Cabin air quality - frequently asked questions (FAQs)

Concerns have been raised in the media about the possibility of air crew and passengers being exposed to toxins in cabin air.



Concerns have been raised in the media about the possibility of air crew and passengers being exposed to fumes in cabin air. The Department for Transport (DfT) has received a number of enquiries, and these are our answers to the most frequently asked questions.

Is aircraft cabin air contaminated?

Studies such as the European Cabin Air project have shown that normally the levels of chemical and biological contaminants in aircraft are less than in many work environments such as office buildings.

There are, however, occasional bad smells or ‘fume events’ during flights, and these have been reported on a number of aircraft types which are in use around the world. Reports to the Civil Aviation Authority (CAA) show that sometimes one pilot reports a bad smell and the other detects nothing. An unpleasant smell is undesirable but does not necessarily harm health. Conversely carbon monoxide has no smell yet kills people in the home every year.

Some pilots who have experienced these events report a variety of short or long term symptoms or ill health. But it is not certain that these symptoms are work related.

The independent Committee on Toxicity (a panel including toxicologists from various universities - and known as COT) completed a substantial review of evidence in September 2007 and concluded that the evidence available did not establish a link between cabin air and pilot ill health, but nor did it rule one out.

What has the government done?

Both the COT and the House of Lords Committee on Science & Technology identified a gap in the world’s knowledge. The government has tried to fill that gap through research. No-one had previously captured samples of cabin air during normal conditions and fume events and analysed them to see what substances they contain and in what concentrations. The science is difficult because fume events are unpredictable and can last just a couple of minutes.

To fill the knowledge gap the DfT put 4 research studies in hand. All have been completed and the department’s programme in this area has now stopped.

We have Commissioned and completed functionality tests to identify scientific equipment capable of capturing fume events in real time. The report was published by Cranfield University in February 2008.

We have commissioned and completed an exploratory data analysis study of fume events and operational parameters - especially whether there is any link between ‘full power take-offs’ and fume events. The report was published by Cranfield University in December 2009. Its conclusion was that - data obtained in this way could be used to support engineering discussions about how to anticipate and possibly mitigate event occurrence. It may be that oil pressures, duct temperatures and engine power would merit further investigation.

We have commissioned and completed real time in-flight testing, using the scientific equipment and methodology tested earlier, to assemble data on substances in cabin air. This is the main cabin air study and was conducted by Cranfield University. Several airlines volunteered to take part by allowing an independent scientist to come on board their aircraft with sampling equipment. Testing began in 2008 and finished in 2010. The report was peer reviewed over the winter of 2010/2011 and published by Cranfield University in May 2011.

We have commissioned and completed swab test research into the prevalence of isomers of TCP (organophosphates) on surfaces in aircraft and non-aircraft locations for comparison. The report was published by the Institute of Occupational Medicine in June 2012.

Who did the research?

Three of the research studies were conducted by Cranfield University; the fourth was conducted by the Institute of Occupational Medicine (IOM) in Edinburgh.

What did the main Cranfield report say?

The main message from the principal research study is that, with respect to the conditions of flight that were experienced during the study, there was no evidence for target pollutants occurring in the cabin air at levels exceeding available health and safety standards and guidelines. Moreover, levels observed were comparable to those typically experienced in domestic settings.

The study monitored a total of 100 flights in five different aircraft types, Boeing 757, Airbus 319, 320 and 321 and the BAe 146. A series of air samples were taken at defined points on all flights, and all flight crew, cabin crew and researchers were also requested to complete a post-flight questionnaire including questions about any fumes or smells that occurred during the flight.

The study’s objective was to analyse cabin air for volatile organic compounds, semi-volatile organic compounds, particles and carbon monoxide in normal operations during all phases of flight (e.g. climb, cruise, descent), and to detect and characterise any anomalous elevations of these elements during any ‘fume events’ where unusual smells or similar occurrences were reported.

The European standard ‘Aircraft internal air quality standards, criteria and determination methods’ sets safety, health and comfort limits for a number of substances, including two that were measured in the study - carbon monoxide and toluene. The study’s results indicate that concentrations of both carbon monoxide and toluene remained within these limits. In the absence of specific cabin air standards for the other pollutants measured in the study, the study referred to other standards and guidelines established, for example, for domestic (home) or occupational environments. Again, none of these standards or guidelines was exceeded.

What happens now the projects have reported?

The Department for Transport has formally submitted them to the COT for consideration.

How frequent are fume events?

The COT estimated in 2007 that fume events occur on roughly 0.05% of flights overall (1 in 2000). The most recent figures show that in 2010 there were 207 contaminated air events reported to the CAA mandatory reporting scheme (MORS) out of 1.12 million passenger and cargo flights by UK carriers (0.018%). Not all fume events are reported, but even if the number was doubled or tripled this would still be a very small proportion.

How many passengers have been affected?

There are very few passenger complaints about health issues to airlines or the authorities.

CAA figures from 2011 showed that out of a total of 48,000 written complaints in the 10 years from January 2001, 244 (0.5%) were categorised as medical. The main health problems raised were pregnancy issues; ski-ing injuries; infectious diseases; allergies (typically from peanuts); food poisoning and passengers being scalded by coffee/tea.

Why not just fit filters to aircraft?

DfT has discussed this with a major filter manufacturer who said that, to produce an effective filtration system, they would first need to know what particular substance had to be filtered out. That is why it is logical to analyse cabin air first, to identify what remedy might be needed.

Compulsory fitting of filters would have to be required by regulators (in this case the European Aviation Safety Agency - EASA) on the basis of evidence that cabin air contains a particular substance in a harmful concentration and that a particular specification of filter could remove that substance. It is important to remember that the same aircraft types are flown world wide.

Why do fume events happen?

In any mechanical system malfunctions can occur which result in abnormal operating conditions. The CAA has already taken remedial action to help operators of particular aircraft reduce the incidence of fume events e.g. engine oil servicing procedures and engine sealing modifications.

Should there be a public enquiry?

There have already been 2 public enquiries:

First, in 2006/7 when the Committee on Toxicity - an independent advisory panel of toxicologists - was commissioned to look into the evidence on the subject. The COT reported in 2007 and found that no connection between pilot ill health and cabin air could be proved or disproved, but that more research was needed. That research has been completed and the DfT has now formally reported back to the COT.

Second, in 2007/8 when the issue was revisited by the House of Lords Committee on Science and Technology. The Committee urged the government to complete the air sampling research. This was done and the research was published by Cranfield University in May 2011.

Are there organophosphates in cabin air?

With regard to organophosphates the Cranfield University report notes that

  • ‘in over 95% of the cabin air samples, no detectable amounts of TOCP or other TCPs were found. TBP was detected more routinely, but not in the majority of samples. The highest level of TBP recorded was 21.8 µg m-3 (overall mean 1.07 µg m-3) which exceeds any reported domestic indoor air level. TBP levels were highest during first engine start.’

TBP is an element in aircraft hydraulic fluid so it is not surprising that it would not usually be found in domestic air. The measurement µg.m-3 is “micrograms per cubic metre” - the mass of something in micrograms (i.e. 0.000001 grams) in a given volume (one cubic metre) of air. It represents an extremely small amount - most exposure limits are expressed as mg.m-3 or milligrams (0.001 grams) per cubic metre which is 1000 times greater. It is the concentration of a substance which determines its health effect.

Why not use engine oil containing no TCP?

TCP is an organophosphate. Organophosphates are anti-wear agents and are used as aviation lubricants to make engines safe. Although there is a lubricant on the market which uses an alternative organophosphate to TCP, according to the manufacturer it is not typically used in civil aviation and research about its health impacts is not conclusive. So we do not know if it would be safer or healthier.

Will you do an epidemiological study?

The logical first step in the research programme was to examine potential exposure as recommended by the COT. That is what the Cranfield study has done. The COT said epidemiological research would best be done on an international basis. The scale of pilots and control group needed for reliable results would be large. It is unlikely that the UK could fund such a study. We are also aware that it could be difficult to recruit pilots, who in the UK would be legally obliged to report any health impairments found (whether related or not to cabin air) to the CAA who licenses them.

Department for Transport, June 2012

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