In the first recommended exposure limit for nanotechnology set by a government agency, NIOSH says that carbon nanotubes (CNTs) and nanofibers (CNFs)should be considered a respiratory hazard and worker exposure to those materials should be limited to no more than 1 microgram per cubic meter of air. This is the lowest airborne concentration that can be accurately measured.
CNTs and CNFs are only two of many types of nanomaterials created through nanotechnology, which is described as the manipulation of matter on a microscopic scale. This matter is smaller than what has been studied for the past 100 years by material scientists; their size gives them new and different properties that have not been seen before. CNTs and CNFs are being incorporated into different products to increase strength, durability, versatility, heat resistance, and other useful properties. These products include plastics and ceramics, paints and coatings, textiles, and electronics. Though it cannot be determined with certainty how many workers are currently potentially exposed to these nanomaterials, demand for CNTs and CNFs is expected to grow over the next decade with increasing use in medical devices, structural materials, consumer goods, and energy-saving products.
Recent results from experimental animal studies with rodents indicate that exposure to CNTs and CNFs may pose a respiratory hazard if inhaled. NIOSH's recommendations are expected to assist industry in establishing good risk management practices for controlling occupational exposures to free, unbound CNTs and CNFs during their manufacture and industrial use.
Suggestions for companies that manufacture or use carbon CNTs or CNFs:
- Apply strategic approaches for controlling occupational exposures, giving priority to engineering controls that enclose processes where CNTs or CNFs could be released into the air, such as transfer of the dry, fine powders from one container to another.
- Educate and train workers on the safe handling of bulk quantities of CNTs and CNFs or CNT-and CNF- enabled products.
- Train workers on the proper use of engineering controls, administrative controls, and safe work practices. These are standard risk management practices that employers have followed for many decades to reduce worker exposures to dusts and other materials in workplaces.
- Establish health surveillance and medical screening programs to help identify early signs of respiratory disease. Such surveillance programs can assist in determining if additional exposure control measures are needed, and if individual medical attention is needed.
Consumers are unlikely to be exposed to CNTs or CNFs in their free, dry powder form. These materials are almost always bound up or incorporated into a final product as a very small percentage of the final formula. It is the free form of CNTs and CNFs that creates the greatest possibility for inhalation exposure and the greatest concern. The workplace is the most likely place for this type of exposure, says NIOSH.