Before handling liquid nitrogen its important you understand the basic properties so you can take the necessary precautions to avoid a disaster!
1) It is extremely cold: 77.3K = -196C = -320F at atmospheric pressure. This can cause severe frost bite.
2) On vaporization it expands by a factor of 700; one liter of liquid nitrogen becomes 24.6 cubic feet of nitrogen gas. This can cause explosion of a sealed container, or it can displace oxygen in the room and cause suffocation without warning.
3) It can become oxygen enriched and cause ordinarily noncombustible materials to burn rapidly.
PRECAUTIONS TO TAKE WHEN HANDLING LIQUID NITROGEN:
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. Camlab have a range of lightweight aluminium Cryolab Dewars including a 25 litre capacity made specifically for pouring liquid nitrogen with a tipping trolley.
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.
Immersion and withdrawal of racks and cryocanes into dewars must be slow
Take great care when placing your aluminium or stainless steel racking systems into the liquid nitrogen. If you rush this your cryo boxes could easily fall out. This also includes cryocanes containing you cryogenic vials which ideally should be labelled. If you lose any vials into the liquid nitrogen and you can’t identify them clearly then that can create more problems for you. Camlab have a range of Micryolabels to withstand these adverse conditions. Click CRYOVIAL RESCUE to find out how rescue your vials from liquid nitrogen in a previous blog post.
To prevent the unnecessary loss of refrigerant the necktube core should remain in the container when the stored material is not being assessed.
Grasp the rack handle lift and tilt the canister toward the center of the refrigerator. Withdraw the rack only far enough to remove the desired box. Comletely removing the rack will unnecessarily expose stored material to warm conditions.
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.
If you need more information about handling liquid nitrogen or any of our cryogenic equipment and accessories please contact our team on 01954 233110 or e mail firstname.lastname@example.org