Nanotechnology is expected to be the basis of many technological innovations in the 21st century. Research and development in this field are growing rapidly, resulting in the development of new materials in the nanometer (nm) scale. A nanometer is one billionth of a meter, or roughly one 25-millionth of an inch. Nanoparticles have at least one dimension less than 100 nm. To put things in perspective, the size of a DNA molecule is about 2 nm, simple organic molecules have sizes ranging from 0.5 to 5 nm, and the width of a red blood cell is approximately 5,000 nm.

Nanoparticles exist in a variety of forms and shapes, including tubes, shells, and cylinders. The terms “nanoparticles” and “ultrafine particles” (UFP) are often used synonymously. The great scientific interest of nanoparticles stems from their unique properties, which bridge bulk materials and molecular structures.

Because of the special chemical and functional properties of materials at the nanoscale, nanoparticles are being developed, evaluated, and used in a wide variety of potential applications. The unique properties that make nanoparticles attractive for so many applications also lead to increased health concerns. The high surface-to-volume ratio of nanoparticles allows them to be more reactive than larger particles. Therefore, selection of appropriate personal protective equipment for protection against dermal exposure to nanoparticles is increasingly important in the workplace.

NANOPARTICLE SOURCES Nanoparticles can be created from human-made combustion processes or in fumes associated with any human-made process involving volatilizable material at elevated temperatures. Examples of these processes include polymer fabrication and welding.

A comprehensive review of the sources of nanoparticles appeared in the Journal of the Air & Waste Management Association in 2005. Ultrafine particles in the workplace can be categorized as fumes from hot processes such as welding, refining, and smelting; fumes from incomplete combustion processes within engines and during carbon black manufacture; and bioaerosols, including viruses and endotoxins. Most recently, the concern regarding nanoparticle exposure has centered on intentionally engineered nanoscale components of engineered products and advanced technologies. Engineered nanomaterials (ENMs) exist in many sizes, shapes, and materials and have various chemical and surface properties.

Over the past decade, much more information regarding the health risks of ENMs has been published, particularly in vitro and animal model toxicology studies. However, the epidemiological evidence for health risks is still limited, and much remains unknown regarding ENM exposure. Given the ever-increasing variety of nanomaterials in use, each with the potential to interact with the human body, it is prudent to take precautionary measures following the hierarchy of controls to minimize worker exposures. For most processes and job tasks, airborne exposure to ENMs can be controlled through a variety of techniques such as source enclosure (that is, isolating the generation source from the worker) and a well-designed local exhaust ventilation system equipped with a high-efficiency particulate air (HEPA) filter.

FACTORS AFFECTING PPE SELECTION The following are among the performance criteria that need to be considered whenever selecting PPE to protect against dermal exposure to ENMs:

• penetration (the flow of a chemical through zippers, weak seams, pinholes, cuts, or imperfections on a nonmolecular level that occur without changing the PPE’s properties)

• durability (resistance to wear, tear, abrasions, punctures, and chemical degradation) • dexterity and flexibility

• ability to be decontaminated (for multi-use PPE only)

• comfort

• compatibility with other equipment and the regions where they interface (for example, where gloves and coats overlap)

It is important to recognize that the selection and evaluation of PPE for performance should include a thorough evaluation of the types and degrees of hazards the user may encounter. Assessment of each potential hazard is necessary because not every type or style of PPE may be effective for that hazard, and a combination of protection may be needed. In addition to the inherent hazards associated with the chemical nature of the nanoparticle, several other hazards, including the presence of solvents, may be associated with a particular job task. Additional factors that should be considered include:

• type of work • work duration • material concentration • exposure sources • exposure pathways • body protection areas • frequency and duration of contacts with hazards • size of nanoparticles • special properties (for example, anti-explosion measures in the handling of flammable ENMs or specific protection measures in the handling of reactive or catalytic ENMs) • physical effort of the work • capacity of personnel to work in the assigned PPE ensemble • the worker’s medical or health status • daily work and rest schedule

Currently, there are no regulatory standards specific to ENMs. In the absence of OSHA standards for nanoparticles, section 5(a)(1) of the Occupational Safety and Health Act of 1970 (29 U.S.C. 654), often referred to as the General Duty Clause, can be applied. This clause requires employers to “furnish to each of [their] employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to [their] employees.”

To address concerns regarding the lack of universally accepted guidelines and practices, various government and consensus standards organizations have stepped in to fill the gaps. NIOSH has taken a lead role in conducting research and partnering with other organizations involved in nanoparticle health and safety research. The NIOSH guidance document “Approaches to Safe Nanotechnology: Managing the Health and Safety Concerns Associated with Engineered Nanomaterials” raises awareness of the occupational safety and health issues involved with nanotechnology and makes recommendations on occupational safety and health best practices in the production and use of nanomaterials. Another NIOSH publication, “Workplace Design Solutions: Protecting Workers during the Handling of Nanomaterials,” discusses engineering control options such as chemical fume hoods, nanomaterial handling enclosures, biological safety cabinets, and glove boxes. These and other NIOSH guidance documents are listed in the Resources section at the end of this article.

RECOMMENDED PERSONAL PROTECTIVE CLOTHING AND EQUIPMENT Recommended protective clothing for ENMs includes respirators with HEPA cartridges, closed-toed shoes made of material with low permeability, long pants without cuffs, a long-sleeved shirt, gauntlet-type gloves or nitrile gloves with extended sleeves, and laboratory coats. Disposable over-the-shoe booties are suggested to prevent tracking nanomaterials from the work area.

Body Protection Chemical protective clothing (CPC) should be selected based on the materials being handled and the risk of exposure to prevent both dermal contact and contamination of personal clothing. Some tasks may require workers to handle both solvents and nanoparticles.

For situations involving low-hazard materials and low exposure risk, the use of cotton or cotton-polyester lab coats or coveralls may provide sufficient protection against ENMs. For scenarios involving high hazard materials or high ENM exposure potential, a nonwoven material with low dust retention and low dust release should be used to provide a high level of protection. Protective clothing made of wool, cotton, or other woven fabrics such as polyester should be avoided for handling materials of high concern. Common types of CPC for handling nanoparticle powder include a laboratory coat, long sleeves without cuffs, long pants without cuffs, coveralls, and closed-toe shoes made of low-permeability material.

Respiratory Protection Respirators equipped with HEPA cartridges may be necessary when engineering and administrative controls do not adequately prevent exposures. Current scientific evidence indicates that nanoparticles may be more biologically reactive than larger particles of similar chemical composition and thus may pose a greater health risk when inhaled. Currently, there are no specific limits for airborne exposures to engineered nanoparticles, although occupational exposure limits exist for some larger particles of similar chemical composition.

When determining the need for respirators, it would be prudent to consider the current occupational exposure limits or guidelines (for example, OSHA permissible exposure limits, NIOSH recommended exposure limits, and ACGIH threshold limit values) for larger particles of similar composition; existing toxicologic data on the specific nanoparticle; and the likelihood of worker exposure based on airborne concentration, time exposed, job tasks, and so on.

Eye Protection Full-facepiece respirators provide both respiratory and eye protection. If another type of respirator is used, select appropriate eye protection based on the potential exposure hazard. For higher exposure potential—from airborne dispersion of nanoparticles, for example—tight-fitting, dustproof safety goggles are recommended.

Gloves Wearing good-quality, disposable, single-use polymer gloves is recommended when handling engineered nanomaterials and particulates in liquids. The gloves should be made of neoprene, nitrile, or another chemical-resistant material. Choose gloves only after considering their resistance to the chemical attack by both the nanomaterial and, if applicable, the liquid it’s suspended in. A precautionary approach includes double-gloving, especially when using thinner gloves or when handling materials of high concern. Gauntlet-type or extended-sleeve gloves can protect wrists from exposure covering the gaps between the gloves and the CPC. All gloves should be changed routinely to minimize potential exposure hazards.

Comfort vs. Effectiveness Making appropriate recommendations for dermal protection against ENMs requires a balance between comfort and protection. Garments that provide the highest level of protection, such as an impermeable Level A suit, are also the least comfortable to wear for long periods of time. Garments that probably offer the least dermal protection for ENMs, such as thin cotton lab coats, are the most breathable and comfortable for employees to wear. The key for industrial hygienists is to perform a complete risk assessment to determine the level of protection needed based on the material being used, the task being performed, the site conditions, and the duration of the task.

In 2008, NanoSafe2, a project funded by the European Union, disseminated a report to answer pressing questions about the ability of fibrous filters, body garments, gloves, and other types of PPE to protect against nanoparticles. The report suggested:

• HEPA filters respirator cartridges and masks made with fibrous filters should be used for more efficient respiratory protection for nanoparticles. • Nanoparticles may penetrate through commercially available gloves; at least two layers of gloves should be used for dermal protection. • Workers should avoid wearing cotton and other woven fabrics as they might allow for nanoparticles to penetrate to the skin. Nonwoven fabrics (that is, air-tight materials) seem much more efficient against nanoparticle penetration.

Other organizations are actively engaged in developing guidelines for workers who handle nanomaterials. ASTM International has issued ASTM E2535-07, Standard Guide for Handling Unbound Engineered Nanoparticles in Occupational Settings, which premises exposure control guidance on the principle that, as a cautionary measure, occupational exposures to unbound ENMs should be minimized to levels that are as low as reasonably practicable. Although specific protective clothing is not addressed, the standard advises users to select protective clothing appropriate to the hazard identified and the circumstances of nanoparticle handling by consulting the best available performance data and obtaining the clothing manufacturers’ recommendations based on the properties of the specific unbound engineered nanoparticle of concern.

At this time, it is unknown whether government agencies will pursue additional federal regulation of nanoparticles that would affect the use of protective clothing and equipment for personal protection. However, existing regulations such as OSHA’s PPE standard (29 CFR 1910 subpart I) already require employers to conduct an assessment to identify hazards and then select PPE based on the information gained from the assessment. In lieu of new standards or regulations, federal agencies may develop tailored recommendations on how to reduce worker exposure to nanoparticles. But OSHA standards provide minimum protection, and employers should strongly consider using current information to create best practices that will reduce risk and minimize exposures to nanoparticles.

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