elroy
Sapling
Th process of heating DE in the calcining process converts the silica from an amorphous state to crystaline silica. Exposure to crystaline silica through breathing leads to silacosis which in the case of prolonged exposure can lead desth. Here is an OSHA publication on that: Silicosis
See also http://dx.doi.org/10.1136/oem.58.1.38
Crystalline silica exposure and lung cancer mortality in diatomaceous earth industry workers: a quantitative risk assessment