The answer depends on the country in which the materials are being used and the relevant regulations for handling materials that can generate respirable amorphous silica containing titanium dioxide dust. For example, because the percentage of crystalline silica in aerogel is 0%, OSHA’s particulate limits of 15 mg/m3 (total dust) and 5 mg/m3 (respirable dust) apply to Aerogel exposure. The US National Institute for Occupational Safety & Health (NIOSH) standard for amorphous silica is 6 mg/m3. The German MAK for amorphous silica is 4 mg/m3 (inhalable fraction). Please consult your local governing regulatory information for guidance and/or recommendations for exposure limits.
It should be recognized that actual exposure levels to dust will depend on how the material is handled as well as where it is being handled (outdoors versus confined spaces). Availability of ventilation and other engineering controls will also impact actual exposures. Industrial hygiene studies conducted during intensive aerogel fabrication operations typically show total measured dust concentrations ranging from 0.2 to 5 mg/m3 and respirable dust concentrations ranging from <0.1 to 1.2 mg/m3.