regulatory guidance and safety standards
TRANSCRIPT
Regulatory Guidance and Safety Standards
Andrew H. Thatcher, MSHP, CHP
March 19, 2018
University of Washington
Overview
• 60 Hz power frequency exposure standards
• Static Fields
• RF (current fields to 3 GHz)
• Upcoming applications for mm Wave and exposure limits
Frequencies below ~100 kHz
• The limiting hazard is electrostimulation of tissue, either from electric fields induced within the body or by exposure to external fields, or from contact currents that occur when a person touches a charged conductive object.
60 Hz Power Frequency Field Exposure Limits
• No state or federal standards exist with regards to power frequency fields.
• Three relevant guidelines are used for exposure limits: • International Commission on Non-Ionizing
Radiation Protection (ICNIRP), 2010 • IEEE C95.6-2002 Standards for Safety Levels with
Respect to Human Exposure to Electromagnetic Fields, 0-3 kHz
• American Conference of Governmental Industrial Hygienists (ACGIH), 2009
Power Frequency Fields Continued
• From ACGIH: • Arms and legs – 50,000 mG
• Hands and feet - 100,000 mG
• Electric field limit of 25 kV/m
ACGIH Induced and Contact Current Limits (mA)
From IEEE C95.1-2005
Frequency
Through
Both Feet
Through
Either Foot
Grasping
Averaging
Time
30 kHz – 100 kHz
2000 f
1000 f
1000 f
0.2 s
100 kHz – 100 MHz
200
100
100
6 min
Note that the current limits above may not adequately protect against startle reactions and burns caused by transient discharges when contacting an energized object. Maximum touch current is limited to 50% of the maximum grasping current. The ceiling value for induced and contact current is 500 mA.
Static Magnetic Fields: MRI
• FDA: Criteria for Significant Risk Investigations of Magnetic Resonance Diagnostic Devices (2014), which identifies the operating conditions for MRI systems that FDA considers significant risk. An MRI system that exceeds any of these operating conditions would be considered significant risk and require FDA oversight via an IDE:
• Main static magnetic field over 8 tesla (80,000 Gauss) for adults, children, and infants >1 month of age; main static magnetic field over 4T for infants less than 1 month of age, or
• Specific absorption rate (SAR) greater than 4 W/kg whole body for 15 minutes, >3.2 W/kg averaged over the head for 10 minutes, or
• dB/dt sufficient to produce severe discomfort or painful stimulation, or
RF Safety Standards: Philosophy
Contemporary exposure limits are biologically based and reflect a consensus interpretation of relevant studies from the bioelectromagnetics literature by qualified scientists, physicians and engineers
Classifications of findings are made without pre-judgment of mechanisms of effects
The intent is to protect exposed human beings from harm by any mechanism, including those arising from excessive elevations of body temperature
The bases (basic restrictions) of contemporary RF safety standards are essentially the same; differences in exposure limits are engineering related - not philosophical – and are being resolved through standards harmonization programs
Adverse Health Effects
An adverse health effect is a biological effect characterized by a harmful change in health that is supported by consistent findings of that effect in studies published in the peer-reviewed scientific literature, with evidence of the effect being demonstrated by independent laboratories, and where there is consensus in the scientific community that the effect occurs for the specified exposure conditions. [IEEE Standard C95.1™-2005]
Standards and Guidelines
ICNIRP (1998): “…this publication is to establish
guidelines for limiting EMF exposure that will
provide protection against known adverse health
effects”.
*ICNIRP reconfirmed its guidelines in 2009.
IEEE ICES C95.1-2005: “The purpose of this
standard is to provide exposure limits to protect
against established adverse effects to human health
induced by exposure to RF electric, magnetic and
electromagnetic fields over the frequency range of 3
kHz to 300 GHz.”
Established Adverse Health Effects
Expert panels that review the literature agree that the only adverse effects that have been established are the following:
Aversive or painful electrostimulation due to excessive RF internal electric fields (< 5 MHz)
RF shocks or burns due to contact with excessively high RF voltages (< 110 MHz)
Heating pain or tissue burns due to excessive localized RF exposure (> 100 kHz)
Behavioral disruption, heat exhaustion or heat stroke due to excessive whole body RF exposures (> 100 kHz)
Literature Evaluation
Recommendations in contemporary RF safety standards and guidelines (Basic Restrictions and Exposure Limits) are based on the following:
the results of comprehensive reviews and evaluations of the scientific literature (more than 1300 relevant citations in C95.1-2005) –
More than 6200 articles currently found on
www.emf-portal.org
findings of studies published mainly after 1950
studies that involve low level exposures (especially important)
conclusions supported by a lack of credible scientific and medical reports showing adverse health effects for RF exposures at or below similar exposure limits in past standards
Results of Literature Evaluations
The most sensitive measure of potentially harmful biological effects is disruption of food-motivated behavior in laboratory animals
The threshold was found to reliably occur over a narrow SAR range between ~ 3 and 9 W/kg in several animal species under widely varying exposure parameters and was accompanied by an elevation in core temperature
The C95.1 standard, and all modern RF safety standards and guidelines, are based on a threshold SAR of 4 W/kg
Basic Restrictions
basic restrictions (BR):
Exposure restrictions that are based on established adverse health effects that incorporate appropriate safety factors. BRs are expressed in terms of the in situ electric field (< 100 kHz), specific absorption rate (100 kHz to 3 GHz), or incident power density (3 GHz to 300 GHz).
Because of the difficulty in determining the BRs under typical exposure conditions, exposure limits (ELs) derived from the BRs are used for assessing compliance.
Basic Restrictions (SAR)
Specific absorption rate (SAR) is the basic dosimetric quantity for comparing and extrapolating laboratory results (bioeffects studies) for frequencies above ~ 100 kHz
All modern RF safety standards are based the threshold SAR for the most sensitive, reproducible biological effects that can be related to human health
Despite slight differences in field limits, all modern RF safety standards (less than 6 GHz) are based on limiting the whole-body-averaged SAR to 0.4 and 0.08 W/kg, for exposures in controlled and uncontrolled environments, respectively
Greater than 6 GHz the safety standards are based on limiting the power density as the absorption is limited to the skin layer
Comparison of Power Density and SAR Thresholds for Behavioral Disruption
Species and
Conditions
CW
225 MHz
Pulsed
1.3 GHz
CW
2.45 GHz
Pulsed
5.8 GHz
Norwegian Rat
Power Density:
SAR:
-----
-----
10 mW/cm2
2.5 W/kg
28 mW/cm2
5.0 W/kg
20 mW/cm2
4.9 W/kg
Squirrel Monkey
Power Density:
SAR:
-----
-----
-----
-----
45 mW/cm2
4.5 W/kg
40 mW/cm2
7.2 W/kg
Rhesus Monkey
Power Density:
SAR:
8 mW/cm2
3.2 W/kg
57 mW/cm2
4.5 W/kg
67 mW/cm2
4.7 W/kg
140 mW/cm2
8.4 W/kg
Safety Factors
Whole body exposure:
Behavioral effects in several animal species over many frequencies; threshold between ~ 3 and 9 W/kg
10X - 0.4 W/kg for upper tier
50X - 0.08 W/kg for lower tier
Localized exposure (averaged over any 10 g)
Lens opacities (cataract) observed in rabbits, threshold 100 W/kg
10X – 10 W/kg for upper tier
50X – 2 W/kg for lower tier
Basic restrictions for frequency range 100 kHz to 6 GHZ
47 CFR 1.1310 Radiofrequency Radiation Exposure Limits
General Public /
Uncontrolled
Exposure (W/kg)
Occupational/
Controlled Exposure
(W/kg)
Whole Body
exposure Whole Body Average 0.08 0.4
Localized exposure Localized (peak
spatial average) 1.6a 8a
Localized exposure Extremities and
pinnae 4b 20b
aAveraged over any 1 gram of tissue
bAveraged of any 10 grams of tissue
Relevant Scientific Literature
Several thousand relevant RF bioeffect studies in the extant
literature cover a wide range of frequencies and modulations
The literature database in of uneven quality
Absence of support for the “non-thermal hypothesis”
— Biophysical analyses and reviews do not provide
convincing evidence that non-thermal interactions are
plausible at RF frequencies
— Examination of biological effects literature does not
provide a consistent body of data supporting theoretical
postulates on “non-thermal” mechanisms
Source: FCC OET Bulletin 65. 1997
30 30
20.1 0.8 0.2 1.6 0.2 0.04
0
10
20
30
40
50
60
70
80
90
100E
xp
osu
re (
µW
/cm
²)
Cordless
phone
Bluetooth Baby
Monitor @
7 feet
FM & TV Wireless
Laptop
WiFi maximum
outdoor
exposure
Typical
outdoor
exposure
Max
indoor
exposure
nearby
home
Typical Radiofrequency Exposures in our Lives
The Public exposure limit is:
200 µW/cm² for FM
425 µW/cm² for TV (UHF)
570 µW/cm² for cellular
1,000 µW/cm² for PCS
Copyright ©2011
Andrew H. Thatcher,
FCC OET 65
What About Exposures to Multiple RF Frequencies?
1)(1
n
i iTLVMPE
densitypower
Exclusions
The electric field, magnetic field and power density MPEs can be exceeded if it can be shown by appropriate techniques that:
the whole-body-averaged (WBA) SAR does not exceed the
appropriate WBA SAR limits, and
the spatial peak SARs do not exceed the corresponding spatial
peak SAR limits (except in the hands, wrists, feet and ankles),
and
the spatial peak SAR in the hands, wrists, feet and ankles do
not exceed 20 W/kg and 4 W/kg in any 10 g of tissue in the
shape of a cube for the controlled and uncontrolled
environments, respectively, and
the induced currents in the body do not exceed the appropriate
induced current MPEs
What is 5G? What Frequencies are Involved?
• FCC makes changes to allow for millimeter wave (mmW) technology
• Changes in rules to promote 3.5 GHz as a core frequency for 5G
• Expand use in Mid-Band spectrum between 3.7 GHz and 24 GHz (3.7 – 4.2 GHz, 5.925-6.425 GHz, 6.425-7.125 GHz)
• Additional 1700 MHz in 24 GHz and 47 GHz bands
• Allocations in 28 GHz, 37 GHz, and 39 GHz bands
What about 5G frequencies?
• Exposures > 6 GHz have very shallow penetration limited to the skin. Limits are related to incident power density as opposed to a SAR due to the limited penetration distance.
• A number of articles are reviewing the models and results of mmW absorption:
• Foster, KR. Ziskin, MC. and Balzano, Q. Thermal Response of Human Skin to Microwave Energy: A Critical Review, Health Physics, 111(6): 528-541. 2016
• Foster, KR. Ziskin MC. and Balzano, Q. Thermal Modeling for the Next Generation of Radiofrequency Exposure Limits: Commentary. Health Physics, 113(1); 41-53, 2017.
• Ziskin, MC, Alekseev, SI, Foster KR, and Balzano, Q. Tissue Models for RF Exposure Evaluation at Frequecies above 6 GHz. Bioelectromagnetics, In Review.
• And others in review
• Aside: Expectations is that the current 8.4 Billion connected devices will grow by 10X in the next few years
What About Low-level RF Biological Effects?
Despite more than 60 years of RF research, there is no convincing evidence that supports low-level biological effects, i.e., effects that occur at exposure levels below the limits found in contemporary standards and guidelines
No theoretical mechanism has been established that supports the existence of any effect characterized by trivial heating other than microwave hearing
The relevance of reported low-level biological effects remains speculative and such effects are not useful for developing exposure limits
The study of the biological effects of RF energy is a mature scientific discipline with more than a 60 year history
The RF bioeffect literature database is extensive but of uneven quality
Scientists have been developing RF safety criteria based on critical evaluations and interpretations of the scientific literature for almost 60 years
Despite many thousands of studies that have been reported on all aspects of the subject since the first safety criteria were proposed, the exposure limits have not changed significantly
Changes in the exposure limits over the years have mainly resulted from a better understanding of the dosimetry
Both IEEE C95.1-2005 and ICNIRP guidelines are undergoing major revisions – estimated completion ~late 2018.
Final Thoughts