1. RF amplifiers frequently use high-voltage power sources. See Section 7.0, "Work in Excess of 600 V", for high voltage requirements.

2. There may be x-ray hazards (when supply voltage exceeds 10 kV).

3. Currents maybe induced in conductive objects or metal structures that are not part of the RF structure.

4. RF currents can cause severe burns.

5. Falls from towers may result from RF burns from antennas.

6. Electromagnetic interference may cause equipment to malfunction.

7. Electromagnetic fields may cause unintended ignition of explosives, fuel, and ordnance.

8. Grounding and bonding conductors that are adequate for do and power frequencies may develop substantial voltage when fast pulses and radio frequency currents are present, due to induction and other means.

10.8.4.2 DESIGN AND CONSTRUCTION

Engineering control in accordance with ANSUIEEE C95.1 (1991) should be the primary method used to restrict exposure whenever practical. If engineering controls are not practical, such as: worktime limits, based on the averaging intervals and other work-practice and administrative controls, must be used.

1. Warning Signs. Signs commensurate with the RFMW level must be used to warn personnel of RFMW hazards. These signs must be posted on access panels of irradiated enclosures and at entrances to and inside regulated areas.

2. Access Limitation. Access can be limited by controls such as barriers, interlocks, administrative controls or other means. The operation supervisor controls access to regulated areas and must approve nonroutine entry of personnel into these places. When practical, sources of RFMW radiation should be switched off when not in use.

3. Shielding. Shielding that encloses the radiating equipment or provides a barrier between the equipment and the worker may be used to protect personnel; the shielding design must account for the frequency and intensity of the field.

4. Interlocks. Chamber or oven-type equipment that uses microwave radiation must have interlocks designed to (1) prevent generation of the radiation unless the chamber is sealed and (2) shut off such equipment if the door is opened.

5. Lockout/Tagout. The design shall incorporate features that allow the equipment to be locked out and tagged out for servicing.

6. Personnel Protective Equipment (PPE). PPE such as eyewear is not readily available and is generally not a useful option as protection against RFMW radiation and fields. Protection must therefore be achieved by other means.

10.8.4.2.1 EXEMPTIONS TO RFMW EXPOSURE LIMITS

The following items are exempt from the RFMW exposure limits; however, their manufacture is subject to Federal RFMW emission standards:

1. Cellular phones

2. Two-way, hand-held radios and walkie-talkies that broadcast between 10 kHz and 1 GHz and emit less than 7 W

3. Microwave ovens used for heating food

4. Video display terminals.

10.8.4.2.2 EXPOSURE CRITERIA FOR PULSED RFMW RADIATION

The basic considerations for peak-power exposure limits are consistent with ANSI/IEEE C95.1 (1991) as follows:

1. For more than five pulses in the averaging time and for pulse durations exceeding 100 milliseconds, normal time averaging applies and the time-averaged power densities should not exceed the Maximum Permissible Exposure (MPE) given in Table 10-1 for controlled and Table 10-2 for uncontrolled environments, per AN C95.1 (1991).

2. For intermittent pulse sources with no more than five pulses during the averaging time, the peak power density for any of the pulses should not exceed the limit given by the following equation.

This limits the specific absorption (SA) of each pulse to SA=28.8 J/kg (whole-body or spatial average), or SA=144 J/kg for 5 pulses.

For intermittent pulse sources with no more than five pulses during the averaging time, the single-pulse SA of < 28.8 J/kg, though higher than the threshold for auditory effect (clicking), is three orders of magnitude lower than the SAs that produce RF-induced unconsciousness.

3. Maximum E field for any of the pulses should be no more than 100 kV/m. This peak E-field limit is prescribed to eliminate the possibility of air breakdown or spark discharges, which occur at 2,900 kV/m. A large safety factor is applied to account for local field enhancements where nominally lower fields may result in arcing discharges.