In which conditions is emergency 100% oxygen required?

The requirement for 100% emergency oxygen is critical in specific situations where the integrity of the cabin environment is compromised or where there is a risk to passenger safety due to altitude or medical emergencies. At altitudes above 34,000 feet, the atmospheric pressure decreases significantly, which can lead to a lack of sufficient oxygen in the air—conditions where supplemental oxygen becomes necessary.

In addition to high-altitude situations, the need for 100% oxygen arises in medical emergencies where a passenger may be experiencing serious health conditions that require increased oxygen levels. Furthermore, the presence of smoke or fire necessitates 100% oxygen to mitigate the effects of smoke inhalation, ensuring that individuals have a clean air supply free from harmful contaminants.

The other scenarios listed do not universally mandate 100% oxygen. For example, moderate turbulence might require heightened awareness and safety procedures, but it does not inherently risk oxygen deprivation. Similarly, flying over populated areas generally does not influence oxygen requirements unless altitude or other emergency circumstances dictate it. Cases of engine failure during ascent may demand emergency procedures, but they do not automatically necessitate the use of 100% oxygen unless additional factors, like altitude or cabin depressurization, are present.