Thermo Scientific 7452 Operating And Maintenance Manual page 119

AA-6 7007452 CryoMed Freezer
Use containers designed for low temperature liquids.
Cryogenic containers are specifically designed and made of materials that can withstand
the rapid changes and extreme temperature differences encountered in working with
liquid nitrogen. Even these special containers should be filled SLOWLY to minimize
the internal stresses that occur when any material is cooled. Excessive internal stresses
can damage the container.
Do not cover or plug the entrance opening of any liquid nitrogen refrigerator or dewar.
Do not use any stopper or other device that would interfere with venting of gas.
These cryogenic liquid containers are generally designed to operate with little or no
internal pressure. Inadequate venting can result in excessive gas pressure which could
damage or burst the container. Use only the loose-fitting necktube core supplied or one
of the approved accessories for closing the necktube. Check the unit periodically to be
sure that venting is not restricted by accumulated ice or frost.
Use proper transfer equipment.
Use a phase separator or special filling funnel to prevent splashing and spilling when
transferring liquid nitrogen into or from a dewar or refrigerator. The top of the funnel
should be partly covered to reduce splashing. Use only small, easily-handled dewars for
pouring liquid. For the larger, heavier containers, use a cryogenic liquid withdrawal
device to transfer liquid from one container to another. Be sure to follow instructions
supplied with the withdrawal device. When liquid cylinders or other large storage con-
tainers are used for filling, follow the instructions supplied with those units and their
accessories.
Do not overfill containers.
Filling above the bottom of the necktube (or specified maximum level) can result in
overflow and spillage of liquid when the necktube core or cover is placed in the open-
ing.
Never use hollow rods or tubes as dipsticks.
When a warm tube is inserted into liquid nitrogen, liquid will spout from the top of
the tube due to gasification and rapid expansion of liquid inside the tube.
Warning Nitrogen gas can cause suffocation without warning! ▲
Store and use liquid nitrogen only in a well-ventilated place.
As the liquid evaporates, the resulting gas tends to displace the normal air from the
area. In closed areas, excessive amounts of nitrogen gas reduce the concentration of
oxygen and can result in asphyxiation. Because nitrogen gas is colorless, odorless and
tasteless, it cannot be detected by the human senses and will be breathed as if it were
air. Breathing an atmosphere that contains less than 18% oxygen can cause dizziness
and quickly result in unconsciousness and death.
Note The cloudy vapor that appears when liquid nitrogen is exposed to the air is
condensed moisture; not the gas itself. The issuing gas is invisible. ▲
Never dispose of liquid nitrogen in confined areas or places where others may enter.
Disposal of liquid nitrogen should be done outdoors in a safe place. Pour the liquid
slowly on gravel or bare earth where it can evaporate without causing damage. Do not
pour the liquid on pavement.
If a person seems to become dizzy or loses consciousness while working with liquid
First Aid
nitrogen, move to a well-ventilated area immediately. If breathing has stopped, apply
artificial respiration. If breathing is difficult, give oxygen. Call a physician. Keep warm
and at rest.
If exposed to liquid or cold gas, restore tissue to normal body temperature (98.6°F) as
rapidly as possible, followed by protection of the injured tissue from further damage and
infection.
Remove or loosen clothing that may constrict blood circulation to the frozen area. Call a
physician. Rapid warming of the affected part is best achieved by using water at 108°F.
Under no circumstance should the water be over 112°F, nor should the frozen part be
rubbed either before or after rewarming. The patient should neither smoke nor drink
alcohol.
Thermo Scientific