Cabin Pressurization Effects

The Protective Role of Cabin Pressurization

Pressurization systems maintain the cabin at a pressure equivalent to an altitude typically between 6,000 and 8,000 feet, even when the aircraft is cruising much higher. This prevents hypoxia by ensuring there is enough partial pressure of oxygen for normal physiological function. The percentage of gases in cabin air remains constant with altitude, but the pressure—and thus the available oxygen—would drop without pressurization.

Effects of Cabin Pressurization

• Prevention of Hypoxia: By maintaining a lower cabin altitude, pressurization ensures the body receives sufficient oxygen, preventing the symptoms of hypoxia such as impaired judgment and reduced performance.
• Decompression Sickness: Pressurization reduces the risk of decompression sickness (DCS), which can occur when nitrogen dissolved in body tissues forms bubbles due to rapid pressure reduction.
• Gas Expansion: It also prevents the excessive expansion of gases in body cavities (e.g., intestines, sinuses), which could cause pain or injury.
• Humidity Control: Relative humidity in the cabin is affected by outside air, pressurization, and temperature. Typically, cabin air is quite dry, which can lead to dehydration or discomfort on long flights.

Pressurization Failure and Crew Actions

If cabin pressurization is lost:

• Oxygen Masks: Crew and passengers must don oxygen masks immediately to prevent hypoxia.
• Emergency Descent: Initiate a rapid descent to a safe altitude where supplemental oxygen is no longer required.
• Land as Soon as Possible: The flight must divert and land at the nearest suitable airport.
• No Further Flight: Crew should not fly for at least 24 hours after a pressurization failure due to the risk of delayed decompression sickness symptoms.

Preventing and Managing Pressurization Problems

• Pre-flight Checks: Ensure pressurization systems and oxygen supplies are functional.
• Monitoring: Continuously monitor cabin altitude and differential pressure during flight.
• Clearing Pressure Issues: Swallowing, yawning, or performing the Valsalva manoeuvre can help equalize pressure in the ears and sinuses during ascent and descent.

Factors Affecting Cabin Humidity

• External Air Source: Air drawn from outside at high altitude is extremely dry.
• Temperature and Pressurization: Both influence the relative humidity inside the cabin.

Decompression Sickness Prevention

• Limit Exposure: Avoid rapid ascents to high altitudes and minimize time spent at cabin altitudes above 18,000 feet.
• Post-Flight Precautions: Avoid flying again within 24 hours after a decompression event.