10.7.2 Substitution
If elimination is not reasonably practicable, substitution replaces the plant, process, source, or work method with a less hazardous alternative.
The substitute must achieve the required operational outcome while reducing the inherent RF hazard; merely adding a barrier or changing access arrangements is not substitution.
Examples include:
- replacing RF plant with a lower-power or lower-leakage model;
- using a non-RF or lower-exposure process where it is technically suitable;
- using a low-power test source instead of operating the full-power transmitter;
- selecting system technology that achieves the required service with lower transmitted power; or
- replacing a continuous high-power process with a lower-power or lower-duty-cycle technology where it provides an equivalent result.
Substitution should be considered during procurement, design, and modification, with any new hazards introduced by the alternative included in the assessment.
10.7.3 Engineering Controls
Engineering controls are generally the most effective practical option after elimination and substitution because they act on the source, transmission path, or physical access arrangement without relying primarily on individual behavior.
They should be designed for the maximum intended operating conditions and, where failure could permit excessive exposure, should be fail-safe or supported by appropriate monitoring and testing.
Examples include:
- physical barriers that prevent access;
- RF shielding around sources, feeders, waveguides, or enclosures;
- fail-safe interlocks that disable transmission when an access door or panel is opened;
- automatic shutdown or power limiting under specified access or maintenance conditions;
- antenna location, height, orientation, or beam control that reduces accessible exposure;
- built-in low-power maintenance or test modes;
- earthing large conductive objects to reduce contact-current hazards;
- waveguide-below-cutoff ventilation or penetration shielding;
- built-in RF leakage detectors, alarms, or equipment-status indications; and
- remote control and monitoring that remove the need to work near an active source.
- Engineering controls should be commissioned, functionally tested, inspected, and maintained so that their continuing effectiveness is known.
Good engineering design reduces both exposure and dependence on more restrictive administrative arrangements throughout the life of the installation.