Cryopreservated human biological tissues and/or cells that are properly rate frozen in prepared media with compatible cryoprotectant and then rapidly transferred to low temperature storage within a -20 degree C to -196 degree C range freezer chamber are generally considered viable upon proper thawing. Also, containment bags, vials, straws or specialized individual storage containers selected to maintain the integrity of the stored product should normally exhibit a tight seal during the entire process to prevent any leakage into the cryogenic storage chamber.

Compromised containment bags have been linked in a specific case (Hawkins et al., 1996) as the source of marrow/stem cells with Hepatitis B antigen A, and HBV that reportedly lead to confirmation that the free floating virus from this compromised bag was transferred onto the surface of another bag which ultimately resulted in a cross contamination to those virus-free viable cells before transplantation. The medium of transfer was reported as being Liquid Nitrogen [LN2] since it is both a refrigerant and can act as a viscous liquid vehicle. Later testing of cells with the virus found floating in the vessel's LN2 liquid nitrogen showed a DNA match to the infected patients. Normally, good laboratory decontamination procedures and awareness of this potential ( Webb et al., 1996) should have been in place to prevent this unfortunate event.

Cross contamination can be eliminated through the use of liquid nitrogen vapor freezers instead of direct LN2 liquid nitrogen contact. Liquid nitrogen vapor freezers keep the LN2 liquid nitrogen level physically below the samples, freezer racks, or storage vials, therefore only cooling with vapor instead of LN2 liquid nitrogen. Nitrogen vapor cannot serve as a medium for biological contaminants, and therefore prevent broken or unsealed samples from contaminating other samples. The MVE HE series and the Eterne series are these very liquid nitrogen vapor freezers that prevent cross contamination. Cross contamination is especially important when dealing with umbilical cord storage, or diseased whole blood storage, whereas this is not as crucial with semen storage (see 808 series semen tank). For more information about cryogenic refrigeration solutions, refer to Cryogenic Temperature Storage Freezer Advances.