Dr. Armin Ansari, Centers for Disease Control and Prevention (CDC), and Dr. Matt Heavner, Office of Science and Technology Policy (OSTP), the White House, provided opening remarks on the possible motivation for adopting SI units for radiation measurements in the United States. They provided different perspectives, but both speakers endorsed actions that support scientific and technological advances and improve the nation’s ability to respond to large-scale disasters.
Dr. Ansari stated that units of radiation measurements need to be standardized internationally for the purposes of commerce and science, and in his view standardization equates to adoption of SI. He explained that the discussions during this workshop are restricted to adopting SI units for radiation measurements only and not for other measurements such as distance, volume, and temperature. Changing the units for these other measurements would require considerable effort by members of the public to replace a familiar system with a new one.
Dr. Heavner spoke about his office’s mandate, which is to advise the President and others within the Executive Office of the President on the effects of science and technology on domestic and international affairs. The three main goals of the office are
- Ensure that policy decisions at the White House are informed by the best science.
- Understand how policy decisions at the White House affect the scientific enterprise, nationally and internationally.
- Lead interagency efforts to develop and implement sound science and technology policies.
Dr. Heavner recognized that these three goals are relevant to adoption of SI units. He also said that communicating information related to radiation can be complex even among experts because of the potential for misuse of radiation quantities, for example, when describing total dose and dose rate. He acknowledged that using two systems of radiation measurements complicates communication.
The United States has been taking steps toward adopting SI units for all measurements for many years. Drs. Ansari and Heavner provided the time line of U.S. policies toward adopting SI. Some milestones not mentioned by the two presenters, likely because of time limitations, were filled in by the rapporteur of this proceedings to provide a more complete timeline to the reader.1
The Metric Act of 1866 legally recognized the metric system in the United States. In 1875, the United States solidified its commitment to the development of the SI by becoming one of the original 17 nations to sign an international agreement, known as the Meter Convention. The Meter Convention established—among other organizations—the General Conference on Weights and Measures (French: Conférence générale des poids et mesures or CGPM), a conference made up of official delegates of member nations. CGPM established the SI, the modern metric system of measurement, in 1960.
In 1968, Congress authorized a 3-year feasibility study of adopting SI. The study was conducted by the U.S. Department of Commerce (De Simone, 1971). It concluded that the United States would eventually join the rest of the world in the use of the metric system and that conversion to the metric system was in the best interests of the country, particularly in view of the importance of foreign trade. This recommendation led to the passage of the Metric Conversion Act of 1975 (PL 94-68; Ford, 1975), which called for a national policy of coordinating and planning for the increased use of the metric system for U.S. trade and commerce.
The adoption of SI was anticipated to become mandatory in the 1970s, but the movement to adopt SI stalled. Congress included new encouragement to adopt SI in the Omnibus Trade and Competitiveness Act of 1988.
1 The rapporteur used primarily this source for information: http://physics.nist.gov/cuu/Units/international.html.
This legislation aimed to enhance the competitiveness of the U.S. industry in international markets and designated the metric system as the preferred system of weights and measures for U.S. trade and commerce. The legislation states that “the federal government has a responsibility to assist industry, especially small business, as it voluntarily converts to the metric system.”2 To accelerate the use of the metric system within the federal government, President George Bush signed Executive Order 12770, Metric Usage in Federal Government Programs, in 1991. The order required all agencies to develop conversion plans within the period 1993-1996. It also gave the National Institute of Standards and Technology (NIST) the primary responsibility to direct and coordinate the metric transition; the institute’s role was advisory only. Several agencies took actions following the 1991 directive toward adopting SI. The Nuclear Regulatory Commission’s (NRC’s) actions were discussed in some detail at the workshop.
The NRC examined the possibility of exclusively3 using SI units for radiation measurements as early as 1980, when it contracted with Oak Ridge National Laboratory to provide a cost–benefit analysis (CBA) of adoption of SI units in health physics (Eichholz et al., 1980). The agency published its Metrication Policy (57 FR 46202) in 1992 in response to the 1991 Executive Order. The NRC policy “supports and encourages the use of the metric system of measurement by licensed nuclear industry.”4 The NRC publishes new regulations, regulatory guides, and other documents in both SI and conventional units to facilitate use of SI units for radiation measurements. However, the metrication policy requires that event reporting and emergency response communications between the NRC’s licensees (including the nuclear power industry), the NRC, and state and local authorities be in conventional units.
The NRC’s policy statement also called for the Commission to reexamine whether the metrication policy would need to be modified after 3 years of implementation. In 1995, the Commission decided that the agency did not need to change its policy and considered the agency’s conversion to the metric system to be complete. However, NRC staff revisited the topic in 2012 and proposed to the Commission that it increase use of SI units for radiation measurements in the agency’s regulations to—among other reasons—increase alignment with international standards and practices by other countries. The proposal was rejected by the Commission by a three-to-two vote. Workshop participant Mr. William Ostendorff, who was an
2 H.R. 4848 (100th): Omnibus Trade and Competitiveness Act of 1988.
3 Workshop participant Dr. Fred Mettler argued that the term “exclusive” is not correct because there will always be some exceptions. The rapporteur of this Proceedings of a Workshop agrees with this argument and uses the term “exclusively” to denote the predominant use of SI (or conventional) units and that some exceptions may apply.
4 See: NRC’s Metrication Policy (57 FR 46202), 1992.
NRC commissioner at the time (he served on the Commission from April 2010 to June 2016), said that the Commission rejected the staff’s proposal because there was no evidence that the adoption of SI units for radiation measurements would improve worker and public safety or nuclear plant safety and security. Three of the commissioners stated that they had concerns that adoption of SI units could negatively impact nuclear power plant safety.
As discussed in Chapter 5, many workshop participants suggested that the NRC’s refusal to require SI units for radiation measurements is inhibiting federal, state, and local governments from adopting the SI units for radiation measurements.
A number of national and international organizations have endorsed the use of SI units for radiation measurements (see Table 1.1). Two of these national organizations (National Council on Radiation Protection and Measurements [NCRP] and NIST) and one international organization
TABLE 1.1 Endorsement of Use of SI Units by National and International Organizations
|Institution||Reference or Year of Endorsement|
|National Institute of Standards and Technology||Taylor and Thompson, 2008; Thompson and Taylor, 2008|
|National Council on Radiation Protection and Measurements||NCRP, 1985|
|Health Physics Society||Roessler, 1984; Health Physics Society, 2012|
|Conference of Radiation Control Program Directors, Inc.||CRCPD, 2000|
|International Commission on Radiation Units and Measurements||1975|
|International Commission on Radiological Protection||ICRP, 1977|
|United Nations Scientific Committee on the Effects of Atomic Radiation||1982|
|International Atomic Energy Agency||1982|
(International Commission on Radiation Units and Measurements [ICRU]) were represented at the workshop. Specifically, Dr. Paul DeLuca, University of Wisconsin School of Medicine, Madison, spoke in his capacity as vice chairman of ICRU; Dr. Steven Simon, National Cancer Institute (NCI), spoke in his capacity as vice president of NCRP’s Program Area on Radiation Measurements and Dosimetry; and Dr. Ronaldo Minniti represented NIST.
ICRU, which is primarily concerned with the physical aspects of radiation, and the International Commission on Radiological Protection (ICRP), which is primarily concerned with the biological effects of radiation and radiation protection, adopted and recommended the exclusive use of the SI units for radiation measurements in 1975 and 1977, respectively. Dr. Paul DeLuca emphasized that although it is an international organization, ICRU has had several U.S. scientists in leadership roles since the early years of its establishment. Therefore, the opinions and recommendations that this international organization issues also represent the thinking of prominent U.S. scientists, not only scientists from other countries. The main motivation for ICRU to recommend the use of SI units for radiation measurements is to ensure accurate and conformal communications among scientific organizations.
NCRP recommended in 1985 that the United States gradually adopt SI units for radiation measurements, but the recommendation has not been implemented. The NCRP recommended the simultaneous use of SI and conventional units (referred to as present units in that report) for a period of 2 years and the exclusive use of SI and elimination of conventional units over a 5-year transition period, that is, by 1990 (NCRP, 1985). However, in a 2010 guide for decision makers who respond to radiological or nuclear terrorism incidents (NCRP, 2010), NCRP endorsed the use of conventional units in emergency response and recommended that the corresponding SI units be displayed in parentheses. Dr. Simon, NCI, clarified that this newer recommendation was not a reversal of NCRP’s 1985 recommendation; it was a necessary adjustment to the previous recommendation for addressing a new threat—radiological and nuclear terrorism incidents. NCRP acknowledged that first responders and decision makers would face difficulties converting from conventional units for surface contamination (disintegrations per minute per unit area) to SI units (Becquerel per square centimeter).
The workshop discussions summarized in this chapter can be organized in the following theme (Theme 1):
The United States has a long history of government policies supporting the adoption of SI units for all measurements. National and international organizations have recommended the exclusive use of SI units for radiation measurements for more than 30 years. However, the United States continues to use conventional units for radiation measurements. As a result, most radiation professionals in the United States must understand both conventional and SI units for radiation measurements and make conversions between the two.