This forum is about wrong numbers in science, politics and the media. It respects good science and good English.
I found a 'Sting' in the tale of the 'green' scenario which Dave Gardner introduced us to. It is, I believe, of significant relevance to our ailing host, John Brignell.
John has given us his thoughts in the past about the health risks associated with air travel, specifically, the risk of infection from breathing other people's germs in partially re-circulated cabin air. When Dave Gardner offered the number 15 for the month of August as a universal example of the silliness of 'green' propaganda or scare tactics, he was referring to a reduction of atmospheric Oxygen to 15%, and correctly co-relating this to the Altitude Pressure Lapse, whereas I followed up by defining it as a reduction of Partial Pressure, which is the same thing. --- I now offer you the number 15 again, because this is also equal to the effect of the average cabin pressure in commercial aircraft. They operate at 18 to 26% reduced pressure which equals the effect of a drop in the Oxygen's Partial Pressure of 5 to 7%, or 14 to 16% Oxygen.
There is, however, a double 'sting' arising from this pernicious practice. The HEPA filters used for the 50% recirculated air do not remove anything below 0.1 microns, so some bugs do get through and infections persist. The first 'sting', (literally), comes from the arid air which averages only 22% relative humidity: dehydration will weaken your defences. The second 'sting', comes from the reduced oxygen partial pressure, this reduces the rate of oxidation in your system. And it is the free radicals produced by oxidation which our immune system uses to destroy a lot of 'bugs', providing, of course, that these free radicals are not excessive. --- It probably this balance that determines our Oxygen tolerance level.
It stretches credibility to suggest that the concentration of free radicals in phagocyte lysosomes will be relevantly affected by a few hours at slightly reduced partial oxygen pressure.
Its my understanding that such free radicals are continually formed and destroyed in one of the countless balanced feedback processes used by the body to control its internal operations. I believe that in many such processes where the body needs to keep a small "ready for use" stockpile and ramps up production when a demand arises the control loop effectively tracks the relative creation and destruction rates. Hence when the items are used the internal destruction rate falls so production rises to meet the external demand. Such control loops are simpler and far more responsive than any attempt to track a static or pseudo static level.
Given the myriad ways that oxygen is used in the body its a safe bet that any reduction in partial oxygen pressure will alter the various balances in a manner that, in evolutionary terms, is pretty safe for the continual survival of the organism. In the longer term physiological changes to offset, as far as possible, such environmental changes will be implemented.
Please do not make silly exaggerations for the purpose of 'scoring points'. A 5 to 7% reduction of Oxygen's partial pressure is equal to a reduction of 24 to 33% below the norm of 21%. That, is not a slight reduction! And that can hurt you in a matter of minutes, particularly if your immune system is flat out fighting off the effects of some disease injury or infection. Remember, also, that most of the research by the airlines into the health effects of reduced cabin pressures is based on healthy young males. Remember, also, that medical authorities and researchers, around the world, have been spelling out the dangers of Hypoxia Hyperoxia and Oxygen toxicity for several decades. --- I, will Not quote references to support my carefully researched statements, simply because in order to validate them you only have to leave your 'armchair' and engage your very competent brain.
You raise a major, and valid point. However, there is a rather tough 'fly in the ointment'. Our system Can Not 'stockpile' the Oxygen Radical as you suggest because, substantially, it is only available as a result of our metabolic processes (energy production). The brain makes significant use of the O2 radical in its neurological activity. And the brain can only sustain O2 deprivation for a few minutes: then you are dead! --- If our bodies could store oxygen, we would not need such a rapid response respiratory system; and if there was a biological way to store it, evolution would have discovered it by now, don't you think? Further evidence against there being any reserves is clearly indicated through a study of our immune system. The immune system is driven by the metabolic rate, and when it is fighting hard, our temperature rises and our heart 'hammers away', seriously deplete its oxygen resource, and anybody who is not in robust good health can suffer irreversible damage.
In fact, Clive, the subject you raised about the workings of our body's 'chemical factory' is an immense study, and I only comprehend a small part of it. I do, however, have considerable knowledge of Radical Chemistry from my work in combustion science. The only difference between the two disciplines is one of temperature. In the combustion process intense radical formation cannot be avoided due to the very high temperatures. The biological process has to do work I.e. expend energy to produce them due to the constraints of comparatively very low temperatures. Metabolisation is just a form of low temperature slow combustion.
But the use of 'radical' chemistry by bio systems is the very stuff of life, and possibly one of evolution's crowning achievements. --- A very lucid explanation of biomedical 'radicals' can be found here:-
O2 radicals exist transiently in all tissues for the purpose of respiration. Other free radicals are present in lysosomes, cellular organelles which exist in all cells but which in some immune cells (phagocytes) serve the purpose of destroying ingested bacteria. Here they are desirable, elsewhere they are undesirable and cause damage to your cells.
I personally do not believe (and I spent my PhD analysing the biological effects of several chemicals which are known free radical scavengers, how's that for point scoring?) that exposing yourself to reduced partial atmospheric O2 pressure for a few hours will have a meaningful effect on the ability of phagocytes to kill bacteria - particularly as free radicals are only one of several different approaches used by these cells. Occam's razor provides for a far more obvious source of "flyer's 'flu", namely the spending of up to several hours in confined quarters with up to 400 other people from hundreds of different places is bound to expose you to a large number of infectious bacteria, some of which you are unable to mount a primary immune response to before it causes disease.
But my beliefs and your beliefs, expressed as speculation on a web forum are of little merit in the world of empirical science. We need to do an experiment.
What I suggest, is that you endow me a chair at Manchester University as "Professor of Aviation Medicine", and I will give up my current day job to accept the position. In addition to the salary, I will need research funding for a three year research project consisting of a minimum of 12 return long-haul flights a year (about average for a professor these days anyway), business class of course, and %£60,000 a year for a postdoc, technician and PhD student plus lab space and consumables. I will have blood samples taken before and after each flight and analyse the free radical component of my phagocytes. I'm sure I can think of all sorts of other self-promoting experiments to do while flying around the world as well. What do you reckon?
I reckon I will start wearing masks on long haul flights OR just avoid them altogether.
According to some Australian researchers the oxygen levels are better on long-haul flights. They found 15% was a typical in-flight oxygen level, but on long-haul Boeing 747s, it was 17%.
Was that with or without large sections of the fuselage?
That piece is twaddle. They keep talking about higher when they obviously mean lower and v/v.
They say that cabin altitude pressure was higher on short flights. Well, that would mean more oxygen per breath, wouldn't it? - unless they meant that the cabin was pressurised to the pressure found in free air at a higher altitude. Either way, their writing skills need improvement.
Aircraft cabins are pressurised to the pressure found at about 8,000 feet (which saves carrying about a ton of air in a large airliner). However, since all gases are completely mixed in air at all levels (to a first approximation) the proportion of oxygen is still 21%. What matters for chemistry (and biochemistry), though, is the partial pressure, i.e. the pressure the gas would exert if it alone filled that volume. I think this is where our scientifically ignorant journalists are rather losing it.
Anyway, 8000 feet is only 50% higher than Denver, Colorado, USA and considerably lower than many locations in the Andes and Himalaya.
Know its been said before but… here goes. I have been a regular air traveller for the past 34 years , both long haul and short. I simply cannot remember there being all these problems for passengers prior to the smoking ban.
But what other confounding factors?
I used to fly quite a bit on business back in the 80s and early 90s. Usually in smoking areas back then.
Rarely was a plane full, especially in business class. So risks emanating from other passengers were fewer. The same could be said for airports.
Secondly some parts of the world, or travel relating to them whether directly (visiting) or indirectly (fellow travellers from those areas or planes that regularly visit those areas) are more risk likely than others. Expansion of air travel to and from such locations has most likely expanded over about the same period that smoking has been reducing and ultimately banned.
On balance I would guess that the likely cause would be reduced maintenance for reasons of cost reduction (or profit enhancement to put the other spin on it) and that such would have been the case in any event.
I rarely fly these days. It has become such a disappointing experience compared to earlier times.