What is the first response to be taken in case of an emergency during hypoxia?

In an emergency situation involving hypoxia, the primary and most immediate response is to restore a safe environment where oxygen levels are adequate. Descent below 10,000 feet Mean Sea Level (MSL) is crucial because, at lower altitudes, the atmospheric pressure is higher, which results in a higher partial pressure of oxygen available to the body. This natural increase in available oxygen can help alleviate symptoms of hypoxia more rapidly than other interventions.

While increasing oxygen levels and using an oxygen mask are important steps in managing hypoxia, they may not be as immediately effective as descent, especially if the aircraft is currently operating above the altitudes where supplemental oxygen may be necessary. Deactivating cabin pressurization is generally not an appropriate response as it could lead to further complications and is not typically a first-line action in hypoxia situations.

In summary, initiating a descent is the quickest way to respond to hypoxia and provides immediate benefits by enhancing the oxygen supply available to the pilot and passengers.