In this section we present useful information to protect the life of your new
liquid nitrogen dewar but at the same time, make sure that the user is also
protecting their health and well-being and at all times, in ways that would
prevent injuries.
How to take care of your liquid nitrogen dewar while taking care of your own health!
Warning
Use only liquid nitrogen in liquid nitrogen dewars supplied by Ted Pella Inc.
or equivalent. Do not ever use liquid air or liquid oxygen in these dewars because
either of which could present a combustion hazard with some materials used in the
construction of these dewars, or materials stored in them.
Introduction
The safe handling and use of liquid nitrogen in liquid nitrogen dewars or flasks
is possible only by knowing the potential hazards and using common-sense procedures
based on that knowledge. There are two important properties of liquid nitrogen that
present potential hazards:
- It is extremely cold. At atmospheric pressure, liquid nitrogen boils at -320°F / -196° C.
- Very small amounts of liquid vaporize into large amounts of gas. One liter of liquid
nitrogen becomes 24.6 ft3/0.7 m3 of gas.
The safety precautions as outlined must be followed to avoid potential injury or damage
which could result from these two characteristics. Do not attempt to handle liquid nitrogen
until you read and fully understand the potential hazards, their consequences, and the
related safety precautions. Keep a print out of this webpage handy for ready reference
and review.
Maintenance:
Keep the unit clean and dry at all times. Do not use strong alkaline or acid cleaners
that could damage the finish and corrode the metal shell.
Handling Liquid Nitrogen
Contact of liquid nitrogen or any very cold gas with the skin or eyes may cause serious freezing (frostbite) injury.
Protect hands at all times when working with liquid nitrogen with Cryo Gloves.
Handle liquid nitrogen carefully
The extremely low temperature can freeze human flesh very rapidly. When spilled on a surface
the liquid tends to cover it completely and intimately, cooling a large area. The gas issuing
from the liquid is also extremely cold. Delicate tissue, such as that of the eyes, can be
damaged by an exposure to the cold gas which would be too brief to affect the skin of the
hands or face.
Never allow any unprotected part of your body to touch objects cooled by liquid nitrogen.
Such objects may stick fast to the skin and tear the flesh when you attempt to free yourself.
Use tongs, preferably with insulated handles, to withdraw objects immersed in the liquid, and
handle the object carefully.
Wear protective clothing
Protect your eyes with a face shield or safety goggles (safety glasses without side shields do
not give adequate protection). Always wear cryo gloves when handling anything that is, or may
have been, in immediate contact with liquid nitrogen. The gloves should fit loosely, so that
they can be thrown off quickly if liquid should splash into them. When handling liquid in open
containers, it is advisable to wear high-top shoes. Trousers (which should be cuffless if possible)
should be worn outside the shoes.
Any kind of canvas shoes should be avoided because a liquid nitrogen spill can be taken up by
the canvas resulting in a far more severe burn, in fact that would occur if the feet were essentially
open or bare! Now we don't advocate going bare foot when using liquid nitrogen, but we also don't
think that the wearing of canvas shoes is a safe practice either.
Use only 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 ever cover or plug the entrance opening of any liquid nitrogen 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. 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 containers 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 opening.
Never use hollow rods or tubes as dipsticks
When a warm tube is inserted into liquid nitrogen, liquid will spout from the bottom of the tube
due to gasification and rapid expansion of liquid inside the tube. Wooden or solid metal dipsticks
are recommended; avoid using plastics that may become very brittle at cryogenic temperatures which
then become prone to shatter like a fragile piece of glass.
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 19 percent 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 gas actually causing the condensation and freezing is completely 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 the pavement.
First Aid Notice
If a person seems to become dizzy or loses consciousness while working with liquid 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 (37°C) 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/42°C). Under no circumstances should the
water be over 112°F/44°C, nor should the frozen part be rubbed either before or after rewarming. The
patient should neither smoke, nor drink alcohol.
Most liquid nitrogen burns are really bad cases of frostbite. We don't mean to belittle the harm that
can come from frostbite, but at the same time, we wanted to keep the dangers associated with liquid
nitrogen burns in perspective. Indeed, liquid nitrogen burns could be treated as frostbite.
Handling Liquid Nitrogen Dewars
Keep unit upright at all times except when pouring liquid from dewars specifically designed for that purpose.
Tipping the container or laying it on its side can cause spillage of liquid nitrogen. It may also damage
the container and any materials stored in it. If tipping is anticipated, be sure to purchase a dewar
that can be outfitted with a tipping stand.
Rough handling can cause serious damage to dewars.
Dropping the container, allowing it to fall over on its side, or subjecting it to sharp impact or severe
vibration can result in partial or complete loss of vacuum. To protect the vacuum insulation system,
handle containers carefully. Do not "walk", roll or drag these units across a floor. Use a dolly or
handcart when moving containers, especially the larger dewars. Large units are heavy
enough to cause personal injury or damage to equipment if proper lifting and handling techniques are not used.
When transporting a liquid nitrogen dewar, maintain adequate ventilation and protect the unit from damage.
Do not place these units in closed vehicles where the nitrogen gas that is continuously vented from unit
can accumulate. Prevent spillage of liquids and damage to unit by securing it in the upright position so
that it cannot be tipped over. Protect the unit from sever jolting and impact that could cause damage,
especially to the vacuum seal.
Keep the unit clean and dry
Do not store it in wet, dirty areas. Moisture, animal waste, chemicals, strong cleaning agents and other
substances which could promote corrosion should be removed promptly. Use water or mild detergent for
cleaning and dry the surface thoroughly. Do not use strong alkaline or acid cleaners that could damage
the finish and corrode the metal shell.
Protect Dewar Contents
Materials stored in a liquid nitrogen dewar with a wide mouth are protected by the extremely low temperature
of the liquid nitrogen or the gas that issues from the evaporating liquid nitrogen. When all of the liquid
nitrogen has evaporated, the temperature inside the unit will rise slowly to ambient. The rate at which
the liquid nitrogen will evaporate depends upon the pattern of container use and the age and condition of
the container. Evaporation increases as insulation efficiency deteriorates with age and rough handling.
Opening and closing to insert and remove materials and moving the unit will also increase the evaporation rate.