If operation of the vent blower fan is desired prior to starting engines, how long must you wait after turning off the vent blower before opening the cabin door or emergency exit?

• A. 30 seconds
• B. 45 seconds
• C. 60 seconds
• D. 90 seconds

Answer: (B)

The main idea here is allowing the cabin to settle after you stop ventilating before you open the door. When you turn off the vent blower, the cabin air is no longer being actively circulated, but the aircraft’s pressurization system may still hold a differential pressure or the outflow valve is adjusting to bring the cabin back to ambient. Opening the cabin door or emergency exit while there’s still pressure or a strong air flow can slam the door, cause injury, or create a gust of air that’s uncomfortable or unsafe.

Waiting 45 seconds gives the cabin enough time to depressurize and the air to settle through the outflow valve, so the door can be opened safely with minimal surprise air movement. It’s a short but important precaution to ensure safe door operation after stopping ventilation.