Liquid nitrogen storage - liquid or vapour phase?

Model Organism: Worms Methods & Reagents
1

Following on from my previous thread http://forums.wormbase.org/index.php?topic=944.0 I was hoping to get some opinions about how best to store our precious worms using liquid nitrogen - in the actual liquid or in the vapour phase created by the liquid nitrogen in the container.

We have purchased a BioRack Series dewar from Statebourne and the model is compatible with either storage phase, although storing it in liquid phase offers more capacity.

Does anybody have an opinion on this question? Are there concerns about keeping the worms in either phase for a prolonged time?

Any input would be much appreciated.

Cheers,
Toby

2

We keep our worms completely submerged. The top most box actually goes through submerged or vapor phase depending on the liquid N2 levels in the dewar. We never had any problems thawing out worms from any of the boxes.