Our stocks of frozen cells are a very important resource, which is often shared between researchers in our lab and sometimes provided to other labs. Following proper procedures for freezing cells increased the recovery of live cells upon thawing. Furthermore, failure to follow proper procedures when dealing with the liquid nitrogen tank jeopardizes not only your sample but also imperils irreplaceable lab stocks. Therefore, if you are not confident in your ability to handle the liquid nitrogen tank ask a colleague to chaperone you.

Resuspend your cells in the appropriate freezing media and slow-cool them in the -80 deg C. Feel free to use the special (round blue plastic) high heat capacity containers that improve cell viability by slowing the cooling process. Do not use these containers for long term storage in the -80 deg C as this deprives your colleagues of this resource.

When you decide to move your cells to liquid N2, first find space for them. Bring with you a container of dry ice. Remove the vials of cells from the plastic container (it may crack if placed on dry ice) and place your cells on dry ice. This insures that the cells will not warm up during transfer from the -80 deg C or during manipulation of the liquid nitrogen tank. Knowing that your cells are safe, will allow to work in a relaxed environment.

Working with the liquid nitrogen is uncomfortable and hazardous, both to you and to the frozen cells. Before you access the tanks, please take a few minutes to organize a comfortable work space for yourself: Move the phosphoimager cassettes that are stored near the liquid nitrogen tanks out of the way to create a work surface (please take care not to place the ultra-cold boxes, racks or dry ice containers on the phosphoimager cassettes stored nearby as this can damage the sensitive detection screens). If you anticipate anything but a brief search through the box, bring with you a dry ice container in which to place the tubes and boxes you retrieve.

The boxes of cells are secured in the rack by a flimsy horizontal wire and by a more sturdy vertical rod. If these are not in place, the boxes may slip from the rack and fall to the bottom of the tank. This may occur either during insertion or removal of the rack. Retrieving such boxes is a major hassle and if their contents spill to the bottom of the tank, precious samples may be lost. To safeguard against such spillage, look down the shaft of the tank before you remove the rack and check for loose boxes that protrude over the edge. If you identify any such protruding boxes, DO NOT REMOVE THE RACK from the tank; gently put it back in place and find a colleague that knows what to do.

After removing the rack and removing the securing rod, put the rod in a conspicuous place so that you don't forget to replace it before returning the rack to the liquid nitrogen tank (some people suspend the rod from the lip of the tank, physically interfering with the replacement of the rack). If your business is short, remove the box you want to work on, recover or place the vials in the box, replace the box in the rack, secure it with the horizontal wire, replace the vertical rod and replace the rack. If you need to work on the box for any lenght of time, you must place it on dry ice to safeguard its contents and you must replace the rack in the liquid nitrogen container. Remember, by leaving the rack out at room temperature for any length of time, you are compromising the viability of countless, possibly irreplaceable, samples.

What to do if a box does fall from the rack and is lodged at the bottom of the container? The first priority in such cases is to safeguard the contents of the rack you have just removed (the box may have fallen rom that rack or from an adjacent rack). Gently replace the rack in the liquid nitrogen tank. The box that has fallen will likely prevent you from being able to restore the rack to its original position and you will not be able to close the tank's lid. However, as long as the boxes in the rack do not protrude above the base of the tanks neck, their contents are safe. Forget about the lid, cover the tank's mouth with aluminium foil and get help. .

Please help us preserve this important resource

July 9, 2004