'Contaminated air' on planes linked to health problems

"Toxic fumes in aircraft cabins could cause serious health problems, scientists warn," reports The Sun. This is based on a UK study investigating air contamination on aircraft and its possible effects on the health of pilots and cabin crew.

The researchers say the air supply on planes can become contaminated by leaks of oil or other chemicals from the engines and they wanted to find out if this was associated with any health problems.

The study, published in the World Health Organization journal, found there is a link between exposure to contaminated air and short-term problems such as drowsiness, loss of consciousness, headache and tremors, and longer-term issues such as problems with memory or concentration and fatigue.

This is mainly worrying for pilots and staff on aircrafts, but could also be a concern for passengers if exposure to highly contaminated air causes a pilot to feel drowsy or pass out. However, only a few case studies of serious air contamination were investigated in this study, suggesting these events are rare.

The study didn't look in detail at whether exposure to contaminated air on planes was harmful to passengers, so it's not possible to draw firm conclusions about whether there's a health risk for people who fly regularly or only occasionally.

Where did the story come from?

The study was carried out by researchers from the University of Stirling and the University of Ulster in the UK, as well as a consultant respiratory physician from Melbourne in Australia. It received no sources of funding.

The study was published in the peer-reviewed journal Public Health Panorama, a journal of the World Health Organization. It is open access, meaning you can read it online for free (PDF, 314kb).

The UK media generally reported the story accurately, although the Sun's message of "Flying should 'come with a health warning' as toxic fumes contaminate air in cabins leading to serious health problems, research suggests" is fairly misleading as it suggests the research was done on passengers, when it was actually only carried out on aircraft staff.

What kind of research was this?

This was a combination of two studies, one involving a survey of pilots from the UK and the second an analysis of 15 case reports of potential cabin air quality incidents. They both aimed to look at the circumstances and symptoms of aircrew working in the pressurised air environment of aircraft. 

There have been concerns over the years regarding the health effects of exposure to aircraft contaminated air for aircrew. Unfiltered breathing air is provided to the cabin by the engine compressor. If oil leaks over the engine oil seals, chemicals can enter the air being supplied to the cabin. This might mean those on board may be exposed to some potentially harmful substances.

By combining these two types of studies, the authors aimed to carry out a more in-depth investigation of aircrew involved in suspected aircraft contaminated events by seeing if the reported symptoms were consistent with exposure to pyrolysed (heated) jet engine oil and other chemicals.

What did the research involve?

Researchers carried out two independent studies to investigate the circumstances and symptoms of aircrew who worked in the pressurised air environment of aircraft.

The first was a survey of UK British Airways pilots between 2005 and 2009 who agreed to a telephone interview or responded to a written questionnaire.

The pilots were asked:

• whether they were aware of exposure to contaminated air
• how they thought the contaminated air affected them
• about any medical diagnoses they had

Of all the pilots who were contacted, 274 (14%) agreed to participate.

The second study involved 15 case reports from Australia, the US, Germany and the UK, of potential cabin air quality incidents. These particular cases were chosen because the health problems reported were suggestive of exposure to contaminated air.

Data sources included: the airlines, crew and maintenance reports, incident investigation and regulator reports, health effects and medical records, as well as media, union and legal reports.

Symptoms for both studies were recorded. 

The substances found in the engine oils and other chemicals were then measured against European standards to see if they were at hazardous levels or not.

What were the basic results?

From the survey:

• Of the 274 pilots surveyed, 88% reported exposure to aircraft contaminated air, mostly in the form of fumes, and 34% reported frequent exposure.
• 142 pilots reported specific symptoms and diagnoses, 30 reported health problems but gave no specific details, 77 reported no health effects and 25 failed to respond either way.
• Acute adverse effects most commonly reported were: breathing problems, exhaustion or fatigue, dizziness and reduction in performance level.
• Long-term effects most commonly reported were: breathing problems, poorer levels of performance, memory impairment and chronic fatigue.

Among the case studies:

• In 33% of the incidents both pilots ability to fly the plane was affected during the air contamination.
• 53% of events included long-term adverse effects for one or more crew members.
• Chronic health problems diagnosed at some point after the exposure event included asthma, post-traumatic stress disorder (PTSD), problems with memory or concentration, seizures (fits) and cancer.
• Nine pilots either became unfit to fly or died.
• 80% of incidents occurred during take off or landing and 87% were linked to positive maintenance findings of oil leakage.

How did the researchers interpret the results?

The authors concluded that "aircraft air supplies contaminated by pyrolysed [heated] engine oil and other aircraft fluids can reasonably be linked to acute and chronic symptoms, findings and diagnoses, thus establishing causation".

They further add that "there is an obvious need for a clearly defined internationally recognised medical protocol, occupational syndrome and disease recognition, and health and environmental data collection".

Conclusion

These findings indicate that on rare occasions, pilots have not been able to perform as usual due to poor air quality in the cabin. Also poor air quality has been linked to health problems in the long term.

However, there are some limitations of the study that need to be considered:

• The authors claim they have demonstrated a cause-and-effect relationship based on certain criteria. But with the exception of the acute air toxicity incident investigation reports in the second study, these types of study cannot prove causality. While it is likely that exposure to chemicals is toxic, this study did not link many of the symptoms with on-board air samples. There is still a possibility that the acute symptoms experienced by the pilots and crew were brought on by other things too, not just the contaminated air. With regard to the potential chronic effects, it is even harder to eliminate other factors that may have played a role.
• The data in the pilot survey was self-reported, which might be subject to bias as people might not remember accurately or might exaggerate health outcomes. There was also a high risk of selection bias as only a small proportion of pilots invited to participate agreed. It is likely that those who didn’t participate hadn’t experienced any obvious health problems.
• The data from the case studies comes from multiple sources that might not have consistent ways of reporting things, so analysing them as a group might lead to inaccuracies.
• We do not know if frequency of exposure affects the health outcomes (if the symptoms get worse the more times staff are exposed to contaminated air). This might have some consequence for frequent flyers, so it’s important to know.