Occupational Exposure to Carbon Nanotubes and Nanofibers

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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
Table 6–6. Examples of engineering controlsContainment categoryand description Advantages DisadvantagesA. Dilution ventilation and noengineering controlsSupply and exhaust largevolumes of air (typically > 10air changes/hr.) throughout thework area to dilute airborneemissions.For general facility HVACneeds. Not recommended forcontrolling worker exposure toCNT and CNF.B. Local exhaust Ventilation(LEV)Hoods or enclosures on processequipment that exhaust airat the emission source tocollection equipment and awayfrom the worker’s breathing zone.Includes:B.1. Laboratory fume hoods(typically 80–120 ft/minface velocity) with HEPAfilterB.2. Biological safety cabinetClass IIB.3. LEV incorporated atsource of exposure andcan be built into handheldtoolsC. Down flow boothsSmall room or enclosure withlow velocity (100 ft/min)downward airflow to push/pullcontaminants away from theworker’s breathing zone.No local exhaust ventilation (LEV) orequipment enclosures required.Disperses/dilutes airborne emissionsthroughout work area.Capture emissions at their source withwell-designed hoods.Hoods can be tailored to the processor work task to optimize the capture ofemissions.Usually requires less overall exhaustairflow rates than dilution ventilationsystems.Emissions pushed away from theworker’s breathing zone.Flexible control that can be used forseveral tasks/operations.Useful for manual operations forwhich a more contained enclosure isnot feasible (e.g., larger amounts ofmaterials or equipment).Does not control exposure at the source,spreads emissions throughout work areapotentially exposing other workers.Often requires large airflow exhauststo dilute contaminants to below OELincreasing operating costs.Should only be considered whencontaminant generation is reasonablyuniform and toxicity of material is low.Air volumes and face velocity of LEVmust be maintained to ensure thecapture of emissions.Workers must be trained in thecorrect use.Fume hood sash opening needs tobe adjusted to ensure proper hoodface velocity.System exhaust flow rate may needcareful evaluation to ensure adequatecapture while minimizing loss ofproduct.Air volumes and control velocities ofbooth must be monitored/maintainedto ensure proper performance.Worker technique and interface withthe work process can interfere with thecapture of emissions.Workers must be trained in thecorrect use.(Continued)NIOSH CIB 65 • Carbon Nanotubes and Nanofibers59
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CURRENT INTELLIGENCE BULLETIN 65Occ
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Current Intelligence Bulletin 65Occ
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ForewordThe Occupational Safety and
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Executive SummaryOverviewCarbon nan
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2009; Pauluhn 2010a; Porter et al.
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neurogenic sig nals from sensory ir
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possible. Until the results from an
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••Follow exposure and hazard as
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Periodic Evaluations••Evaluatio
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ContentsForeword ..................
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A.3.2 Comparison of Short-term and
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ESPFeFMPSFPSSgGMGSDHCLHECHEPAhrISOI
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AcknowledgementsThis Current Intell
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1 IntroductionMany nanomaterial-bas
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2 Potential for ExposureThe novel a
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CNMs, with MWCNT agglomerates obser
Page 34 and 35: composite materials with local exha
Page 36 and 37: information on air contaminants. Sa
Page 39 and 40: 3 Evidence for Potential Adverse He
Page 41 and 42: decreasing agglomerate size increas
Page 43 and 44: examined up to 60 days post-exposur
Page 45 and 46: 3.3 SWCNT and MWCNTIntraperitoneal
Page 47 and 48: The same potency sequence was obser
Page 49 and 50: Table 3-3. Findings from published
Page 55 and 56: Table 3-7 (Continued). Findings fro
Page 57: Table 3-8. Findings from published
Page 60 and 61: length, respectively) [Muller et al
Page 63 and 64: 5 CNT Risk Assessment and Recommend
Page 65 and 66: A-6). Risk estimates derived from o
Page 67 and 68: Table 5-4. Factors, assumptions, an
Page 69 and 70: and analytical methods. NIOSH is re
Page 71 and 72: Table 5-5. Recommended occupational
Page 73 and 74: deficits in animals or clinically s
Page 75: (3) Rat lung dose estimationIn the
Page 78 and 79: tasks where worker exposures exceed
Page 80 and 81: As part of the evaluation of worker
Page 82 and 83: Table 6-1. EC LODs and LOQs for 25-
Page 86 and 87: Table 6-6 (Continued). Examples of
Page 88 and 89: Table 6-7 (Continued). Engineering
Page 90 and 91: exposure estimates for SWCNT on ind
Page 92 and 93: Table 6-8. Respiratory protection f
Page 94 and 95: ••Workers in areas or in jobs w
Page 97 and 98: 7 Research NeedsAdditional data and
Page 99 and 100: ReferencesACGIH [1984]. Particle si
Page 101 and 102: Bolton RE, Vincent HJ, Jones AD, Ad
Page 103 and 104: eport issued on July 22, 2011. NEDO
Page 105 and 106: Kobayashi N, Naya M, Mizuno K, Yama
Page 107 and 108: Methner M, Hodson L, Geraci C [2010
Page 109 and 110: Human Services, Centers for Disease
Page 111 and 112: Piegorsch WW, Bailer AF [2005]. Qua
Page 113 and 114: AD, Baron PA [2003]. Exposure to ca
Page 115: Varga C, Szendi K [2010]. Carbon na
Page 119 and 120: ContentsA.1 Introduction ..........
Page 121 and 122: A.1 IntroductionThe increasing prod
Page 123 and 124: provide an informal check on the es
Page 125 and 126: these same dose groups; this effect
Page 127 and 128: Table A-1. Rodent study information
Page 129 and 130: the deposited (no clearance) and th
Page 131 and 132: The other BMDS models failed to con
Page 133 and 134: Figure A-2. Benchmark dose model (m
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Figure A-3 (continued). Benchmark d
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Table A-3. Benchmark dose estimates
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Table A-5. Benchmark dose estimates
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histopathology grade 2 or higher lu
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Table A-8. Working lifetime percent
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developing early-stage adverse lung
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Figure A-4. Dose-response relations
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cell surface area). However, the wo
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purified or unpurified (with differ
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Table A-9. Comparison of rat or hum
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A.6.1.3 Pulmonary Ventilation RateT
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used as the effect levels in evalua
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the DF estimate, although a larger
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or overloading, of particle clearan
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Table A-13. Human-equivalent retain
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A.7.1 Particle CharacteristicsBoth
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and density. The following MMAD and
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Table A-15. CNT lung dose normalize
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B.1 Key Terms Related toMedical Sur
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APPENDIX CNIOSH Method 5040
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filter. In the method evaluation, d
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Most of the studies on sampling art
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e analyzed to determine the onset o
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Delivering on the Nation’s promis
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