Rooftops and Antennas
What You Don't Know Can Hurt You or your Employees
We provide facility engineering services for building rooftops that have antennas mounted on them. Some are mounted well away from areas people can access and some are mounted in such a way as to create unnecessary exposure to the people who have to access the roof.
Antennas don't always present hazards. It depends on their design as well as how much power is input to them. Since RF and microwave cannot normally be felt, heard or seen, it presents an invisible issue to the stakeholder.
RF Surveys are needed when antennas present exposure risks to people. If this site had required the antennas to be mounted 6 - 7 feet from the rooftop a safety program would not have been required. In this case, the signs and ineffective barriers would not meet government standards and had already failed when we inspected the site. This link is a good resource for general information on the subject, Rooftop Antennas.
Antennas
An antennas job is to transmit or receive RF or microwave energy. Some antennas radiate energy in almost all directions (all directions would be called "isotropic"), like a low gain dipole antenna. There are other types of antennas that radiate energy in only one direction in order to communicate signals from point A to point B. Antenna exposure hazards are based on a very simple principle of Power/Area. You could think of it as the power density of the field around or in front of the antenna. An antenna with 250 Watts of power input to it and a relatively small area to to spread it out over is the antenna that presents the higher exposure hazard. A directional antenna with only 1 Watt of power input to it does not have enough energy to create a near field or far field hazard and does not need to be measured on a routine basis.
When we Perform a Safety Evaluation of Antennas:
1. Collect RF Information - (Power, frequency, antenna size, antenna gain)
2. Perform calculations - (Near field, Intermediate field, Far field)
3. Perform measurements - (Compare measured fields to calculations)
4. Institute Program - (Engineering and/or Administrative controls, if necessary)