Occupational Exposure to Carbon Nanotubes and Nanofibers

to below the REL, then workers should be providedrespiratory protection. The use of respiratorsmay also be advisable for certain work tasksthat place workers at risk of potentially highpeak concentrations of CNT and CNF (e.g., thecleanup of CNT and CNF spills or debris, maintenanceof equipment used to process CNT- andCNF-materials, the cleaning or disposal of filtrationsystems used to capture CNT and CNF aerosols).The OSHA respiratory protection standard (29CFR 1910.134) sets out the elements of a respiratorprogram for both voluntary and required respiratoruse. When respirators are provided for workerprotection, the OSHA respiratory protection standardrequires that a respiratory protection programbe established 29 CFR 1910 (c)(1). Elements of theprogram include (1) a medical evaluation of theworker’s ability to perform the work while wearinga respirator; (2) regular training of personnel; (3)periodic workplace exposure monitoring; (4) proceduresfor selecting respirators; (5) respirator fittesting;and (6) respirator maintenance, inspection,cleaning, and storage. The effectiveness of the programshould be evaluated regularly and respiratorsshould be selected by the person who is in chargeof the program and knowledgeable about the workplaceand the limitations associated with each type ofrespirator. The voluntary use of respirators are permitted,but must comply with the provisions set forthin CFR 1910.134(c)(2)(i) and 1910.134(c)(2)(ii).Based on published workplace monitoring datafor CNT [Maynard et al. 2004; Han et al. 2008a;Bello et al. 2008, 2009, 2010; Dahm et al. 2011]and CNF [Methner et al. 2007; Evans et al. 2010],a NIOSH-approved filtering facepiece respirator,or elastomeric half-facepiece particulate respiratorequipped with a 95 or 100 series filter, should provideadequate protection when properly fit-testedon the worker [Shaffer and Rengasamy 2009], andwhere engineered controls have been installed toreduce exposures. A properly fit-tested, half-facepieceparticulate respirator or a filtering facepiece respiratorwill provide protection at exposure concentrationsup to 10 times the REL. Other classes ofrespirators are available that provide a higher levelof protection (Table 6–8). The publication NIOSHRespirator Selection Logic 2004 provides guidancefor selecting an appropriate respirator [NIOSH 2005].When selecting the appropriate respirator, therespirator program manager should consider theparticle size in which workers will be potentiallyexposed [Rengasamy and Eimer 2011], and thepresence of other workplace aerosols. Based on thisinformation, the respirator program manager maydecide to choose a respirator with a higher assignedprotection factor (APF) or choose a respiratorwith a higher level of filtration performance (e.g.,changing from an N95 to a P100). Studies on thefiltration performance of N-95 filtering facepiecerespirators have found that the mean penetrationlevels for 40 nm particles range from 1.4% to 5.2%,indicating that 95 and higher performing respiratorfilters would be effective at capturing airborneCNT and CNF [Bałazy et al. 2006; Rengasamyet al. 2007, 2008]. Recent studies also show thatnanoparticles