If it is found that MPE limits are exceeded at any given point on a rooftop where people could be exposed, a safety plan must be developed and in place to ensure the safety of workers, tenants, and the general public. Under OSHA and FCC guidelines there are two separate limits for exposure, one for workers in what are referred to as "controlled areas," and one for the general public in what are called "uncontrolled areas." Exposure problems in uncontrolled areas are typically less common than exposure problems in controlled areas. Upon learning that MPE limits are exceeded on a rooftop, there are several steps that need to be taken to mitigate potential hazards and liability.
Restricting access to an area where MPE limits are exceeded is the easiest
and most cost effective way of controlling access to high RF levels. On a rooftop,
one practical means of access restriction would be fencing off the high RF areas
and having the proper signs posted. Figure 2 shows the American National Standard
Institute (ANSI) approved Radiation Hazard Signs. Additional solutions to limiting
public exposure to RF emissions include elevating rooftop antennas and applying
shield devices to protect personnel from the antennas' radiation. Because there
are personnel, such as HVAC workers, who must work in or near these high RF
areas, it is important that these workers are properly trained in RF safety.
Workers must be alerted to exposures and trained to work within the time averaged
exposure limits set forth by OSHA and the FCC. To ensure that the time-averaged
MPE limits are not exceeded for workers, possible solutions include dividing
the work up into several intervals, limiting access to specific periods of time,
and shutting off or reducing the transmit power of antennas in the effected
area. These are just a few of the practical steps that will both ensure the
radiation safety of a rooftop RF site and decrease any liability issues.
