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Publication: February 2006, updated
May 2009. For information about changes,
please see the
Revision History.
Chapter 36: Cryogenic and Oxygen Deficiency Hazard Safety
Cryogens are super-cooled substances, typically stored in liquid form, that
are used to cool other materials to extremely low temperatures. Cryogenic
equipment is used to support the photon science and high-energy physics
program here at the SLAC National Accelerator Laboratory by maintaining
certain beam line and accelerator equipment at cryogenic temperatures.
Cryogens may be present in the accelerator housing, the end stations, the
refrigeration units and their support buildings, Central Lab facilities, and
SPEAR3. Cryogens may also be present anywhere portable cryogen containers
can be transported.
Cryogens used at SLAC include liquid nitrogen, liquid helium, liquid carbon
dioxide, liquid argon, and liquid hydrogen. Physical properties of cryogens
commonly used at SLAC are noted in Cryogenic and Oxygen Deficiency Hazard
Safety: Physical Properties of Common Cryogens (see Section 6, “Exhibits”).
These liquefied gases have the property that, if they warm to a temperature
above their boiling point, their volume increases by a factor of seven to
nine hundred times. The resulting large volume of gas can displace part or
all of the air in an unventilated enclosure, thereby creating a potential
for asphyxiation for persons entering the enclosure. This hazard is
particularly serious in enclosed volumes that have no vents or ventilation
systems. The chapter also addresses oxygen deficiency hazards (ODHs) that
may result from boil-off gas and non-cryogen compressed gas use.
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