On a flight in 2010, the aircrew – two pilots and five flight attendants, smelt a kind of dirty socks odour while boarding their flight. Not knowing about the source or cause of this foul odour, they undertook the flight. But on landing the entire crew and few passengers needed emergency medical care. Both the pilots have not recovered fully, and four of the five flight attendants continue to suffer from headaches, memory loss, tremors and other symptoms (1). In another instance, an Australian appeal court in 2010 was probably the first one to award substantial damages to a cabin crew, whose respiratory illness was attributed to toxic fumes in cabin air (2).
Bluish haze or smoke in cockpit could occur due a “fume event”, emanating foul odour like “sweaty socks, wet dog, vomit, sweet oily smell” (3). These “fume events” reportedly occur in 1 in 2000 flights (0.05% overall) in commercial aviation (4).
The toxic effect of the fumes is most likely due to Tri-cresyl phosphate (TCP), an anti-wear agent in complex synthetic oil used for aircraft engines to withstand extreme environments. TCP is an organophosphate compound with neurotoxic properties (3, 5). Such pyrolised contaminants, and particles of heavy metals from the engines (nickel, cadmium, beryllium), as part of the bleed air, may be introduced into the aircraft cabin for pressurisation. This may result in regular commuters by air and the aircrew being exposed to contaminated cabin air during flight.
This exposure to the cabin air could give rise to an array of short term or prolonged non-specific physical and psychological symptoms (5). This includes fatigue, blurred vision, tremors, vertigo, tinnitus, seizures, dizziness, headache, confusion, irritation of eyes, nose and throat, respiratory discomfort, vomiting and diarrhoea, cognitive impairment, seizures etc. (3, 5).
These exhaustive and wide ranging neuro-cognitive symptoms amongst aircrew or airline passengers are due to Aerotoxic Syndrome. This illness is likely to be caused by prolonged exposure to contaminated cabin air resulting in “Organophosphate Ester Induced Chronic Neurotoxicity” (3, 5). The first such case of ‘Aerotoxic Syndrome’ was reported by Montgomery et al in 1977 (6), wherein a flight navigator in C-130 Hercules suffered an in-flight incapacitation – neuromuscular and cognitive disturbances, requiring medical attention (7). This term, ‘Aerotoxic Syndrome’, was introduced in 1999 by Hoffman, Winder and Balouet (3, 8), but has not yet been accepted in the medical parlance (3).
Since the toxic effects are dependent on the exposure to the contaminants and individual susceptibility to the toxic exposure, symptoms could be short lived or long lasting. There are no in-built safety mechanism in commercial airliners since even the oxygen drop down masks meant for loss of cabin pressure, partially recirculate air. So also, there are no known remedies except supportive treatment.
In view of increasing public awareness, some regulators have instituted research to identify gap in the scientific knowledge about Aerotoxic Syndrome, particularly the potential long term health effects of likely exposure to low level chronic exposure to contaminants in aircraft cabin air (4, 9).
Prevention of Aerotoxic Syndrome can be possible if airlines implement SOPs where aircrew are trained to recognize and/or respond to odours or fumes with appropriate action on ground (including refusal to operate flight) and in air (including option to divert to the nearest airfield). A collaboration between BAE and Quest International has announced adaptation of Quest’s technology for air sanitation for use in aircraft, called as AirManager (10). This simple to use technology is capable of decontaminating biological and chemical contaminants, including pollutants, from the aircraft cabin. Boeing 787 Dreamliner has offered the best solution to prevent any accidental contamination by engine oil. In this aircraft, cabin air is supplied by independent electrical compressors through dedicated cabin air inlets, unlike the conventional bleed air from engine as in present generation airliners (3, 11).
While considering commercial airliners, one must not forget the combat pilot in single cockpit. A word of advise to them: it is prudent to remember that even in combat aircraft, such a possibility of cockpit contamination exists. It can, however, be averted by an alert pilot when if he selects 100% oxygen on the slightest suspicion of such “fume event” and takes correct actions as per SOP for ‘smoke in cockpit’.
5. Fitzgerald D. Cabin Air Quality. Flight Safety Australia Sep-Oct 2007: 60-61
6. Montgomery, M.R., Wier, G.T., Zieve, F.J. and Anders, M.W. (1977) Human Intoxication Following Inhalation Exposure to Synthetic Jet Lubricating Oil. J. Toxicol. Clin. Toxicol. 11: 423-426.
7. Hale M, Al-Seffar J. Preliminary report on Aerotoxic Syndrome (AS) and the need for diagnostic neurophysiological tests. Journal of the Association of Neurophysiological Scientists 2008: 107-118
8. Winder, C. (Ed.) (2002) The Toxicity of Synthetic Jet Engine Oils. School of Safety Science, University of New South Wales, Sydney, Australia (as referred in 7 above).
Acknowledgement: Image courtesy www.commons.wikimedia.org