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Aerotoxic syndrome is a term describing the alleged short-term and long-term ill-health effects that are attributed to exposure to cabin air that has been contaminated with atomized engine oils and other chemicals.
The alleged ill-health effects that have been reported include cognitive problems, dizziness, disorientation, fatigue, nausea, breathing difficulties, anxiety, mood swings, and various other neurological problems, particularly related to the autonomic nervous system. Chronic fatigue syndrome (CFS) and Multiple chemical sensitivity (MCS) are also commonly reported by sufferers. UK government research states that adverse health effects of short duration do occur, but although it cannot rule it out, says that the available evidence is unable to conclude a link to long-term symptoms.
As of 2009 this syndrome is not officially recognized in aviation medicine.
Potential sources of contamination
With the exception of the new Boeing 787, the air in a jet or turboprop aircraft cabin is typically supplied by bleed air from the aircraft’s engines. Several advocacy groups have claimed that some aircrew and passengers have been made ill by toxins in engine oil that can enter the air supply.
Modern jetliners have an Environmental Control System (ECS) that manages cabin air. Some of the air is recirculated, while the remainder is drawn from the outside, typically via compressed engine bleed air. Airborne contaminants may potentially originate from substances used in the maintenance and treatment of aircraft, including seasonal chemicals such as de-icing fluids, or from the ECS systems.
A service information leaflet from the UK-based Committee on Toxicology (COT) provided a list of possible sources of poor quality cabin air. Some of the items on that list include:
- Underfloor hydraulic leaks.
- Ingestion of deicing fluid into APU inlet.
- Periodic maintenance task that is required to clean the forward galley oven.
- Inappropriate or excessive use of CO2 (dry ice) by caterers.
- Toilet fluid spillage, leakage and also unapproved mixing of different disinfectant fluids within the toilet.
- Leakage of the rain repellent system, or rain repellent contamination within the cabin or flightdeck.
- Spillage within baggage bays.
- Items stowed in overhead baggage bins.
Jet engines require synthetic oils for lubrication. These oils contain ingredients such as tricresyl phosphate (TCP), an organophosphate, that could possibly be toxic to humans in large quantities. Engine bearing seals are installed for the purpose of ensuring that critical engine bearings are continuously lubricated, and also to prevent engine oil from leaking into the compressed air stream. If a bearing seal fails and begins to leak, depending on the location of the seal, some amount of engine oil may be released into the compressed air stream. Oil leaks may be detected by odour, or in more serious cases, by smoke in the cabin. This is known in the industry as a “fume event”. Although most jet aircraft cabins have filters for the recirculated cabin air, the bleed air supply is not filtered.
In a flight safety bulletin to all operators, dated January 5, 2001, BAE Systems included the following information:
- During the last year there have been several reports of the appearance of smoke or fumes originating from the air conditioning system. Investigation has identified most of the root causes of these incidents:
- Technical (the majority), rectification of which prevented further occurrences.
- Self-inflicted, such as ingestion of de-icing fluid, through the APU intake and into the cabin air supply.
- Perceived, due to condensation in the air supply. This may occur if an inappropriate cabin temperature is selected, causing the air conditioning system to over cool the cabin air.
- There are many technical reasons why aircraft have smells or minor appearances of smoke from air conditioning systems including, for example, inappropriate temperature settings relative to ambient conditions or inadvertent ingestion of hydraulic fluid or de-icing fluids. Recently the main focus of attention has been on the possibility of oil from either the main power plant or the APU contaminating the cabin air via these systems. The air supply is protected from contamination by seals, which achieve maximum efficiency during steady state operation. However, they may be less efficient during transients (engine acceleration or deceleration) or whilst the engine is still achieving an optimum operating temperature. Improvements in seal design continue to improve efficiency, and when available, modifications are provided for the engines and APU.
Incidents and symptoms
Two airline labor unions claim that flight crews have been impaired or incapacitated on a number of occasions, following exposure to fumes during flight. On 5 November 2000, both the pilot and co-pilot of a Jersey European Airways BAe 146 became unwell while landing at Birmingham International Airport, with both becoming nauseous, and the pilot experiencing double vision and having difficulty judging height. Despite this, he managed to land the aircraft safely. "The first officer and commander were taken to hospital and examined, but no abnormalities were found." The subsequent incident investigation report concluded that "There is circumstantial evidence to suggest that the flight crew on G–JEAK were affected by contamination of the air supply, as a result of oil leakage from the auxiliary power unit (APU) cooling fan seal into the APU air stream, and into the ECS system ducting. This contamination allowed fumes to develop, a proportion of which entered the cabin and cockpit air supply."
That same AAIB Report also noted that both the captain and the first officer had visited the forward toilet, before the onset of their symptoms. About the same time of the G-JEAK incident, another operator reported overuse of a disinfectant (formaldehyde) for the toilets and to clean the galley floor and then inhalation of the fumes from that chemical, would produce the identical symptoms reported by both the captain and first officer of G-JEAK. "The CAA notified UK Operators at that time (CAA ref. 10A/380/15, dated 2 August 1996) of this potential hazard, as the misuse of this agent was apparently widespread."
The alleged ill-health effects that have been reported include cognitive problems, dizziness, disorientation, nausea, breathing difficulties, anxiety, mood swings, malaise, diarrhoea and various other neurological problems, particularly related to the autonomic nervous system. Chronic fatigue syndrome (CFS) and Multiple chemical sensitivity (MCS) are also commonly reported by sufferers. UK government research states that adverse health effects of short duration do occur, but although it cannot rule it out, says that the available evidence is unable to conclude a link to long-term symptoms.
Aviation Organophosphate Information Site (AOPIS) is a non-profit group set up by airline crews in Australia in 2001. AOPIS provides campaigns and information by way of articles, scientific papers, research papers, governmental policy and a documentary, on medical and flight safety issues relating to contaminated air exposure on commercial and military aircraft.
The Global Cabin Air Quality Executive (GCAQE) was established in 2006 to represent air crew with regard to cabin air quality.
Lastly, the Aerotoxic Association was set up on 18 June 2007. The association is run by a group of airline pilots who believe they were made ill by contaminated cabin air.
In 1986, the United States Congress commissioned a report by the National Research Council (NRC) into cabin air quality. The landmark report recommended a ban on smoking on aircraft in order to improve air quality, which was brought into effect by the FAA soon after.
However little research took place into cabin air quality in the following 15 years, despite ongoing concerns raised by passengers and crew. In 2000, Congress responded by once again directing the NRC to conduct an independent study into cabin air quality, and to make recommendations for improvements.
Ongoing research commissioned by the UK government's Department for Transport (DfT) has not managed to conclude a link to long term health. In its response to the many complaints received "from a number of witnesses, particularly the Organophosphate Information Network, BALPA, and the International Association of Flight Attendants, expressing concerns about the risk of TOCP poisoning for cabin occupants, particularly for crew who might be subjected to repeated exposure in some aircraft types, as a result of oil leaking into the cabin air supply," the UK Parliament's Select Committee on Science and Technology, concluded:
- "This question - including the potential effects on aircrew from any long-term exposure - has been looked at in much greater detail by a Committee of the Australian Senate inquiring into particular allegations of such contamination in the BAe 146. Although its Report referred extensively to cabin air quality and chemical contamination in the aircraft, and recommended that the engine lubricating oil used (a Mobil product) be subjected to a further hazardous chemical review, it made no specific points about TCP or TOCP that have given us additional concerns. The absence of confirmed cases of TOCP poisoning from cabin air and the very low levels of TOCP that would be found in even the highly unlikely worst case of contamination from oil leaking into the air supply lead us to conclude that the concerns about significant risk to the health of airline passengers and crew are not substantiated."
According to a report by Prof Michael Bagshaw, there have been no peer-reviewed recorded cases of neurological harm in humans following TCP exposure. He points to an unpublished report from the Medical Toxicology Unit at Guy's Hospital in 2001 which looked at all exposures dating back to 1943 that showed that all documented exposures are to high concentrations greatly in excess of the amount present in jet oil. He also noted that studies in Canada and the USA were unable to detect TCP in the cabin during flight. Prof Bagshaw notes that the symptoms are "largely the same as those reported by participants in all phase I drug trials", and are similar to the symptoms experienced by patients suffering from chronic fatigue syndrome, gulf war syndrome, Lyme disease, chronic stress and chronic hyperventilation.
In a 2006 article in Aviation Week, Dr. Simon Bennett[Notes 1] found that media coverage of contaminated cabin air has been sensationalized, with distortions of facts. He cited headlines such as "You are being gassed when you travel by air," and "Death in the Air" and a sub-title of "Every day, planes flying in and out of London City Airport are slowly killing us." Dr. Bennett noted that the article with the latter subtitle stated in its body that the Department of the Environment, Transport and the Regions (DETR) found that oil seal failures occur only once in every 22,000 flights. Similarly, the Sunday Sun in an article entitled "Flight Fumes Warning", cited the industry pressure group AOPIS in saying that passengers jetting off to their holidays were unknowingly exposed to deadly chemicals, and that brain damage could result if they breathed the toxic fumes. However the Sun too admitted that the UK Civil Aviation Authority found that leakage into aircraft cabins is a very rare event that occurs only if there's a fault with an aircraft.
He found that when Sarah Mackenzie Ross submitted the results in 2006 of a clinical audit of the "cognitive functioning of aircrew exposed to contaminated air" to the UK government's Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (COT), some media used it to write articles that were sensational and misleading.
The Dagbladet.no, a Scandinavian news-based Internet site, wrote that the Ross report "... adds weight to the hypothesis that compounds resembling nerve gas in cabin and flight deck air have caused irreparable neurological damage to aircrew." That, despite the fact that:
- The report was a "clinical audit of aircrew seen for clinical purposes," and was not a valid research study.
- The "'aircrew seen for clinical purposes' were in fact a self-selecting sample of pilots." Meaning that they all came from a group that already believed they had been damaged by contaminated air.
- That self-selected sample group "was not compared to a control group."
- Ross herself said "The conclusions that can be drawn from these findings have limitations."
- She further stated: "The author ... makes no attempt to ascribe causality."
- The report's conclusions were ambiguous: "There was no evidence of ... intellectual decline, language or perceptual deficits .... Indeed pilots were intact on the vast majority of tests. However, there was evidence of under- functioning on tests associated with psychomotor speed, executive functioning and attention ...."
- And finally, "[T]he evidence available to us in this audit does not enable us to draw firm conclusions regarding a causal link with exposure to contaminated air."
The most prominent feature of Dagbladet.no's reporting was its sensationalism. One article used the banner headline: "You are being gassed when you travel by air." That implied that cabin air is contaminated on a routine basis, but, that is not true. In another article, the Dagbladet.no contradicted itself: "When asked by Dagbladet.no for information, the Norwegian Civil Aviation Authority's analysis section ... revealed 13 mysterious incidents which may be connected with contaminated cabin air in aircraft [between 2001 and 2005]." Dr. Bennett asked, "...how a report that was careful not to ascribe causality could be seen to support the hypothesis that organophosphates in flight-deck and cabin bleed air cause neurological damage among aircrew?"
The Times also reported on Dr. Bennett's research into flight crew fatigue and stress. Dr. Bennett commented on that article: "Despite its positioning as a 'quality' newspaper, The Times produced a determinedly skewed account of the research. Important facts—like the limitations of the research methodology (the research paper was based on interviews with just 11 pilots)—were not mentioned by The Times."
- Dr. Bennett is director of the Scarman Centre's distance-learning MSc in Risk, Crisis and Disaster Management, with a PhD in sociology from Brunel University, London.
- Nicolas Mateesco Matte (2002). Aerotoxic Syndrome. Annales de Droit Aérien et Spatial 27: 86–87.
- Balouet, Winder & Hoffman. "Aviation and Exposure to Toxic Chemicals".
- Cabin Air Quality, House of Commons Library, 2009
- Hale MA, Al-Seffar JA (September 2009). Preliminary report on aerotoxic syndrome (AS) and the need for diagnostic neurophysiological tests. Am J Electroneurodiagnostic Technol 49 (3): 260–79.
- Mike Sinnett. 787 No-Bleed Systems: Saving Fuel and Enhancing Efficiencies. Aero 2007-04.
- GCAQE, 2009
- National Research Council (U.S.), Committee on Air Quality in Passenger Cabins of Commercial Aircraft (2002). The Airliner Cabin Environment and the Health of Passengers and Crew, National Academies Press.
- Learmont Flight International, 6 May 2008.
- Helen Muir. Cabin Air Sampling Study Functionality Test. Cranfield University via Department for Transport. URL accessed on 2010-05-13. [dead link]
- (2001). All Operator Message Ref: 00/030V. BAE Systems.
- Air Accidents Investigation Branch Report on the incident to BAe 146, G-JEAK during the descent into Birmingham Airport on 5 November 2000, p.1.
- Air Accidents Investigation Branch Report on the incident to BAe 146, G-JEAK during the descent into Birmingham Airport on 5 November 2000, pp. 3– 4.
- Air Accidents Investigation Branch Report on the incident to BAe 146, G-JEAK during the descent into Birmingham Airport on 5 November 2000, p.56.
- Air Accidents Investigation Branch Report on the incident to BAe 146, G-JEAK during the descent into Birmingham Airport on 5 November 2000,p.31.
- Geoffrey Thomas (January/February 2010). Clearing the Air. Australian Aviation.
- Balouet, Winder & Hoffman. "Aviation and Exposure to Toxic Chemicals".
- Cabin Air Quality, House of Commons Library, 2009
- "You are being gassed when you travel by air" - Dagbladet
- "Contaminated air questions persist" - Australasian Business Intelligence
- "AOPIS - Air Travel and Health Follow-Up Inquiry: Call for Evidence"
- United States National Research Council (1986). The Airliner Cabin Environment: Air Quality and safety, National Academic Press.
- Template:Cite report
- Template:Cite report
- Professor Michael Bagshaw. The "Aerotoxic Syndrome". European Society of Aerospace Medicine.
- Dr. Simon A. Bennett. Through a Glass Darkly. Air Safety Week. URL accessed on 2010-04-30.
- Victoria Gill. Defra Leaves Organophosphate Study Hanging in the Balance. Royal Society of Chemistry.
- Martin B. Hocking, Diana Hocking (2005). Air Quality in Airplane Cabins and Similar Enclosed Spaces, Springer Science & Business.
- Lord Alec Broers Broers, Air Travel and Health: An Update, Report with Evidence, 1st Report of Session 2007-08, The Stationery Office, Great Britain: Parliament: House of Lords: Science and Technology Committee, ISBN 0104011785, http://books.google.com/books?lr=&id=CWOMPpCoXp4C
- Captain Susan Michaelis (2007). Aviation Contaminated Air Reference Manual, Susan Michaelis.
- Interests and the shaping of an occupational health and safety controversy: the BAe 146 case, Nickolas Vakas, University of Wollongong, 2007
- Ill health Following Exposure to Contaminated Aircraft Air: Psychosomatic Disorder or Neurological Injury?, S Mackenzie Ross, A Harper, J Burdon, 2006
- Aerotoxic research project at the University of New South Wales
- Cabin Air Systems at Boeing
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