If you are referring to motorised sit/stand desks we have a few in our offices.  I have not identified any crushing risk per se (if the desk came down on someone it's likely that it starts lifting itself off the floor and putting all its weight on the person, but that's not so much that it will cause significant injury).  The moving parts on the ones we have are well shrouded and don't seem a problem.

The problem I did identify is that when they are tight alongside another table or desk there's a potential for a sort of guillotining crush as the edge of  the desk top comes down alongside the edge of the adjacent.  It's quite slow, so it won't actually cut any appendages off, but it would do crushing type damage if someone didn't move their finger / whatever out of the way.  We solved that by not putting them tight alongside anything else - there's an at least 50mm gap between the motorised desks edges and anything else.

I'm not aware of any published guidance, however.  I just looked at what was in front of me and what it did and assessed for obvious foreseeable risks.