Introduction to Radio Frequency Radiation

Robert Curtis, USDOL/OSHADirectorate of Science, Technology

and MedicineMarch 2003

Health Effects and Standards

Frequency and Wavelength

Electromagnetic Spectrum

How RF Transfers

Specific Absorption Rate

• Measure absorbed power in watts per kg of tissue

• Basis of most RF standards

A Quick Review of RFMW Biological Effects (II)

Immune (animals only) - T lymphocyte activity alteration @ 1.4 W/Kg

Blood - no consistent results Cancer - No specific animal life span

study seeking cancer has been done; epl' studies of radio hams, electrical workers, and physical therapists found excess cancer, but other studies have not found association

A Quick Review of RFMW Biological Effects (III)

• Neurological (animals only) - Test of blood/brain barrier contradictory; unreplicated studies with AM & PM fields show brain metabolism changes @ >0.02 W/kg 200 & 591 MHz, but not @ 2450 MHz

• Mutations - Mutations not found in replicated studies to date

A Quick Review of RFMW Biological Effects (III) (cont.)

• Reproduction - (animals only) Temporary make sterility @ 5.6 W/kg Testicular changes @ 15 W/kg Leutenizing hormone changes @ >2 W/kg

Teratology (animals only) - Malformed offspring found @ 31 W/kg, strong thermal dependance (temp >41°C)

• Thermoscoustic - (Pulsed only)

A Quick Review of RFMW Biological Effects (III) (cont.)

Observed in radar operators in WWII as perceived clicking sound. Possible cause of neurological, central cholinergic, effects observed by James Lai @ 0.6 W/kg (0.45 W/kg NOEL, brain SAR #2 W/kg for effect)

Basis of RF Standards

Behavioral disruption threshold Limit temperature increase to 1 degrees C 1-4 W/kg SAR 10-fold safety factor

Maximum Permissible Exposure (MPE) for Occupational (Controlled) Environment

Same Basis, but Standards Differ

General population vs. Controlled RF Sites

Localized exposure limits (spatial averaging)

Time averaging Special exclusions, such as low-power

devices, peak exposures.

Maximum Permissible Exposure (MPE) for Public (Uncontrolled) Environment

Maximum Contact Current for Occupational (Controlled) Environment

Maximum Contact Current for Public (Uncontrolled) Environment

RF Exposure Standards are Typically Based on 6 min. TWA

Excursions allowed if 6 min time weighted average is within limits

Up to 30 min intervals used for public exposure standards

Spatial Averaging

ANSI standard is confusing regarding partial-body vs. non-uniform exposure.

Exception for testes and eyes (See interpretation).

OSHA standards, based on old ANSI, does not allow for spatial averaging.

Microwave Measurement

Antenna Equations

• Equation

Microwave Applications

Cassegrain Antenna

Radio Frequency Measurement

Radio-Frequency MeasurementsIEEE c95.1 - 1991

>300 MHz - E or H or S; spatial average

100 - 300 MHz - E & H; spatial average

3 kHz - 100 MHz - E & H; spatial average; including current; contact current

FCC Limits for MPE

• Table Notes

Spatial Average

Single Roof-Top Antenna,various exposure locations.

Single Tower, co-located antenna, on-tower exposure.

Radio Frequency Applications

•Communication Transmitters

•Industrial Applications

RF Safety Programs

Elements of a Comprehensive RF Protection Program: Role of RF Measurements

• Full Text

RF Protection Program

• Utilization of RF source equipment which meet applicable RF standards when new and during its lifetime.

• RF hazard identification and periodic surveillance by a competent person.

• Identification and Control of RF Hazard Areas.

• Implementation of controls and SOPs to reduce RF exposures to levels in compliance with applicable guidelines.

RF Protection Program (cont.)

• RF safety and health training to ensure that all employees understand the RF hazards and control methods used. Employee involvement in the structure and operation of the S&H Program.

• Implementation of an appropriate medical surveillance program.

• Periodic (e.g. annual) reviews of the program to identify and resolve deficiencies.

RF Protection Program (cont.)

• Assignment of responsibilities, including adequate authority and resources to implement and enforce the program.

Notice

Caution

Warning

RF Symbols

• RF energy advisory symbol and RF electric current hazard advisory symbol.

Symbols (cont.)

Summary of Contact Current