At what RPMs should the engine be set when leaving the apparatus running?

When leaving the apparatus running, setting the engine RPMs in the range of 900-1000 RPMs is appropriate for several reasons. This is typically the optimal range for maintaining the necessary power output while ensuring the engine operates efficiently without putting undue stress on its components.

Operating at this RPM range allows for adequate battery charging and sufficient power for auxiliary systems like lights, radios, and pumps without overworking the engine. In many fire service applications, this RPM setting helps maintain a steady idle without burning excessive fuel or increasing wear on the engine's internal parts. Additionally, it provides enough cooling and lubrication, which is essential for the longevity of the engine.

Higher RPMs could lead to increased engine wear and fuel consumption, while lower RPMs might not effectively support the required systems during operation. Thus, this choice strikes a balance that is generally accepted in fire service protocols, making it the suitable choice for safely leaving the apparatus running.