NIOSH Recommends Lower REL for Carbon Nanomaterials

The agency's new Current Intelligence Bulletin recommends that exposures to carbon nanotubes and carbon nanofibers be kept below the recommended exposure limit of 1 μg/m3 of respirable elemental carbon as an eight-hour TWA.

NIOSH released an important new Current Intelligence Bulletin on April 24 that establishes it as the first federal agency to issue recommended exposure levels for carbon nanotubes and carbon nanofibers, based on research showing exposures can cause pulmonary fibrosis, inflammatory effects, and granulomas in lab animals exposed to them by inhalation. NIOSH said it considers these animal studies relevant to human health risk because similar lung effects have been observed in workers exposed to respirable particulates of other materials in dusty jobs.

NIOSH issues Current Intelligence Bulletins to disseminate new scientific information about occupational hazards. The agency had issued a draft CIB about these substances in 2010 in which it proposed a REL of 7 μg/m3 elemental carbon as an eight-hour TWA, which was set at the upper limit of quantitation (LOQ) for NIOSH Method 5040. In the draft CIB, NIOSH acknowledged workers could still have an excess risk of developing early-stage pulmonary effects, including fibrosis, if exposed over a full working lifetime at the proposed REL. It now recommends the lower REL "in view of these health risks, and ongoing improvements in sampling and analytical methodologies," according to the new document.

The 184-page Current Intelligence Bulletin recommends that exposures to carbon nanotubes and carbon nanofibers be kept below the recommended exposure limit of 1 μg/m3 of respirable elemental carbon as an eight-hour TWA. It contains recommendations for employers and for workers. How many workers are potentially exposed to nanomaterials cannot be determined with certainty, according to the agency, but it reports demand for nanomaterials is expected to grow in the next decade as their use increases in energy-saving products, consumer goods, and medical devices. These nanomaterials also are in plastics, ceramics, paints, coatings, and electronics.

The new CIB is available at

The recommendations for workers include these:

  • Ask your supervisor for training in how to protect yourself from potential hazards associated with your job, including exposure to CNT and CNF.
  • Know and use the exposure control devices and work practices that keep CNT and CNF out of the air and off your skin.
  • Understand when and how to wear a respirator and other personal protective equipment (such as gloves, clothing, eyewear) that your employer might provide.
  • Avoid handling CNT and CNF in a "free particle" state (e.g., powder form).
  • Store CNT and CNF, whether suspended in liquids or in a powder form, in closed (tightly sealed) containers whenever possible.
  • Clean work areas at the end of each work shift (at a minimum) using a HEPA-filtered vacuum cleaner or wet wiping methods. Dry sweeping or air hoses should not be used to clean work areas.
  • Do not store or consume food or beverages in workplaces where bulk CNT or CNF, or where CNT- or CNF-containing materials, are handled.
  • Prevent the inadvertent contamination of nonwork areas (including take-home con-tamination) by showering and changing into clean clothes at the end of each workday.

Recommendations for employers include these:

  • Use available information to continually assess current hazard potential related to CNT and CNF exposures in the workplace and make appropriate changes (e.g., sampling and analysis, exposure control) to protect worker health. At a minimum, follow requirements of the OSHA Hazard Communication Standard [CFR 1910.1200(h)] and the Hazardous Waste Operation and Emergency Response Standard [29 CFR 1910.120].
  • Identify and characterize processes and job tasks where workers encounter bulk ("free-form") CNT or CNF and materials that contain CNT/CNF (e.g., composites).
  • Substitute, when possible, a nonhazardous or less hazardous material for CNT and CNF. When substitution is not possible, use engineering controls as the primary method for minimizing worker exposure to CNT and CNF.
  • Establish criteria and procedures for selecting, installing, and evaluating the performance of engineering controls to ensure proper operating conditions. Make sure workers are trained in how to check and use exposure controls (e.g., exhaust ventilation systems).
  • Routinely evaluate airborne exposures to ensure that control measures are working properly and that worker exposures are being maintained below the NIOSH REL of 1 μg/m3 using NIOSH Method 5040.
  • Follow exposure and hazard assessment procedures for determining the need for and selection of proper personal protective equipment, such as clothing, gloves, and respirators.
  • Educate workers on the sources and job tasks that may expose them to CNT and CNF, and train them about how to use appropriate controls, work practices, and PPE to minimize exposure.
  • Provide facilities for hand washing and encourage workers to make use of these facilities before eating, smoking, or leaving the work site.
  • Provide facilities for showering and changing clothes, with separate facilities for storage of non-work clothing, to prevent the inadvertent cross-contamination of nonwork areas (including take-home contamination).
  • Use light-colored gloves, lab coats, and workbench surfaces to make contamination by dark CNT and CNF easier to see.
  • Develop and implement procedures to deal with cleanup of CNT and CNF spills and decontamination of surfaces.

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