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• Do not use a funnel.
• Do not store container(s) of Liquid Nitrogen in a cold room or any other location where a person could physically enter an anoxic atmosphere. Cold rooms have not ventilated in any way so there is no air changing per hour. A person entering a room with elevated nitrogen gas levels in the air can quickly pass out and die within several minutes of entering.
• Liquid nitrogen will condense oxygen from the air. This is most alarmingly demonstrated if a person leaves his/her vacuum pump's coldfinger in a Dewar of liquid nitrogen overnight. In the morning the coldfinger will contain LIQUID OXYGEN up to the level of the nitrogen in the Dewar.
• Guard against pressure build-up by using a pressure relief vessel or a venting lid.
• Glass Dewars must be taped solidly around the outside. The plastic mesh that surround smaller thermoses are sold to protect the Dewar itself, but does not protect very well against injury from glass shards resulting from an unexpected implosion.
• Asphyxiation - nitrogen is a simple asphyxiant. Nitrogen does not have good warning properties. You cannot see it or smell it. In fact, 78% of the air we breathe is nitrogen with oxygen making up about 21%. The rest is trace gases. However, if sufficient liquid nitrogen is vaporized so as to reduce the oxygen levels to below 19.5%. At this level, you are at risk of oxygen deprivation. Rapid venting of liquid nitrogen can cause near-total displacement of normal air, leading to a local concentration of about 100% nitrogen. If there is too much nitrogen in the air, you might not feel light-headed, you may simply pass out without any warning whatsoever. You can then die without regaining consciousness.
• Use only vessels designed for extreme cold. Not all Dewars are rated for liquid nitrogen. Always follow manufacturers' guidelines for use of cryogen vessels of any size.
• Never not carry liquid nitrogen in a passenger elevator.
• Always have at minimum of two people moving a large Dewar through a hallway.
• Cryotubes containing samples stored under liquid nitrogen may explode without warning. Tube explosions are thought to be caused by liquid nitrogen entering the tube through minute cracks and then expanding rapidly as the tube thaws. Serious accidents have occurred around the country due to tube failures. A researcher in California lost an eye; numerous others have suffered plastic shards embedded in their hands and faces.
• Liquid Nitrogen is to be dispensed into smaller Dewars that (a) have carrying handles or (b) are on wheels, or (c) are 500 mL or smaller, and have pressure relief valves or pressure venting lids. A wide-base Dewar which is stable on a wheeled cart qualifies as "on wheels."
• Persons filling smaller dewars from a larger liquid nitrogen tank must be constantly vigil during the filling process.
• If the receiving vessel is small enough to be placed on an adjustable table, adjust the table so that the delivery is immediately at the mouth of the receiving vessel. Do not allow the liquid nitrogen to fall a distance to reach the mouth of the receiving vessel. If the receiving vessel is too large to sit on a table during the filling process, other provisions must be made so that the vessel sit can be raised up to the delivery tube.
• Always wear proper Personal protective equipment (PPE) while filling a vessel. Persons filling dewars should wear: full length non-cuffed trousers (covering tops of shoes) or full length apron, shoes that will not admit spilled cryogen liquid and are easy to remove quickly, cry-gloves and safety goggles or a shield. Remove all watches and jewelry.
• Do NOT move/bend the copper fill tube. This will cause undue wear to the tube and will eventually cause the tube to break.

Airgas is the preferred gas vendor at ¶¶Òõ̽̽. They have dedicated staff at ¶¶Òõ̽̽ daily. Contact AIrgas to have them move gas cylinders for you. If you need to move a large liquid nitrogen cylinder in the hallway, take the following preccautions:

• Large mobile Dewars used for transport should always be equipped with a braking mechanism. Do not use feet to brake.Ìý
• Steel toed or closed toed boots are recommended.Ìý
• Take care to avoid crushing hands or fingers between the vessel or cart and walls or door frames.
• If there is any risk of the cylinder tipping, a cart should be used. Wheeled trolleys may not be used if the vessel must pass over slots/crevasses wider than 25% of the wheel width.
• Never transport a large nitrogen Dewar outside -- over pavement, sidewalks, wheelchair curb-cuts. The casters welded to the tank, and/or the casters on the trollies in common use, are not meant for transport over pavement and concrete.
• Inside buildings, from room to room, the best transport is to transport Dewars that have carrying handles (4 L and less) or are on wheels (larger Dewars), and which have pressure relief valves or pressure venting lids. (A wide-base Dewar which is stable on a wheeled cart qualifies as "on wheels.")
• For short distances in hallways or from building to building, it is acceptable to hand-carry a pint (~ 500 mL) or smaller Dewar of nitrogen which has no handles. All other dewar sizes must have handles. NEVER carry books, coffee, and other items while carrying a dewar.
• Watch carefully for people who may run into you
• Carry the vessel with both hands and as far away from your face as comfortably possible.

The hazards associated with the handling of cryogenic fluids include cold contact burns and freezing. This happens when skin comes in contact with cold liquid, gas or surface.

The potential for freezing by contact with the extreme cold of cryogens necessitates varying degrees of eye, hand and body protection.

When a cryogenic fluid is spilled on a person, a thin gaseous layer apparently forms next to the skin. This layer protects tissue from freezing, provided the contact with the cryogen involves small quantities of liquid and brief exposures to dry skin. However, having moist skin, exposure to moving cryogens, or extended periods of time, can freeze tissue.

The most likely cause of frostbite to the hands and body is contact with cold metal surfaces. Since there is no protective layer of gas formed, frostbite will occur almost instantaneously, especially when the skin is moist. The damage from this freezing (frostbite)occurs as the tissue thaws. Intense hypothermia (abnormal accumulation of blood) usually takes place.

Additionally, a blood clot may form along with the accumulation of body fluids, which decreases the local circulation of blood.

Adequate protection and clothing is required at all times when handling, transferring or operating near cryogenic fluids. Should a burn occur, immerse the injured tissue in tepid water but do not rub or scratch the area.

Whenever handling or transferring cryogenic fluids from one vessel to another, protective clothing should be worn.

This includes:

• Face shield and safety goggles (or face shield and safety glasses)
• Loose-fitting, insulating cryo-gloves (inspect for holes before using)
• Long pants
• Long-sleeved over-shirt, lab coat or apron
• Closed-toe shoes (no sandals or crocks
• Ear protection, such as ear muffs or ear plugs, may be required where excessive noise occurs when filling or venting liquid nitrogen systems. For routine filling of small dewars for research or teaching purposes, ear protection is not necessary.

A special note on insulated gloves:

Gloves should be loose-fitting so they are able to be quickly removed if cryogenic liquid is spilled on them. Insulated gloves are not made to permit the hands to be put into a cryogenic liquid.

They will only provide short-term protection from accidental contact with the liquid.

All personnel working with cryogenic fluids must be thoroughly familiar with the hazards. Employees who have not worked with cryogenic fluids and systems must be trained on the job by experienced employees until thoroughly familiar with safe methods of operation. A buddy system is recommended when working with or around cryogenic liquids.

• The safety training should address:
• The physical, chemical and physiological hazards associated with cryogenic fluids
• The proper handling procedures for cryogens and cryogenic containers
• The emergency procedures required in case of an accident
• The reporting procedures in case of an accident

Each employee should also receive equipment-specific training if they are working with a piece of equipment that uses cryogenic liquids. The training should cover:

• Description of the equipment (use the manual) and its use
• Safe operating procedures
• Maintenance schedule and procedures
• Specific hazards involved
• Reporting procedure for incidents

As with all other training, cryogen training should be documented. Documentation, at a minimum, should include:

• an outline of the content of the training provided
• the date of the training
• name of trainer
• a dated training attendance list showing names of the trainees (typed or printed) and their signatures.

A liquid nitrogen burn causes the death of living tissue by extreme cold.

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Safe Dispensing of Liquid Nitrogen

• Under no circumstances should you leave the area while filling a dewar.
• Put on protective clothing.
• Look for any warning signs or indications that the tank should not be used.
• Ensure that the tank is more than 20% full. If not, do not fill your dewar.
• Attach the hose fitting to your dewar or attach the fill-tube (you will need at least one wrench) and place the tube in the dewar.
• Open the venting valve on your dewar, if applicable.
• Open the valve on the fill line. (Turn the valve handle counterclockwise.)
• If filling a wide mouth dewar, keep one hand on the tube and adjust the flow to reduce resonance (whistling).
• As the dewar is filling, watch and listen for indications that it is nearly full.
• Close the valve and check the level to avoid overspill.
• When finished, close the valve (turn the valve handle clockwise) and remove the hose or the fill tube from the dewar.
• Move your dewar from the filling area back to the lab.

Cold contact burns, freezing, frostbite (contact with cold liquid, gas or surface).

The potential for freezing by contact with the extreme cold of cryogens necessitates varying degrees of eye, hand and body protection. When a cryogenic fluid is spilled on a person, a thin gaseous layer apparently forms next to the skin. This layer protects tissue from freezing, provided the contact with the cryogen involves small quantities of liquid and brief exposures to dry skin. However, having moist skin, exposure to moving cryogens, or extended periods of time, can freeze tissue.

The most likely cause of frostbite to the hands and body is contact with cold metal surfaces. Since there is no protective layer of gas formed, frostbite will occur almost instantaneously, especially when the skin is moist. The damage from this freezing (frostbite)occurs as the tissue thaws. Intense hypothermia (abnormal accumulation of blood) usually takes place. Additionally, a blood clot may form along with the accumulation of body fluids, which decreases the local circulation of blood.

Adequate protection and clothing is required at all times when handling, transferring or operating near cryogenic fluids. Should a burn occur, immerse the injured tissue in tepid water but do not rub or scratch the area.

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Asphyxiation (displacement of oxygen by inert gas)

When liquid cryogens are expelled into the atmosphere at room temperature, they evaporate and expand on the order of 700 to 800 times their liquid volume. Even small amounts of liquid can displace large amounts of oxygen gas and decrease the oxygen content of the atmosphere below a safe level with a possibility of asphyxiation.

The evaporation of cryogenic liquids in closed or badly ventilated rooms can lead to oxygen deficiency. Due to the fact that most cryogens are odourless and colourless, this hazard cannot be detected without special equipment. Furthermore, argon and nitrogen are heavier than air and can therefore collect near the floor or in pits.

The symptoms of oxygen deficiency are (oxygen concentration in %):

19% - 15% pronounced reduction of reaction speed
15% - 12% deep breaths, fast pulse, co-ordination difficulties
12% - 10% vertigo, false judgement, lips slightly blue
10% - 8% nausea, vomiting, unconsciousness
8% - 6% death within 8 minutes, from 4-8 minutes brain damages
4% - coma within 40 seconds, no breathing, death

Whenever possible, handling of cryogenic fluids, where release into the atmosphere is possible, should be done in open and well-ventilated areas.

When there is the possibility of an oxygen deficiency hazard, oxygen monitors should be installed. If such a monitor triggers an ODH (oxygen-deficiency hazard) alarm, personnel are to immediately leave the area.

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Explosion (excessive buildup of pressure in container of cryogenic fluid)

Heat flux into the cryogen is unavoidable regardless of the quality of the insulation provided. Since cryogenic fluids have small latent heats and expand 700 to 800 times to room temperature, even a small heat input can create large pressure increases.

Dewars must be moved carefully. Sloshing liquid into warmer regions of the container can cause sharp pressure rises.

Pressure relief devices must be provided on each and every part of a cryogenic system. Satisfactory operation of these devices must be checked periodically and may not be defeated or modified at any time.

Vents must be protected against icing and plugging. When all vents are closed, enough gas can boil off in a short time to cause an explosion. Vents must be maintained open at all times.

Liquid helium is cold enough to solidify atmospheric air. Only helium should be introduced or allowed to enter the helium volume of a liquid helium dewar. Precautions should be taken to prevent air from back-diffusing into the helium volume.

Some materials may become brittle at low temperature and fail in the case of over-pressure or mechanical shock. Only suitable materials may be used to store or transfer liquid cryogens.

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Fire/explosion (condensation of liquid oxygen)

Liquid oxygen liquefies at a higher temperature than liquid helium or nitrogen. Consequently, liquid oxygen can condense on the exterior of cryogenic containers or transfer lines. An explosive situation may result if this oxygen-rich liquid is allowed to soak insulating or other materials which are not compatible with oxygen.

Some oils can form an explosive mixture when combined with liquid oxygen. Surfaces where there exists a possibility of liquid oxygen condensation must be thoroughly cleaned and de-greased.