The National Institute for Occupational Safety and Health (NIOSH) establishes guidelines to protect workers from hazardous occupational chemicals exposure. These occupational exposure limits (OELs) set limits on the amount of exposure to a given chemical that is considered to be safe. As more chemicals are introduced industries cannot provide the enough information define the chemical risks. The NIOSH occupational exposure banding process helps to define recommended exposure levels in the absence of complete toxicological data. It presents five occupational exposure bands (OEBs) of chemical concentration that sequence the health hazard potential from lowest to highest. Four respects distinguish this process:
- A three-tiered assessment that is available to an audience of diverse backgrounds;
- Nine health factors used to assess chemical toxicity;
- Quantitative exposure range based on health impact;
- Consistency of OEBs with OELs.
Tier 1 is for chemicals with little data and determines risk based on the Globally Harmonized System of Classification and Labelling of Chemicals (GHS); Tier 2 assembles reliable literature data and is used as a semiquantitative resource for trained occupational users; Tier 3 is quantitative and could be an integration of all related data mainly for expert evaluation.
Nanoscale materials (primary size <100 nanometers) gain attention in the report due to their behavior differences from their bulk materials. For example, poorly-soluble solid nanoparticles are generally more toxic than relevant microscale ones. Therefore, NIOSH recommends modifying the original process for nanoscale solid particles, that is “shifting the banding assignment to the next more stringent band” if nano-form data are not available. Additionally, as for nanoscale fibers and tubes, the toxicology properties differ from other scale forms and are directly related to their shapes and sizes. Consequently, Tier 3, instead of Tier 1 and Tier 2, is used to evaluate these compounds.
Currently, NIOSH is making efforts to obtain data and methods that can derive OELs and OEBs for nanomaterials via models and chemical properties.