NIH 3T3 cells cross contamination - (Jun/18/2013 )

Dear all,
In our lab we usually keep cells immersed in liquid nitrogen
when I thaw my cells, I found some liquid nitrogen inside the tube.
So I put it in the clean bench and waited till all liq evaporate and melted by room temp to avoid explosion of the tube if I tried to thaw in warm water bath.
and it really worked out, and cells melted without any breakage of tube.

However, I am afraid of cross contamination.

I have this threat inside my head < perhaps other cells are just like these tubes and cells my transferred from one tube to another .
all NIH 3T3 tube contain the same problem, I checked our stock, all tubes has LN leaked inside the tube,
and I could not check all other cell tubes as the container contains other people work too., and a lot of tubes
any advice about this threat???
Thank u
madelin

The cells are very unlikely to come out of the frozen pellet and then happen to enter another tube. There is a higher chance that there will be some bacteria that have come in with the LN2, bu even then, the risk is quite low.