The collapsing floor creates blowback on every z-level it passes through. If you have a wide bridge, it will help insulate the mason from the wind - fast masons can even outrun it. Ideally, surround the hopper entirely with bridge.
Also, a wide bridge will stop them from falling if they do get caught. I figured out what killed my one guy - he fell down the stairs. I suspect a hatch will fix that, too, though it needs to have actual support, not fake bridge-support. And, if you're only up one level, you don't need to worry about anything.
Yes, falling floors will crush anyone under them. Sadly, this design is slightly inferior to the atom smasher - it cannot attack rock. Everything else, though, sure.
Amusingly, I dropped my whole test apparatus by deconstructing the bottom stair...several levels of bridge dismantled itself, which means the worker survived without a scratch.
So I have a question. Are constructed walls supposed to survive cave-ins when they're the target? As the hammer, they're duly pulverized, but as the anvil they seem unmoved.
Hmm, I wonder what happens if...
Side view. Ramp up to bridge with (^)spot for floor over a (|||)pillar supported cavern, over yet another cavern. Usually cave ins will go through any number of floors and constructions.
___^
/||______
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The constructed wall will act as a natural wall, and halt the cave-in, in case you ever want to do bas-relief. Upward stairs seem to be able to perform the same function, as I suspect will supports.
Further tests showed that upward stairs, supports, and walls are all good as anvils, even if placed over empty space.
__ ^
/__||
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Constructed floors will be pulverized, as will downward stairs, but they can safely support natural floors.
I tried deconstructing the tower with bridge immediately above everywhere you can stand to deconstruct it, and...it shattered my tax collector. He suffocated to death.