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Nanomaterial sampling at NIST
 

Nanomaterial sampling at NIST

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Sampling protocols used to determine employee exposure to nanoparticles at NIST

Sampling protocols used to determine employee exposure to nanoparticles at NIST

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  • 1. Speaking from perspective of applied Industrial Hygiene2. Assuming audience has limited familiarity with Industrial Hygiene – will touch on traditional IH practices and philosophies
  • Instruments were selected to match NIOSH’s work. More comparable instruments available each year.Will provide basic descriptive statistics.
  • Applied industrial hygiene not researchGaithersburg – Center for Nanoscale Science and TechnologyBoulder – smaller # researchers, Optoelectronics, Materials Reliability, Electromagnetics
  • As an Industrial Hygienist I measure people’s exposures to air contaminants.
  • NIOSH Current Intelligence Bulletin for CNT 2010 as a draft that was released for public commentCNT REL = 7 µg/m3, 8-hr TWA = LoD for analytical methodTiO2 REL = 0.3 mg/m3 for ultrafine (<100 nm), 2.4 mg/m3 for fine
  • Nanoparticle Emission Assessment Technique (NEAT)Pre-dated draft CIB for CNTs and carbon nanofibersInstruments shouldbe specific, field-portable and affordable (not an SMPS Scanning Mobility Particle Sizer)
  • Pros: Gets down to nanometer size rangeCons: Provides a single count combining all sizes of particles Non-specific Does not correlate with traditional OELs
  • ** Increase in small size WITHOUT increase in large sizes = nanoparticles** Small sizes correlate with CPC = nanoparticlesPros: Provides six separate size channelsCons: Only gets down to 300 nm particle size Limited data memory forces longer logging intervals, difficult to match to CPC
  • Higher flow rate will capture more material; may be able to reach 7 lpm with personal pump; 10 lpm maximumSEM/TEM difficult to quantify air concentration, especially as mass
  • Fume hoods not intended to control spraying of materials.
  • Standard chemical fume hood, HEPA filtered exhaust; Checked that face velocity was adequateTarget leaning against center of back wallSonicator enclosure back right cornerDry weighing performed in front on enclosure – partial blockage of inward airflow
  • Left photo shows researcher holding air brush in right handNote metal target, sample filters behind targetRight photo shows researcher using canned air with left hand
  • Pumps and Filters on stand at face of hoodFilters inside hoodAqua sonicator inside hoodPersonal pumps usually reach 3.5 – 5.0 lpm; some rated at 7.0 lpm; AC pumps to 10 lpm (NIOSH max.)
  • Note CPC, OPC, target, air brush
  • Sampling period included both rounds of prep and spraying, along with final cleanupAll samples below analytical laboratory’s lower limit of detectionBEST PROOF OF RESEARCHER’S SAFETY: Adequate to prove exposure level was below the OELSEM – Preliminary results = not seeing anything
  • Background in hallway outside labEnter lab; previously unoccupiedWeigh and sonicate MWCNTVacuum lab floor – skews range of measurementsTurn on HEPA-filtered recirculating fume hood – Totally changed background level within labSeen the same thing when recirc. hood left on in lab after sampling and sampler left running, 2 hours and background = 0Beginning of data shown in following charts – much of this variation would have been lost at higher backgroundEnd of data shown in following charts>7 Move instrument to hallway outside of lab – back to original background level
  • Slight increase in small and large particles on the OPCNo corresponding increase on CPCNo proof of individual nanoparticles; seeing liquid aerosols??
  • Strong match for high and low pointsSee increases in small and large particles at the same times
  • Limited correlation between the two instrumentsTime scale of the two instruments slightly different – difficult to ID specific brief events

Nanomaterial sampling at NIST Nanomaterial sampling at NIST Presentation Transcript

  • Applying NIOSH’s Nanomaterial Sampling Methods in the Laboratory Setting – Preliminary Observations
    Michael K. Blumer, CIH
    Jason T. Capriotti, CIH, CSP
    National Institute of Standards and Technology (NIST)
    Office of Safety, Health and Environment (OSHE)
  • Presentation Outline
    Review Occupational Exposure Monitoring
    Review NIOSH Sampling Methods & Limitations
    Case Study: Spraying Multi-walled Carbon Nanotubes
    Photo: Carbon nanotubes with impurities; Credit: NIST
    2
  • Disclaimers
    Certain commercial instruments are identified in this paper in order to specify the sampling procedures adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the equipment identified is necessarily the best for the purpose.
    Due to the preliminary nature of the sampling activities, no attempt at deriving statistical inferences was made.
    3
  • Introduction
    NIST Safety Office is evaluating exposures in working labs
    NIST researchers fabricate, test, and use variety of nanomaterials
    Laboratory Setting
    Small amounts of many different materials
    Short-duration activities
    Small population of highly educated, specialized workers
    Exposure controls are commonly present
    Local exhaust ventilation; fume hood, etc.
    Personal protective equipment; lab coats, gloves, glasses
    Ref: NIST HSI #23
    Photo: Assembly of polystyrene particles held together by polyelectrolyte interaction fabricated by the Complex Fluids Group; Credit: NIST
    4
  • Occupational Exposure Monitoring
    Traditional Exposure Monitoring
    Occupational Exposure Limit (OEL)
    Airborne concentration – mass of contaminant
    Set by governmental agency or scientific association
    Based on medical case studies, toxicology, epidemiology
    Collect physical sample of airborne contaminant with pump and filter or adsorption tube
    Laboratory analysis to quantify material collected
    Calculate concentration and compare with OEL
    5
  • ENM Exposure Monitoring
    No OELs in most cases
    Instead, evaluate change over background(Standard philosophy is to control exposure to carcinogens as low as technically possible)
    Chemical-specific OELs for Carbon Nanotubes and Nanowires and Titanium Dioxide
    Methods sensitive enough to reach lower OEL
    NIOSH sampling methods for ENMs
    6
  • NIOSH NEAT Sampling Protocol
    Particle Counters - Hand-held direct-reading
    Condensation Particle Counter (CPC)
    Optical Particle Counter (OPC)
    Together provide semi-quantitative estimate of nanoparticles
    Filter sample for SEM/TEM analysis
    Particle identification and morphology
    Filter sample for airborne chemical mass concentration
    Traditional NIOSH sampling & analytical methods
    Filter pairs at nanoparticle source and researcher’s personal breathing zone (PBZ)
    Ref: Methner, M. , Hodson, L. and Geraci, C. (2010) 'Nanoparticle Emission Assessment Technique (NEAT) for the Identification and Measurement of Potential Inhalation Exposure to Engineered Nanomaterials — Part A', Journal of Occupational and Environmental Hygiene, 7: 3, 127 — 132, First published on: 16 December 2009 (iFirst)
    7
  • Condensation Particle Counter
    Saturated alcohol condenses on particles to grow them to 10 micrometers (µm)
    Count with optical detector
    10 nm – 1,000 nm particle size
    1 – 100,000 (particles/cm3)
    Concentration accuracy ± 20 %
    8
  • Optical Particle Counter
    Counts particles based on laser light scattering
    Six size channels: 300 nm – 10,000 nm
    Smallest size channel = 300 nm – 500 nm
    Limited data-logging memory
    Counting efficiency 50 % @ 300 nm,100 % @ >450 nm
    Results in particles/liter of air
    9
  • Filter Sampling
    Carbon Nanotubes
    NIOSH Method 5040, Diesel Particulate Matter (as Elemental Carbon)
    Thermal-optical analysis, flame ionization detector
    Estimated LoD: 0.3 µg per filter portion
    Precision: 0.19 @ 1 µg Carbon, 0.01 @ 10 – 72 µg Carbon
    SEM/TEM Analysis
    Filter selection: Analyst’s preference or NIOSH Method 7402, Asbestos by TEM
    Bulk sample to assist analyst in ENM identification
    Difficult with under- or over-loaded filter
    Ref: National Institute for Occupational Safety and Health (NIOSH):Methods 5040 and 7402. In NIOSH Manual of Analytical Methods(NMAM), 4th ed. DHHS (NIOSH) Pub. No. 94-113. P.C. SchlechtandP.F. O’Conner (eds.) Cincinnati, Ohio: U.S. Department of Health andHuman Services, Centers for Disease Control and Prevention, NIOSH,
    1994.
    10
  • Case Study: Spraying Carbon Nanotubes
    All work performed in fume hood, HEPA filtered exhaust to outside
    Weigh dry powder
    Add 20 ml water and surfactant
    Sonicate solution inside enclosure and in open-top aqua sonicator
    Spray liquid solution of MWCNTs by use of air brush
    Apply “canned” compressed air to speed drying
    Two rounds of spraying totaling 30 minutes
    11
  • Work Location
    12
  • Spraying MWCNTs
    13
  • Filter Sampling
    Three pairs of filters
    Researcher’s personal breathing zone
    Stationary samples at face of fume hood
    Inside fume hood, next to target
    Pump flow of 3.5 lpm for 82 minutes provides limit of quantification below REL for carbon nanotubes
    14
  • Personal Samples
    15
  • Particle Counters
    CPC logs data every 1 minute
    OPC logs data every 30 seconds, 1-sec. delay
    Background levels before and after ENM handling
    Hand-held from point of operation to PBZusually at face of hood
    16
  • Filter Sampling Results
    17
  • Particle Counter Results
    Three sets of data
    Smallest size channel on OPC (0.3 µm – 0.5 µm)
    Five larger OPC size channels combined (0.5 µm – >5 µm)
    CPC data (0.1 µm –>1 µm)
    Four stages of work
    Background
    Two rounds of prep combined
    Two rounds of spraying combined
    Cleanup
    Compare geometric means, work / background
    18
  • Effect of Background Particulate Levels
    19
  • Comparison of Work and Background Particulate Concentrations (Geometric means)
    OPC Small Size Channel
    OPC Large Size Channels
    CPC
    20
  • Optical Particle Counter MeasurementsSmall- and Large-Size Channels (one scale)
    21
  • Optical Particle Counter MeasurementsSmall- & Large-Size Channels (two scales)
    22
  • 23
  • Conclusions
    Researcher was not exposed to measureable levels of airborne MWCNTs during spraying
    Local exhaust ventilation with HEPA filtration is effective at controlling nanoparticles
    Limitations of particle counters significantly hamper identification of nanoparticles
    Difficult to identify ENMs over normal background
    Can improve sensitivity by activelylowering background particleconcentration
    - Do not need to HEPA filter incoming air
    Photo: Nanowires that emit UV lightCredit: Lorelle Mansfield/NIST
    24
  • Questions?
    michael.blumer@nist.gov
    Photo: A 40-nanometer-wide NIST logo made with cobalt atoms on a copper surface. The ripples in the background are made by electrons, which create a fluid-like layer at the copper surface. Each atom on the surface acts like a pebble dropped in a pond. Credit: J. Stroscio, R. Celotta/NIST
    25