Aerotoxic syndrome

Aerotoxic syndrome is a phrase coined by the Australian toxicologist Chris Winder (†2014) the US flight surgeon Dr Harry Hoffman (†2004) and Jean-Christophe Balouet in 2000, to describe their findings of short- and long-term ill-health effects caused by breathing airliner cabin air which was alleged to have been contaminated to toxic levels (exceeding known, parts per million, safe levels) with pyrolyzed (heated to the point of decomposition) engine oils or other chemicals and their respective combustion products. Ever since there is a ongoing and highly controversial discussion among medical and scientific experts about the terminology, reported and medically diagnosed symptoms among flight crew and passengers and their possible cause. Repeated industry based investigations of such claims have failed to document cabin air has ever contained contaminants which exceeded known safe levels, applicable at ground level. An assessment by the UK's House of Lords Science and Technology Committee found that claims of health effects were unsubstantiated. An update in 2008 found no significant new evidence. As of 2013 this syndrome is not recognized in medicine.

Potential sources of contamination

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.

In rare instances, it is possible for contaminants to enter the cabin through that air-supply system. 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. While ground and flight crews, as well as passengers themselves can be sources of contaminants such as pesticides, "...bioeffluents, viruses, bacteria, allergens, and fungal spores," they have not been implicated as contaminants related to the alleged aerotoxic syndrome.

According to an information leaflet from the UK-based Committee on Toxicology (COT) possible sources of poor-quality cabin air include:

• Engine or auxiliary power unit (APU) oil leaks
• Engine or APU bay leaks
• 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 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.

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

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 in quantities much larger than are found in aviation engine oil.

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.

History

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 describe 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".

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. Both became nauseous, and the captain experienced double vision and had difficulty judging height, but managed to land the aircraft safely. Both pilots were taken to a hospital but no cause for their illness was found. 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."

The report noted that both captain and first officer had visited the forward toilet before the onset of their symptoms. 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."

Research

In 1986, the United States Congress commissioned a report by the National Research Council (NRC) into cabin air quality. The report recommended a ban on smoking on aircraft in order to improve air quality, which was brought into effect by the FAA soon after.

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."

"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."

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".

In 2011, mass spectrometric protocols were described which allow documenting exposures of individuals. A 2011 Aircraft Cabin Air Sampling Study was published in 2 parts:

According to a 2008 report by Michael Bagshaw, Director at King's College London, formerly chief medical examiner at British Airways and consultant to Airbus, there have been no peer-reviewed recorded cases of neurological harm in humans following TCP exposure. 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.

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.

This particular study cited was conducted on behalf of the mutual employer insurance BG-Verkehr which also is the insurer on behalf of the German Airlines. The methodology used in the analysis of the samples was based at large on the PhD thesis of Dr B. Schindler (who also participated in this study) and which according to its author is not capable to determine:

"...if the two isomers of cresyl-phosphate are absorbed, metabolized and segregated in urine". The author of the thesis concludes that "...possibly the present concentrations are below the detection threshold of 1.0 μg/l and can therefore not be detected with this method."

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."

In a National Institutes of Health (NIH) study, dated April, 2013, the conclusion was "Health complaints reported by air crews can hardly be addressed to o-TCP exposure in cabin air. Elevated metabolite levels for TBP, TCEP and TPP in air crews might occur due to traces of hydraulic fluid in cabin air (TBP, TPP) or due to release of commonly used flame retardants from the highly flame protected environment in the airplane."

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."

Forensic-pathological research on samples from deceased flight crew

File:Richard Mark Westgate.jpg

Richard Mark Westgate

On 12.12.2012 British Airways pilot Richard Mark Westgate was found dead in his hotel room in a suburb of Amsterdam. Since Spring 2012 he had been staying in the Netherlands for medical treatment after he became convinced that the severe neurological symptoms and pain, he was suffering, were caused by contaminated cabin air and aerotoxic syndrome. Already prior to his death he has donated his body to science in order to research the phenomenon.

File:Westgate Microscopy t-lymphocytes.jpg

Westgate Microscopy t-lymphocytes

The results of this two year long medical-forensic analysis on retained samples from his brain, spinal cord, nerves and heart muscle were published in a peer-reviewed scientific case study, authored by the participating scientists and medical experts, at the end of July 2014. The findings were pointing to the die-back of vital cells in these organs. According to the scientists involved this was caused by long-term-low-level intoxication with small quantities of organophosphates (such as they are exclusively used in aircraft lubricants).

These findings caused HM Coroner, Mr Stanhope Payne, who is in charge of the Westgate Investigation and Inquest, to notify Westgate’s former employer as well as the British Civil Aviation Authority about his concerns and calls for remedy. According to Mr Payne there is a potential risk of future deaths, especially due to failures of affected pilots. Both entities addressed by HM coroner submitted written responses in which they emphasized that the European Aviation Safety Agency (EASA) is currently conducting further research into the issue and that "the available evidence does not suggest that organophosphate chemicals are present in cabin air in sufficient quantities to pose a risk to health."

Meanwhile similar autopsies have been performed by the same team of scientists on a yet undisclosed number of deceased flight crew members, serving different international airlines. Here similar or even identical findings to those of Mr Westgate were made on these retained samples. This was made public during a video recorded press-conference, held in Berlin, Germany on July 15, 2015 by the head of the research team, Professor Dr Jeremy Ramsden (University of Buckingham), Dr Michel Mulder and the Scottish aviation lawyer Frank Cannon in regards to the findings on the samples retained from British Airways flight attendant Warren Edward Brady,. Mr Brady died on June 22, 2014 in the crew bunk aboard a British Airways flight from Rio de Janeiro to London-Heathrow.

File:Brady Microscopy.jpg

Brady Microscopy

Sensational media coverage

In a 2006 article in Aviation Today, Simon Bennett 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.

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. 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.

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), some media used it to write articles that were sensational and misleading. 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,", 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 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."

See also

• Sick building syndrome

Further reading

• Work is Related to Disease, What Establishes Evidence for a Causal Relation? Jos Verbeek, National Instutes of Health, PMC3440459, June, 2012
• Interests and the shaping of an occupational health and safety controversy: the BAe 146 case Nickolas Vakas, University of Wollongong, Australia, 2007

External links

• Aerotoxic Association - Official Webpage
• Webpage "Unfiltered Breathed In" a 126 min. documentary feature film by German aviation journalist Tim van Beveren, released in 2015