What term describes a device or system that prevents operation unless specific conditions are met?

• A. Hazard Analysis
• B. Permit
• C. Operating Instructions
• D. Interlock

Answer: (D)

Interlock is a safety mechanism that prevents equipment from starting or continuing to operate until predefined conditions are met. This keeps unsafe states from being entered accidentally, enforcing a safe sequence or prerequisite before any operation can occur. In flammable-refrigerant systems, interlocks might stop a compressor from starting if a service panel is open, or prevent ignition sources from energizing while a gas detector indicates a hazardous condition, ensuring the system only runs when conditions are safe.

Hazard analysis is about identifying potential hazards and assessing risk, not a device that blocks operation. A permit is authorization to perform work, not a device that enforces safe operation. Operating instructions are the guidelines for how to operate, not a mechanism that prevents action.