Definitions

American Society of Mechanical Engineers (ASME). A standards-setting body for mechanical and pressure equipment

Cryogen. A super-cooled substance (usually liquid) used to cool other materials to extremely low temperatures

Cryostat. An apparatus used to maintain a constant low temperature

Dewar. Approved container for storing cryogens

Non-life supporting gas. A gas or gaseous mixture that presents insufficient oxygen to sustain human respiration

Oxygen deficiency hazard (ODH). An oxygen concentration equal to 19.5 percent or less (by volume) of dry air at a typical barometric pressure of 760 mm Hg

ODH 0. Hazard classification for areas with an estimated ODH fatality risk of less than 10-7/hr. ODH awareness training is required for entry into these areas.

ODH 1. Hazard classification for areas in which, without countermeasures, the fatality risk from an ODH is less then 10-5/hr. ODH awareness training is required for entry into these areas.

ODH 2-ODH 3. Hazard classification for areas with an ODH fatality risk of greater than 10-5/hr. Access is restricted to cryogenic technicians only.

ODH4. Hazard classification for areas that require the use of a self-contained breathing apparatus. These areas are restricted to trained fire personnel only.

Standard temperature and pressure (STP). Standard temperature and pressure conditions, which are the reference conditions for which the physical and chemical properties of a gas are normally given. Standard temperature = 25 deg C (298 deg K) and standard pressure = 1 atmosphere (760 mm Hg).