Fume Event - Aerotoxic Syndrome

Fume events – not just hot air

Martina Roters
10.08.2020
5 minutes

A gigantic, winged aluminium can with people, in an ice-cold environment not conducive to life, 40,000 feet above the ground. The most precious commodity for survival is air to breathe. You do wonder:

How are we able to breathe on board a jet aeroplane in the first place?

Breathing is simple on the ground, but just as mountain climbers know, air becomes ‘thinner’ as you near the summit. Whereas every breath brings the same amount of air into the lungs, this contains only 80 per cent oxygen at an altitude of 6,000 feet compared to at sea level. The haemoglobin in the blood compensates for this, meaning that the oxygen content only falls to 97 per cent.

There are three essential factors to enable us to breathe well on board:

1) Appropriate cabin pressure

2) Clean air

3) Conducive air temperature

The intricacies of the on-board air conditioning system

When aviation was in its infancy, the air ending up in the cabin was guided as ram air through openings at the rear of the plane, compressed and heated.

However, some industrious designers then hit upon the idea of bleeding the hot air, already compressed, directly from the engine and mixing it into the ice-cold ambient air. The benefit is that you can do without a compressor, saving not only weight but also benzene for the flight.

This bleed air concept can be found today in almost all jet aircraft.

When it comes to a two-jet aeroplane, two units (known in aviation jargon as ‘packs’) receive air from each engine.

As a flight captain once put it: depending on whether a co-pilot or flight attendant complains about the ‘burned chicken’ smell, you can tell which engine has been affected by birdstrike (feeding from separate packs).
It goes without saying that parts of the air conditioning system can be isolated, e.g. in the event of an engine fire.

Approx. 50 per cent of the air is then conditioned again to relieve the packs. In the process, HEPA filters remove dust, skin peeling and microorganisms.

What are fume events?

A ‘fume’ or ‘smell’ event is deemed to be the sudden occurrence of smoke, steam or a smell leading to bodily symptoms.

Crews report breathing difficulties, headaches, dizziness right through to feelings of numbness and unconsciousness. If the cockpit is affected, pilots even need to put on oxygen masks right at this time and make a premature landing. Press reports are mounting that crew members are having to be admitted to hospital due to fume events.

The Cockpit pilots’ association, who have been following this subject matter for years, sees a clear link between this and the bleed air, which may pick up traces of engine oil, hydraulic fluids and de-icer. In addition, these substances are thermally decomposed by the very hot temperatures (pyrolised).

One mystery remains: whereas most of the crew members are back at work the day after the fume event, others are unfit for work for months, with some never recovering. How is that possible?

You can find out more about fume events in this video:

Aerotoxic syndrome?

People in the industry talk about aerotoxic syndrome, even if to date (?) it has not been recognised by either the WHO or the employers’ liability organisation as an illness.

The physician Michel Mulder, who himself used to be a KLM flight captain, has solved this riddle: people are able to break down organophosphates with varying degrees of success: 3 per cent of those affected are not able to break them down at all, and 30 per cent are able to do so only very slowly.

It is true that flying staff have a different exposure to organophosphates compared to the normal population.

A long-running row about air quality on board

Patients, committed journalists and doctors from various continents accuse the aviation industry of a conspiracy regarding bleed air – for which there is even historical evidence:
A secret agreement from the year 1993 regarding a payment of 750,000 dollars by British Aerospace to the Australian ANSETT to settle all current and future compensation entitlements due to oil or other steam. This paper sparked off a scandal in the Australian parliament in 2007, as it had been withheld from a senate investigatory committee in 1999.

It is meanwhile undisputed that additives in the engine lubricants contain organophosphates not conducive to human health.
Aircraft builders, airlines and supervisory authorities however dispute that the bleed air can release these substances in a concentration that can damage health. Their argument is that even if all (!) engine oils (!) were to enter the bleed air, you would reach only one quarter of the permitted workplace limits.

You can find comprehensive documentation of aerotoxic syndrome (German source) here.

A study throws up mysteries

The EASA (European Aviation Safety Agency) has carried out a measurement campaign for carbon monoxide, carbon dioxide, ozone and VOCs (volatile organic compounds) and published the 2017 Results.

The on-board air has been graded as ‘good quality’ (‘less polluted than normal interior spaces’). However, there has now ironically not been any fume event on the 69 measurement flights.

A further riddle: eight flights involved a Boeing 787, which in terms of innovation does not possess a bleed air system at all, rather it once again has a ram air system with electrical compressor.

However, the contaminations with the suspicious TCP substance (Tricresyl phosphate) were comparable with the 61 other bleed air flights.

Might it be the case that the aircraft absorb a basic dose of TCP from the exhaust gases when aeroplanes are waiting to take off and queuing behind one another with rotating turbines?

An analogy to Gulf War syndrome

An expert for aerotoxic syndrome, Professor Abou-Donia at Duke University, has drawn a parallel to the Gulf War syndrome. This involved soldiers suffering from a raft of symptoms, with governmental bodies for a long time also not recognising such as an illness. The studies by Abou-Donia and colleagues show that the symptoms were not able to be explained by high doses of individual substances, rather by interaction between organophosphates and medication (by chemical weapons and insecticides).

Hope for those affected?

A new study ordered by the European Commission called FACTS (FreshAircraft) is intended to shine new light on the safety of fume events, as well as their short and long-term health risks.

Among the objectives is to investigate the potential toxicity of substance mixtures from turbine gases. After all, it is surely clear by now that the woe of those affected cannot be explained exclusively by ‘hyper ventilation’ or the ‘nocebo effect’.

Preventative measures

The Pall company is meanwhile offering not only HEPA filters, but also combined HEPA/carbon filters, intended to catch the organic substances trying to escape. That being said, these filters still affect only the conditioned proportion of the air. Filters for the bleed air 50% are – still – ‘in the pipeline’.

The Cockpit pilots’ association is expressly demanding that sensors are installed to monitor the air quality instead of relying on the ‘pilots’ noses’. Upon enquiry by WingMag, Gröger & Obst has confirmed that the sensor, which has long since been available, continues to be met with a lack of interest in the aviation industry.

Practical recommendation

Smoke events are extremely rare: they affect only 0.05 per cent of all flights. However, if something did happen, the oxygen masks on the aeroplane would not be of help, as they generate the oxygen only using the contaminated ambient air. Whereas pilots have ‘real’ oxygen masks and the cabin crew have ‘smoke hoods’ to a certain extent, passengers do not have anything. Therefore, you ought to have your own HEPA / carbon filter mask to hand in case of emergency.

by Martina Roters

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