Interlocks shall be provided in the control system and must be which of the following?

• A. Fail Safe
• B. Fail Operational
• C. Manual
• D. Automatic

Answer: (A)

Interlocks are safety features that prevent hazardous operation by forcing a safe condition whenever prerequisites aren’t met or a fault occurs. Requiring them to be fail-safe means that if any part of the control system fails, the interlock automatically defaults to a safe state, stopping the hazardous action or preventing ignition. This automatic safe fallback is essential in flame effects control, where a fault could quickly lead to an unsafe situation if the system continued operating.

If interlocks were fail-operational, the system would try to keep running after a fault, which could allow a dangerous condition to persist. Manual interlocks rely on a person to intervene, which introduces delay and variability. Automatic alone doesn’t specify how the system behaves in a fault, potentially leaving unsafe conditions unaddressed.