NIOSH Proposes Occupational Exposure Levels for Carbon Nanotubes and Nanofibers

January 12, 2011

Late last year, the National Institute for Occupational Safety and Health (“NIOSH”) initiated a public comment process on its draft Current Intelligence Bulletin Occupational Exposure to Carbon Nanotubes and Nanofibers. Written comments on the draft document will be accepted until 5:00 p.m. EDT on February 18, 2011. Carbon nanotubes (“CNTs”) and carbon nanofibers (“CNFs”) are utilized in a variety of industrial and biomedical applications and are handled in research facilities and industrial plants.

Relying on several animal studies that “consistently show that relatively low mass doses of CNT are associated with early-stage adverse lung effects in rats and mice,” including pulmonary inflammation and fibrosis, NIOSH has proposed a recommended exposure limit (“REL”) of 7 μg/m3 elemental carbon (EC) as an 8-hour time-weighted average (“TWA”) respirable mass airborne concentration. This proposal follows a similar draft related to occupational exposure to titanium dioxide, which was drafted in 2005, was subjected to peer review in 2006, and is currently under further development.

Although the REL is proposed to be set at the lowest airborne CNT and CNF concentration that can be accurately measured by NIOSH procedures, this level is above that at which NIOSH suggests that an excess risk of adverse lung effects is predicted.

Therefore, in addition to proposing an REL, NIOSH is suggesting recommended practices for employers and employees to further minimize exposure to airborne concentrations of CNT and CNF. NIOSH is proposing that employers:

  • 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 workers health.
  • Identify and characterize processes and job tasks where workers come in contact with bulk (“free-form”) CNT and CNT-containing materials (e.g., composites).
  • When possible, substitute a non-hazardous or less hazardous material for CNT and CNF when feasible. 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 on 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 REL of 7.0 μg/m3 using NIOSH Method 5040 or an equivalent method. 
  • 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 on how to use appropriate controls, work practices, and personal protective equipment to minimize exposure.
  • Provide facilities for hand-washing and encourage workers to make use of these facilities before eating, smoking, or leaving the worksite.
  • Provide facilities for showering and changing clothes, with separate facilities for storage of non-work clothing, to prevent the inadvertent cross-contamination of non-work areas (including take-home contamination).
  • Use light-colored gloves, lab coats, and work bench surfaces to facilitate observation of contamination by dark CNT and CNF.
  • Develop and implement procedures to deal with clean-up of CNT and CNF spills and de-contamination of surfaces.
  • When respirators are provided for worker protection, comply with the OSHA respiratory protection standard found at 29 CFR § 1910.134.

NIOSH’s recommendations can be implemented in coordination with an auditing process that can ensure that a facility’s CNT and CNF operations are designed in a manner that is consistent with the most current scientific and occupational safety information applicable to these operations. Third-party participation in the auditing process provides additional credibility that can serve to reduce potential liability in the event of any claim arising from injuries alleged to have been caused by workplace exposures to CNTs and CNFs.

NIOSH is proposing the following recommendations for workers: 

  • Ask your supervisor for training on how to protect yourself from the 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, or eyewear that your employer might provide.
  • Avoid handling CNT and CNF in a “free particle” state such as a powder.
  • 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 either a HEPA-filtered vacuum cleaner or wet wiping methods.
  • Do not store or consume food or beverages in workplaces where bulk CNT or CNF or where CNT- or CNF-containing materials are handled.
  • Do not use dry sweeping or air hoses to clean work areas.
  • Prevent the inadvertent contamination of non-work areas, including take-home contamination, by showering and changing into clean clothes at the end of each work day. 

This article was prepared by Paul C. Sarahan from Fulbright's Environmental Law Practice Group. Paul Sarahan is Counsel in Fulbright & Jaworski L.L.P.’s Houston office, where he consults and advises clients on environmental, health and safety issues including enforcement, auditing, environmental litigation, permitting, nanotechnology and workplace safety issues. In 2009, Paul was honored as one of the "Top Ten Experts in Environmental, Health, and Safety Issues Related to Engineered Nanomaterials," by Nanotechnology Law & Business, Vol. 6, No. 1, Spring 2009. Paul has written and spoken extensively on environmental, health and safety issues related to nanomaterials operations, including: "Emerging Safety Issues at University Nanomaterials Labs: Calling Officer Buckle and Gloria," Nanotechnology Law & Business, Winter 2009; "Evaluating a Nanomaterial Operation's Compliance with Environmental Requirements: Selected Environmental Audit Statutes and Policies," Nanotechnology Law & Business, Vol. 6, No. 2, Summer 2009; and "Auditing as a Tool for Ensuring Compliance with Nanotechnology Safety Requirements," Nanotechnology Law & Business, Vol. 5, No. 4, Winter 2009.