Gas Cylinder Safety Guidelines 23 Appendix I. Definitions Absolute Pressure - Based on a zero pressure reference point, the perfect vacuum. Measured from this point, standard atmospheric pressure at sea level is 14.7 pounds per square inch (psi) or 101.325 kilo Pascals (kPa). This is usually expressed as psia where the ‘a’ indicates an absolute measurement or kPa. Asphyxiant Gas - Any non-toxic gas which displaces atmospheric oxygen below limits required to support life. These gases are usually colorless, odorless and tasteless and include, nitrogen, argon and helium. Compressed Gas - A compressed gas is any gas which when enclosed in a container gives: An absolute pressure reading greater than 276 kPa (40 psi) at 21 ° C (70 ° F) or An absolute pressure greater than 717 kPa (104 psi) at 54 ° C (129.2 ° F) or Any flammable liquid having a vapor pressure greater than 276 kPa (40 psi) at 38 ° C (100.4 ° F). Compressed Gas Cylinder - A compressed gas cylinder is any metal cylinder of the type approved by the U.S. Department of Transportation (DOT) for storage and transportation of gases under pressure, including liquefied gases. Metal cylinders are the only approved DOT packaging for compressed gases. Corrosive Gas - A gas that is in contact with living tissue causes destruction of the tissue by chemical action. Cryogenic Liquid - A liquid with a normal boiling point below -150 ° C (-238 ° F). Cryogenic Liquid Cylinder - Pressurized container designed and fabricated to hold cryogenic fluids. There are three common types of liquid cylinders: gas dispensing; liquid dispensing; or gas and liquid dispensing. Cylinder Valve - A mechanical device attached to a compressed gas cylinder that permits flow into or out of the cylinder, when the device is in the open position and prevents flow when in the closed position. Dewar - Is an open-mouthed, non-pressurized, vacuum-jacketed container used to hold cryogenic fluids. Flammable Gas - A material that is a gas at 68° F (20°C) or less at 14.7 pounds per square inch atmosphere (psia) (101 kPa) of pressure [ a material that has a boiling point of 68°F (20°C) or less at 14.7 psia (101 kPa)] which: Is ignitable at 14.7 psia (101 kPa) when in a mixture of 13 percent or less by volume with air; or Has a flammable range at 14.7 psia (101 kPa) with air of at least 12 percent, regardless of the lower limit. The limits specified shall be determined at 14.7 psi (101 kPa) of pressure and a temperature of 68°F (20°C) in accordance with ASTM E 681. Gauge Pressure - The pressure above or below atmospheric pressure. Therefore absolute pressure minus local atmospheric pressure equals gauge pressure and is usually abbreviated as psig or kPa. Handling - Moving, connecting or disconnecting a compressed or liquefied gas container under normal conditions of use.