## 4 Internationalization of Bioelectromagnetics Research
### Incorporation of Improved Dosimetry in Exposure Limits  
The first RF exposure limit in the U.S., USAS C95.1-1966, was developed by a committee chaired by [PERSON]. The standard had a single frequency-independent limit: an incident power density of 100 W/m\({}^{2}\) for 10 MHz-100 GHz averaged over 6 min. The limit applied for both whole or partial body exposure. The limits were based on a review of the scientific literature, as well as on approximate paper-and-pencil calculations of tissue heating by RF fields. This standard was later updated and revised under the auspices of the Institute of Electrical and Electronics Engineers (IEEE), with subsequent editions building on improvements in exposure assessment and dosimetry, as well as on updated reviews of the bioeffects literature. The following comments pertain to the IEEE family of exposure standards, denoted generally as IEEE Standard C95.1- x. For a comparative review of RF exposure limits see [26] and for description of the latest IEEE C95.1-2019 standard see [27]; for a detailed historical review of the development of U.S. exposure limits see Chapter 12 in [28]. The International Commission on Nonionizing Radiation Protection (ICNIRP), an independent international organization, introduced generally similar guidelines. For a history of the development of ICNIRP guidelines see [29]. Confusingly, the two sets of limits employ different, and sometimes changing, terminology. IEEE refers to its limits as'standards', while ICNIRP uses 'guidelines'. ICNIRP terms the maximum permissible exposure measured outside the body as the'reference level', and the maximum permissible dose (SAR) inside the body as the 'basic restriction'. IEEE has used different terminologies for these quantities in different editions of its standard. The IEEE C95.1 standard has been revised and updated several times since its first (1966) edition. Some of the more important revisions include:  
C95.1-1982 (300 kHz-100 GHz) specified frequency-dependent limits, in terms of field strength or incident power density. The limits (equivalent to reference levels in ICNIRP) had a 'U' shaped dependence on frequency, with a broad minimum between 30-300 MHz reflecting the frequency-dependence of RF absorption in the body of a human standing erect in a vertically polarized RF field, as established by [PERSON], [PERSON], and others. This standard introduced a limit for'spatial peak' SAR of 8 W/kg (equivalent to ICNIRP's basic restriction) over one gram of tissue. The concept of'spatial peak' SAR was incorporated into the 1996 FCC exposure limits, leading to the \"SAR testing\" requirements for cell phones used throughout the world. All C95.1 standards from 1991 to the present distinguish between two tiers of exposure, for exposures in \"controlled\" and \"uncontrolled\" environments, which correspond to occupational and general public limits in ICNIRP. C95.1-2005 was based on what the standards document described as a 'complete reassessment of the technical rationale' and was designed to protect against \"' scientifically established adverse health effects in human beings resulting from exposure to radio frequency electromagnetic fields'. The documentation included a detailed analysis of adverse effects in animals of potential relevance to humans. In addition, this edition made several adjustments to the limits based on dosimetric considerations. IEEE C95.1-2019, the most recent edition, incorporated numerous changes, chiefly at frequencies above 6 GHz, to address the shallow energy penetration depths in body tissues at those high frequencies. For frequencies above 6 GHz, IEEE C95.1-2019 introduced a new dosimetric concept, 'epithelial power density' ('absorbed power density' in ICNIRP). Notwithstanding differences in terminology, the two sets of limits are now largely \"harmonized\", i.e., brought into agreement. As a result of these developments, exposure limits have evolved that rely increasingly on dosimetry and exposure assessment, although without major changes in the underlying scientific rationale.