Safety interlocks are appropriate for personnel protection in many situations where there is danger from sources of energy. The use of interlocks for personnel protection rather than sole reliance on administrative controls, depends on the nature and severity of the hazard and on the interactions of personnel with the hazard.
Interlock systems act automatically to protect personnel from danger, and are valuable where exposure to a hazard is frequent or routine and human error is likely. Primary safety shall be provided by proper operating procedures. When appropriate a Safety Analysis Document (SAD) or Safety Analysis Report (SAR) shall be in place which embodies commitments to operate the facility according to stated procedures and within a stated safety envelope. If an interlock system is required, the design and implementation must be adequate to assure that the facility operates in compliance with the SAD/SAR. Individuals tend to rely on interlock protection, and a poorly designed interlock or one which is not maintained or tested may actually increase the likelihood of an accident. For this reason the use of a safety interlock system carries technical design requirements, as well as an ongoing responsibility for maintaining, testing and controlling its configuration.