During rapid decompression, which of the following dense atmospheric changes can occur in the cabin?

• A. A dense fog will form in the cabin
• B. The cabin becomes completely silent
• C. The air becomes cold but clear
• D. The oxygen level increases

Answer: (A)

Rapid decompression makes cabin air expand and cool quickly. That rapid cooling can push water vapor in the humid cabin air to its dew point, so moisture condenses into fog or mist inside the cabin. This is why dense fog may appear during a rapid decompression. Oxygen level doesn’t rise; the partial pressure of oxygen actually falls as the air expands and the cabin altitude rises. The cabin isn’t expected to become completely silent; wind noise and structural sounds are typical. So the formation of dense fog is the most consistent change with rapid decompression.