When the doors of your aircraft close you might have some thoughts about safety. Where's your lifejacket, the nearest exit, what to do if you have to adopt the brace position, but what if the greatest danger is the air you breathe?
The air you inhale aboard a jet aircraft is known as bleed air. Since this air is bled off from the compressor stage of a jet engine, before fuel is added and ignited, it should be as clean and pure as the air outside the cabin, but that's not necessarily the case.
The engine's fan blades rotate constantly and at high speed around the central shaft of the engine. This requires a lubricating oil and one of the most commonly used ingredients in this oil is tricresyl phosphate, TCP, an organophosphate that also happens to be a potent neurotoxin.
Carbon seals are designed to prevent the oil from leaking into the forward stages of the engine and mixing with the bleed air, but these seals can degrade over time or simply fail. In that event, it becomes possible for the oil to burn, mix with the bleed air and enter the aircraft, where its harmful cargo of TCP enters the lungs of passengers and crew.
There are no sensors to tell flight crew when this is happening, nor will the high efficiency particulate air filters that scrub cabin air have any effect since this is a gas. Passengers and crew might detect a burning smell. In an extreme case smoke might fill the cabin, known as a fume event.
Passengers and crew whose health is affected as a result of exposure to this contaminant in the aviation environment have been described as suffering from aerotoxic syndrome, and the effects can be long-term and life-threatening. Symptoms include fatigue, blurred vision, nausea, breathing difficulties, headache, memory loss, convulsions, tremors and cognitive impairment, which includes the inability to carry out routine tasks, not a skill you want your pilot to lose.
Nicknamed "asbestos of the skies", in some cases aerotoxic syndrome will bring your career to a grinding halt. It can even kill you, and elevated levels of TCP have been found on autopsies performed on flight crew who reported symptoms associated with aerotoxic syndrome.
Not surprisingly, pilots and cabin crew are the industry that most commonly reports these symptoms and the Aerotoxic Association was founded 2007 by medically retired aircrew to raise public awareness and pressure airlines to develop solutions.
The response of airlines has been to bat away reported incidents of aerotoxic syndrome with statements to the effect that they take every precaution to ensure the health and safety of their passengers and crew and that they act in compliance with airline regulatory authorities, and compliance is a no-pain item for airlines. For example, there is no requirement for an aircraft that experiences a fume event to land at the nearest airport, even when a smoke-filled cabin leaves everyone on board coughing, wheezing and with watery eyes. If it happens at the beginning of a long flight, the aircraft can continue to its destination.
Organophosphates are an ever-present fact in the modern environment. They're found in offices, in cars, on computer screens and probably in the dust in your lounge room due to the flame retardants used in the foam in soft furnishings. Not surprisingly, swabs will often detect measurable quantities of organophosphates in aircraft interiors. An analysis conducted by German airline Condor revealed that 19 per cent of swabs of their aircraft interiors tested positive for TCP.
Despite several studies since the term "aerotoxic syndrome" was coined in 1999, there is a lack of scientific evidence that points the finger of responsibility at the airline industry. A report commissioned by Britain's Department of Transport and conducted by Cranfield University, a postgraduate facility specialising in science, engineering and technology, tested air quality in 100 flights in five different aircraft types.
The main finding from the study concluded there was no evidence for target pollutants in the aircraft cabin environment, including TCP, at levels exceeding health and safety standards. Levels observed were comparable to those typically experienced in domestic settings. Comforting as it sounds, this does not alter the fact that aircrew report a higher incidence of aerotoxic syndrome than the general population.
One of the problems for anyone seeking to blame the airline industry for poor health due to aerotoxic syndrome, and possibly looking to claim for damages, is the difficulty of ascribing blame.
It appears that our bodies don't all respond to organophosphates in the same way. Dr Michel Mulder, a medical doctor specialising in aviation medicine, puts it down to basic biochemistry, depending on the type of enzymes in an individual's liver. Just as the individual ability to detoxify and metabolise alcohol varies, so too does the ability to deal with organophosphates.
According to Mulder, a DNA test of about 70 individuals devised by two laboratories in Europe revealed a small category identified as "poor metabolisers" who would develop problems in about three to four years after regular, low-level exposure to organophosphates. That exposure could come from the everyday environment as much as from flying, giving yet more ammunition to airlines seeking to deflect claims that they are responsible for health problems that an individual might attribute to aerotoxic syndrome.
One exception to the universal adoption of the bleed-air system in jet airlines is Boeing's 787 Dreamliner, the first with a no-bleed system. The intakes that duct air into the cabin are located well away from the engines, with no possibility of that air being contaminated by burnt oil from the aircraft's own engines. According to Boeing their non-bleed system offers improved fuel consumption and reduced maintenance costs, but any flyer concerned about the risk of aerotoxic syndrome has reasons to cheer.