Fume event

From Wikipedia, the free encyclopedia

A fume event occurs when bleed air used for cabin pressurisation and air conditioning in a pressurised aircraft is contaminated by fluids such as engine oil, hydraulic fluid, anti-icing fluid, and other potentially hazardous chemicals.^[1]

How cabin pressurisation works

Because airliners fly at very high altitudes, the cabin must be pressurised to provide a safe quantity of breathable oxygen to passengers and crew. The cabin is pressurised with bleed air tapped from the jet engine’s compressor sections, which are prior to the combustion sections. Bleed air is very hot and must be cooled by heat exchangers before it is directed into the air conditioning units, which cool it even further.^[2]

To prevent fume events, the Boeing 787 pressurises its air with electrical compressors rather than the engines.^[3]

Handling of fume events

In the event of fumes or smoke in an aircraft, flight deck crew will wear pressurised oxygen masks in order to avoid breathing in irritating fumes. Goggles are also available if necessary. Cabin crew may be able to use portable oxygen masks if they identify the fume event in time. If the fumes do not subside after an attempt is made to diagnose and fix the problem, the flight is diverted to a nearby airport. In a severe fume or smoke event, the aircraft might descend to an altitude of 10,000 feet (3,000 m) or lower where it can safely be depressurised.^[4]

An FAA-funded study found that fume events occur on 1 in 5,000 flights; some planes may have multiple consecutive events if the leak is not fixed.^[3] Sensors that can detect air quality issues are available and the airline Lufthansa has requested their installation, but Boeing declined due to fear of litigation from crew or passengers sickened by detectable fume events.^[3]

Health effects

The human physiological effects of fume events are yet to be fully understood by the medical community. Signs and symptoms of exposure can be misdiagnosed as other common ailments, due particularly to the delay between exposure to fumes and the onset of associated symptoms. While most aeromedical professionals believe no long-term health effects exist from fume events, some consumer and aircrew advocacy groups claim that it can cause a medically-unrecognised condition called aerotoxic syndrome.^[5]^[6]

Turbine engine oil is an irritant and contains neurotoxic chemicals such as tricresyl phosphate. The aviation industry claims that engine oil does not contain sufficient quantities of such chemicals to cause long-term damage.^[5] However, there is some historical evidence that would seem to contradict this statement; in 1959, over 10,000 people in Morocco were paralyzed or otherwise adversely affected after ingesting small quantities of tricresyl phosphate in their cooking oil.^[7]

Hydraulic fluid, although non-toxic in small quantities, is extremely irritating to the eyes and skin, which creates a hazard to pilots during a fume event but causes no lasting damage.^[8]

Deicing fluid has a strong smell but is not very irritating or toxic if inhaled (though it has significant toxicity when ingested).^{[citation needed]}

It is not mandatory for fume events to be reported in the U.S.^[3]

Many lobbying groups have been set up to advocate for research into this hazard, including the Aviation Organophosphate Information Site (AOPIS) (2001), the Global Cabin Air Quality Executive (2006), and the UK-based Aerotoxic Association (2007). Cabin Environment Research is one of many functions of the ACER Group,^[9] but their researchers have not yet established any causal relationship.^[10]^[11]

Although a study made for the EU in 2014 confirmed that contamination of cabin air could be a problem, the study also stated:

“A lot of reported fume events caused comfort limitations for the occupants but posed no danger. A verification of cabin air contamination with toxic substances (e.g. TCP/TOCP) was not possible with the fume events the BFU investigated.”^[12]

While no scientific evidence to date has found that airliner cabin air has been contaminated to toxic levels (exceeding known safe levels, in ppm, of any dangerous chemical), in March 2010 a court in Australia in ruled in favor of a former airline flight attendant who claimed she suffered chronic respiratory problems after being exposed to oil fumes on a flight in March 1992.^[13] Such testing is infrequent due to Boeing’s refusal to install air quality sensors in its planes, fearing litigation from passengers or crew over fume events. In the U.S., airlines refused to allow flight attendants to carry air samplers after Congress mandated chemical measurements.^[14]

The FAA has revoked the medical certificates of several pilots who developed neurological issues after fume events.^[15]

A Los Angeles Times analysis^[3] of NASA safety reports from January 2018 to December 2019 identified 362 voluntarily-reported fume events, in which almost 400 pilots, flight attendants and passengers received medical attention. On 73 or more of those flights, pilots used emergency oxygen. Four dozen pilots were impaired so far as to be unable to perform their duties. Boeing told the Times that they believe no credible data shows that oil leaks into the bleed air stream can cause serious injuries. By contrast, a judge who awarded workers’ compensation to a pilot who had suffered toxic encephalopathy (brain damage) from a fume event condemned the airline industry’s obstructionism around fume events.^[3]

Fume events: The toxic gases that may be harming aircrew and passengers

25 February 2020 BBC

Aircraft fume events

NHS

Doctors and other health professionals may see patients who report symptoms following a ‘fume’ event – an unusual odor, mist or smoke – on an aircraft. The pattern of symptoms reported is quite variable and health professionals have asked for guidance on how best to manage such patients.

The Care Pathway has been developed by an independent working group including experts in toxicology, epidemiology, aviation medicine and primary care, in order to provide advice to health professionals in managing such patients. The working group has also developed an information sheet for patients.

NHS Care Pathway – patients exposed to fumes onboard commercial aircraft

D Wood, P Durgan, N Dowdall, D Coggon, R Hunter, T Stevenson, M Hoghton

Objective

Crew or passengers who experience symptoms during or following exposure to a fume incident, or symptoms which they think may have been caused by exposure to contaminants in aircraft cabin air, may seek advice from their GP, hospital A & E Dept, occupational health service or Aeromedical Examiner. These doctors may be uncertain how such patients should be assessed or what investigations might be required.

It is important to consider the possibility of underlying disease that is unrelated to exposure to contaminated cabin air, since the symptoms described are generally non-specific and can occur in a range of conditions. People with symptoms should have the same investigations and, if necessary, specialist referral as would be the case for someone with the same symptoms but who had not been exposed to contaminated cabin air.

This care pathway has been developed by the working group to assist doctors in managing such cases.

Background

The cabin air supply on most large commercial aircraft is provided using engine bleed air systems. Fume events – abnormal odours, smoke, haze or fumes in the cabin – may arise from various internal or external sources, and some are due to contamination of the bleed air supply, for example as a result of a failure of an oil seal in the engine. In recent years concerns have been expressed about possible adverse health effects of exposure to contaminants in cabin air.

There is strong evidence that some people experience acute symptoms as a consequence of fume events. Some of the chemical contaminants that are present during such events are irritant, and may cause itching or soreness of the eyes, nasal discharge, sore throat or coughing. In other cases, there may be a psychologically mediated nocebo response (see note) triggered by awareness of irritation or an odour. From the research that has been done to date on the chemicals that may be present in contaminated air, the concentrations at which they are present, and the reported patterns of symptoms in affected individuals, non-irritant toxic mechanisms for the acute health effects seem unlikely.

In addition to the occurrence of acute health effects, a small number of people have attributed longer term illness to one or more contamination incidents or to repeated exposure to lower levels of contamination. However, it is currently unclear whether any form of long-term illness occurs to excess in people with such exposures, and if so, whether it arises through toxic or nocebo mechanisms. From what is currently known about the concentrations of potentially toxic chemicals in contaminated air, long-term toxic effects would not be expected, but this remains an area of scientific uncertainty. (see Further reading 1,2)

Nocebo effect Note: Illness, often with physical symptoms and signs, which is triggered through psychological processes in response to a perceived harmful exposure. The phenomenon is analogous to a placebo effect in which symptoms improve in response to a perceived beneficial exposure.

Author affiliations

Dr David Wood, Consultant Physician and Clinical Toxicologist, Guys’ & St Thomas’ NHS Foundation Trust and King’s Health Partners and Reader in Clinical Toxicology, King’s College London, UK
Professor Paul Dargan, Professor of Clinical Toxicology, King’s College London and Consultant Physician and Clinical Toxicologist, Guys’ & St Thomas’ NHS Foundation Trust and King’s Health Partners, London, UK
Dr Nigel Dowdall, Head of Aviation Health Unit, Civil Aviation Authority, Gatwick, UK
Professor David Coggon, Emeritus Professor of Occupational and Environmental Medicine, University of Southampton, Southampton, UK
Dr Rob Hunter, Head of Flight Safety, British Airline Pilots Association, Hounslow, UK
Dr Tim Stevenson, Company Medical Adviser, easyJet Airline Company Ltd, Luton, UK
Dr Matthew Hoghton, Medical Director CIRC, RCGP