common diatomaceous earth formulations are safer to use, as they are predominantly made up of amorphous silica and contain little or no crystalline silica. The crystalline silica content of diatomaceous earth is regulated in the United States by the Occupational Safety and Health Administration (OSHA) and there are guidelines from the National Institute for Occupational Safety and Health that set maximum amounts allowable in the product (1%) and in the air near the breathing zone of workers, with a recommended exposure limit at 6 mg/m3 over an 8-hour workday. OSHA has set a permissible exposure limit for diatomaceous earth as 20 mppcf (80 mg/m3/%SiO2). At levels of 3,000 mg/m3, diatomaceous earth is immediately dangerous to life and health. In the 1930s, long-term occupational exposure among workers in the cristobalite diatomaceous earth industry who were exposed to high levels of airborne crystalline silica over decades were found to have an increased risk of silicosis. Today, workers are required to use respiratory-protection measures when concentrations of silica exceed allowable levels. Diatomite produced for pool filters is treated with high heat (calcination) and a fluxing agent (soda ash), causing the formerly harmless amorphous silicon dioxide to assume its crystalline form. See also References Occupational exposure to crystalline silica and autoimmune disease. External links CDC – NIOSH Pocket Guide to Chemical Hazards Diatomite: Statistics and Information – USGS Tripolite: Tripolite mineral data Citat: "...A diatomaceous earth consisting of opaline silica..." Diatomaceous Earth: A Non Toxic Pesticide Sedimentary rocks Inorganic insecticides Swimming pools Water treatment Soil Soil improvers Fodder Microfossils Biomineralization Industrial minerals Sustainable agriculture