RF Radiation Safety for

February 16, 2010

Presented by

Richard Strickland

5 Marblestone Lane ● So. Setauket, NY 11720 tel: 631-698-6765 ● fax: 631-698-6765 e-mail: [email protected] www.rfsafetysolutions.com ©2010 RF Safety Solutions LLC South Setauket, New York This presentation is copyrighted and intended for the use of National Association of T ower Erectors (NATE) students that attended the RF safety training course on February 16, 2010 in Orlando, Florida. No right to distribute copies publicly for sale, rental, lease, and lending or to third parties is authorized.

Course Outline • Part I. Overview of Hazards

RF Radiation Safety Sources, Biological Effects, Standards, and Safe Work Practices

– Biological Overview – Potential Hazards – Work Procedures

• Part II. Biological Theory and Regulations – Biological Basics – FCC Regulations – Safety Code 6

• Part III. RF Hazard Protection Equipment – RF Personal Monitors – RF Protective Garments

Overview of RF Safety Issues

Part I. Overview of Hazards Potential RF safety hazards for tower climbers, personnel working on rooftop sites with wireless antennas, and at ground level at RF transmission sites.

Overview of RF Safety Issues • RF energy can cause shocks and burns at low frequencies, such as near AM radio stations and AM detuning networks. Many wireless sites have AM detuning networks. • The eyes are especially vulnerable to concentrated levels of RF energy at microwave frequencies. Waveguide leaks are a significant hazard for anyone in close proximity to the origin of the leak.

• RF energy can cause excessive body heating if a person is exposed to relatively high concentrations of energy as occurs inside a microwave oven. • Exposure to RF energy below the threshold has no impact on the body—the body deals with tiny amounts of heat from RF in the same way it adjusts to temperature changes.

Potentially Hazardous Locations • Towers

– Wireless systems antennas at the same elevation as the climber – FM radio and television antennas, often at elevations well below the antennas – Near waveguide should it be open or leak; potential eye hazard within 3 feet of any junction or section of flexible waveguide or near a bullet hole if there is a leak in any high power system – AM towers have unique RF safety hazards

• Rooftops

– Wireless systems antennas – FM radio antennas – Satellite-uplink antennas

• Ground

– AM detuning networks – AM antennas: burn hazards at tower , feed line, and inside tuning huts – Near waveguide should it be open or leak

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Radio and T elevision

T ypical TV Broadcast Antennas

T ypical FM Radio Antennas

Wireless Tower Sites

TV Broadcast Antennas

Rooftop Wireless Antennas

AM Detuning Networks • Many towers located near AM stations have AM detuning networks installed. • Under some conditions, it is possible to get a shock or burn if you touch some of the wires in the circuit since they are in essence functioning as AM receiving antennas.

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AM Stations

Wireless System Antennas

• AM stations can generate very high RF field levels, especially under the tower . The problems is most severe when the tower is very close to the ground.

• Wireless antennas, such as for cellular systems, have locally intense RF field levels within a few feet of the antennas.

• RF burns are a very serious concern. They a can occur if you touch the tower or especially if you touch the feed line. Remember that at an AM station, the tower is the antenna!

Feed line between tuning hut and tower

• The intensity of the RF energy from the antennas represents potential safety hazards for anyone directly in front of these antennas at the same elevation .

Insulator

RF Levels at Ground Level • Wireless systems antennas have very little energy directed downward. The RF field levels at ground level are insignificant. • Similarly, there are insignificant levels of RF energy generated by the towermounted antennas that exists inside the equipment shelters associated with these towers.

Potential Ground Level RF Hazards 1. Burn hazard if you contact an AM detuning network, common at wireless sites. 2. Burn hazard if you touch an AM radio antenna tower . There is a growing trend to install wireless antennas on AM radio towers. 3. Eye hazard if you were to get within 3 feet of a waveguide transmission line leak. 4. RF exposure hazard if someone were to energize an antenna inside a shelter while you were inside.

RF Levels Inside Shelters • The most significant potential hazard would occur if anyone were to set up a test antenna inside the shelter . This is not a good idea, especially with metal shelters! • It is possible to be exposed to low levels of RF energy if you were to lean over an open drawer containing amplifier cabinets with cover shields removed. • A limited number of equipment shelters contain high power amplifiers that feed high power microwave systems such as weather radar and satellite uplink systems. Leaks from waveguide transmission line is a potential eye hazard within 3 feet of the site of the leak.

Waveguide • True waveguide is limited to hollow metal tubes— normally rectangular but occasionally circular or elliptical in cross section. • If it has a core, it is not waveguide! • The higher the frequency, the shorter the wavelength and thus the smaller the waveguide.

Flexible W-G is very prone to failure.

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Potential Rooftop Hazards

Waveguide Leaks • The eyes are particularly vulnerable because the limited blood flow provides limited circulatory cooling. • Leaks, although not especially common, are acute problems that can occur at any time. • Even a few watts of energy can be a concern if it is concentrated in a very small area (same principle as a laser). • Energy drops off rapidly with distance—three feet is enough under most conditions with the equipment you are liable to encounter .

Omni Antenna Safety Zones

Radiation Pattern of Omni Antennas • Omni-directional antennas radiate over 360° in azimuth with only a very slight amount of downward radiation.

• Wireless omnidirectional antennas when you at the same elevation. • Wireless sector antennas when you at the same elevation and on the transmit side of the antenna. • FM radio and television antennas. • Satellite-uplink antennas.

T op View

Side View

Effects of Antenna Height • The spatially-averaged field strength that you may be exposed to can be calculated using the “cylindrical model”. • It is appropriate for all typical co-linear dipole array antennas, both omni-directional whip antennas, and directional or sector antennas. • The method is very accurate for situations where you are at the same elevation as the antenna. • The method is appropriate in the near field of the antenna, typically 8 to 15 feet for most wireless antennas.

• It is safe to approach omni antennas providing the base is a minimum of 1 foot above your head. • Do not remain within 10 feet of an omnidirectional antenna if you are at the same elevation (unless wearing an RF personal monitor). • Time averaging may be used on roof tops so that you may briefly pass much closer to these antennas.

Cylindrical Model • Although the energy close to the antenna has peaks and nulls, the spatial average can be represented by a cylinder equal in height to the antenna and with a radius equal to your distance from the antenna.

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Effect of Antenna Size 6-foot antenna:

12-foot antenna:

An adult at the same elevation is illuminated by all the energy in his/her direction.

An adult at the same elevation is illuminated by half of the energy in his/her direction. Although the gain is higher, close (95% of the RF personal monitor market with its Nardalert XT (~75%) and the RadMan (~25%) monitors. • Both the Nardalert XT and the RadMan are broadband monitors with shaped frequency response. • Available from distributors such as RF Safety Solutions.

Personal RF Safety Monitor

Radman

• The SafeOne™ is a low-cost European monitor introduced in mid-2008.

Nardalert XT

• Rated performance is 400 MHz to 3 GHz. It has extremely limited specifications with wide tolerances in sensitivity . • It is almost totally non-responsive at VHF . In other words, if you are near a VHF communications antenna, an FM radio antenna or low band TV antenna, it may never sound an alarm even if you are exposed to extremely high RF fields! • There is no On/Off switch.

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Monitor Comparison

Nardalert XT* RF Personal Monitors

• The Nardalert XT is by far the most accurate and has a number of unique features. • The RadMan is oversensitive and sometimes responds to static but it does protect you although it can indicate a problem when one doesn’t exist. Since the price is identical to the Nardalert XT, there is little reason to buy it. • If you are on a shared site, ignore what anybody reports that their SafeOne is indicating. It is not even rated for the most dangerous antennas.

Nardalert XT RF Personal Monitor

Photo sensor used to dim LEDs in low light

On/Off switch

Green LED flashes every 10 seconds at fields 100% is indicated by 4 LEDs. Three position switch selects audio, vibrator, or alternating. Make selection before you turn the monitor on. Alternating is suggested.

Why Shaped Frequency Response • Exposure limits very significantly over with frequency. • If you were exposed to a RF field level of 2 mW/cm² the significance would vary with frequency: – – – –

40% of MPE limit if a PCS source 67% of MPE limit if cellular source 200% of MPE limit if VHF 2-way (160 MHz) 2% of MPE limit if an AM station

• Multiple emitter exposure requires weighting.

• 100 kHz to 100 GHz operation covers essentially the entire usable RF spectrum. • Frequency response is “shaped” to conform to the FCC’s MPE limits for Occupational/ Controlled Environments. Indicators and alarms are in “Percent of Standard” . • Monitor averages and updates on a one second basis. *Recommended by RF Safety Solutions.

Shaped Frequency Response • Monitor automatically weights and sums all signals and gives the total in percent of occupational MPE limit. • Its sensitivity tries to follow a standard using techniques similar to filter design by using RC circuits. • Each monitor design follows a particular standard or regulation. A monitor designed for the FCC standard has a different frequency response than one designed for the Canadian (Safety Code 6) standard.

Shaped Frequency Response mW/cm2 106 105 104

FCC MPE limit for Occupational/Controlled exposure Frequency Response/sensitivity of Nardalert XT

103 100 10

f/300 900/f2

1.0 0.1 0.01

3 10 30 100 300 1 3 10 30 100 300 1

kHz

MHz

3 10 30 100 300

GHz

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RF Protective Suits • Stainless wire (10-25%) blended with Nomex. • Provides >10 dB of protection at most frequencies (concerns at AM band). • Protection is only about 3:1 w/o hood. • Hood is required above 800 MHz under all conditions. • Conductive socks must be worn and in conductive contact with suit for energy to “drain” off the body . • Do not enter any RF field higher than 1000% of the occupational MPE even when wearing a full protective suit.

Suits and Monitors • RF Personal Monitors DO NOT function properly if worn under RF suits (a common, misguided practice)! • The Nardalert XT High Power monitor is available for use outside the suits. Full scale on this monitor is 1,000% of the occupational/controlled MPE which allows for a 10:1 reduction from the RF protective garment.

Contact RF Safety Solutions for details

RF Radiation Safety Common Sense and Following Procedures Help Keep You Safe

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