Which is NOT a material effect of decompression?

The correct response identifies that internal atmospheric cooling is not a material effect of decompression. When decompression occurs, the immediate effects primarily relate to changes in cabin pressure and the physiological implications for those on board.

Upon decompression, one significant consequence is that oxygen masks drop down to provide supplemental oxygen, compensating for the lack of breathable air due to the sudden loss of cabin pressure. Passengers and crew are at risk of hypoxia, so this response is crucial for maintaining safety.

Furthermore, the seatbelt sign is activated as a safety measure, signaling passengers to remain seated and secure. This action is part of standard operating procedures during sudden changes in cabin conditions.

While dense fog in the cabin may occur as a result of the sudden change in pressure and air temperature, it is the more immediate measures and protocols—like the deployment of oxygen masks and the activation of the seatbelt sign—that define the material effects of decompression.

Internal atmospheric cooling does not necessarily result from decompression. The air in the cabin does experience a decrease in temperature due to pressure changes, but this is not a direct, material effect in the same sense as the other options, which directly pertain to safety protocols and immediate responses to decompression situations.