Module 2 - Microwave and Radiofrequency Radiation Safety

The campus contains many potential sources of microwave/RF radiation exposure. Some of these sources (primarily antennas) are designed to emit microwave/RF radiation into the environment. Other types of sources (co-axial cables, waveguides, transmission generators, heaters, and ovens) are designed to produce or safely contain the microwave/RF radiation, but may present a hazard should they leak for some reason. A third type of source (primarily power supplies) may create microwave/RF radiation as a byproduct of their operation.

The hazards from exposure to microwave/RF radiation are related to the following parameters:

• Frequency of the source
• Power density at the point of exposure
• Accessibility to the radiation field
• Does the exposure occur in the near or far field
• Orientation of the human body to the radiation field

This combination of factors is used in both evaluating and mitigating the hazard.

In general, most biological effects of exposure to microwave/RF radiation are related to the direct heating of tissues (thermal effects) or the flow of current through tissue (induced current effects). Non-thermal effects resulting in carcinogenesis, teratogenesis, etc. have been demonstrated in animals but have not been proven by epidemiological studies on humans. The following biological effects have been demonstrated in humans:

• Cataract formation (from eye exposure).
• RF (induction) burns.
• Burns from contact with metal implants, spectacles, etc.

A large number of standards have been developed for use in protecting individuals against overexposure to microwave/RF radiation. These standards often address only specific frequency bands or exposure conditions. In an effort to address the broad research potential for microwave/RF radiation exposure at UC Berkeley, the following table of exposure standards was developed. The table is a synthesis of several regulatory standards and guidelines (as indicated).

UCB Radio Frequency Exposure Standards

Occupational Exposure Limits - All exposures averaged over 0.1 hour (6 minutes)

Non-OCCUPATIONAL EXPOSURE LIMITS - ALL EXPOSURES AVERAGED OVER 0.5 HOUR (30 MINUTES)

(Derived from ACGIH TLV, CCR Title 8, IRPA NIR, FCC OET 65, and IEEE C95.1)

Key to Reference Standards

1. International Non-ionizing Radiation Committee (INIRC) of the International Radiation Protection Association (IRPA) - Interim Guidelines on Limits of Exposure to 50/60 Hz Electric and Magnetic Fields (1989).
2. Institute of Electrical and Electronics Engineers (IEEE) Publication C95.1 - Standard for Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 3 kHz to 300 GHz (1991).
3. California Code of Regulations, Title 8 - Industrial Relations, Division 1 - Department of Industrial Relations, Chapter 4 - Division of Industrial Safety, Subchapter 7 - General Industry Safety Orders, Group 14 - Radiation and Radioactivity, Article 104 - Non-ionizing Radiation, Section 5085 - Radio frequency and Microwave Radiation.
4. American Conference of Governmental Industrial Hygienists (ACGIH) ­ Threshold Limit Values for Chemical Substances and Physical Agents ­ Physical Agents Section ­ Sub-Frequency (30 kHz and below) Magnetic Fields & Sub-Frequency (30 kHz and below) and Static Electric Fields
5. Federal Communications Commission Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields ­ OET Bulletin 65, Edition 97-01, 1997

The Office of Environment, Health & Safety (EH&S) will work with you to identify and assess the microwave/RF radiation hazards in your work area. Because of the difficulties of performing actual microwave/RF radiation surveys (near field measurements, cost of equipment, etc.), it is often necessary to use calculations and/or computer models to replace actual measurements in evaluating the hazard.

Operation of radio, television, microwave, and other related communication systems using electromagnetic radiation, and carrier-current systems require prior review and approval by Communication and Network Services (CNS) and Environment, Health & Safety (EH&S). Per UC Business and Finance Bulletin IS-5, CNS, in coordination with ORS, will advise you on licensing requirements, operational issues, FCC regulations, and the appropriate exposure model to use in your hazard assessment process. Please provide ORS with a copy of your hazard assessment for regulatory review. CNS coordinates all FCC applications with the Office of President and maintains all campus-approved licenses. EH&S, in coordination with CNS, maintains an inventory of all transmission antennas on campus. Please contact EH&S before you place a new transmission antenna in or on any campus building or location.

Radio frequency-based wireless local area networks based on the IEEE 802.11b Standard are becoming available on the campus. Wireless LAN systems (indoor and outdoor) are very safe when properly installed and used. WLAN systems operate on extremely low power (less than that of a cell phone). It is important that only approved equipment be used to build a campus operated WLAN.

Construction or Modification of campus operated WLAN equipment must be reviewed and approved by CNS and EH&S in order to prevent potentially hazardous conditions from existing. The placement of base station antennas should be high on a wall or on the ceiling. This not only increases the useful range of the system but also allows for a separation distance of 50 cm, which is sufficient for safe operation. In general, persons should avoid direct contact with antennas attached to computer cards. A separation distance of 10 cm is sufficient for safe operation.

For waveguides, co-axial cables, generators, sealers, and ovens, probably the most important aspect of controlling microwave/RF radiation hazards is a careful physical inspection of the source. Leaking sources will normally show misalignment of doors or plates, missing bolts, or physical damage to plane surfaces. Sources, which are suspected of leaking, should be repaired and then surveyed with appropriate instrumentation to verify they are no longer leaking. Contact EH&S if you need assistance with evaluating microwave/RF radiation leakage hazards.

Because of the large number of microwave ovens used and their presence in nearly every Department, EH&S has special concerns about safety with these devices. Specific guidance on microwave oven safety can be found in Appendix C. It is very unusual for a commercial microwave oven to leak, but misuse, damage, and interlock failures have caused ovens to leak. Any microwave oven suspected of leaking will be surveyed, upon request, by EH&S. Please contact EH&S if you would like your ovens surveyed.

Many high voltage power supplies operate in the microwave or radiofrequency regions. If damaged, or not properly shielded, these sources can leak, producing unintended microwave/RF radiation exposure. Most of the time, the leakage from these sources is minimal and does not present a hazard. However, if you have an indication of microwave/RF radiation leakage (RF interference with other equipment or documentation warning of interference), please contact EH&S for a survey.