In reply to HenryC:
They are very good at holding down planes onto snow when in the Arctic Convoys - i believe that this is what they were invented for.
My understanding, though I'm happy to be corrected, is that they are not designed for a dynamic/shock load. Due to the intricacies of plate angle, strop angle, snow layers etc etc being so specific the chances of getting these bang on for a dynamic load are relatively small. Direction of pull could differ considerably dependant on where you were when you fell. Also were you to fall right over the top of it and roll down over the top and considerably alter the compaction/condition of the snow in-front of the deadman then this could also have a detrimental effect on the holding strength of the Deadman.
The American's call them "Flukes" for good reason.
They are a rubbish shovel but can be used to good effect as a stand for your stove.