TAM-E - Special Session: Non-Ionizing Radiation (NIR) Section Orange B 08:20 - 11:50
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| Chair(s): Jerrold Bushberg, Fred McWilliams
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TAM-E.0
08:20 Introduction
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TAM-E.1
08:30 Overview of Safety Standards for Non-ionizing Electromagnetic Fields (0-300 GHz) CK Chou*, IEEE ICES TC95
; Chou
Abstract: Exposure to man-made electromagnetic fields (EMF) has been part of contemporary life for over 100 years. Common exposures are from power lines, radio and TV broadcasting antennas and wireless communication devices involving both whole-body and local exposures. Safety standards developed by organizations and regulations enforced by governments have been used to protect against adverse health effects of EMF exposures.
Two international organizations develop EMF exposure standards or guidelines. The history of IEEE’s involvement with RF safety issues predates the 1966 publication of the first C95.1 EMF standard by the American Standards Institute. There are many revisions over the years. The latest version of the IEEE C95.1 standard published in March 2019 covers the frequency band from 0 to 300 GHz and replaces C95.6-2002 (0 to 3 kHz) and C95.1-2005 (3 kHz to 300 GHz). The International Commission on Non-Ionizing Radiation and Protection (ICNIRP), a collaborating organization of the World Health Organization, published guidelines for up to 300 GHz in 1998. In 2010, ICNIRP published revised guidelines for low frequencies below 100 kHz. Currently, ICNIRP is working on revised guidelines for radiofrequencies above 100 kHz.
In 1999, the European Union adopted the ICNIRP 1998 guidelines for general public exposure. In 2013, the EU adopted the ICNIRP 2010 and 1998 guidelines for occupational exposures. In November 2015, NATO and its 29 member countries adopted the IEEE C95.1-2345-2014 standard as Edition 4 of STANdardization AGreement (STANAG) for military workplaces. Information on global national exposure limits for whole body and portable devise exposures will be discussed.
In the USA, the Federal Communications Commission (FCC) based its 1997 regulations (Office of Engineering and Technology Bulletin 65) for RF exposures from broadcasting and wireless communications on recommendations from both IEEE C95.1-1991 and NCRP Report 86-1986. The Occupational Safety and Health Administration (OSHA) has its Code of Federal Regulations (CFR) for general industry (29 CFR 1910), and construction industry (29 CFR 1926), specifying 10 mW/cm2 as an exposure limit which is from C95.1-1966. However, OSHA also refers to FCC regulation, ANSI/IEEE and American Conference of Governmental Industrial Hygienists (ACGIH) limits. Periodically, ACGIH publishes threshold limit values (TLV) and biological exposure indices (BEI) guidelines; the 2018 RF exposure limits are based on recommendations from the IEEE C95.1 -2005 standard and other sources.
Varying exposure limits cause confusion and distrust in standards. It is highly desirable that all countries adopt a set of world-wide harmonized science-based exposure limits to protect human beings from adverse health effects of EMF exposure (0-300 GHz).
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TAM-E.2
09:10 Transient Thermal Responses of Tissue to Millimeter-wave Pulses KR Foster*, University of Pennsylvania
; MC Ziskin, Temple University Medical School; Q Balzano, University of Maryland
Abstract: There has been a rapid increase in use of millimeter waves (30-300 GHz) for communications and other applications. Designing RF exposure limits in this frequency range against thermal hazards poses special challenges due to the very short energy penetration depth into tissue, 0.5 mm or less. This results in two greatly different time scales for heating, a short time scale (< 1 sec) representing thermal diffusion away from the exposed layer of tissue, and a longer timescale (hundreds of seconds) representing thermal washout by blood perfusion. This talk will review thermal modeling studies to determine transient and steady state temperature increases in tissue exposed to both CW and pulsed mm-wave radiation and their implications for setting exposure limits. Under extreme exposure conditions, brief high-fluence mm-wave pulses can produce significant (>1 ⁰C) and even potentially painful or hazardous transient temperature elevations that dissipate quickly even though the time-averaged exposure may be within standard limits. Such effects require high-fluence pulses that are not characteristic of communications or other civilian technologies. Nevertheless, proposed additional limits on pulse fluence appear to provide adequate protection against such transients.
references
K. R. Foster, M. Ziskin, Q. Balzano, Thermal Modeling for the Next
Generation of Radiofrequency Exposure Limits: Commentary. Health
Physics 113:41-53 (2017).
K. R. Foster, M. C. Ziskin, Q. Balzano, G. Bit-Babik, Modeling Tissue
Heating From Exposure to Radiofrequency Energy and Relevance of Tissue
Heating to Exposure Limits: Heating Factor.
Health Physics 115 : 295–307 (2018).
K. R. Foster, M. C. Ziskin, Q. Balzano, A. Hirata, Thermal Analysis of
Averaging Times in Radio-frequency Exposure Limits above 1 GHz. IEEE
Access 6 (1) 74536-74546 (Dec. 2018)
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TAM-E.3
09:40 Assessing RF Exposure by Analysis: Estimating RF Fields through Calculation RA Tell*, Richard Tell Associates, Inc.
Abstract: Theoretical analysis of RF fields can provide useful insights to potential exposure associated with proposed installation of transmitting equipment and can help guide preparation for measurements at existing facilities. This presentation will provide an introduction to estimating RF power densities produced by a wide range of antenna types, discuss those situations where the RF fields are not amenable to straightforward calculations, explain the different analysis approaches commonly applied in RF exposure assessment and show what is involved in performing calculations. The concepts of antenna gain, radiation patterns and effective radiated power will be discussed with special emphasis on evaluating exposure in the near field. Effective application of the cylindrical model for estimating near-field, spatially averaged power density will be illustrated for vertical collinear antennas most commonly used at cellular telephone base stations. Other antenna types that will be treated in the presentation include parabolic dishes, stacked dipolar arrays, omnidirectional sticks, yagis and monopoles. Antenna design characteristics that can reduce ground level RF fields will be explained. Suggestions will be given on creating spreadsheets for calculating RF fields using manufacturer supplied antenna elevation patterns. Factors crucial to minimizing uncertainty in the analysis process will be covered. An overall emphasis in the presentation will be to make the process of antenna analysis for RF safety purposes easily understood, simple to use and fun to apply.
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TAM-E.4
10:50 RF FIELD MEASUREMENTS: Overview of Instruments and Techniques DL Haes*, Consultant
Abstract: While performing Radio-Frequency (RF) field measurements may appear to be simple, obtaining accurate and reproducible measurements of levels of electric and magnetic RF field levels can be quite challenging. The user of any RF field measurement instrumentation must have a thorough understanding of the types and limitations of the instruments, along with the conditions of the measurements. There are safety and perhaps special considerations to consider, in addition to interactions with the surveyor’s instrumentation and body. Near field exposures are difficult to measure and almost impossible to calculate (simply), because of mutual coupling effects. SAR is impossible to practically measure. RF field measurement types include RF Safety compliance, RF conformance, and RF leakage surveys.
The presentation will present information relative to instrumentation types, including both broadband and narrowband systems. RF measurement techniques discussed include spatial averaging, compliance in a multi-signal environment, complex far-field sources, near field conditions and conditions of non-uniform fields. Special considerations of the environment in which measurements are obtained will be discussed.
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TAM-E.5
11:20 RF Safety Programs: The What, Why, When and Where RA Tell, Richard Tell Associates
; DL Haes*, Consultant
Abstract: Radiofrequency (RF) safety programs exist to help ensure safety when there is potential for exposure to RF energy that exceeds relevant standards, guidelines or regulations. This presentation will explain when an RF safety program should be implemented and what it should contain based on guidance in the IEEE Standard C95.1-2014 Recommended Practice for RF Safety Programs. Using an approach of classifying exposures into a series of categories, based on potential exposure levels, control measures appropriate to the exposure category will be discussed. Safety program elements including the identification of potential RF hazards, administrative and engineering controls, the use of personal protective equipment and training will be examined with comment on the appropriateness of when certain elements are required in relation to the particular conditions of potential exposure. Important concepts will be explored to help program managers better understand how to implement safety programs that are optimally designed for their specific application. Two of these concepts include how the term “readily accessible" is interpreted in understanding when certain controls are necessary and how different standards or regulations define safety in relation to adverse health effects. It will become evident that RF safety programs can range from minimal to substantial detail and complexity depending on the circumstances, each being equally effective for their stated purposes. A secondary purpose of this presentation is to draw awareness to a perceived reality that implementation of RF safety programs in the U.S. are not necessarily in sync with the need for such programs. For example, while the guidelines on human exposure to RF fields promulgated by the Federal Communications Commission first became effective in 1997, many broadcast facilities have yet addressed, some 22 years later, the matter of possible noncompliant exposure of personnel and the general public. A similar trend can be observed in other industrial and medical settings with comments on why this may be the case. These observations will be included in the panel discussion part of this workshop.
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