Search

Workers are increasingly exposed to nanoparticles, mostly via inhalation. Respiratory protection is recommended as an additional control measure. Particulate respirators are certified for protection against micro-sized particles, where a most penetrating particle size (MPPS) of 100–400 nm is assumed. Commonly used N95 respirators are certified by the National Institute for Occupational Safety and Health after passing a 95% collection efficiency test. Electret media used in respirators have been demonstrated to be shifting the MPPS to a nanosized region. Experimental studies have therefore been conducted to assess N95 respirator penetration specifically by nanoparticles. This systematic review and meta-analysis was aimed at systematically reviewing these studies and meta-analysing the mean penetration percentage (PP). The review was conducted following a Preferred Reporting Items for Systematic Reviews and Meta-Analyses guideline. Fourteen studies were selected to be reviewed qualitatively, while 13 of these with 29 data points were included in the meta-analysis. Sensitivity analysis was performed based on a respirator mounting protocol, while subgroup analysis was done for aerosol dispersity and repeated for the respirator mounting protocol. The size range of particles used across the reviewed studies was 1 nm–10 μm. The MPPS for all studies was in the nanosized particle range, with the lowest at approximately 39 nm. The estimated mean PP was between 1 and 6%, exceeding the 5% guideline threshold for four of the studies. All the meta-analysed mean PPs were however below the 5% guideline. This means that the N95 respirators may be effective for nanoparticles in workplaces, but subject to factors including respirator characteristics and particle dispersity.

Assessing the need for and effectiveness of controlling airborne exposures to engineered nanomaterials in the workplace is difficult in the absence of occupational exposure limits (OELs). At present, there are practically no OELs specific to nanomaterials that have been adopted or promulgated by authoritative standards and guidance organizations. The vast heterogeneity of nanomaterials limits the number of specific OELs that are likely to be developed in the near future, but OELs could be developed more expeditiously for nanomaterials by applying dose–response data generated from animal studies for specific nanoparticles across categories of nanomaterials with similar properties and modes of action. This article reviews the history, context, and approaches for developing OELs for particles in general and nanoparticles in particular. Examples of approaches for developing OELs for titanium dioxide and carbon nanotubes are presented and interim OELs from various organizations for some nanomaterials are discussed. When adequate dose–response data are available in animals or humans, quantitative risk assessment methods can provide estimates of adverse health risk of nanomaterials in workers and, in conjunction with workplace exposure and control data, provide a basis for determining appropriate exposure limits. In the absence of adequate quantitative data, qualitative approaches to hazard assessment, exposure control, and safe work practices are prudent measures to reduce hazards in workers.