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This is kind of a split out from the BA emergency descent thread in Rumours and News following some PM correspondence with some interested parties.
With relation to Decompression Injuries and Sickness. As may be obvious from my ID I'm a keen diver and as well as instructing, dive decomression dives using a) Mixed Gas (Trimix) and b) Using high % O2 for accelerated decompression.
Now if we exclude traumatic DCS which will not occur in standard air travel, (Pulmonary / Arterial Gas Embolism, Pnumothorax, Subcutaneous Emphesyma) my question relates to crew experiences with the 'Off gassing' DCS (Cassion disease).
A few years agoo I was flying MAN-LHR with a pilot positioning sat next to me. We were talking about diving and actually about navigation with limited visual resources.
However, as with any diving converation I was asked about DCS and the flying after diving guidelines. He then mentioned that some flights coming back from the Red Sea were quietly briefing diverts into Athens as that was the nearest decompression chamber to the flight route.
Now our guidelines state no diving 24 hrs before a flight. However, from experience. Bends don't read tables. [1] My computer has never given me more than 18hrs no fly time even after a length series of dives and the conventional wisdom / textbooks based on the longest half life tissue compartments only give a half time of 10hrs for nitrogen (Bones / Joints). Whilst a helium bend is more severe the half times are so much shorter the won't come into play flying. So given the above...
a) Are diverts routinely (if unofficially) planned or a planning consideration?
b) Is Athens the best choice? As I obviously don't know the airways around that area. I do know that the Chamber in Malta is a 5 minute drive from the airport .
c) Are incidents getting more / less frequent? If more, do you think that it's a personal issue or lack of training / awareness of the issue.
I think that's enough for now. As I've stated I'm not an aviation professional but have a keen interest in none of my students (or myself) giving you a bad day at the office.
Regards and any opinions / information welcome.
DaveA
[1] I got lucky the other way in Scapa Flow after a runaway ascent and missing 19 minutes of stops. I should have taken a hit but got lucky. Possbly the cold water, I was well hydrated and having slept well.
I was intrigued by the point about possible diversions. I have done many many flights across the Med to Egypt, Cyprus, Greek Islands, Italy and Spain. I don't ever recall being briefed on locations of Pressure Chambers. Also, in the annual medical classes, I don't recall being taught about recognition of severe bends when inflight. Peculiar when we obviously carry many passengers going on diving holidays. Of particular interest would be charter or scheduled flights to diving locations like Maldives, Seychelles, Hurghada, Greece etc.
I am just happening to do my annual Safety Equipment Procedures ground school tomorrow. I shall raise the point!
I know naught about diving .. but ... on a decompression chamber run years ago (and that only to FL240, as I recall) we had a couple of divers along for the ride ... one had been diving a little too recently and experienced problems ... main thing, I suspect, to keep in mind re diving, and then flying .. is enroute decompression of the pressure vessel ... not a high risk but not one the diver might wish to expose him/herself to ?
I'm not sure of the stats for Full decompressions Vs Scheduled passenger carrying flights but would imagine that the ratio is, hopefully, very very small. Zero would be nice but nothing is certain.
The chap you were with really really should have known better. How did it manifest? Was it joint / skin pain or nurological symptoms? The nuro one would be particularly had to spot given the similarities to Anoxia in places.
I'm of the opinion that IF and it's a big IF, pilots are being forced to plan diverts my end needs to look at the reasons WHY you've had to divert.
I said above, 'bends don't read tables', for which I'm eternally grateful. However, if on examination after, someone has 'chanced it' and takes a hit who ends up paying? I have no idea as to the cost of diverting an airliner, however, I do know how much it costs to put someone through a chamber series. (£12,000+)
Also on the SEP front, given the amount of First Aid training done by crews is DCS (Bend) awareness covered?
Sorry if I'm droning on....
DaveA
Last edited by Diver_Dave : 3rd July 2008 at 09:03. Reason: Clarity, Return key use AGAIN...
And the Aircrew first aid course given in Aberdeen which should be more Diving savy than most places in the UK doesn't mention it. But quite alot of the first aid courses are in house these days so I presume its the luck of the draw if the airline has had a problem with DCS before. If they have it maybe included, if not I doudt very much it will be.
It was quite a shock in Sharm the number of divers that went climbing up mount Sinai which is 2285m (7500ft) on their day off after diving 3 times a day to 20m+ for the last 3 days.
We get the same thing, telling people that the day trip up Mt Etna from Malta isn't a good idea.
As far as DAN goes, they are the main supporters of the chamber in Malta as it tends to be used for a lot of reserch dives as well as emergency casualty decompression.
Interesting point about not noting the symptoms as whilst a skin / joint bend is fairly easy to recognise a type 2 or 3 nurological is very similar to Anoxia / intoxication.
Well I queried the extremely pretty cabin crew medical trainer today about cabin crew recognition of decompression/bends symptoms. I regret to say there is no mention of it in training or any instruction given of what to expect. In my long career I have never been given any information about location of decompression facilities on any flights, or even been advised of any in NOTAMs.
Perhaps we need an official body like the British Sub Aqua Club or the PDSA (or whatever they are called!) to approach the CAA and try and find how many divers have actually experienced difficulties on UK airlines to establish if it is a problem. That climb the divers did was equivalent to the cabin altitude of a cruising jet. It doesn't appear to me to be much out of order!
Could you perhaps explain: in aviation we do all our work in the band from Zero>1 atmosphere. In diving you go from 1 atmosphere>what ....3 or 4? Does it really matter much if a person goes from say 3 atmospheres>1 atmosphere one day, then next day up a 7,500' hill- ie from 1 atmosphere>say 60% atmosphere? It doesn't seem like much compared to a deeper dive.
Normally the pressur increases by (roughly) 1ata pre 10m of depth.
Sport diving tends to teach no-stop diving so that decompression isn't required. However, finishing any dive there is still residual nitrogen dissolved in the blood, how much is a factor dependant on the relationship between Depth and Time (although not straight line) and also for repeat dives cumulative.
this leads to teh tissue loading I was talking about earler, in that whilst the residual nitrogen won't form bubbles as it liberates at 1ata (sea level) it will as the ambient pressure reduces.
Given that the total tissue desaturation times can be up to 24hrs therefore in your example the drop to 60-55% ata could induce bubbles.
As luck would have it bends come in 3 sorts, with type 1 being by far the most common.
Type1 skin (Looks like nettle rash and itches like hell! Caused by small nitrogen bubbles under the skin.
Type2 Joints. Pain and immobility in joints caused by larger gas bubbles in Joint soft tissue, relieved by contracting joint, elbows and knees most comon hence 'Bends'. Can lead to paralysis
Type3 Nuro. Bubbles liberated in brain causing pressure, Symptoms vary from mild imparement (appears intoxicated) to the symptoms of a sever stroke.
In all 3 cases O2 administration as soon as possible. Type 1 *should* be OK but the others require recompression.
This essentially is in controlled conditions taking the diver back to depth (in air / O2) and carefully managing the ascent.
I'm actually glad there hasn't been a chorus of 'Oh yes we do that' so maybe the problem isn't that bad, although I may ask the DDRC (Deep Diving Research Centre) who deal with a lot of UK incidents if they've got any figures.
Thanks to everyone who's contribute, please keep it coming if anyone has anything else to add.
thanks again for yor time.
DaveA
Last edited by Diver_Dave : 3rd July 2008 at 21:08. Reason: Typo
The chap you were with really really should have known better
.. of course. I can't remember any of the details (early 70s) other than that the surgeon on the ride took some time to sort out the problems .. which were complicated by an ear blockage as well ... all seemed to resolve once we were back to SL.
I would have hoped that the average conservative diver would consider the (definitely non-zero) probability of a decompression .. and plan his ground rests appropriately .. given that one could see the cabin altitude peaking anywhere from 15,000 to 30,000-odd feet for a short while ...
That leads to the question, if you were to have a full flying decompression and spend, say, up to 10 minutes going up there and back down, and you had been diving the day before, would it put you in a crisis immediately that you would not otherwise have suffered had you remained at a standard cabin altitude of 8,500'? Can you say how severe the symptoms would be likely to be? Do you pass out- in which case on your own without any knowledge of your diving, your symptoms would be unrecognised. Obviously dangerous, but is there any way the crew could know? Sorry, but we just do not receive any training in this at all!
May I take the opportunity of invading this thread to ask a question which has long perplexed me? Suppose that one were in an archipeligo and had laid on a heliecopter on pontoons to ferry divers quickely and comfortably from one inaccessible dive site to another. If no helicopter flight were to take place at an altitude greater than 1,000ft above the sea level, would such a venture be feasible in terms of divier safety?
Hello there Rainboe! How thrilling to see that you are back!
Very interesting information and thank you. What I really had in mind was something like the new Grumman lookalike flying boat with a couple of PT6s, banging around the Indian or Pacific Oceans where distances can be considerable. An enterprise really that would be to diving what off piste heli skiing is to that sport.
And hello to you Sire! Missed the cut and thrust too much!
That sounds like a rich man's hobby, dedicated planes for divers! Would be useful to go looking for the divers the boats leave behind too.
But I can see it working as the rich are getting richer and no thrill seems to be enough these days. One can't walk up a Maldivian beach without falling over dive tanks and rubber gear. Everybody's doing it. But me. Spending half my life above 30,000' where you can't breath anyway, I find I am extremely nervous relying on a rubber tube underwater for breath, and hyperventilate. It just scares the hell out of me. I'll get my pleasures above msl! However I would like to be sure any diver in crisis on our planes would be recognised.
I've carried a number of divers including commercial divers, always returning at low level (500' or 1,000' depending on the dives). One group of commercial divers were extremely reluctant to fly back until they confirmed that the Australian Standards for Occupation Diving (AS2299) permitted it.
The following information is based on the AS 2299:
LEGEND: Category 1: A single dive to ≤ 50% of the DCIEM no-decompression limit, or two short dives within 18h with a total, combined bottom time of ≤ 50% of the no-decompression limit for the depth of the deeper dive. No decompression dives or repetitive dives to have been performed in the preceding few days. Category 2: Dives exceeding category 1 but not included in Category 3, e.g. one or more dives to ≤ 50% of the no-decompression limits, or a single decompression dive in a day. Category 3: Repetitive deep diving over multiple days; multiple decompression dives on one day; extreme exposures; omitted decompression, or other adverse events.
Interestingly, the standard makes no allowance for changing atmospheric pressure - with a QNH as high as 997 a person at sea level is physiologically experiencing altitude affects as if they are at 500 feet (150m) on an ISA day.
I think NASA has done a heap of research on high altitude DCS problems.
The space suits are pressurised at a relatively low pressure and atmosphere inside is a 100% o2 (wonder if they get a flash back if they fart?)
Before going into the suit they have to go onto O2 to try and lower the N saturation. I think they are only at 0.3 bar in the suits.
My personal opinion is that after a de-pressurisation event unless the person involved is a diver they won't have a clue that there is anything wrong. Aches and pains will be explained away as travel aches. And balance problems will be put down ear clearing problems. In any event there just isn't enough infrastructure to deal with a 737 never mind a 747 worth of pax with suspected bends. From a pilots point of view you can help yourself by staying on the mask on emergency 100% mode for as long as possible even when below 10k.
For a couple of years before bends boxes became affordable for Uni students we used to regularly have aches in our calfs and shoulders running on US navy tables. At the time we put it down to man handeling the rib in and out the water shifting the compressor and humping 30 odd plus cylinders which was typical for a club weekend end on the west coast of scotland. They all dissappeared anyway when we entered the pub. 10 years later after we all started earning money, playing with mixed gas levels of education and dive planning, the use of bend computers. The aches and pains stopped. The running of nitrox on air tables and always using a 50/50 deco mix at 16meters when diving below 30 meters I think was the main difference. The rate of ascent were quite high in the early days going up with the smallest bubbles, these days the bends box seems to start beeping at you if you move your arm to fast. I suspect we were having niggles nearly every month for a couple of years.
There has been a study at Aberdeen Uni on Brain Lesions and decompression. Pilots and commercial divers where in the study group. I can't find the web page which used to published on the study on the web. From memory there wasn't much difference between the levels of lesions between the two professions.
Now our guidelines state no diving 24 hrs before a flight. However, from experience. Bends don't read tables. [1] My computer has never given me more than 18hrs no fly time even after a length series of dives and the conventional wisdom / textbooks based on the longest half life tissue compartments only give a half time of 10hrs for nitrogen (Bones / Joints).
Then your own experience should give you the clue: "BENDS DON'T READ TABLES"!!!
Why would you cavort eith the edge of the envelope when dealing with the possibility of the bends, when a simple matter of waiting a few more hours before you fly will give you a substantial margin? Why would you put others at risk because of YOUR medical emergency which was caused by YOUR selfish "want" to go somewhere when you shouldn't?
"BENDS DON'T READ TABLES"! Even a 24-hour wait before you fly is no guarantee against the bends. While you may have an idea of your general susceptibility, are you acutely aware of all the daily changes in that susceptibility? As a "keen diver," do you REALLY think that being a proponent of 'busting the tables' will do other divers any good -- especially the ones whose susceptibility to decompression sickness may be higher than yours?
The half-life of N2 may be 10 hours, but does that mean that you really want to risk flying with 35% of the residual excess N2 still dissolved in your blood? If so, please do it in your own private airplane with your own hired pilot, so when the bends does bite you, you don't put others at risk.
The way I read the first post it was mearly asking a procedure question not actually advocating flying after diving.
Divers don't normally survive to be technical diving instructors if they have a lazy attitude to risk managment. In fact is some ways the technical diving risk managment is far more conservative than our fuel contingency. It's normal to surface with 33% of your gas left to cover cock ups.
So I think that last post was a bit harsh. I presume the question was asked to further the education of Dave's students who will not be thick or gash when it comes to thier own risk managment.
The problem occurs with the ever increasing PADI open water divers who do a bit of theory, dive maybe every couple of years in warm water with thier hands held by some PADI divemaster. Most will not think twice about doing a couple of 20m dives then going out on the lash all night to jump on a plane 18 hours after surfacing.
The Scottish SubAqua club and it's younger cousin the British SubAqua club have completly different training philosophy's compared to PADI. decompression theory gets hammered into the student if they like it or not. If you get onto daves level in tech diving it requires no small amount of degree level maths to understand it properly.
I didn't my first post could be that badly misinturpreted given my comments about "do we need to change something?"
Also that my scare didn't involve flying!
You'll find the BSAC,SSAC and PADI gudelines are all the same,a MINIMUM of 24hrs, however with the advent of Dive computers these can give no fly times FAR SHORTER than the 24, in my case mine (Aladin SmartZ, Nitek3 and Suunto Viper, if interested) can give shorter no fly intervals whilst still giving a longer total De-sat time.
Intruder, I'll assume you mis-read rather than get offended, I'm trying to find out if there IS an issue out there that we need to hammer home during training. I'm a PADI Instructor about to do a cross over instructor course, oh and my original traing up to dive leader was BSAc so I've covered both sides. Along with Adv Nitrox and Trimix. I (and my partner) always take the whole full day off the day BEFORE we fly back. That way as we do a lot of Deco we're well clear of any danger area.
Werbil:
Very interesting table, I haven't seen that before, I'm guessing it's a commercial table, the De-sat / exposure timings are a LOT more conservative than any sport tables (BSAC**, PADI, Buhlmann etc)
Rainboe:
Give it a try in the pool, when you get to the Nitrox courses you'll love the O2 exposure calculations!
Thanks to everyone who's replied.
Has anyone reading actually had to divert, or, even covered it in a brief?
Mate to be honest PADI is a pile of pooh. And for gawds sake don't ever ever call your self a tech diving instructor with PADI quals. A PADI instructor doesn't even qualify for a safe diver in scotland never mind taking a trainee in.
I know its all a pile of bollocks which agency you train with.
John Thorton up in scapa is the undesputed stroppy arsehole in tech diving but he knows his shit. His boat ther Karin is a smelly tub, but be it rebreather or mix gas he has walked the walk got the t-shirt and proberly told the printer to feck off as well.
He was running gas through the inlet of a compressor before most had even heard of nitrox.
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