Paul, 

After a police officer line of duty death last year, the question was raised here.  We ended up looking at all of the rooms that had large Dewars and calculated the air volume of the space.  If the calculations dictated that there was a risk of an oxygen deficient atmosphere, we placed sensors in the room.  The standard places were storage rooms, the NMR facility, and an interior loading dock area where the vendor drops them and leaves them.  We did have a couple of labs that met our thresholds as well.   

Because we are in the process of switching over to an outside vendor running our controls shop, central plant, and BMS systems, I had them install the units and wire them in with the BMS system. They are also on a preventative maintenance schedule for calibration and sensor changes. If a deficient atmosphere is recorded, EHS and PD are notified.  We have signage on doors regarding entry when the alarm is sounding. The storage areas routinely go into alarm briefly when they vent (the alarm threshold is currently 19.5% and they drop to the 19% range).

Our most recent addition was Athletics.  We have a cryogenic treatment unit that was installed in a very small training room - which definitely warranted sensor installation. We found that athletics was storing 2 large dewars at a time to serve the unit.