Which of the following is NOT a typical interlock safety signal?

• A. Guards in place
• B. Oil pressure is at a safe range
• C. Oil temperature is at a safe level
• D. Operator badge present

Answer: (D)

Interlocks are safety signals that reflect the machine’s actual safe state and prevent operation if something could be dangerous. Guards being in place is a classic interlock signal because opening a guard typically triggers a switch that immediately stops the machine, preventing exposure to moving parts. Oil pressure being in a safe range is another interlock signal: if pressure is too low or erratic, the machine should not run to avoid damage or failure. Oil temperature at a safe level likewise acts as an interlock signal to prevent overheating and potential harm.

Operator badge presence, while related to who is allowed to operate equipment, is not a direct indicator of the machine’s immediate safety state. It’s an access control measure rather than a live safety signal that gates machine operation based on current conditions. So it’s not a typical interlock safety signal.