Wow, you're absolutely right Chris - the
Materials Safety Data Sheet has been updated since I last bought any, and the exposure limits are WAY down on what they were before. It's now 0.025 mg/m3, whereas I'm pretty sure it used to be 10 mg/m3, which is just a typical level for a non-hazardous nuisance dust, so a simple dust mask would have been ok.
Here's an older MSDS which backs up my rememberance.
So, if I was specifying an industrial system to handle DE, I would now have to recommend a downflow booth with operator barriers for this, along with a personal respirator or high quality dust mask (selection chart
here if anybody's interested. [25 micrograms per m3, divide by ten once more for safety puts you in band D, with an exposure potential of EP1 or EP2, so you're most likely in the green region of the chart].
Of course that's for charging the material into a chemical reactor. If the operators were having to apply it repeatedly to flapping chickens, I might have to rethink that!