It depends on the volume in use/stored. Once you are over 55 gallons (~200L) it spurs the requirement to have atmospheric monitoring in my jurisdiction.
One dewar is about 200L and is constantly evaporating, one large dewer per/ lab unit is okay without the need to have oxygen sensors. Be sure there is a secondary egress and that aisles are not locked by the dewar.
If you store a second, as a backup, we risk exceeding this limit per control area. We use Administrative controls (policy and signs) so that two dewers are never in a single lab unit at the same time, therefore, never more that 200L per control area.
We did put a hard wired O2 detection system in our main gas cylinder storage area where we can have more than 1 dewer of LN2 at a given time interval.
Most Fire departments refer to NFPA 55 – there is also guidance from the Compressed Gas Association (CGA p-18).
More than 200L – I say yes. If you have a pressurized cryogen system, yes again. Do what is right and then ask “am I meeting the minimum requirements of the law”.
We are in the process of building a new biology building and one of the labs will regularly contain a liquid nitrogen tank. Are oxygen depletion sensors required? The only thing I have come across said “recommended if room doesn’t have adequate ventilation.”
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