Toxic cabin air is more poisonous than reckoned

Neurotoxic poisons in bleed air is not a new subject on this blog, but the more information we get on it, the more serious looks the aviation industry’s studied decision to ignore the dangers associated with contaminated cabin air, or to obfuscate.


To read about the human misery caused by cabin air contamination in airliners, go to The toxic subject that won’t die, and also, to read the personal testimony of suffering pilots and cabin crew, visit our AirSpace forum.


Meanwhile aviation journalist Tim van Beveren has conducted an interview with toxicologist Prof Dietrich Henschler of Wuertzburg University, Germany, who has been one of the world’s leading experts in workplace contamination since the 1950s. Then he was doing research on the precise group of chemicals that are often pumped into aircraft cabins when engine oil seals become faulty – tri-cresyl phosphates (TCP).


Such industry studies as are being done are looking for one particular variant,  tri-ortho-cresyl phosphate (TOCP) when in fact, Henschler reveals, other variants are present and are far more harmful. 


In his interview, Henschler reveals that TCP is much more dangerous than widely realised when it has been broken down into isomers, which is what happens when aircraft engine oils are heated and vapourised: 



Tim van Beveren:  Is it a major concern to you as a toxicologist that aircrews and passengers are being exposed to TCP, including MOCP (mono-ortho-cresyl phosphate) and DOCP (di-ortho-cresyl phosphate) at higher levels than TOCP in the aircraft cabin?


Prof. Dr. Henschler: As long as the mixture, which is almost a technical product, contains ortho-cresyl in whatever concentration, it is a matter of concern. So therefore [all efforts] should be made to lower the concentration of ortho-cresyl as far as possible.


Tim van Beveren:  Is is acceptable for the aviation industry to focus on the TOCP content of the TCP only?


Prof. Dr. Henschler: No, this is completely misleading because this underestimates the real toxic potency of the mixture of the product.


Tim van Beveren:  Given that TCP in jet oils contains a variety of isomers of TCP including MOCP and DOCP, is it acceptable for those monitoring for TCP to state levels are acceptable as they are below government-set exposure standards?


Prof. Dr. Henschler: To my information there is a lack of threshold limit values with TCP. One has been elaborated by the American Governmental Hygienists group who establish occupational exposure standards. They call it tri-ortho-cresyl phosphate and the value is 0.1 mg / m³. I think this has been elaborated on a very vague basis of data. The publication they are referring to comes from two Englishmen who have been paralysed during World War II, and there have been two or three air analyses performed there. This is trivial data to establish an official occupational standard. To my information no other country has established such a value up to now.


Tim van Beveren:  You were heading the MAK commission (Maximale Arbeitsplatz Konzentration = maximum workspace concentration – this German government commission established/s the limit values for toxic substances in the working environment) in Germany, so how did you deal with this standard of exposure limits?


Prof. Dr. Henschler: I was always against establishing an exposure standard in view of the lack of relevant data we have at hand.


Tim van Beveren:  Would it be more appropriate to look at the mixture of contaminants in the jet oils rather than to the individual chemicals?


Prof. Dr. Henschler: You have to look at the mixtures because they are very complicated, they are varying in the content of the individual compounds and they are changed in the course of being heated up on metal surfaces, so that decomposition products will result. So you always have to look at what in the exposure air. And my recommendation is to establish competent analytical procedures to look at what is that exposure.


Tim van Beveren:  Is it possible with today’s existing technology?


Prof. Dr. Henschler: It certainly is. It’s a matter of what you invest in, in such methodology. Modern analytical techniques are so sensitive, so reliable, so competent.


Tim van Beveren:  So it’s just a matter of money?


Prof. Dr. Henschler: Maybe, yes


Tim van Beveren:  Have you ever discussed your findings with oil manufacturers, governments or the military?


Prof. Dr. Henschler: Oil manufacturers, at least in our country are familiar with what I’ve published. My only contact with military people has been in Morocco. France had been the protecting country for Morocco and the French government asked me in 1959 when this epidemic occurred in Morocco, to be helpful in identifying the active agent and what could be done. So we had a sample at hand, analysed this and came to an evaluation what type of phosphate was active there.


Tim van Beveren:  What initiated your research into TCP back in 1956?


Prof. Dr. Henschler: Interesting question. After World War II the economic miracle in Germany ended up with an explosive increase in goods transportation by railway and they needed a paint which is resistant to UV irradiation and to meteorological influences, and this company who tried to develop such a product as an additive to lacquers asked me to have a look at what they had at hand at present with tricresyl phosphate with low content of ortho-cresyl. So this was the very beginning of the whole thing, and much to my surprise the mono-ortho esters were by far the most toxic components of the mixture of ten isomers.


Tim van Beveren:  Would you say that breathing synthetic jet engine oils containing organophosphates such as TCP are likely to be harmful?


Prof. Dr. Henschler: These are harmful compounds.


Tim van Beveren:  Why?


Prof. Dr. Henschler: Because they exert a toxic activity which we are well aware of, which is very nicely explainable how the mechanism of action is with these simple compounds. So, in view of the severity of the clinical symptoms and the ensuing fate of the patients involved, I would say it’s a dangerous material – it should be avoided as far as possible.


Tim van Beveren:  When you started your research, what for you were the most interesting or maybe surprising findings?


Prof. Dr. Henschler: The extremely high toxicity of the mono-ortho ethers, which went completely against expectation. If you had at hand the three symmetric ethers tri-ortho, tri-meta, tri-para, you would have expected that with a lowering of the ortho-cresyl content of the mixture that toxicity will go down. But the contrary is right – it goes up. This was the most interesting and surprising finding I had.


Tim van Beveren:  And is this common knowledge since?


Prof. Dr. Henschler: Hopefully, yes. Some people know, others do not, I don’t know the reason why. Sometimes chemistry is a little bit complicated, and thinking into molecular structures is, to some people an awful business, and though they resist a little bit in going deeper into the matter.


Tim van Beveren:  Would you think that proper scientific studies of the phenomena we’re facing here, of contaminated cabin air should be done, and can it be achieved with today’s technology?


Prof. Dr. Henschler: They should be done on a large scale where you monitor with analytical techniques what is the outlet, what comes into contact with the individuals at exposure, and what is the composition of these complex mixtures. And this in relation to the complaints brought forward by the cabin personnel and the passengers on a large epidemiological basis.


Tim van Beveren: So if TCPs shouldn’t be in the engine oil, there should be other substances which are available?


Prof. Dr. Henschler: Less toxic or non-toxic ones! Better alternatives, yes.

Certainly TCP is a very toxic compound, but not the only one. There is another candidate for being eliminated, beta-naphthylamine which is a proven human carcinogen of high potency. The others I don’t know of.


Tim van Beveren: What makes these chemicals so dangerous to the human being?


Prof. Dr. Henschler: Cancer is one of the irreversible phenomena in medicine. If cancer comes into consideration, the evaluation changes from non-irreversible. Cancer in humans is in some way inevitable, the efficiency of treatments is still a little low.


Tim van Beveren: So given the fact that some claim that TOCP is the most toxic but there is MOCP and DOCP as well in the oil, what would you say as a toxicologist about just focusing on the TOCP?


Prof. Dr. Henschler: This is a crude underestimation of the toxic potential. If you focus on TOCP, tri-ortho-cresyl phosphate which has the lowest toxicity of all isomers containing ortho-cresyl. So, we have to focus on the di- and particularly the mono-ortho ethers. For regulatory purposes I would recommend to say an amount of TCP as a whole containing ortho-cresyl to a certain extent. This is a clear-cut definition.


Tim van Beveren: Would you say that there are differences between inhaling TCP and ingesting TCP?


Prof. Dr. Henschler: Principally not, because what is active is not the compound itself but a metabolite which has to be taken up either through the digestive tract or the skin or the pulmonary tract, to be transported to the blood and from there to the liver where it is enzymatically converted to the highly reactive intermediate. So it doesn’t matter through which entry the compound gets access to the circulation.


Tim van Beveren: Would you inhale heated engine oil?


Prof. Dr. Henschler: Me? No, never! I was very much surprised to read these reports that people get exposed to these compounds.


Tim van Beveren: You did research back 50 years ago. You initiated research, you found that there is a high toxicity. What does it tell you now 50 years later? It seems that people do not draw the right conclusions?


Prof. Dr. Henschler: It tells me that they haven’t picked up the recommendations of careful toxicologists. I have always recommended to keep emission exposures as low as possible and look for better alternatives, so it was much of a surprise to me to be informed of those types of incidents.




10 Responses to Toxic cabin air is more poisonous than reckoned

  1. Poisoned 16 April, 2009 at 10:04 pm #

    So, having lost my flying career through contaminated cabin air I should now worry about a possible cancer diagnosis? I never thought becoming a pilot would lead to such sickening hell: both the personal effects and the obscene official denials.

  2. Monika Kurz 17 April, 2009 at 8:37 am #

    If I read this it must be the key of my sickness as a flight attendant and I don’t understand why the airlines still say it is not dangerous and it is not inside of the cabin?

  3. Phil Small 17 April, 2009 at 9:52 am #

    The more evidence that is gathered from real experts like Dr Henschler (not psuedo experts appointed by governments) the greater the chance that a time will come when the denials from the authorities will be seen for the lies that they are.

    No one is suggesting original foul play in the design of aircraft pressurisation and air conditioning systems but now that more information becomes available and the chemicals are better understood rectification action should be mandated.

    Bodies such as the GCAQE (Global Cabin Air Quality Executive) should be supported in their lobbying for a clean environment in aircraft cabins.

  4. Poisoned pilot 17 April, 2009 at 12:40 pm #

    If the UK govenment actually cared about solving the problem of contaminated cabin air, they would immediately contact genuine experts such as Prof Henshler and appoint them to advise them. They would also act promptly on the advice received.

    What happens in reality is that the Government tries hard to look like its doing something, for example by comissioning further research, while doing nothing to actually solve the problem.

    Meanwhile, the health and careers of many flight crew members are being ruined, along with thousands of passengers.

    Well done to everyone fighting to bring this issue into the open – this is a necessary step in bringing about an eventual solution.

  5. TCP Overload 18 April, 2009 at 2:51 am #

    Interesting that Prof Henschler produced these findings way back in the 1950′s when the aircraft didn’t use bleed air! Typically it was advise ignored. I have the distinct impression that Prof Henschler is as disgusted with this situation as we (the terminal sufferer’s) are. This entire sorry scenario smells of the “Asbestos” debarcle down in Australia, which still continues to this day.
    Once again we see politicians being influenced by the larger corporations, an appauling state of affairs if allowed to continue in this instance. I sometimes wonder whether these ill-informed lot would be prepared to sit in a room for fourteen hours, or maybe even four hours and be subjected to “cooked” jet engine oil vapors if they aren’t so detrimental to ones health!
    Both manufacturer’s, airline management and politicians maybe able to prove a point here!
    I guess the “Light at the end of the tunnel” is Boeing’s decision to change the system on the B787, a winning move in more ways than one for both Boeing & us, the travelling public. It is a pity that they aren’t also working on retro-fitting such a system to older model A/C.

  6. sick f/a 21 April, 2009 at 11:29 pm #

    Thank you Dr. Henschler and Tim Van Beveren…I had a great career as a f/a for 20 yrs with an American major airline and fell extremely ill. It took many years to get some answers but with the current medical/science evidence coming forward I feel that we may be getting to the correct answers about this horrible illness. (much to the airlines dismay)I have never given up on finding a possible cure or relief from this illness nor will I ever….but the others who are young and new at their jobs must BEWARE as I had no idea, that I a healthy athletic person would end up severely disababled from these exposures.I continue to fight for my rights and been engaged in the battle of my life as the airline/corporation does not want this information out to the flying public!!So be careful as they play hard ball. I and family have been run off the road, followed 24/7 breakins at home,vandalism and other such harassment ploys to shut me up!!So continue on, we must fight for justice concerning this terrible travesty. The flying public must be informed.

  7. It was a good career 27 April, 2009 at 11:18 pm #

    I had no idea that the symptoms I experienced in flight for so many years with fumes present could be any more than short-term. We knew fine well it was oil, they used to tell us, but they also told us there was nothing to worry about & my colleagues & I believed them. I don’t any longer & my health and career have been willingly taken. I now discover the industry knew all about this & I agree with the previous post,, there are plenty of ‘no experts’. Perhaps if they took their Government or corporate allegiance hat off they would see the overwhelming evidence. it is there for those who want to know. It is immoral, negligent & corrupt to continue to put profit ahead of people. The truth is coming out & there will be a lot of people who sat on the wrong side of the fence for far too long.

  8. M. Peters 23 November, 2010 at 1:47 am #

    Cabin air used to be fresh before the 1980s when airlines let in fresh air. Due to cost savings, they stopped letting in fresh air, and simply “recycled” the existing air and have been doing so ever since!

    While there is a current study of airline cabin air quality, the studies MUST ensure that at the time of testing, airlines are NOT letting in the fresh air — rather recycling it as they have for about 20 years. If airlines know the study is being done, they will inevitably let in the fresh air and the studies will be irrelevant.

  9. David Learmount 23 November, 2010 at 10:38 am #

    Actually cabin air is a mix of fresh and recirculated air. The mix can be managed according to passenger load and actitivity in the cabin (night time or day).

    The introduction of oil-based organophosphate fumes into the cabin in the “fresh” air is a result of oil escaping from faulty oil seals. It is an occasional occurrence, not a state of affairs, but it is never welcome because these fumes are neurotoxins.

  10. Okmulgee Lawyer 26 June, 2011 at 2:42 pm #

    It took many years to get some answers but with the current medical/science evidence coming forward I feel that we may be getting to the correct answers about this horrible illness. (much to the airlines dismay)I have never given up on finding a possible cure or relief from this illness nor will I ever….but the others who are young and new at their jobs must BEWARE as I had no idea, that I a healthy athletic person would end up severely disababled from these exposures.