Science Buddies: "Ask an Expert"

Hello. For my SF experiment, I am freezing plant seeds in different cryoprotectants. I am nearly done with research; I am now on the last few details of my procedure. To decide whether I'm doing this experiment at school or going to a specialized lab, I need to know exactly what equipment I need to deal with liquid nitrogen. Our lab at school is pretty well-stocked, but we don't keep liquid nitrogen on hand and don't work with it regularly. My teacher said that if all we need is to purchase the liquid nitrogen, I'll be fine conducting the experiment in school.
I know I need a lot of protective gear: heavy gloves, clothes covering all my skin, lab coat, goggles and perhaps a full face mask. This is all equipment we own.
What I need to know is EVERY detail about handling liquid nitrogen. Here are a few of the questions I need answered, but these are only off the top of my head and there is probably more:
1. How is the liquid nitrogen stored or disposed of?
2. In what sort of container should the liquid N be kept in when I am putting my samples in?
3. HOW do I lower my samples into the liquid N and how do I take them out?
4. In what sort of vial should my samples be kept in when in the liquid N?
5. While my samples are being kept in the liquid N (they are being kept in there for 3, 5, and 7 day periods), how should the liquid N be stored? Is the temperature OUTSIDE the liquid N container a factor?
Please help! Thank you

Hi,

You need to be aware of this Science Buddies Project Idea on cry preservation of seeds:

https://www.sciencebuddies.org/science- ... p004.shtml

Here is a Material Data Safety Sheet for liquid nitrogen from a major reputable supplier shich outlines their guidelines for safe handling:

http://www.praxair.com/praxair.nsf/0/1a ... p4630j.pdf

Here are additional safety guidelines from other organizations:

http://www.physics.unc.edu/about/safety ... onSW_2.pdf

http://www.bath.ac.uk/internal/bio-sci/ ... asphyx.htm

http://safetyservices.ucdavis.edu/safet ... ic-liquids

Generally liquid nitrogen is rather safe to handle. The biggest risks are frostbite if the liquid makes prolonged contact to your body, explosion if the liquid warms in a confined space, and asphixiation if a large quantity evaporates quickly in a confined space with poor ventilation. Liquid oxygen may accumulate in open dewars of liquid nitrogen over a long period of time as the boiling point of liquid oxygen is higher than liquid nitrogen. Liquid oxygen in contact with anything that can burn is be extremely dangerous.

Your questions::
1. Liquid nitrogen is normally stored in an open dewar (thermos bottle/ vacuum flask). To get rid of waste allow it to evaporate in a well ventilated area.

2. The best container for Liquid nitrogen is always a dewar. I have seen people use a Styrofoam cup for a very few minutes, but if you need to preserve LN for hours a narrow neck open dewar is the best choice.

Bristol University offers the following advice:
“Prevent unauthorised people having access to areas used for delivering, storing, dispensing and using liquid nitrogen. At no time should liquid nitrogen be left unattended in unsecured areas such as outside buildings.
Ensure suitable and sufficient training, appropriate clothing, and appropriate PPE, use tongs for handling materials that are in contact with liquid nitrogen.
Avoid direct skin contact with items that have recently been in contact with liquid nitrogen by using insulated gloves and/or tongs.
Only place hollow tubes in the gas phase of liquid nitrogen.
Use specimen tubes with special neoprene gaskets, and ensure they are securely sealed and only use specimen tubes approved for cryogenic storage.”
Note: the tongs should not be metal. They should be made of an insulating material.


I do not think you will have any trouble with using it if you follow reasonable safety precautions.

Best regards,

Barrett L Tomlinson

Do you know how the liquid nitrogen is dispensed? as in, when I buy it will it come in a dewar-like container that i can put the specimens in? should i put the specimens directly into the dewar or transfer the liquid nitrogen somewhere else? HOW do i put them in -- do i just drop them into the container? suspend them somehow?

My opinion is if you have to ask these questions, then your school lab doesn't have the necessary equipment and equipment expertise for your project.

Determine if there are any university/college labs with the equipment/expertise in your area.

Typically you have to rent/buy a storage dewar for the liquid nitrogen delivery. You then have to buy/borrow appropriate other smaller dewar for your experiments.

I don't know enough about your specimens to know if direct contact with liquid nitrogen is a problem or not and how big and how many samples you have.

If you are going to share a liquid nitrogen bath with others, you will have to utilize some sealed containment vessel to hold your samples to prevent cross contamination. If your samples are small enough, then you can use a small dewar container with a one time fill assuming it is rated to stay cold for the duration you need.

Another possible source of equipment/expertise is a local dermotologist who uses liquid nitrogen in their practice. They typically have several small portable dewar that they fill from a larger one.

Another safety issue is liquid N in a lab may displace air and lead to an oxygen deficient atmosphere. Go to the N supplier and ask them for safety training.

Get help from an experienced cryo technician and let her (or him) give you suggestions for what to do and how to do it safely. Being cold is only one of severl issues.

The main hazard of liquid nitrogen is that it will expand rapidly at room temperature and displace the air in an enclosed space, leaving no oxygen for you to breathe. Always be sure you have adequate ventliation!
You also should not be using vials. If you put LN2 into a sealed vial, the pressure will rise and it will very likey explode.