Investigating the field effectiveness of respirators against metal particle exposure in various workplaces: a systematic review.

Welders are exposed to high levels of metal fumes, which could be resulting in various health impairments. Respirators became a practical protective option in workplaces, as they are lightweight and easy to use. This systematic review attempts to explore the field effectiveness of using respirators to reduce metal particle exposure in workplaces. We reviewed papers published from 1900 to April 2019 in five major bibliographic databases, including Embase, Web of Science, Medline, Scopus, and CINAHL, along with organizational websites to cover gray literature. In total, 983 references were identified from the databases, out of which, 520 duplicates were removed from the EndNote database. The remaining 463 references were screened for their title and abstract. Out of 463, 70 references went through the full-text screening. Finally, eight papers, including 19 workplace respirator studies, satisfied all the inclusion criteria and were reviewed in this report. The geometric means for metal levels in workers' breathing zone with and without respirators were 9.4 and 1,777 µg/m for iron, 1.1 and 139 µg/m for lead, 2.1 and 242 µg/m for zinc, and 27 and 1,398 µg/m for manganese oxide, respectively. Most reviewed studies reported significant differences between measured metal particle levels among workers who worn respirators and who did not. In addition, results showed that N95 provided significantly less protection than elastomeric half facepieces, full-face respirators, and powered air-purifying respirators (p<0.001). More field studies are recommended to investigate Workplace Protection Factor (WPF) and fit factor (FF) of different respirators to understand the actual protection levels that they could be provided to control welding fume exposure among welders in various workplaces.