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Radiofrequency and Microwave Radiation |
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In recent years there has been
considerable discussion and concern about the possible hazards of RF/MW radiation.
Extensive research on this topic is underway in many countries. Natural
low-frequency EM fields come from two main sources: the sun, and thunderstorm
activity, but man-made fields at much higher frequencies have altered this
natural EMF. At sufficiently high power densities, RF/MW energy can cause thermal effects
that can cause blindness, and sterility. Non-thermal effects, such as
alteration of the human body’s circadian rhythms, immune system and the nature of the
electrical and chemical signals communicated through the cell membrane have been
demonstrated.
However, none of the research has
conclusively proven that low-level RF/MW radiation causes adverse health
effects.
General
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General Concepts for Nonionizing Radiation Protection. American
Industrial Hygiene Association (AIHA),
(1998). An
introductory guide that examines non-ionizing electromagnetic energies.
Provides a thorough, up-to-date discussion of non-ionizing
radiation protection and is designed to supplement AIHA''s non-ionizing
radiation guides on the specific spectral regions. Includes
problem-solving
exercises in one of the guide's three appendices. Also includes charts, figures, and an expanded glossary.
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Radio-Frequency and Microwave Radiation,
Third Edition.
American Industrial Hygiene Association (AIHA),
(2004). Provides
a detailed look at the physical characteristics of radio-frequency and
microwave radiation, its generation and sources, how it interacts with
matter, and its biological effects. Discusses existing standards and guidelines,
as well as instrumentation and controls. A handy glossary
provides definitions of important terms, and an appendix presents a list
of problems industrial hygienists and other health professionals might
face.
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"Nonionizing Radiation." Fundamentals of Industrial Hygiene. National Safety Council, Chicago, IL,
(1988). Presents an overview of non-ionizing radiation in a popular text.
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Radiofrequency and Microwave Radiation in the Workplace. Ministry of
Labour, Ontario, Canada. Describes health effects, exposure
limits and ways to control RF/MW radiation.
Interference with Medical Devices
- Human Exposure to Radio Frequency and Microwave Radiation from Portable and Mobile Telephones and Other Wireless Communication Devices.
Institute of Electrical and Electronics Engineers (IEEE) Engineering in Medicine and Biology
Magazine, (2000, September). Sufficiently high levels of RF energy
can interfere with other electronic equipment. This problem is more likely to
occur with pulsed energy, which characterizes digital cellular telephones.
Studies have shown that handheld cellular phones can affect the operation of
heart pacemakers or defibrillators if the phone is placed directly over the
device, and there have been reports of interference between cell phones and
hearing aids. Individuals with pacemakers, implantable defibrillators, or
other body-mounted medical electronic devices, should consult with their
physician and/or the phone manufacturer to determine what precautions, if any,
should be taken. Some manufacturers recommend that cell phones be used on the
other side of the body from the implanted pacemaker.
- COMAR Reports: Radio frequency interference with medical devices: A
Technical Information Statement. Institute of Electrical and Electronics
Engineers ( IEEE) Engineering in Medicine and Biology
Magazine 17.3 (1998): 111-114.
- Hayes DL et al. "Interference with cardiac pacemakers by
cellular telephones," New England Journal of Medicine 336(1997): 1473-1479, 1997. (see also New
England Journal of Medicine 336(1997): 1518-1519; 337(1997): 1006-1007.)
- Update on Cellular phone Interference with Cardiac Pacemakers.
Food and Drug Administration (FDA), Center for Devices and
Radiological Health (CDRH), (1995, November 1). When
some cellular phones are placed very close to implanted cardiac pacemakers,
interference with the pacemaker's normal delivery of pulses can occur. The
type of interference under study is called "electromagnetic interference", or
"Emi". The CDRH concludes that interference issues are limited
to TDMA-type digital technologies, and further, that a distance separation of
~6 inches (~15 cm) is sufficient to mitigate EMI.
Amateur Radio
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American Radio Relay League (ARRL). "RF Radiation and Electromagnetic Field Safety."
ARRL Handbook for Radio Amateurs 1997. Also available as
a 61.7 KB PDF,
5 pages. Presents thermal and non-thermal effects,
safe exposure levels, cardiac pacemakers, typical RF field strengths,
and RF awareness guidelines developed by the
ARRL RF Safety Committee, based on the FCC/EPA measurements
and other data.
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Amateur Radio RF Safety Calculator.
American Radio Relay League (ARRL). This is a main beam power density estimation program
intended for use as part of a routine evaluation of RF safety compliance
with FCC regulations. This is a World Wide Web front end for a public
domain C program
written by Ken Harker WM5R using the cgic library. This program
has been derived directly from a public domain BASIC program
written and published by
Wayne Overbeck N6NB in the January, 1997 issue of CQ VHF, p. 33.
Cellular Phone Base Stations and Hand Held Cell Phones
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Cellular Phone Antennas (Mobile Phone Base Stations) and Human Health.
Contains FAQs and extensive
references including:
- Cell Phone Facts: Consumer Information on Wireless Phones. Food and Drug Administration
(FDA), Federal Communications Commission (FCC). Presents FAQs and references including:
- Use Of "Protective Devices" For Cellular Telephones Technical Information Statement.
Institute of Electrical and Electronics Engineers (IEEE) Engineering in Medicine and Biology Society Committee on Man and Radiation
(COMAR). A Spanish
version is also available.
If a mobile-phone user wants to reduce his or her
exposure to RF energy, for whatever reason, he or she can:
- Limit the duration of calls
- Use a digital handset instead of an older
analog model. In most, but not all cases, digital handsets operate
at lower power levels than analog models. (The actual power level,
however, depends on local conditions and can vary greatly.)
- Use "hands-free kits", which move the handset
away from the body.
- Human Exposure to Radio Frequency and Microwave Radiation from Portable and Mobile Telephones and Other Wireless Communication Devices.
Institute of Electrical and Electronics Engineers (IEEE) Committee on Man and Radiation
(COMAR), (2000, September). Engineering
data indicate that local SARs produced by hand-held, transportable, and
mobile transceivers and cellular telephones normally do not exceed FCC
and other safety limits. Present scientific evidence, as reviewed by
standards setting organizations and other expert groups, does not
demonstrate health or safety risks from cellular and other
communications transceivers. A potential exists for interference between
hand-held units and some medical devices that may be located in close
proximity to them (within a few centimeters).
- Physical Agents Data Sheets (PADs) - Radiofrequency/Microwave Radiation. Alaska Department
of Labor and Development. For incident electromagnetic energy of
frequencies from 10 MHz to 100 GHz the State of Alaska
has specified a PEL of 10 mW/cm as averaged
over any possible six-minute period in its Alaska Occupational Safety
and Health Standards. Employers who have people working around
devices which produce radiofrequency/microwave radiation need to be sure
that those devices are properly shielded to prevent leakage of
radiation.
Heating and Sealing Devices
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Radiofrequency (RF) Sealers and Heaters: Potential Health Hazards and Their
Prevention OSHA, National Institute for Occupational Safety and Health
(NIOSH), Joint NIOSH/OSHA Current Intelligence Bulletin 33, (1979, December
4). NIOSH and OSHA recommend that precautionary measures be
instituted to minimize the risk to workers from unwarranted exposure to RF
energy. The following controls are recommended:
- Properly design and install shielding material.
- Maximize the distance between the worker and the source of RF energy
emission should be maximized. Examples of means to accomplish this include
the use of automatic feeding devices, rotating tables, and remote materials
handling.
- Tune the equipment electronically to minimize the stray power emitted.
- Whenever possible, equipment switch off equipment when it is not being
used. Maintenance and adjustment of the equipment should be performed only
while the equipment is not in operation.
- After the performance of maintenance or repair, all machine parts,
including cabinetry, should be reinstalled so that the equipment is intact
and its configuration is unchanged.
- Post warnings and information.
- Develop a medical surveillance program tailored to the expected degree
of employee use of RF equipment and potential for exposure to RF energy.
- Take exposure measurements at regular intervals.
- Physical Agents Data Sheets (PADs) - Radiofrequency/Microwave Radiation.
Alaska Department of Labor and Workforce Development. Radiofrequency sealers and heaters have been among the
major sources of employee exposure to radiofrequency/microwave radiation.
- When these machines are used, employees should use
mechanical or electrical devices that allow them to stay as far away form the
source of radiation as possible.
- Whenever possible, these sealers should be turned off
when not being used. Maintenance and adjustment of this type of equipment
should be performed only by trained technicians and only when the machines are
turned off.
- Warnings should be posted to keep everyone away from
the source of radiation except for those workers who are absolutely essential
to performing the job.
Microwave Ovens
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Microwave Ovens and their Hazards. Canadian Centre for Occupational
Health and Safety (CCOHS).
Old or faulty door
seals are the most common causes of microwave radiation leakage. Mechanical
abuse, a build-up of dirt, or simple wear and tear of continued use can cause
door seals to be less effective. Theoretically, there will be small amounts of
leakage through the viewing glass but measurements have shown this to be
insignificant. Safety tips for installation and maintenance of microwave ovens
include:
- Take special care to ensure that no damage occurs to the part of the
oven making contact with the door or door seals.
- Ensure that the microwave is unplugged or disconnected from electrical
power before reaching into any accessible openings or attempting any
repairs.
- Ensure that the adjustment of applied voltages, replacement of the
microwave power generating component, dismantling of the oven components,
and refitting of waveguides are undertaken only by persons
who have been specially trained for such tasks. The services of a qualified
repairman should be sought when any malfunction is suspected.
- Do not by pass the door interlocks.
- Do not test a microwave power generating component without an
appropriate load connected to its output. The power generated must never be
allowed to radiate freely into occupied areas.
- Microwave
Radiation. Food and Drug Administration (FDA), Center for Devices and
Radiological Health (CDRH). Contains FAQs about
microwave ovens, checking ovens for leakage, tips on safe microwave oven
operation, and the erupted Hot Water Phenomena in Microwave
Ovens.
Radio Broadcast Antennae
- Employee Exposure to High-Level Radio Frequency Radiation. OSHA Compliance Issues, (2002), 247 KB
PDF, 3 pages.
Illustrates a real-world case of high level RF exposure.
During the exposure, both painters working on the tower momentarily
became a living part, or extension, of the antenna through a phenomenon
referred to as "induced current." As the RF exited the workers' bodies,
primarily through the legs near the ankles, the steel in the injured worker's
shoes caused the current to "arc" and burn the worker's ankles and legs.
The firm revised its work procedures:
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Ensure that, prior to any future work, each of the broadcast
stations would be directly contacted to confirm that it had either shut down or
switched to an alternate antenna.
-
Investigate the possibility of using individual probes linked
to each transmitting section of each antenna to ensure that no RF signal was
being transmitted prior to any worker ascending the towers.
- Notice of Apparent Liability for Forfeiture.
Federal Communication Commission (FCC), (2005,
January 6), 144 KB PDF,
7 pages. Describes a violation of FCC rules resulting in a
$10K fine. The case involves a worker climbing an FM broadcast tower.
Traffic Radar Devices
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Occupational Exposure of Police
Officers to Microwave Radiation from Traffic Radar Devices.
National Institute for Occupational Safety and Health (NIOSH),
(June, 1995). Police officers can take some simple steps which
will sharply reduce their exposure to the low-level microwave radiation which
these devices emit.
- Always point the device away from your body, or your partner's body,
while it is turned on.
- Mount fixed radar antennas so that the beam is not pointed at any
occupant of the patrol car.
- Whenever possible, turn off a hand-held unit when it is not in use. If
your unit has a "standby" mode, always use it when not measuring the speed
of a vehicle. Never rest the unit against your body when it is turned on.
- When it is on, try to avoid pointing the device toward metal surfaces
inside your car, such as the floor or a door, to avoid microwave reflection.
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