Technical information

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Oxygen is removed from the air by liquid nitrogen. Therefore, use liquid nitrogen only in a well-ventilated
area so that the ambient oxygen concentration does not drop lower than 19.5% (same for liquid helium).
The high pressure gas hazard is always present when cryogenic fluids are used, since these are usually
stored at the boiling point. Never obstruct the vent valve on cryogenic containers. Wood or asphalt
saturated with liquid oxygen has been known to explode when subjected to mechanical shock.
When using a liquid nitrogen cold trap, charge the trap only after the system is pumped down. Otherwise,
considerable amounts of liquid oxygen could condense, thus creating a major hazard.
An excellent source of reference, which is strongly recommended for anyone working with cryogenic
materials is
Safety with Cryogenic Fluids
, Michael G. Zabetakis, Plenum Press, New York, New York,
1967.
FIRE SAFETY
Emergency Procedures
Do
not
try to fight a fire yourself if you are uncertain of being able to handle it; call for help.
If a fire starts, call for assistance by pulling the nearest fire alarm box, and evacuate the building (do not
use the elevators). DIAL 100 from a safe location and give what information you have. Do not return to the
building unless permitted to do so by the Fire Department.
If your clothes ignite, "stop, drop, and roll" to smother the flames. Do not run; running only intensifies the
flames. When fire blankets are readily available, use them to wrap around yourself to aid in putting out the
fire.
Precautionary Procedures
Know the location of fire exits, fire alarm pull stations, fire blankets and extinguishers. Each laboratory
should be equipped with an extinguisher or extinguishers. Fire extinguishers are primarily for fire fighters.
In rooms where the air flow is high, a natural gas leak could occur undetected. If there is one or more fume
hoods in a lab, check for leaking valves by brushing a soapy liquid around the valve stem and over exit
hole. If you see any bubbles in the liquid, call Frederick Wilson (13-4078/X3-6866) and Physical Plant
(FIXIT) to report the leak.
Keep all fire doors closed at all times.
Do not block access to fire escape routes.
Neatness prevents many fires. Fire spreads much faster when it has cluttered waste materials to feed on.
Oily rags, waste, or papers improperly stored are important causes of spontaneous combustion. Store these
materials in covered metal containers.
The informational document Guide to Classes of Fires provides some guidance on firefighting methods.