Aerotoxic syndrome

Cabin Pressure and Bleed Air Control Panels on a Boeing 737-800

Modern jetliners have an environmental control system (ECS) that manages the flow of cabin air. Outside air enters the engines and is compressed in the forward section, prior to the combustion section, ensuring no combustion products can enter the cabin. A portion of that compressed bleed air is used to pressurize the cabin. The ECS then recirculates some of that cabin air through HEPA filters, while the rest is directed to outflow valves, ensuring there is a constant supply of fresh, clean air coming into the cabin pressurization system at all times.[6]

It is possible for contaminants to enter the cabin through the air-supply system and through other means. Substances used in the maintenance and treatment of aircraft, including aviation engine oil, hydraulic fluid, cleaning compounds and de-icing fluids, can contaminate the ECS. Ground and flight crews, as well as passengers themselves can be sources of contaminants such as pesticides, bioeffluents, viruses, bacteria, allergens, and fungal spores.

An Airbus A-320 being de-iced before take-off

Possible sources of poor-quality cabin air include exposures related to normal operations of the aircraft:

• Ozone (O₃)
• Fluorohydrocarbons (aircon systems)
• Carbon dioxide (passengers exhaling CO₂)
• Carbon monoxide (CO from jet exhaust fumes or ambient airport air)
• Temperature
• Relative humidity
• Off-gassing from interior material and cleaning agents
• Bioeffluents
• Personal-care products
• Allergens
• Infectious or inflammatory agents
• Cabin pressure/partial pressure of oxygen
• Alcohol
• Formaldehyde
• Deicing fluid
• Particulate matter (including dust which contains microbes)
• Dry ice used to keep food cold
• Toilet fluid, leaked or spilled
• Rain repellent fluid
• Pyrethroid pesticides
• Pre-existing illness—such as anemia, asthma, COPD, and coronary arterial disease—the stresses of flight could exacerbate symptoms.
• Nocebo effects can lead to serious health problems too.[7]

Jet engines require synthetic oils for lubrication. These oils contain ingredients such as tricresyl phosphate (TCP or TOCP), an organophosphate, which can be toxic to humans when in quantities much larger than are found in aviation engine oil.[8]

Engine bearing seals are installed to ensure that critical engine bearings are continuously lubricated, and 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 an odour akin to hot frying-pan fume, or, in more serious cases, by smoke in the cabin. This is known in the industry as a fume event.[9]

A year-long Australian Senate investigation in 2000 received evidence of some "successful applications for workers’ compensation" for illness which the applicants attributed to fumes on the BAe 146. Approximately 20 crew members described oil fumes leaking into the aircraft cabin. That investigative committee concluded "the issue of fume contaminants should also be considered a safety issue with regard to the ability of cabin crew to properly supervise the evacuation of an aircraft and the ability of passengers to take part in an evacuation".[10]

On 5 November 2000, both the captain and first officer of a Jersey European Airways BAe 146 became unwell while landing at Birmingham International Airport.[11]^(p1) Both became nauseous, and the captain experienced double vision and had difficulty judging height, but managed to land the aircraft safely.[11]^(pp3–4) Both pilots were taken to a hospital but no cause for their illness was found.[11]^(p1) The 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."[11]^(p56)

The report noted that both captain and first officer had visited the forward toilet before the onset of their symptoms.[11]^(p3) Four years before the G-JEAK incident, another operator reported overuse of a disinfectant (formaldehyde) for the toilets and to clean the galley floor and that inhalation of the fumes from that chemical, would produce similar 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."[11]^(p31)

In 1986, the United States Congress commissioned a report by the National Research Council (NRC) into cabin air quality.[6] The report recommended a ban on smoking on aircraft in order to improve air quality.[12] In 1988, the FAA banned smoking on domestic flights of less than two hours, and in 2000 extended the ban to all domestic and international flights.[13][14]

Research commissioned by the UK government's Department for Transport (DfT) and published in 2000 found no link to long term health. The UK Parliament's Select Committee on Science and Technology concluded 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 tricresyl phosphate (TCP or 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."[2]

"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[58] 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[59]. 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."[2]

According to a 2008 report by Michael Bagshaw, Aviation Medicine Director at King's College London, there have been no peer-reviewed recorded cases of neurological harm in humans following TCP exposure.[15] He pointed 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 were to high concentrations greatly in excess of the amount present in jet oil.[15]

In 2009 the UK House of Commons Library service to Members of Parliament summarized the research into a "relationship between the [engine oil chemical] leaks and these health symptoms" as inconclusive, citing "problems with identifying the exact chemical that might be entering the air supply and therefore identifying what impact it may have on health" and "reports of problems with fumes and/or health symptoms not being reported correctly".[16] In the same year, a relatively innovative "clean air" system was established onboard the 787 Dreamliner. Boeing, the manufacturer of the airplane, is as of yet the only airline corporation to adopt this mechanism.[17]

In his 2013 paper, "Cabin Air Quality: A review of current aviation medical understanding," Bagshaw noted further: "A German study in 2013 of 332 crew members who had reported fume/odour during their last flight, failed to detect metabolites of TCP in urine samples. The authors concluded that health complaints could not be linked to TCP exposure in cabin air.....A syndrome is a symptom complex, consistent and common to a given condition. Sufferers of the ‘aerotoxic syndrome’ describe a wide range of inconsistent symptoms and signs with much individual variability."[5]

The evidence was independently reviewed by the Aerospace Medical Association, the US National Academy of Sciences and the Australian Civil Aviation Safety Authority (CASA) Expert Panel. All concluded there is insufficient consistency to establish a medical syndrome, and the ‘aerotoxic syndrome’ is not recognised in aviation medicine."[5]

The 'nocebo effect' was among the conclusions published in a 2013 COT (Committee on Toxicity) position paper: "The acute illness which has occurred in relation to perceived episodes of contamination might reflect a toxic effect of one or more chemicals, but it could also have occurred through nocebo effects. There is strong scientific evidence that nocebo effects can lead to (sometimes severely disabling) illness from environmental exposures that are perceived as hazardous."[18]

In a 2006 article in Aviation Today, 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." 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.[19]

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.[19] The Sun also cited the UK Civil Aviation Authority finding that leakage into aircraft cabins is a very rare event occurring only if there is a fault with an aircraft.[19]

When the results of a clinical audit of the "cognitive functioning of aircrew exposed to contaminated air" were submitted by Sarah Mackenzie Ross to the UK government's Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (COT),[20] some media used it to write articles that were sensational and misleading.[19] Dagbladet.no, 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",[19] though the report itself stated that:

"[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." Additionally,

The report was a "clinical audit of aircrew seen for clinical purposes," and thus there were limitations to the 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 ... global 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."[19]

In 2015, Tim van Beveren made a documentary on aerotoxic syndrome called Unfiltered Breathed In.

• Organophosphate-induced delayed neuropathy
• Sick building syndrome

• Work is Related to Disease, What Establishes Evidence for a Causal Relation? Jos Verbeek, National Institutes of Health, PMC 3440459, June, 2012
• Martin B. Hocking; Diana Hocking (2005). Air Quality in Airplane Cabins and Similar Enclosed Spaces. Springer Science & Business. ISBN 3-540-25019-0.
• Interests and the shaping of an occupational health and safety controversy: the BAe 146 case Nickolas Vakas, University of Wollongong, Australia, 2007
• John Hoyte (2014). Aerotoxic Syndrome. Pilot Press (London). ISBN 978-0-9929508-0-4.

• Aerotoxic Association - Official Webpage
• "German Federal Bureau of Aircraft Accident Investigation Study "Fume Events" Four Safety Recommendations". Bundesstelle für Flugunfalluntersuchung (BFU). May 7, 2014. Archived from the original on April 5, 2015. Retrieved January 8, 2015.
• FACTS research - Official Webpage of the FACTS Cabin Air Study initiated by EC and EASA www.facts.aero