The purpose of this AIR is to discuss air quality issues and environmental factors in commercial airplanes. This AIR provides general information and references more detailed SAE references regarding on Environmental Control System (ECS), air quality contaminants, cabin pressurization, temperature, and humidity that affect the perception of the cabin environment. A system safety assessment utilizing a Functional Hazard Assessment approach is also included. The airplane cabin is a unique environment that is low in humidity and pressurized to a cabin altitude of up to 2400 m (8000 ft). Multiple factors affecting our perception of environmental comfort include being subject to continuous noise and vibration, accelerations in multiple directions, and potential exposure to contaminants. The design of the cabin environment system along with the airline maintenance/operations is intended to provide a safe, healthy, and comfortable cabin environment.