Doing maintenance on a -86 freezer and attempting a full defrost that takes around a day or more, need to move samples within (chemicals, DNA samples, cryofrozen bacteria) but do not have another -80 freezer. Would placement in -20C for the time be okay?
I used to defrost -80C freezers all the time. DNA, RNA, enzymes, and tissue samples should be fine in a -20C freezer for 24 hours as long as they don't thaw completely. Chemicals you'd have to check to make sure they can tolerate the change in temperature. To expedite the process of defrosting the freezers, I would remove everything, unplug the unit safely according to equipment procedures, and then (using thermo resistant gloves because it's cold inside!) as the ice was thawing scrape it off (using plastic) into buckets and use paper towels to wipe up any excess water and ice, leaving the doors and interior compartments open the entire time. This way, the interior of the unit had more time to warm up to completely defrost instead of slowly melting the ice all day. This process took me just a day to do. I'd start in the morning, the ice would be completely melted off by lunch time/early afternoon, and then it would warm up overnight. The next morning, I'd plug it back in and by lunchtime the samples would be back in the -80C freezer.
On that note, however, -80C freezers shouldn't need to be defrosted. I also agree with Artur; if there is poor ventilation/circulation it could cause the freezer to build up with ice. Also, if the refrigerant is low. Perhaps a service call might be needed as a checkup for the freezer?
Agree with Artur. DNA will be ok in -20C but for the other chemicals you will probably have to check. We used to dump our samples and chemicals in a -80C in another lab when we defrost or cleaned our freezer.
We would store the very sensitive items in a large cooler full of liquid nitrogen. Make sure the lid is vented and the room is ventilated. Things that were less temperature sensitive can be put in coolers with dry ice or in the -20.
I see from the question that there is not space in another -80 for the most sensitive material ( rna and some enzymes and tissues), We used to keep large inflated polystyrene boxes that nextgen sequencing kits come in and buy a couple of bags of solid carbon dioxide to cover the stored material and half of a 14pound bag will keep a large box of already cold material cold for about 3 days. The rest of the material can go into -20s as suggested above. Be prepared to order more solid co2 because sometimes freezers work fine but when switched off the condenser tubes get blocked and they do not work properly when switched back on again until all of the condensate has been forced back into the compressor sometimes with the help of a hair drier or heater on the heat exchange pipes
I used to defrost -80C freezers all the time. DNA, RNA, enzymes, and tissue samples should be fine in a -20C freezer for 24 hours as long as they don't thaw completely. Chemicals you'd have to check to make sure they can tolerate the change in temperature. To expedite the process of defrosting the freezers, I would remove everything, unplug the unit safely according to equipment procedures, and then (using thermo resistant gloves because it's cold inside!) as the ice was thawing scrape it off (using plastic) into buckets and use paper towels to wipe up any excess water and ice, leaving the doors and interior compartments open the entire time. This way, the interior of the unit had more time to warm up to completely defrost instead of slowly melting the ice all day. This process took me just a day to do. I'd start in the morning, the ice would be completely melted off by lunch time/early afternoon, and then it would warm up overnight. The next morning, I'd plug it back in and by lunchtime the samples would be back in the -80C freezer.
On that note, however, -80C freezers shouldn't need to be defrosted. I also agree with Artur; if there is poor ventilation/circulation it could cause the freezer to build up with ice. Also, if the refrigerant is low. Perhaps a service call might be needed as a checkup for the freezer?
Every time that I have taken cryopreserved bacterial samples and (or even competent cells) out of the -80 and left them overnight in a -20, I witness a reduction in the viability of the cells/cultures. To be on the safe side, I would pack everything into large styrofoam boxes and put solid CO2 on them, like Paul Rutland mentioned above.
Wondered about this question for 40+ years. We have multi-thousand isolate collections of 4 gram negatives and two gram positive, all stored in glycerol at -80C. With three -80C freezers in use, been fortunate to have space to shift storage of isolates when one of the -80C freezers needs to be defrosted for service/repair.
Unlike constant temperature -80C freezers, -20C freezers by design often go through a daily defrost cycle to eliminate icing. When this occurs for our -20 freezers, the temperature rises to -10 C.
On rare occasions when we had to make use of a -20 freezer for temporary storage of bacterial cultures previously stored at -80C, we typically found a 5 – 10-fold drop in CFU titer. I wonder here regarding the survivors, if we might inadvertently be selecting for viability mutations associated with such treatment.
One tip for Richard and for all labs really: get rid of all cycling freezers and have them replaced by freezers that do not defrost.
All advice above are very good and practical. All freezers need to be defrosted from time to time, but only once or twice a year and only after having them emptied and contents placed in other freezer, in dry ice or in liquid nitrogen, depending on the biological material.
Difficult to imagine, source of funding and logical rationale, to replace three large functional/reliable defrost-cycle -20 C freezers adequately serving for storage of thousands of genomic DNA preps.
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