That is not food grade, amorphous DE--DO NOT USE THAT FOR YOUR CHICKENS!
The difference is that is flux-calcined, is crystalline with sharp edges. These sharp edges make it much more irritating and likely to cause cancer. The food grade type is not crystalline (amorphous), and much less likely to cause problems. But use a dusk mask anyway when working with it. That is why I use Stall Dry instead (has DE combined with clay), much less dust and less to inhale.
Right. The crystalline silica is the bad player.
"The type of hazard posed by inhalation depends on the form of the silica. Crystalline silica poses a serious inhalation hazard because it can cause silicosis. Amorphous silica can cause dusty lungs, but does not carry the same degree of risk as crystalline silica. Natural or dried diatomite generally contains very low percentages of crystalline silica. Diatomite produced for pool filters is treated with high heat (calcining) and a fluxing agent (soda ash), causing the formerly amorphous silicon dioxide to assume its crystalline form."
What you want to look for is Codex Food Chemical Grade that is non-treated and non-calcined.
DE is tiny fossilized single cell creatures which found in deposits in the earth- when crushed up they make a super fine dust that is relatively harmless and non-toxic (the full on eatable food grade) and it kills soft bodied insects. Great for dusting chickens with and keeping spiders out of the house!
Wheat flour can even be hazardous if you snort it up your nose. I've used food grade DE for years and no problems at all. I don't even use a mask when I sprinkle it under the roosts and in the nests. Naturally, any powdery substance shouldn't be snorted.