What: RF Exposure & Safety
When: February 16, 1999 7:00 PM

He mentioned that the FCC has on its web site, a program for calculating ground level power density based on a standard antenna. This program was originally developed by the EPA in its study a few years ago when there was a great deal of interest in personal exposure to RF from various sources ranging from cellular phones to broadcast transmitters.

This particular software was written specifically for the FM broadcast calculations.

FM broadcasters are now required to have a study performed on each transmitter site. The study can take the form of simple calculations which assume worst case radiation from the antenna, or a special power density measuring device may be used, which will accurately determine where it is safe to move around or climb on a tower. A policy and procedure must be worked out at each site for tower workers to know at what elevation transmitter power must be reduced or turned off.

Protection can be in the form of limited time exposure to higher levels of radiation. Some tower sites may have signs establishing a cycle, which will protect the workers. Three minutes exposed and three minutes in safety (such as a shelter) is a typical example of an acceptable cycle time. Some special garments have been developed which reduce the amount of exposure the wearer will experience.

Personal clip-on units can be purchased to help a worker know when he is exposed to higher levels of radiation. Typically, the unit will trigger a light which must be manually reset, and may even sound a beep. In the case of someone wearing a protective garment, a specially desensitized version of the clip-on unit may be worn to indicate when even the suit may be inadequate.

The FCC does not put itself in the position to set standards. They have taken the studies and recommendations of the EPA, OSHA, and others to set limits on the specific absorption rate (SAR) experienced in RF fields.

In answer to the problem of broadcasters running into local and state power limits that are even more restrictive than the federal ones, Dr. Cleveland answered that the only preemption allowed at present is the personal wireless service. Broadcasters have been hit from all directions in recent years when they try to change locations or even change the present facility.

One of the studies Dr. Cleveland was involved with included a rooftop where cellular phone and paging service was heavily sprinkled over the rooftop. They discovered that one structure was a paging service, which transmitted intermittently. The antenna was not elevated, and a person could stand directly in front of the radiating element. The exposure was well above the limits, and the installation had to be changed. In this case, there were two choices - raise the height of the antenna, or limit access by means of a fence.

Dr. Cleveland showed pictures of a test setup, which was used to test RF exposure to cellular phones and handy talkies. It was a hollowed-out dummy, which was filled with a solution to simulate human tissue, and a probe was inserted in the head at strategic locations to measure the potential exposure of the brain to the near field RF.