As noted in Theme 2 in the previous chapter, SI units for radiation measurements are finding increasing use in the United States. Many workshop participants said that the exclusive use of SI units is bound to occur sometime in the future. However, at present there is a large variability in the degree of adoption of SI units for radiation measurements within the U.S. government and the intent to use SI units exclusively for radiation measurements in the near future. As a result, radiation professionals in the United States must understand both systems and be able to make conversions between the two.
This chapter examines views on whether the continuing use of conventional units for radiation measurements is problematic. It also summarizes opinions of the workshop participants on the benefits and challenges of the exclusive use of SI units.
One focus of the workshop discussions was on whether the continued use of conventional units for radiation measurements is problematic for emergency response, most notably the response to the 2011 Fukushima Daiichi Nuclear Power Plant accident in Japan. Several examples were provided by workshop participants showing how the use of conventional units for radiation measurements complicated their agency’s response to the accident. It also placed their agency’s credibility and trust in jeopardy because of near-miss conversion mistakes and related issues.
Ms. Rajah Mena, who supported DOE’s response to the Fukushima nuclear plant accident, said that DOE’s data entry experts who were receiving environmental monitoring information from the Japanese in SI units and converting them to conventional units made conversion mistakes. These mistakes resulted in underestimations and overestimations of radioactive contamination and could have had serious consequences had they not been caught. Still, the conversion mistakes had a negative impact on DOE’s response because they caused delays in assessing environmental contamination: the conversions had to be repeated and the correct data re-uploaded to databases. Consequently, communicating information on environmental contamination with the various stakeholders was also delayed.
DOE faced additional delays during its response to the Fukushima nuclear plant accident because of the need to produce radiation contamination mapping products using both SI and conventional units, or a combination of the two systems, depending on the stakeholder who was requesting the maps. Ms. Mena said that it would take about 30 minutes to produce each map and, because of the large number of maps produced, there was less time available for data checks and reviews. Reducing the available time to review the data increased the risk of errors.
Two workshop participants who were not directly involved in the Fukushima nuclear plant accident response during the first few critical days were surprised that DOE and others faced conversion issues because such conversions can be made using computers.
The use of both conventional and SI units was problematic for DOD during Operation Tomodachi1 because the two sets of units were sometimes improperly annotated and communicated, and conversion from one system to the other introduced errors and delays. As a result, DOD recommended the exclusive use of SI units for radiation measurements in a technical after-action report.
Dr. Armin Ansari, CDC, made a typographical error after converting from SI to conventional units (he typed microsievert instead of milli-sievert) while communicating with a colleague stationed in Japan during the Fukushima nuclear plant accident. The content of the communication was Japan’s Ministry of Agriculture, Forestry, and Fisheries protocol for testing and release of cattle. Dr. Ansari realized his mistake and was able to correct it before any harm was done.
A workshop participant quoted the Association of State and Territorial Health Officials’ report (ASTHO, 2012, p. 6), which states that “the difference in radiation units used in the United States and other countries was a source of confusion” when interpreting radiation data. Another workshop
1 Operation Tomodachi was DOD’s operation to provide disaster relief to Japan following the 2011 Great East Japan Earthquake and Tsunami.
participant quoted a second report by Dr. Charles Miller, chief of CDC’s Radiation Studies Branch at the time, who stated “the fact that traditional units are generally considered obsolete outside of the U.S. makes it imperative that we quickly and fully adopt SI units for all of our guidance and communication materials related to radiation and its safety. This will remove one potential source of error and confusion in the event of another radiation incident of the magnitude and world-wide impact of Fukushima” (Miller, 2012, p. 4).
Several other workshop participants commented that the continuing use of conventional units during the Fukushima response was problematic. For example, Dr. Steven King, director of health physics at Penn State Hershey Medical Center, said that the need to convert from/to SI “made a tense situation even tenser”; Mr. Michael Boyd, EPA, described the situation as “confusing.”
The confusion extended to communicating information to the public. Mr. Andrew Scott, Department of Homeland Security (DHS), said that “it was hard to educate the public in two units.” Dr. David Ropeik, an expert in risk communication and currently an instructor at Harvard University, and Ms. Jessica Wieder, EPA, provided examples of news articles in which conventional and SI units were used interchangeably (The New York Times [Tabuchi, 2011] and The Wall Street Journal [Naik, 2011]). This made it difficult for members of the public to understand the health significance of the reported numbers. Dr. Ropeik and Ms. Wieder thought that it is possible that the writers of the news articles did not understand that they had interchanged systems.
A few workshop participants expressed an opposite opinion: that the continuing use of both conventional and SI units for radiation measurements is justified and is not problematic.
Dr. Nicholas Dainiak, director of REAC/TS, explained why his center needs to train its staff to use both SI and conventional units for radiation measurements. REAC/TS is a deployable asset of DOE with two missions related to response to a radiological incident:
- Deliver education and training to emergency responders and others.
- Provide emergency radiation medicine advice and consultation to medical professionals and other health care providers.
Dr. Dainiak noted that local first responders primarily use conventional units, and medical professionals primarily use SI units, especially when they are concerned with acute radiation syndrome.
Former NRC Commissioner Mr. William Ostendorff stated that in his view, the NRC did not face any challenges in responding to the Fukushima
nuclear plant accident related to the use of conventional units in the United States. He did acknowledge that other agencies might have faced difficulties.
Dr. Mettler stated that there are no reports of anyone dying during the response to the Fukushima nuclear plant accident because of a conversion mistake. Although others agreed with his statement, they pointed to the many near-miss mistakes that occurred during the accident that could have had severe consequences, if left uncaught and uncorrected.
Workshop participants cited several benefits that could result from the exclusive use of SI units for radiation measurements. These benefits fell under the following four broad categories (described in the sections below):
- alignment of the United States with international practice
- traceability to the national standard
- communications with the public
- simplicity of SI
Alignment of the United States with International Practice
The United States is the only large country in the world that does not use SI units for radiation measurements. Burma and Liberia are often listed as the other two countries that do not use SI.2 Several workshop participants commented that it is important for the United States “to speak the same language” as the rest of the world to
- facilitate emergency response to radiological incidents. This was the most emphasized application during the workshop. Two participants (Dr. Armin Ansari, CDC, and Dr. Stephen Musolino, Brookhaven National Laboratory) said that radiation emergencies are global, and that no matter how limited the expected health consequences, there will be widespread public concern and political and media interest nationally and internationally. Therefore, there is a need for consistent and accurate information to help ensure the effectiveness of the response to the radiological incidents and to promote international cooperation in the response.
2 A workshop participant noted that Burma and Liberia either adopted SI the past couple of years or have plans to adopt SI. The rapporteur was not able to confirm this information using official government sources.
Ms. Rajah Mena, DOE, noted that with the rest of the world already using SI units, the United States would be at a disadvantage if a radiological incident was to happen domestically. Agencies that support responses to international incidents, such as the IAEA, use SI units. In her view, the United States would face the same challenges during a domestic response to a radiological incident as it did during the Fukushima nuclear plant accident, unless it adopts the SI units for radiation measurements. Ms. Mena has participated in a number of international activities, including delivering emergency response training courses and observing international exercises. She commented that when she interacts with international radiation experts, she has to make unit conversions in her head and often second-guesses whether they are correct.
- increase international market prospects. Ms. Binika Shah, senior project manager at the World Nuclear Association, was not present at the workshop but provided comments through a workshop participant.3 She commented that consistency and harmonization could help support the U.S. nuclear power industry’s access to international markets. Mr. Peter Burgess, Radiation Metrology Ltd., United Kingdom, noted that the continuing use of conventional units in the United States adds to the cost of importing or exporting labor, because additional training is required to deal with the different units for radiation measurements. Adoption of SI units would help with the competitive economic success of the U.S. instrumentation industry.
- promote scientific understanding. Mr. Michael Boyd, EPA, and Dr. Vincent Holahan, NRC, noted that when U.S. radiation experts work with international experts at agencies such as the Nuclear Energy Agency, the IAEA, and the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), they have to use SI units exclusively. Dr. Paul DeLuca, University of Wisconsin School of Medicine, Madison, added that consistency in units allows for simple, straightforward comparisons between experiments, investigative teams, and countries.
Traceability to the National Standard
NIST maintains national standards for radiation dose and disseminates these standards through calibrations of radiation detection instruments. Dr. Ronaldo Minniti, NIST, noted that over one million radiation detection instruments, including ionization chambers, optically stimulated lu-
3 Ms. Shah’s input was transmitted by Mr. Willie Harris, Exelon Nuclear.
minescent and thermoluminescent dosimeters, solid-state detectors, survey meters, electronic personal dosimeters, and portal monitors, are calibrated annually in the United States to ensure traceability to the national standard and therefore the accuracy of measurements performed. The calibrated instruments are used by radiation workers and users in medicine, radiation protection, instrument manufacturers, U.S. military, emergency response, and homeland security.
Dr. Minniti said that the ability to transfer the primary standard measurement of dose maintained at NIST through the traceability chain to end users of instruments is currently challenged by the mixed use of SI and conventional units. This is reflected during comparison measurements between facilities and during blind tests conducted between NIST and end users.
Communications with the Public
Workshop participants engaged in a vigorous discussion about whether the adoption of SI units for radiation measurements could improve communications with the public on radiation-related issues. Public communication experts Ms. Jessica Wieder, EPA, and Dr. David Ropeik, Harvard University, said that the public neither cares about nor understands radiation units, but it does care about what the numbers and associated units mean in terms of health effects. However, both participants acknowledged that the continuing use of a mix of SI and conventional units for radiation measurements by the government and other organizations complicates communications with the public for two reasons:
- Measures of radiation contamination and dose in SI and conventional units vary by a large degree and therefore may appear to the public as inconsistent. This can create distrust toward the sources that report these numbers, primarily the government, and may lead members of the public to ignore advice on how they should behave during emergencies.
- Members of the public may need to do conversions from one system to the other during a personal or general emergency because the information they receive is in both SI and conventional units. The conversions they make can be wrong, resulting in misinformation and unnecessary stress.
Dr. Steven King, who directs the Health Physics Division at Penn State Hershey Medical Center, shared his experience relevant to point (1) above. He said that he is often contacted by patients, family members of patients, or other members of the public who are trying to make sense of the information they receive from government or professional societies’ websites
some of which is in SI units and some in conventional units. He suggested that providing all the information in SI units would give members of the public confidence that the information they receive is correct, which would allow them to make more informed decisions.
The discussion about communications with the public raised a larger issue related to radiation risk communication. There was a general agreement among most workshop participants that the scientific community has made relatively little progress in communicating with the public about radiation risks. Although risk communication was not the focus of the workshop, it was recognized by many participants to be related to the workshop’s topic. Dr. Ropeik, Harvard University, said that how the scientific community handles the adoption of SI units for radiation measurements (in terms of communicating the unit conversion of the different measurements and what these measurements mean) is an opportunity to undo some of the harm related to failing to communicate with the public effectively about radiation risks. In his opinion, the longer the scientific and user communities wait to exclusively use SI units for radiation measurements the longer the problem persists. He also said it is the scientific community’s responsibility to improve how it communicates with the public about radiation risks.
Dr. Steven Simon, NCI, commented on why radiation experts have not done a good job communicating to the public about risks. He said that experts lack information on individual risk, which is typically what interests members of the public. Instead, experts can provide information on population risk based on knowledge accumulated from epidemiological studies. The difference between individual and population risk can be difficult to explain to a member of the public. Dr. Simon shared his experience of communicating with American citizens in Japan during his deployment to the U.S. Embassy in Tokyo at the time of the Fukushima Daiichi Nuclear Power Plant accident, where he served as a U.S. Department of Health and Human Services technical expert in radiation dose and risk. American citizens wanted to know whether it was safe to be in Japan, drink the water, and eat the food, questions that were difficult to answer at an individual level. Dr. Ropeik responded that the goal of risk communication is not to dispel fear of radiation. Rather, it is to communicate what the scientific community knows about radiation in a trustworthy way to allow individuals to make their judgments about risk.
Simplicity of SI
Dr. Alan Du Sautoy, Canadian Nuclear Safety Commission (CNSC), referred to the “conceptual simplicity” of SI. This system is often described as a coherent system based on the seven independent physical quantities (base units) and derived quantities (derived units). This advantage of the SI
system compared to the conventional system of units was not discussed in detail at the workshop, but a participant referenced a report that discusses this issue in some detail (Eichholz et al., 1980, p. 31).
Some workshop participants identified two main challenges related to the exclusive use of SI units for radiation measurements (discussed in the sections below):
- risk of inadvertent overexposure
- cost and effort of conversion
Risk for Inadvertent Overexposure
Workshop participants noted that a momentary confusion between doses expressed in SI units as opposed to the more familiar conventional units could put the life of a first responder or a radiation worker at risk, if that responder or worker underestimates the amount of his or her radiation exposure. There was no discussion about how probable such confusion might be, but some participants suggested that the risk could be higher during the transition period from conventional to SI units, especially if it is prolonged.
Ms. Sara DeCair, who works on policy, planning, training, and outreach for EPA’s radiological emergency preparedness and response program, noted that first responders are often placed in situations in which they have to use their instincts and make snap judgments to protect themselves and others from radiation. Responders’ judgments could be impeded if they need to make mental conversions between SI and conventional units. She acknowledged that she would have to do conversions in her head to understand whether a dose rate expressed in SI units requires a protective action. In her view, this challenge can be mitigated by intensive training.
Ms. Ellen Anderson, NEI, said that there are approximately 100,000 nuclear power workers in the United States; about 56,000 are utility workers positioned in the 99 currently operating nuclear power reactors and 44,000 are supplemental workers such as laborers, carpenters, millwrights, and radiation protection technicians. About 65 percent of utility workers have no formal education beyond high school, and their average age is 55 years old. For these reasons, utility workers would likely have difficulty adjusting to SI units and therefore would not welcome a change. She also said that converting the occupational dose limit for nuclear workers from 5 rem to the SI equivalent, which is 50 millisieverts per year could raise concerns
among workers about why the dose limit is 10 times higher. Ms. Anderson’s arguments were supported by Mr. Willie Harris, Exelon Nuclear.
Other workshop participants, including Dr. Paul DeLuca, University of Wisconsin School of Medicine, Madison, and Dr. Armin Ansari, CDC, noted that these workers learned the conventional units and could learn the SI units. Dr. Ansari added that Oak Ridge National Laboratory trained its health physics technicians who did not have advanced degrees on the use of SI units in three 1-hour sessions and a refresher course afterward (Eichholz et al., 1980). Mr. Peter Burgess, Radiation Metrology Ltd., United Kingdom, suggested that Ms. Anderson and Mr. Willis were underestimating the versatility of utility workers. He often has to train British radiation workers, including radiation-monitoring technicians, who come to the United States for temporary employment. In his experience, training these workers in conventional units is feasible through intensive training over a couple of days.
There was some discussion about whether the risk of inadvertent overexposure related to the use of SI units for radiation measurements correlates with familiarity with radiation concepts and units. That is, is the risk greater among those who use radiation units in their daily jobs, for example, health physicists, or among those who are trained in radiation protection infrequently and do not have a good working knowledge of units, for example, front-line local emergency responders including firefighters. Dr. Stephen Musolino, Brookhaven National Laboratory, stated that those trained in radiation protection infrequently may not have great difficulty with the change.
Cost and Effort of Conversion
Adoption of SI units for radiation measurements would have several associated costs related to changes in regulations, reporting, training, and instrumentation. The costs were described by many workshop participants as substantial and a driving reason for some federal agencies, states, and the nuclear power industry to resist a conversion. Dr. Joseph Cordes, George Washington University, who specializes in public economics and policy analysis, said that if costs were a barrier to conversion, some budgetary relief could come from appropriations to federal stakeholders, federal grants to state and local governments, and possible tax incentives to the nuclear power industry for new equipment purchases.
Regulations and Reporting
Revisions to radiation-related regulations and guidelines issued by DHS, DOE, EPA, NRC, and other federal agencies with regulatory or
oversight responsibilities would require a major effort and expense, according to some federal officials who participated at the workshop. Ms. Sara DeCair, EPA, and Dr. Mark Maiello, New York City Department of Health and Mental Hygiene, said that the burden would be especially heavy at state, local, and tribal levels. There is typically one person in every state and local program who knows the radiation protection program and can make the needed updates. However, only about 10 percent of this person’s time is typically devoted to emergency response activities; the remainder is devoted to other tasks.
Ms. Alexis Reed, Counterterrorism Operations Support (CTOS) program, and Dr. Mark Maiello, New York City Department of Health and Mental Hygiene, provided perspectives on the training challenges of adopting SI units for radiation measurements. Training involves learning how to interpret instrument readouts and reporting results internally and externally to other agencies and public information officers.
Ms. Reed said that recertifying CTOS courses and updating training materials for SI units is trivial. The CTOS program offers several DHS-certified courses (online, resident, or mobile)4 to different stakeholders including federal, state, local, and tribal agencies, first responders, and members of the public. The courses are reviewed annually, and if the United States was to adopt the exclusive use of SI units for radiation measurements, changes could be incorporated into the courses during the annual reviews.
Dr. Maiello argued that for local programs like the one in New York City, the cost and burden of updating, reprinting, and redistributing training documents would be large. He said that some documents published by New York City would need to be updated; some of these documents were prepared within the past 5 years and relate to
- radiological response and recovery plans,
- community reception center field guides,
- community reception center health and safety guides, and
- community reception center decontamination plans.
Dr. Maiello noted that city agencies (e.g., fire and police departments within New York City) have additional internal documents that would also need to be updated to use SI units. He also noted that the effort of updating documents needs to be coordinated across cities within the state as well as
across U.S. states for harmonization within existing programs such as the Secure the Cities Program.5
Most radiation detection instruments use digital readouts and can be modified by the user to report in SI units. Mr. Frazier Bronson, scientific director at Canberra Industries, who has 50 years of experience designing instruments, said that this modification needs to be done by an authorized instrument repair facility or by the factory to ensure that it is done properly and then be recalibrated. However, there is a large number of pocket ionization dosimeters in wide use among emergency responders which cannot be economically modified for SI display. The cost for replacing these instruments would be significant for instrument users according to Ms. Reed and Dr. Maiello. There would be additional costs associated with testing the modified instruments.
The cost of modifying or replacing instruments will also be large for the nuclear power industry. Mr. Willie Harris, Exelon Nuclear, estimated that there are on average 250 radiation detection instruments in each power plant unit. These include monitoring instruments, personal dosimeters, and other instruments. He estimated that the cost to replace these instruments would be about $14 million per reactor. Mr. Burgess, Radiation Metrology Ltd., United Kingdom, who played a leading role in the transition of the U.K. instrumentation industry to SI in the 1980s, argued that although there is a one-time expense associated with buying new instruments that read in SI units, there is a long-term gain on the reduction in maintenance costs for older and less reliable instruments.
Mr. Frazier Bronson, Canberra Industries, surveyed 27 U.S. instrumentation companies on their perspectives on challenges related to adoption of SI units for radiation measurements. The companies were described as follows:
- 4 large instrument companies with significant international business
- 13 small instrument companies, some doing business primarily in the United States
- 5 analytical service laboratories primarily doing business in the United States
- 3 dosimetry service providers primarily doing business in the United States
5 This DHS-sponsored program assists state and local partner agencies to build regional capabilities to detect, analyze, and report radiological and nuclear threats.
- 2 source manufacturers; 1 with international business, 1 doing business in the United States
The overall response rate of his survey was 30 percent. Nonresponses were higher among small instrument companies.
Mr. Bronson found that if the United States were to exclusively use SI units for radiation measurements,
- all companies will have expenses for internal documentation, training, and external documentation.
- large companies would be the least affected because their instruments are already designed for sale to both domestic and international markets. Some small companies with primarily analog displays and with primarily a U.S. business base will bear a greater financial burden to modify their instruments. (But they might benefit from future international sales.)
- dosimetry service companies and analytical service laboratories would also be affected because they hold large amounts of historical data that are in conventional units.
- radiation-source manufacturing companies that do international business welcome the adoption of SI units for radiation measurements because it simplifies the preparation of shipping. Smaller companies selling only domestically will have to modify their shipping documents and procedures.
Dr. Fred Mettler, professor emeritus at the University of New Mexico School of Medicine, noted that the United States remains resistant to exclusively using SI units for radiation measurements despite 30-year-old national and international recommendations. He suggested that the factors that delay progress be carefully examined before attempting to reendorse adoption. Two of these factors were discussed at the workshop (see sections below):
- updating regulations, guidance documents, and source literature
- generational differences in training
Updating Regulations, Guidance Documents, and Source Literature
As noted in Chapter 2, older federal regulations and guidance documents are written in conventional units. The units in these documents can
be converted to SI when the documents are updated. However, updates occur infrequently, despite the intention to do so when authoritative reports from national and international organizations (e.g., ICRP; the National Academies; NCRP; UNSCEAR) provide new scientific information. Regulated entities who use these older regulations must continue to use conventional units in their practices and reporting documents.
Dr. Vincent Holahan, NRC, said that updates to older regulations are less likely to occur in times of decreasing resources. The NRC has been discussing the possibility of updating 10 CFR Part 20 (Standards for Protection Against Radiation) over 10 years and has decided not to because of budgetary restrictions.6,7
When updates to federal regulations and guidance documents do occur, the process is long. EPA, for example, revised the 1992 PAG manual (EPA, 1992) and issued a draft for interim use and public comment in 2013 (EPA, 2013). The manual was only finalized in November 2016 (EPA, 2016).
Besides regulations and guidance documents, Dr. Mark Mendonca, editor-in-chief of the journal Radiation Research, identified long process to update radiation science textbooks and the necessity to reference older source literature as factors that delay progress toward the exclusive use of SI units.
Generational Differences in Training
Whether a radiation expert is most comfortable with SI or conventional units for radiation measurements and supports the exclusive use of SI units depends on the expert’s training and current practices. Typically, the older generation of radiation professionals who was trained in conventional units is less comfortable with SI units and the younger generation who is trained in SI units is comfortable with SI. However, there is a barrier to a natural transition to SI as the younger generation replaces the older: Ms. Rajah Mena, DOE, who was trained in SI at college, noted that she had to go back to using conventional units for radiation measurements when she joined DOE to comply with practices within the agency (see Chapter 2). As a result, she has now lost her ability to readily think in SI units.
6 The NRC’s budget and staffing levels are declining due to the overall shrinkage of the nuclear power industry in the United States and therefore the lower new reactor licensing applications and renewals. See Project Aim 2020 (http://www.nrc.gov/reading-rm/doccollections/commission/slides/2015/20150218/project-aim-2020.pdf) for more information.
7 See the December 2016 Federal Register announcement here: https://www.federalregister.gov/documents/2016/12/28/2016-31372/rulemaking-activities-being-discontinued-by-the-nrc.
The workshop discussions summarized in this chapter can be organized in the following theme (Theme 3):
Several workshop participants noted that the continuing use of conventional units for radiation measurements is problematic, particularly with respect to emergency response. Workshop participants from several agencies, including the Centers for Disease Control and Prevention, the Department of Homeland Security, the Department of Defense, the Department of Energy, and the Environmental Protection Agency, said that their agency’s credibility and trust was placed in jeopardy during the response to the 2011 Fukushima Daiichi Nuclear Power Plant accident because of near-miss conversion mistakes and other related issues. The exclusive use of SI units for radiation measurements has benefits, including alignment of the United States with international practice and improving communications with the public. There are several associated costs to the adoption of SI units related to changes in regulations, reporting, training, and instrumentation. Some budgetary relief in the form of grants or tax exemptions could assist various stakeholders, including state and local governments and nuclear and instrumentation industries, with the adoption of SI units for radiation measurements.