We thank Peter Hatto for reminding readers about the principle of consensus on which the International Organisation for Standardization (ISO) process is based. In fact, the main objective of our article was to ensure that such a consensus is based on informed decisions and is reached as a result of all stakeholders and experts in the global community participating actively in the ISO process. We would like to reiterate that in the presence of incomplete risk information about nanomaterials, prudent measures should be taken to minimize exposure in the workplace. However, this does not require occupational exposure limits (OELs) to be established before any actions can be taken and, given the limited amount of health information, it may be premature to recommend OELs for specific nanomaterials. The problem with "assumed" OELs - such as those described in BSI PD 6699-2 - is that they could have adverse human and societal effects if used within the traditional riskmanagement framework. Specifically, they might not be protective enough and give a false sense of security leading to potential adverse health effects in the future. Or they might be overly protective, requiring employers to implement unnecessary exposure mitigation techniques (for example, comprehensive engineering controls) that could be prohibitively costly and, therefore, unduly restrict innovation, and/or require workers to wear highly protective personal protective equipment that may introduce other health and safety risks. Moreover, technology may not exist to assess exposure using the "assumed" OEL metric of interest. Instead, risk-management practices that focus on controlling nanomaterial emissions would be a more prudent approach until adequate toxicity data are available to conduct a quantitative assessment of risk. For example, the pharmaceutical industry has developed performance-based approaches for controlling exposure to pharmaceutical drugs with limited toxicity data. In this approach, air monitoring and wipe-test data are used to evaluate the effectiveness of performancebased controls to ensure that optimum performance is maintained. Although, this approach has been successful in the pharmaceutical industry, other proactive risk-management approaches have been prescribed for protecting workers exposed to engineered nanomaterials. These take into account information on the hazard potential of the nanomaterial, its physicochemical properties and the potential for worker exposure. Finally, it was not our intention to suggest that the UK could convert a national standard into an international standard against the wishes of the international community, although we do note that the BSI website claims a history of "converting" BSI standards into ISO standards. The technical committee for nanotechnologies (ISO TC 229) has a critical role in establishing elements of proactive risk-assessment and risk-management frameworks for nanotechnology workplaces based on science and a global consensus among participating member countries. We therefore look forward to continuing our active engagement with the commitee.
Vladimir Murashov, National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, US Department of Health and Human Services, Washington, DC 20201