A fume event occurs when bleed air used for cabin pressurization and air conditioning in a pressurized aircraft is contaminated by fluids such as engine oil, hydraulic fluid, anti-icing fluid, and other potentially hazardous chemicals. Turbine engine oil is an irritant and contains neurotoxic chemicals such as tricresyl phosphate. The aviation industry claim that engine oil does not contain sufficient quantities of such chemicals to cause long-term damage. However, there is some historical evidence that would seem to contradict this statement. In 1959, over 10,000 people in Morocco were paralyzed or otherwise affected after ingesting small quantities of tricresyl phosphate in their cooking oil. Unlike tricresyl phosphate, hydraulic fluid — although non-toxic in small quantities — is extremely irritating to the eyes and skin, which creates a hazard to pilots during a fume event but causes no lasting damage. Deicing fluid has a strong smell but is not very irritating or toxic if inhaled.
Because airliners fly at very high altitudes, the cabin must be pressurized to provide a safe quantity of breathable oxygen to passengers and crew. The cabin is pressurized with bleed air tapped from the jet engine's compressor sections, which are prior to the combustion sections. That air is very hot and must be cooled by heat exchangers before it is directed into the air conditioning units, which cool it even further.
Handling of fume events
In the event of fumes or smoke in an aircraft, flight deck crew will wear pressurisedoxygen masks in order to avoid breathing in irritating fumes. Goggles are also available if necessary. However, no protection is available for passengers, as cabin oxygen masks are not intended to protect against fumes, and will not drop unless a depressurisation occurs. Cabin crew may be able to use portable oxygen masks if they identify the fume event in time. If the fumes do not subside after an attempt is made to diagnose and fix the problem, the flight is diverted to a nearby airport. In a severe fume or smoke event, the aircraft might descend to an altitude of or lower where it can safely be depressurized.
Health effects
The human physiological effects of fume events are yet to be fully understood by the medical community. Signs and symptoms of exposure can be misdiagnosed as other common ailments, due particularly to the delay between exposure to fumes and the onset of associated symptoms. While most aeromedical professionals believe no long-term health effects exist from fume events, some consumer and aircrew advocacy groups claim that it can cause a medically-unrecognized condition called aerotoxic syndrome.
