Occupational Exposure to Carbon Nanotubes and Nanofibers

6.2 Engineering ControlsOne of the best ways to prevent adverse health effectsfrom exposure to CNT and CNF is to eliminateexposure and minimize risks early in the design orre-design of manufacturing and down-stream userprocesses (see NIOSH prevention through design(PtD) at: www.cdc.gov/niosh/topics/PtD/). Thiscan be accomplished through the establishmentof a process safety management (PSM) program.PSM entails the development and implementationof programs or systems to ensure that the practicesand equipment used in potentially hazardous processesare adequate and appropriately maintained.An integral part of the PSM program is the conductof a process hazard analysis prior to the initiationof work to identify where sources of exposure toCNT or CNF may occur so that process equipmentcan be designed or re-designed to minimize therisk of exposure. At a minimum, the elements ofthe PSM program should be consistent with thoserequired in the OSHA Process Safety ManagementStandard [29 CFR 1910.119].In workplaces where CNT or CNF can’t be substitutedwith a less hazardous or nonhazardous materialthen all process equipment and other equipmentinvolved with the handling of CNT and CNFshould incorporate the necessary engineering controlmeasures to prevent worker exposure to CNTand CNF. Because of limited published workplaceexposure data for CNT and CNF, it is unknownwhether worker respirable mass exposures to CNTand CNF can be maintained at all workplaces belowthe NIOSH REL of 1 µg/m 3 EC as an 8-hourTWA. However, exposure control techniques suchas source enclosure (i.e., isolating the generationsource from the worker) and well-designed localexhaust ventilation (LEV) systems equipped withhigh efficiency particulate air (HEPA) filters havebeen shown to be effective for capturing airbornenanoparticles including CNT and CNF [Old andMethner 2008; NIOSH 2009a; Evans et al. 2010]. Ageneral description of exposure control techniquesand their advantages and disadvantages is given inTable 6–6. The selection of the exposure controltechnique should take into account the quantityand physical form of the nanomaterial (e.g., dispersiblepowder, liquid slurry, contained in a matrix)and the task duration and frequency in whichworkers come into contact with the material (Table6–7). For instance, working with materials containingCNT or CNF (e.g., encapsulated in a solid) mayrequire a different type of an exposure control systemthan would be required for large quantities ofCNT and CNF in a highly dispersed free form. Processesinvolved in the cutting, grinding, or drillingof solid materials containing CNT or CNF shouldincorporate appropriate engineering controls (e.g.,local exhaust ventilation) to prevent aerosol release,whereas the manufacturing (i.e., product collectionat reactor) and handling of dry bulk CNT orCNF should be performed in enclosed, and whenwarranted, HEPA-ventilated systems. HEPA filtrationhas been shown to be effective in capturingnanoscale particles and should be considered insituations where emissions may be regular, whereprocesses are repeated, and where higher quantitiesare used in a way that may lead to emissions. Thehandling of research quantities of CNT and CNFin laboratories is best performed using a laboratoryfume hood, such as a low-flow or air-curtain hood[Tsai et al. 2010], or use of a glove box to minimizeworker exposure [NIOSH 2012]. All exposure controlsystems should be properly designed, tested,and routinely maintained to ensure maximumefficiency [ACGIH 2007].6.3 Worker Educationand TrainingEstablishing a program that includes the educationand training of workers on the potential hazards ofCNT and CNF and their safe handling is criticalto preventing adverse health effects from exposure.Research has shown that training can attain immediateand long-term objectives when (1) workersare educated about the potential hazards of theirjob, (2) there are improvements in knowledge andwork practices, (3) workers are provided the necessaryskills to perform their job safely, and (4) there58 NIOSH CIB 65 • Carbon Nanotubes and Nanofibers