1.5.1 Hazards To Personnel (HERP)
HERP arises when RF electromagnetic energy interacts with the human body. Depending upon the operating frequency, field strength, exposure duration, and the manner in which the energy couples into the body, sufficiently strong RF fields may induce electric currents within biological tissues or produce heating through the absorption of electromagnetic energy. Modern RF safety standards are specifically designed to prevent these established adverse health effects by limiting human exposure to levels well below those at which injury is expected to occur.
The potential for HERP is influenced by many factors in addition to transmitter power. These include the operating frequency, antenna characteristics, distance from the source, the direction of the radiated beam, the duration of exposure, and the presence of nearby reflective objects that may alter the local electromagnetic field. Consequently, a relatively low-power transmitter held close to the body may produce greater localized exposure than a much more powerful transmitter located many meters away. Understanding this distinction between transmitter power and human exposure is one of the fundamental principles of RF radiation safety.
Personnel hazards are encountered primarily by people working near high-power RF transmitting equipment, including broadcasting transmitters, radar systems, satellite earth stations, industrial RF processing equipment, and certain medical installations. Maintenance engineers, communications technicians, broadcast personnel, radar operators, telecommunications riggers, and workers servicing industrial RF equipment may occasionally be required to work in areas where elevated electromagnetic fields are present. In such environments, appropriate engineering controls, administrative procedures, warning signs, access restrictions, training, and safe work practices are essential components of an effective RF radiation safety program.
Most members of the general public are not exposed to these occupational environments because transmitting installations are designed so that publicly accessible areas remain well within recognized exposure limits. Modern communications systems are therefore engineered not only to perform their intended function but also to ensure that both workers and the public are protected through appropriate equipment design, site layout, and operational procedures.
Because protecting people is the principal objective of RF radiation safety, this book is concerned primarily with HERP. The following chapters explain how RF energy interacts with the human body, how exposure is assessed, how internationally recognized exposure limits have been developed, and how practical engineering and management measures are used to ensure that RF technologies continue to be employed safely in occupational and public environments.