The recommendations of C95.1-2005 protect against established adverse health effects in human beings.
Daniel D. Hoolihan
Hoolihan EMC Consulting
A new edition of the Institute of Electrical and Electronics Engineers (IEEE) Standard C95.1 was released in early 2006 and has been available for about a year. The new standard is a revision of the 1999 Edition of C95.1 and the 2004 Amendment to the 1999 Edition. It includes recommendations to protect against established adverse health effects in human beings associated with exposure to electric, magnetic, and electromagnetic fields in the frequency range of 3 kHz to 300 GHz. The recommendations protect against effects associated with electrostimulation and tissue/whole-body heating. The standard is 238 pages long, but the main contents of the standard are covered in the first 29 pages. The remaining pages are seven annexes including a “Summary of the Literature on Radio Frequency (RF) Exposure Levels” that covers 44 pages, a “Literature Database” that is 76 pages long and contains 1143 literature references, and a 10-page bibliography referencing 144 documents.
There are three references in the standard:
- IEEE Std C95.3™-2002, IEEE Recommended Practice for Measurements and Computations of Radio Frequency Electromagnetic Fields with Respect to Human Exposure to Such Fields, 100 kHz-300 GHz.
- IEEE Std C95.6™-2002, IEEE Standard for Safety Levels With Respect to Human Exposure to Electromagnetic Fields, 0 to 3 kHz
- IEEE Std C95.7™-2005, IEEE Recommended Practice for Radio Frequency Safety Program, 3 kHz to 300 GHz
There are 81 definitions applied in the standard. They include such terms as adverse health effect, chronic exposure, established effect, localized exposure, non-uniform field, rheobase, spatial average, strength-duration curve, and thermal effects.
KEY ACRONYMS AND ABBREVIATIONS
The key acronyms and abbreviations in the standard include:
- ANSI – American National Standards Institute
- BR (Basic Restrictions). Exposure restrictions that are based on established adverse health effects that incorporate appropriate safety factors and are expressed in terms of the in situ electric field (3 kHz to 5 MHz), specific absorption rate (100 kHz to 3 GHz), or incident power density (3 GHz to 300 GHz).
- ICES – International Committee on Electrical Safety
- ICNIRP – International Commission on Non-Ionizing Radiation Protection
- IEC – International Electrotechnical Commission
- IEEE – Institute of Electrical and Electronics Engineers
- MPE (Maximum Permissible Exposure). The highest RMS or peak electric or magnetic field strengths, their squares, or the plane-wave equivalent power densities associated with these fields, or the induced and contact currents to which a person may be exposed without incurring an established adverse health effect and with an acceptable margin of safety. The MPEs are derived or estimated from the basic restrictions (induced electric field, SAR, or power density). If an exposure is proven to be below the basic restrictions, the MPE can be exceeded. MPEs are sometimes called reference levels, derived limits, or investigation limits.
- RF – Radio Frequency
- SAR (Specific Absorption Rate). The time derivative of the incremental energy (dW) absorbed by (dissipated in) an incremental mass (dm) contained in a volume element (dV) of given density (ρ). The unit of SAR is Watts per kilogram.
The Recommendations part of the standard is divided into eight sections; we will take a look at each of those eight divisions. This area of the standard contains tables and graphs summarizing the recommended limits for BRs and MPEs.
The first section is called “Basic Restrictions and Maximum Permissible Exposures for frequencies between 3 kHz and 5 MHz.” It looks at BRs for in situ electric fields, MPEs for magnetic fields (including uniform and non-uniform exposures to sinusoidal magnetic fields), MPEs for external electric fields, and Contact and Induced Current Limits. Table 2 in this section specifies acceptable exposure levels of magnetic fields for the general public as being below the range of 163 to 182 A/meter.
The second section investigates BRs and MPEs for frequencies between 100 kHz and 3 GHz. It includes BRs for whole-body exposure and localized exposure. It also reviews and recommends contact and induced current limits between 100 kHz and 110 MHz. It is in this section that the most popular table and graph appear; most popular, meaning duplicated in other references relative to health effects of RF.
For example, Table 9 (Table 1 below) shows the Action Level (MPE for the general public when an RF safety program is unavailable). It states the MPE in electric field strength (V/m), magnetic field strength (A/m), RMS power density (W/m2), and averaging time in minutes. This concept is shown graphically in Figure 4 (Figure 1 below). Both the table and the figure show a Maximum Permissible Exposure level of 27.5 Volts per meter in the frequency range 100 – 400 MHz which is equivalent to 2 Watts per square meter. The 2 Watts per square meter rises to 10 watts per square meter at 2 GHz and stays constant at that level until 100 GHz.
Basic Restrictions for frequencies between 3 GHz and 300 GHz are covered in the third section (4.3) of the Recommendations portion of the standard. The BRs protect against adverse effects associated with heating for incident power density. They are derived with consideration of adverse effects thresholds, their distribution among the population, and safety factors. The BRs are the same as the corresponding MPEs shown in Table 8 and Table 9 in the standard, and they are considered appropriate for all human exposure.
The frequency range from 100 kHz to 300 GHz and the recommendations on MPEs in this range is covered in the fourth section of the standard. Because of the difficulty in determining whether an exposure complies with the BRs, derived limits (MPEs) are provided for convenience in the standard and are shown in Tables 8 and 9. For example, in the frequency range from 100 to 300 MHz, the quoted MPE for a controlled environment is 61.4 Volts per meter for the RMS electric field strength.
The topic of Contact Voltages is covered in the fifth section. A suggested limit for contact voltages in the frequency range of 0.1 to 100 MHz is recommended to protect against RF burns. The maximum suggested open circuit voltage is 140 volts (RMS), as measured between any two points of contact with the body.
The sixth section (4.6) addresses relaxing Power Density MPEs for localized exposures. It explains the rationale for the relaxation and describes the use of the relaxation. The general relaxation for localized exposures for the Table 8 and Table 9 values is approximately twenty (20) times the spatial averages for the whole body.
The process for assessing compliance with C95.1 is reviewed in the seventh section (4.7) of the Recommendations part of C95.1. Compliance with the standard would ideally include a determination that the basic restrictions are not exceeded. In general, this means that the whole-body average and the local SARs do not exceed 0.4 Watts per kilogram and 10 Watts per kilogram, respectively. In practice, compliance can be achieved by determining the values of the corresponding MPEs either by measurement or by analysis. For measurements, reference should be made to IEEE Std C95.3-2002.
The last section of the Recommendations discusses the establishment of RF Safety Programs. Where there may be access to RF fields, currents, and/or voltages that exceed the lower tier (Action Level) of the standard, an RF Safety program such as that detailed in IEEE Std C95.7-2005 shall be implemented to ensure that exposure does not exceed the MPEs or BRs for people in a controlled environment.
Annex A covers the general approach to revising the earlier version of IEEE Standard C95.1 to arrive at the newer version. Annex A and all the Annexes in C95.1 are Informative Annexes which means they supply information, but they need not be complied with to conform to the standard.
Annex B summarizes the voluminous literature on levels of RF exposure responsible for adverse effects on human beings. It consists of 44 pages of documents covering many types of publications. The Executive Summary, in part, says “a review of the extensive literature on RF Biological Effects, consisting of over 1300 primary peer reviewed publications published as early as 1950, reveals no adverse health effects that are not thermally related (except for electrostimulation discussed in B.2.4).”
Annex C develops and explains the rationale behind the recommendations for health effects of RF energy. The threshold for whole-body average SAR of 4 W/kg for established adverse effects remains the same as in the 1999 edition of C95.1. This level was based on the decision that the threshold for disruption of ongoing behavior in laboratory animals including nonhuman primates might pose a potentially adverse effect in human beings.
Annex D is a short annex, 10 pages, and covers examples of practical applications of RF effects.
Annex E is the Glossary and contains 16 terms such as conductivity, current density, decibel, duty factor, electric field strength, electromagnetic field, electromagnetic energy, energy density (electromagnetic field), far-field region, magnetic field strength, magnetic flux density, penetration depth, permeability, permittivity, root-mean-square (RMS) value (of a periodic function), and wavelength.
Annex F contains papers from the International Electromagnetic Fields (EMF) Project (IEEE/WHO) database that are cited in C95.1-2005. It covers 76 pages and references 1143 papers.
Annex G is the Bibliography of the standard and covers 10 pages with 144 Documents.
This Overview of C95.1 is intended to review the main contents of the standard. In no way is it intended to substitute for a careful reading of the newest edition of the standard.
The author encourages readers of the Overview to investigate and to read the entire standard as it is a valuable reference in the field of Human Exposure to Non-Ionizing Radio Frequency Electromagnetic Fields.
Daniel D. Hoolihan is a past president of the IEEE EMC Society. He has been a member of the Board of Directors since 1987 and has held several leadership positions in the society. Dan is also active on the ANSI Accredited Standards Committee on EMC, C63 as Chairman of Subcommittee 6 and Subcommittee 8 EMC and Medical Devices. He served as vice president of the Minnesota operation of TÜV Product Service, Inc. from 1994 to 1999. He can be reached at [email protected].