectedagainst by careful and secure handling of containers at all times. For example, cylinders shouldnever be struck nor allowed to fall, because if the cylinder is charged to a high pressure and thecylinder valve is broken off, it could become a projectile. Cylinders should not be dragged orrolled across the floor; they should be moved by a hand truck. Also, when they are upright ona hand truck, floor, or vehicle, they should be chained securely to keep them from falling over.Moreover, cylinders should not be heated to the point at which any part of their outside surfaceexceeds a temperature of 125 F, and they should never be heated with a torch or other openflame. Similar precautions are taken with larger shipping and storage containers. Initialprotection against the possibility of vessel rupture is provided by the demanding requirementsand recommendations that compressed gas containers fulfill in their construction, testing andretesting.CryogenicLiquidsMost cryogenic liquids are colorless, odorless, and tasteless when vaporized to a gas. As liquids,most have no color (except liquid oxygen which is light blue). However, whenever the coldliquid and vapor are exposed to the atmosphere a warning appears. As the boil-off gasescondense moisture in the air, a fog forms that extends over an area larger than the vaporizinggas. Many cryogenic liquids are inert gases, and may inert an enclosed space. Inert gases willnot support life.Both the liquid and its boil-off vapor can rapidly freeze human tissue and can cause manycommon materials such as carbon steel, plastic, and rubber to become brittle or fracture understress. Liquids in containers and piping at temperatures at or below the boiling point of liquifiedair (-318 F) can cause the surrounding air to condense to a liquid.Extremely cold liquified gases (helium, hydrogen, and neon) can even solidify air or other gasesto which they are directly exposed. In some cases, plugs of ice or foreign material will developin cryogenic container vents and openings and cause the vessel to rupture. If a plug forms,contact the supplier immediately. Do not attempt to remove the plug; move the vessel to aremote location.All cryogenic liquids produce large volumes of gas when they vaporize. For example, 1 volumeof saturated liquid nitrogen at 1 atmosphere vaporizes to 696.5 volumes of nitrogen gas at roomtemperature at 1 atmosphere.When vaporized in a sealed container, cryogenic liquids produce enormous pressures. If 1volume of liquid helium at 1 atmosphere is warmed to room temperature and vaporized in atotally enclosed container, it has the potential to generate a pressure of more than 14,500 psig.Because of this high pressure, cryogenic containers are usually protected with two pressure-reliefdevices, a pressure-relief valve and a frangible (easily broken) disk.
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