We recently received a blood bank plasma freezer thermometer 20C to -90C in a bottle filled with sand instead of glycerol or ethylene glycol. Has anyone had experience with blood product freezer thermometers whose measuring bulb is immersed in sand?

That's what I use in our ultra-low freezer. Works fine.

I had never heard of it but it sounds like a great idea to me.  Wish I had thought of it! 

We have used them for a few years.  A lot easier to clean up the sand then glycerol.  

dear Sir, what kind of sand? is it the sand for the cat or any sand will do?

Finer the sand the better. Cat sand should be ok as long as not used

The sand doesn't react to temp changes as quickly, like a door open too long, which causes a false alarm, especially on an ultra low freezer. It provides a bit of a buffer, better than ethylene glycol or glycerol.