Absolute pressure  Pressure measured with respect to zero pressure.

Anhydrous  A substance free of water.

Atmospheric pressure  The pressure exerted by the weight of the atmosphere at sea level. Equivalent to 14.696 pounds per square inch or 101.325 kPa. The pressure exerted by a column of mercury (Hg) 760 mm high.

Cargo tank  A bulk packaging which: (a) is a tank intended primarily for the carriage of liquids and gasses and includes appurtenances, reinforcements, fittings and closures; (b) is permanently attached to or forms a part of a motor vehicle, or is not permanently attached to a motor vehicle but which, by reason of its size, construction or attachment to a motor vehicle, is loaded or unloaded without being removed from the motor vehicle.

Centigrade  Customary unit of temperature is the centigrade degree, 1/100 the difference between the temperature of melting ice and that of water boiling under standard atmospheric pressure.

Compressed gas—flammable  Any material which had a boiling point of 68 degrees F (20 degrees C) or Less at 14.7 psia (101.3 kPa, abs) which is ignitable at 14.7 psia (101.3 kPa, abs) when in a mixture of 13 percent or less by volume with air and has a flammable range of 14.7 psia (101.3 kPa, abs) with air of at least 12 percent regardless of the lower limit. These limits shall be determined in accordance with ASTM E681-85, Standard Test Method for Concentration Limits of Flammability of Chemicals or an approved equivalent.

Compressed gas—nonflammable  A gas which exerts in a packaging an absolute pressure of 40.6 psia (280 kPa, abs) or greater at 68 degrees F (20 degrees C) and is not poisonous or flammable.

Compressed gas—nonliquefied  A gas, other than in solution, which in a packaging under the charges pressure is entirely gaseous at a temperature of 68 degrees F (20 degrees C).

Compresses gas—liquefied  A gas, which in a packaging under the charges pressure, is partially liquid at a temperature of 68 degrees F (20 degrees C).

Critical pressure  The pressure that must be exerted to produce liquefaction at the critical temperature.

Critical temperature  The temperature above which a pure gas cannot be liquefied, regardless of the degree of compression.

Cryogenic liquid  A refrigerated liquefied gas having a boiling point colder the -130 degrees F (-90 degrees C) at 14.7 psia (101.3 kPa, abs).

Density  The ratio of the mass of a specimen of a substance to its volume.

Enthalpy  Heat function at constant pressure. Enthalpy is sometimes also called the heat content of the system. Symbol: H; unit: kJ or Btu.

Gas  A state of matter in which the material has a very low density and viscosity, can expand and contract greatly in response to changes in temperature and pressure, easily diffuses into other gases, and readily and uniformly distributes itself throughout any container. A gas can be changed to the liquid or solid state only by the combined effect of increased pressure and decreased temperature (below the critical temperature).

Gas pressure  The force exerted by a gas in its surroundings. In the United States, gas pressure is commonly designated in pounds per square inch (psi). The analogous SI unit is the kilopascal (KPa). One psi equals 6.894757 kPa. The term psia refers to absolute pressure. Absolute pressure is based on a zero-reference point, the perfect vacuum. Measured from this reference, the standard atmospheric pressure at sea level is 14.696 psi; however, local atmospheric pressure may deviate from this standard value because of weather conditions and distance above or below sea level. Gauge pressure, designated by the term psig, is that pressure above local atmospheric pressure. Therefore, psia minus local atmospheric pressure equal psig.

Inert gas  A nonreactive gas such as argon, helium, neon, and krypton.

LAR  Liquid argon

LCO2  Liquid carbon dioxide

LIN  Liquid nitrogen.

LNG  Liquified natural gas

LOX  Liquid oxygen

LPG  Liquefied petroleum gas.

Molecule  Generally the smallest identifiable particle of a substance that can exist resulting from the chemical combination of two or more like or unlike atoms. Exception: in a few gases and metals the molecule and the atom are one.

Oxidizer  A gas or liquid that accelerates combustion and that on contact with combustible material may cause fire or explosion.

Perlite  A form of volcanic ash that is treated by heating to create a granular insulating material. The heat treatment causes the ash to swell or expand, increasing its porosity and significantly reducing its thermal conductivity. In its powdered form, perlite is easily conveyed with pneumatic lift equipment, and may be poured or dumped into spaces designed to contain it. Perlite insulation is charged in its powder form into insulating jackets of many types of cryogenic equipment and processes. It is most notably used in enclosures used to contain equipment for cryogenic liquid storage, cryogenic air separation, hydrocarbon separation or gas liquefaction processes. The perlite-filled jacketed region of this equipment may be either evacuated or may be purged with a dry oil-free inert gas, depending upon the nature of the equipment and the degree of thermal insulation required.

Portable tank  A bulk packaging designed primarily to be loaded onto, or on, or temporarily attached to a transport vehicle or ship and equipped with skids, mountings, or accessories to facilitate handling of the tank by mechanical means.

Pressure  Force applied to, or distributed over a surface; measured as force per unit area. See absolute pressure, atmospheric pressure, and gas pressure

Pressure relief device  A pressure- or temperature-actuated device used to prevent the pressure from rising above a predetermined maximum and thereby prevent the rupture of a normally charged cylinder when subjected to a standard fire test as required by 49 CFR 173.34 (d) or equivalent Canadian regulations.

psia  Pounds per square inch absolute. (See gas pressure.)

psig  Pounds per square inch gauge. (See gas pressure.)

SI Superinsulation – multilayer insulation for cryogenic systems, composed of many floating radiation shields in an evacuated double-wall annulus, closely spaced but thermally separated by a poor-conducting fiber.

Temperature  The condition of a body that determines the transfer of heat to or from other bodies. Specifically, it is a manifestation of the average translational kinetic energy of the molecules of a substance due to heat agitation.

Vapor  The gaseous form of substances that are normally in the solid or liquid state (at room temperature and pressure). The vapor can be changed back to the solid or liquid state either by increasing the pressure or decreasing the temperature alone. Vapors also diffuse. Evaporation is the process by which a liquid is changed into the vapor state and mixed with the surrounding air.  Solvents with low boiling points will volatize readily.

REFERENCES

Handbook of Compressed Gases, Fourth Edition – 1999