Expect, when in an atmosphere containing flammable gas or vapor, never shut down immediately after full load operation; the engine temperature should be allowed to stabilize by idling it for blank minutes before shutting down.

• A. 1 to 2
• B. 6 to 8
• C. 10 to 12
• D. 3 to 5

Answer: (D)

When you’re in an atmosphere with flammable gas or vapor, you want a safe cool-down before stopping the engine. After full-load operation, the engine and exhaust components are very hot, and shutting down immediately can leave hot surfaces that might ignite nearby vapors. Letting the engine idle allows those hot parts to cool gradually and helps purge residual heat and fuel from the system, reducing ignition risk as you complete the shutdown. The standard idle time of three to five minutes provides enough cooling without delaying shutdown excessively. Shorter periods may not reduce the heat adequately, while longer times offer little extra safety and just waste time.