In semiconductor manufacturing equipment, normally closed gas supply valves that open with air pressure are used, so that if a power outage or a loss of compressed air occurs, the valves close and the supply of hazardous gas stops. Which design concept is this?

Answer: A. Fail-safe

The concept of designing a system so that it goes into a safe state when a failure or abnormality occurs is called fail-safe. A normally closed valve closes by spring force when the air pressure or power that opens it is lost, so an abnormality in power or air leads to the safe state in which the gas stops. Continuing to operate with reduced function despite a failure is fail-soft, and preventing incorrect human operation is fool-proofing.

• A. Correct. The valve closes on an abnormality, giving a safe state.
• B. Fail-soft is the idea of continuing to operate even with reduced function.
• C. Fool-proofing is the idea of preventing incorrect human operation.