Protecting Workers from Risks Associated with Nanomaterials: Part II, Best Practices in Risk Management

Control banding is likely the most well-developed risk management strategy proposed for use with nanomaterials to date.

• By Marisa L. Kreider, Amanda M. Burns, Gretchen H. DeRose, Julie M. Panko
• Sep 01, 2013

In Part I of this two-part article, we presented strategies and tools for exposure assessment of nanomaterials in industrial settings. Information gathered from the exposure assessment process should aid the OSH professional in identifying sources of nanomaterial release and areas of concern. That information can in turn be used to develop risk management practices to minimize worker exposure, when necessary.

Risk Assessment and Risk Management
Traditional occupational risk assessment involved the comparison of an exposure concentration to an allowable or acceptable concentration. In its simplest form, risk management involves the application of control strategies if the exposure concentration exceeds the allowable concentration. Because there are currently no enforceable occupational exposure limits for nanomaterials, the application of risk management measures in light of exposure assessment results will require significant professional judgment. There are currently a variety of resources available for designing a risk management strategy incorporating contemporary best practices for working with nanomaterials.

Since 2005, a number of documents have been published by governmental health research agencies, NGOs, international standards organizations, and academic groups to address best practices for managing occupational exposure to nanomaterials. These documents focus on protecting workers against exposure to nanomaterials during manufacturing, research and development, or use of the materials. Several basic concepts are nearly universally considered when recommending specific practices to industry. The overarching principles governing the recommendations outlined in each of these reports, while not identical, consider the same idea: Because there is a dearth of information on both toxicity and exposure to nanomaterials, in protecting workers, caution should be taken. Some advocate reducing exposure to be “as low as reasonably practicable” (ALARP), while others advocate a control banding approach, where materials with uncertainty about toxicity or exposure are placed in high-risk bands requiring stringent control measures. The net effect is essentially the same, regardless of what the approach is called: A high degree of protection is recommended where there is potential for worker exposure to nanomaterials.

Control banding is likely the most well-developed risk management strategy proposed for use with nanomaterials to date. Several researchers have developed sophisticated recommendations on how to apply the basic control banding process. Perhaps the best and most widely accepted control banding strategy specific to nanomaterials was developed as part of the "Control Banding (CB) Nanotool"^1,2 An important feature of this framework is that it provides a mechanism to assign a numerical score for health effect severity, as well as for the probability or likelihood of exposure that reduces the conservatism associated with making worst-case assumptions in the event there is no hazard data available. As it becomes available, additional information (including material characteristics and toxicity data) can then be used to refine that estimate of hazard. With respect to probability of exposure, data independent of exposure measurements also can be used to inform about the assigned control band and level of risk management required, including dustiness measurements, quantities of use, number of employees potentially exposed, etc.

Regardless of the basic risk management strategy, most incorporate the basic industrial hygiene hierarchy to protect workers: elimination or substitution, isolation, engineering controls, administrative controls, and personal protective equipment. Each of these topics is discussed below in the context of specific recommendations provided in these reports and key aspects described in Table 1.

Elimination, removing the hazard from the industrial operation in an effort to eliminate worker exposure, is not often a practical consideration in the case of nanomaterials, where these materials are under new development and the true hazard is not often known. Substitution, an alternative approach, is the replacement of a hazardous material with a similar but less-hazardous material. In the absence of information about toxicity for some of these materials, those who advocate the substitution approach do so from the standpoint of exposure and recommend using materials that have a reduced propensity for aerosolization (e.g., binding the nanomaterials in a liquid or solid media)³.

Nearly all guidance that proposes recommendations for managing exposure to nanomaterials advocates for the use of isolation, particularly closed processes or containment rooms, to minimize worker exposure.^3-12 By isolating the nanomaterial, it may be possible to reduce the necessity of other engineering controls or PPE to minimize exposure. In addition to isolation, other engineering controls can be implemented to reduce worker exposure, including local exhaust ventilation at access points for maintenance and cleaning in closed process systems.⁷ Some groups specify the type of filter necessary for the local exhaust ventilation (e.g., HEPA or ULPA [Ultra Low Penetration Air]) based on knowledge about the efficiency of filtration systems in eliminating nano-sized materials.⁸ HEPA filters have been demonstrated to be effective for particles of all sizes.¹³

Administrative controls, such as written safety policies, rules, supervision, schedules, and training with the goal of reducing the duration, frequency, and severity of exposure to hazardous chemicals are also frequently recommended.^14,15

The last control strategy for worker exposure is the use of personal protective equipment, including gloves, protective clothing, and respirators. Because respirator use is typically triggered by exposure concentration and there is, as yet, no occupational exposure limit established for nanomaterials that can aid in identification of an appropriate action level, several of the unique aspects related to the recommended best practices focus on when respirator use should be required. Some advocate using respirators where there is any exposure potential or where nanomaterials have been detected in the air (when engineering and administrative controls do not fully protect against exposure) or using professional judgment to determine whether respirator use is required.⁸ Both ASTM and the British Standards Institute have made recommendations on how to define an OEL to aid in decision-making regarding the use of respirators. ASTM proposes using existing particulate-based standards, such as ambient air quality standards, standards for asbestos, etc., to establish occupational exposure limits for nanomaterials.⁵ The British Standards Institute defines exposure limits based on physical characteristics of the non-nano material. In many cases, these recommendations include using occupational exposure limits that are based on adjustments of the bulk compound exposure limits.¹⁶ Japan’s Ministry of Health, Labour and Welfare (MHLW) recommends the use of respirators based on the tasks being performed, rather than the material being used.⁷ However, it is unclear as to whether any of these proposed methods are suitable or sufficient for protecting against potential hazards. OSH professionals must individually decide how to implement PPE requirements, particularly for respirators, when deciding to introduce nanomaterials into their processes.  he control banding strategy as outlined by Paik, et al. (2008) and Zalk, et al. (2009) can aid in this decision-making.

While most of the strategies and specific risk management measures mentioned above are reactionary (i.e., they are instituted once a company or facility has decided to incorporate a nanomaterial into their process), there are also precautionary and preventative strategies that can be incorporated into the research and development of new nanomaterials to reduce potential worker risk. Recently, NIOSH has supported a nationwide initiative for companies to employ a "Prevention through design" (PtD) strategy when managing risks to nanomaterials.¹⁴ Through the PtD strategy, companies incorporate design considerations into the manufacturing process to reduce the likelihood of risk to workers. The consideration of this concept during the initial planning stages of the process or facility can help to ensure that high-risk situations do not occur.¹⁷ This approach could incorporate the following types of considerations, along with many others, to meet the goals of the PtD strategy:

• Development of lower-toxicity raw nanomaterials for use in the process
• Physical manipulation of raw nanomaterials into forms that reduce exposure (e.g., slurries, pellets)
• Development of manufacturing processes that reduce workers’ contact with raw nanomaterials during the design phase

Collectively, there are many sources of information and guidance for developing risk management programs. However, to date, the existing guidance on risk management of nanomaterials is not industry- or material-specific.¹⁸ Therefore, companies may need to take into consideration the unique aspects of their industry in designing a risk management strategy for nanomaterials.

Conclusions
The field of nanotechnology is rapidly developing. There are many tools available to help protect workers at all stages of development, from research to commercialization. It is essential that OSH professionals are familiar with the available strategies for understanding exposure and managing risks so effective programs can be instituted to reduce worker risk and prevent future liability.

References

1. Paik, S.Y., D.M. Zalk, and P. Swuste, Application of a pilot control banding tool for risk level assessment and control of nanoparticle exposures. Ann Occup Hyg, 2008. 52(6): p. 419-28.
2. Zalk, D.M., S.Y. Paik, and P. Swuste, Evaluating the Control Banding Nanotool: a qualitative risk assessment method for controlling nanoparticle exposures. J Nanopart Res, 2009. 11: p. 1685-1704.
3. BAUA, Guidance for Handling and Use of Nanomaterials at the Workplace. 2007.
4. AFNOR, Occupational Risk Management Applied to Engineered Nanomaterials Based on a Control Banding Approach. 2009, ISO.
5. ASTM, Standard Guide for Handling Unbound Engineered Nanoscale Particles in Occupational Settings. 2007.
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11. USDOE, Approach to Nanomaterial ES&H. 2008.
12. Harford, A., et al., Current OHS Best Practices for the Australian Nanotechnology Industry: A Position Paper by the NanoSafe Australia Network. 2007, NanoSafe Australia Network.
13. Steffens, J. and J. Coury, Collection efficiency of fiber filters operating on the removal of nano-sized aerosol particles: I—Homogeneous fibers. Separation and Purification Technology, 2007. 58(1): p. 99-105.
14. NIOSH. Prevention Through Design. 2012 June 25, 2012 [cited 2012 9/7/2012]; Available from: http://www.cdc.gov/niosh/topics/ptd.
15. Kulinowski, K. and B. Lippy, Training workers on risks of nanotechnology. 2011, NIEHS.
16. British Standards, Nanotechnologies- Part 2: Guide to Safe Handling and Disposal of Manufactured Nanomaterials. 2007.
17. Ostiguy, C., et al., Best Practices Guide to Synthetic Nanoparticle Risk Management. 2009, IRRST.
18. ICON, et al., A review of current practices in the nanotechnology industry: Phase Two. Survey of current practices in the nanotechnology workplace. 2006, UCSB.

This article originally appeared in the September 2013 issue of Occupational Health & Safety.