«The Global Cabin Air Quality Executive (GCAQE) established in 2006 is the lead organisation internationally focussed on addressing the issue of bleed ...»
CONTAMINATED AIR OVERVIEW
The Global Cabin Air Quality Executive (GCAQE) established in 2006 is the lead
organisation internationally focussed on addressing the issue of bleed air
contamination. There is extensive data complied over the last 60 years confirming
that contaminated air poses both a flight safety and health risk for those exposed
that should not be ignored.
This overview document provides a one page ‘contaminated air made simple’ introduction, followed by a more in-depth look at the different aspects of the contaminated air debate; it is intended to provide readers with an insight into the issue only. It should be reviewed in conjunction with the educational film on the GCAQE website and other additionally available books, literature and peer reviewed papers. Future updates of this document can be obtained from the GCAQE website.
In this edition:
1. Contaminated air made simple. Page 02.
2. Origins of contaminated air. Page 03.
3. Flight safety issue. Page 06.
4. What is in the oil and fluids? Page 07.
5. Engineering issues. Page 08.
6. Toxicity of tri-aryl phosphates. Page 09.
7. Research into contaminated air. Page 10.
8. Documented exposures. Page 11.
9. Exposure standards. Page 12.
10. Under reporting. Page 13.
11. Aviation regulations. Page 14.
12. Health effects. Page 15.
13. Solutions. Page 17.
14. Warnings and labelling. Page 18.
15. Answers to the seven most frequently asked questions. Page 19.
16. Further reading and information. Page 20.
17. Why join the GCAQE. Page 21.
18. Current GCAQE members Page 23.
19. References. Page 24.
1. Contaminated air made simple.
To enable you to survive onboard an aircraft at high altitude, you need to be provided with a breathing air supply.
The air you breathe in-flight, onboard all currently flying commercial passenger jet aircraft, is provided to passengers and crews from the compression section of the engine in a process known as ‘bleed air.’ The ‘b
‘Bleed air’ is used for breathing air on every pressurised aircraft you fly on, from the latest wide body jet to a regional turboprop aircraft, except for the Boeing 787 Dreamliner that uses electrical compressors.
Most modern jet aircraft also re-circulate some of the aircraft cabin air to reduce the amount of ‘bleed air’ they constantly take from the engine. This re-circulated air can be filtered for bacteria and viruses using HEPA filters, but is not filtered for hazardous jet engine oil byproducts that can contaminate the air supply, such as carbon monoxide.
In addition, hydraulic or de-icing fluids may also contaminate the cabin air supply.
As well as engine oils contaminating the engine bleed air supply, the Auxiliary Power Unit (APU), the small jet engine usually located at the tail of the aircraft, which can provide air conditioning and electrical services to the aircraft, can also be responsible for contaminated air events.
Many of the chemicals that have been measured during a contaminated air event are odourless and colourless, such as carbon monoxide.
Aircraft have no form of contaminated air detection system fitted to warn when the air is contaminated.
Contaminated air exposures are significantly under reported, and they are a flight safety and health issue of significant concern to the GCAQE and our members.
A basic jet engine is composed of a compressor, which has blades like wings that spin very quickly at the front of the engine. This draws in air and compresses it into a high-pressure gas. Fuel is then injected into the gas and ignited. This makes the gas both high-pressure and high-temperature. As the hot, pressurised gas is expelled out the back of the engine at high velocity, thrust is generated. The exhaust gas turns a turbine(s) that rotates the compression section(s) at the front of the engine. Like car engines, jet engines need engine oils for lubrication.
Early jet aircraft used mineral oils for engine lubrication. However, with the rapid advancement of engine technology and rising internal temperatures within an engine, newer man-made or ‘synthetic’ jet engine oils were developed and introduced in the early 1950s. Unlike mineral oils, synthetic oils contain a number of additives of concern such as organophosphates, which are typically triaryl phosphates (TAPs) such as tricresyl phosphates (TCPs). 1944 – Lockheed F-80 Shooting Star The introduction of jet engines also brought a dramatic change in the operational envelope of aircraft in both speed and cruising altitude from propeller aircraft. This, in turn, brought a need to provide crews with a pressurised and heated cabin and cockpit. This was achieved by way of a process known as ‘bleed air’ in which air is ‘bled’ off the hot compression section of jet engines and provided unfiltered to the cockpit and aircraft cabin as needed.
It was with the introduction of synthetic jet engine oils that US Air Force pilots first started to report adverse health and flight safety issues in the early 1950s.
“Approximately 40 minutes after take-off, I experienced blurred vision, became nauseated and experienced considerable dizziness. I recall no strange or unpleasant odors, nor did I taste anything out of the ordinary. I did feel a definite dryness of mouth and throat. This condition lasted possibly a minute or two. As I became more aware of the situation or nearly to the passing out point...” William J. Van Every – USAF - 15 May 1954 (Loomis, 1954) 4 Based on significant research, recommendations were made at that time that passenger aircraft use turbo compressors or blowers to pump in outside air into the passenger cabin for pressurisation, rather than use engine ‘bleed air’ taken from the compression section of the engine, which was now common practice in the military.
Cabin blowers had been extensively used in the pre-jet era to great effect.
Consequently, early commercial jet aircraft such as the Douglas DC-8, Boeing 707, VC-10, or Convair 880/990 did not use a direct engine ‘bleed air’ system in normal operations.
The use of turbo compressors or blowers was very efficient at providing clean air, but heavy and were not a very fuel-efficient solution.
With a growing need to reduce fuel consumption, the Rolls-Royce RA-29 Avon powered Sud Aviation Caravelle was introduced into airline service in 1959, providing unfiltered ‘bleed air’ for passengers and crews to breathe.
The Vickers VC-10 aircraft that first flew in 1962 was the last aircraft to be built with these safer air supply systems. Since 1962, all passenger, transport, military, and corporate jet aircraft have been designed to provide passengers and crews with breathing air through the use of ‘bleed air,’ with the exception of the Boeing 787 that first flew in 2009. The Boeing 787 now uses electrical compressors to supply outside air to the air conditioning system.
Aircraft ‘contaminated air’ refers to the contamination of the breathing air supply by pyrolised synthetic jet engine oil lubricants, hydraulic, and de-icing fluids. Such contaminated air events are generally, but not always, non-visible in nature, and may be described differently
Its important to note that early passenger aircraft used to allow smoking on-board aircraft, so the majority of contaminated air events that occurred were likely masked by cigarette smoke fumes, until the smoking ban came widely into effect in the late 1980s early 1990s.
In modern jet airliner engines, ‘bleed air’ is provided from two regulator valves on the high stage or low stage engine compressor section of the engine that usually turn on and off automatically.
Low stage air is used during high power setting operation, and high stage air (see picture right) is used during descent and other low power setting operations. Because the low stage air is significantly lower temperature than the high stage air, the pyrolised engine oil decomposition products will differ and provide a different smell in the cabin and cockpit due to a different chemical mixture.
The images below show the air supply ducting on a VC-10 removed from an aircraft at the end of its service life. Compare this to the bleed air ducting from a Boeing 737 engine, which is black from pyrolised oil contamination.
If flight crew suspect the air is contaminated onboard an aircraft, they should don 100% emergency oxygen and follow the emergency checklist procedures appropriate for the aircraft type. Flight safety has been compromised by crews who have failed to do so.
Aircraft cockpits and cabins have information on cabin temperature and cabin pressure altitude, but aircraft have no detection systems to warn when the air is contaminated. This can create a serious risk to flight safety because, within minutes, crews (even if they have a good sense of smell) lose the ability to smell any constant level of contamination. They may simply assume the smell has passed, and some may not notice when they start to become mentally slow and partially incapacitated.
Despite no detection systems being fitted, some within the industry acknowledge that crews can be exposed to oil fumes in-flight, and that these exposures can cause acute symptoms, which can compromise flight safety (AAIB, 2012; AAIB, 2007;
SAAIB, 2006; AAIB, 2004; FAA, 2004;
CAA, 2002; ATSB, 1999; Rayman, 1983; Montgomery, 1977).
Typical Air Safety Report There is extensive data showing that inflight impairment is occurring to both crew and passengers. In one study, crew experienced some degree of impairment through to incapacitation inflight in 32% of fume events, with some cases of two-pilot incapacitation or entire crews being impaired (Michaelis, 2010). Further, 45% of pilots reported “Aerotoxic” symptoms during or soon after flight, thus supporting that exposure to oil fumes can compromise flight safety (Michaelis, 2010). The incident summary below is taken from a Boeing 757 incident in the UK in 2000. It highlights how a crew failed to slow an aircraft on approach until air traffic control reminded them to do so. Again, like hypoxia, contaminated air is a serious flight safety issue.
Oily smell on outbound sector. On return sector crew unaware that they were becoming partially incapacitated. P1 then forgot to slow a/c. AAIB report: “Oily metallic smell had also been evident during previous sector. On this occasion, numerous ATC calls were missed, prompting ATC to ask a/c if everything was all right. P1 then forgot to slow a/c during approach until reminded to do so at 3.7d.
Crew unaware that they were becoming partially incapacitated.” 7
4. What is in the oil and fluids?
“The United States Environmental Protection Agency lists organophosphates as very highly acutely toxic to bees, wildlife, and humans. Recent studies suggest a possible link to adverse effects in the neurobehavioral development of fetuses and children, even at very low levels of exposure” (EPA, 2013).
The number of triaryl phosphate combinations in TCP is very high and is not limited to the 10 that can be formed from ortho, meta and para cresol (Mobil, 1999). Additionally, the oils contain antioxidants, such as N-phenyl-alpha-napthylamine (PAN) at around 1% (by weight), its contaminants (Category 1A carcinogen beta napthylamine), and other proprietary substances.
Because the oils are exposed to extreme temperatures up to 500°C (932°F) in the compressor air, a wide variety of pyrolysis (degradation) substances are generated, and those will also contaminate the air supply.
Hydraulic fluids contain very high levels of organophosphates such as tributyl phosphate (TBP) and other phosphates such as triphenyl phosphate (TPP), while deicing fluids contain ethylene or propylene glycols, plus various proprietary additives.
5. Engineering issues.
Engine oil seals will leak oil into the air supply as a feature of their design.
Engines have a large number of seals at different engine locations.
Engineers have access to a wide variety of seal designs such as carbon or labyrinth seals, but labryrinth are the most common.
A variety of factors, including transient engine operations (changes in thrust) and wearing seals, can allow the pressure acting on the outside of the seals/sump to fall below what is required to retain the oil inside the chamber. This allows oil to leak out through the seals and into the bleed air supply, if the leak is upstream of the bleed air off-take point.
Although the industry publically acknowledges the rare cases of failed oil bearing seals as the source of cabin fumes, lower level oil leakage is an expected design and operational factor of using the bleed air system, and explains the frequency of oil fumes leaking into the air supply (Michaelis, 2010).
In 1969, it was recognized that the main sources of oil loss were oil leaking past the seals, oil passing through the engine breather, and losses during servicing (Rolls Royce, 1969).
In 1954, it was reported that TCP caused trace demyelination of nerves (Aldridge, 1954). Sixty years later, in 2014, the pathology report of a deceased 43-year-old pilot who had been exposed to TCP and other pyrolised jet engine oil products showed demyelination of the nerves and nervous system injury consistent with organophosphate-induced neurotoxicity (Abou-Donia, 2014).
The form of TCP that has been most closely studied is tri-orthocresyl phosphate (TOCP), due to mass poisonings in the 1930s and the recognition that it causes a specific type of neurological damage. Some studies and reports wrongly suggest that, given the low levels of TOCP present in jet engine oils and the low levels of TOCP found in aircraft air sampling or swab tests, there should be no reasons for concern because, they claim, the other isomers of TCP are safe. This is untrue.