Own up!
Joined: Sep 2003
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From: UK,Twighlight Zone
polaris missile, a favourite diving term! No I have never done that one! My bends of arisen from helium not air, in the early days of gas diving we used to carry out a deepwater switch from helium based mixes at around 60m this had a double wammy effect in that we recieved somewhat of a massive narcotic shock and a massive outpouring of helium as the tissue groups over presurised. This would lead to an in water bend that would present itself around the 30m mark, leaving you with a choice of another 3-4 very uncomfortable hours of decompression whith a known bend or a descent and repetition of stops at the switch depth. These days we use closed circuit rebreathers and maintain the bottom mix throughout the dive relying on the unit to maintain constant PO2. This gives a favourable deco curve, no narcotic jolt and reduced instance of DCS.
Yes normal means the non O2 range allthough realisticaly you should be fine upto much higher. It is not the altitude it is the rapid depressurization problem that causes the problem following micro bubble seeding. The bubbles are always present, it is the catalyst that causes them to group together like an angry mob that we have to be aware off. In a commercial jet a blow out could be enough to invite all the bubbles floating around your body to a big brain based rave. In a little spamcan we do not have this problem and the time to climb is so slow we do not sned out the party invites.
Yes I know what all the well know books say about flying after diving. It is your choice to follow the very good advice. I am just pointing out the advice is based on liability and not on accurate physiology. So for anyone who does not understand the subject I would suggest your are better off following the guides.
Yes normal means the non O2 range allthough realisticaly you should be fine upto much higher. It is not the altitude it is the rapid depressurization problem that causes the problem following micro bubble seeding. The bubbles are always present, it is the catalyst that causes them to group together like an angry mob that we have to be aware off. In a commercial jet a blow out could be enough to invite all the bubbles floating around your body to a big brain based rave. In a little spamcan we do not have this problem and the time to climb is so slow we do not sned out the party invites.
Yes I know what all the well know books say about flying after diving. It is your choice to follow the very good advice. I am just pointing out the advice is based on liability and not on accurate physiology. So for anyone who does not understand the subject I would suggest your are better off following the guides.
Joined: Feb 2003
Posts: 420
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From: Io
So are you not a very good diver then? Get the impression you often surface like a Polaris missile...?
His workshop makes Jacques Cousteau's Calypso look like a PADI beginners rowing boat. Aside from re-breathers assorted cylinders and other diving odds and sods I also noticed a rather meaty looking motorbike.
Joined: Oct 2006
Posts: 45
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From: Scotland
Bose-X, what you say is interesting regarding it being impossible to get DCS at VFR heights, i think you might be right and have come up with a fairly reaonable mathematical proof.
Lets say you fly at 5000 ft, the pressure there is about 850 hpa. This is about 150mb than a typical surface pressure (1000 mb say).
Now, any diver will know that when you dive, the pressure is doubled for every 10 depth of water you are in. Ie a pressure increase rate of 1000 mb / 10 m, or 100 mb / m.
Now, say a diver were to dive to say 20m and thenjump in a plane and go up to 5000ft he would be subjecting himself to an decompression of 2000mb in surfacing from the dive, plus an additional 150mb due to the climb, ie a total decompression of 2150mb.
A diver who dived to 21.5 m would experience the same decompression of 2150mb in reaching the surface.
Hence jumping in a plane and then clmbing to 5000ft straight after diving gives you the same chance of getting DCS as if you had dived to a mere 1.5 m greater depth, ie bugger all!
Essentially, the pressure loss in climbing to VFR heights is insignificant compared to the pressure change in surfacing from a decent depth, hence it is my opinion that the risk of getting DCS from VFR flights, or for that matter passenger flights, where the cabin altitude is I believe 6000 ish ft (?) is minimal.
I may well be wrong however, as there are complex phisiological factors associated with DCS that I dont know about but the above argument does make good sense.
Lets say you fly at 5000 ft, the pressure there is about 850 hpa. This is about 150mb than a typical surface pressure (1000 mb say).
Now, any diver will know that when you dive, the pressure is doubled for every 10 depth of water you are in. Ie a pressure increase rate of 1000 mb / 10 m, or 100 mb / m.
Now, say a diver were to dive to say 20m and thenjump in a plane and go up to 5000ft he would be subjecting himself to an decompression of 2000mb in surfacing from the dive, plus an additional 150mb due to the climb, ie a total decompression of 2150mb.
A diver who dived to 21.5 m would experience the same decompression of 2150mb in reaching the surface.
Hence jumping in a plane and then clmbing to 5000ft straight after diving gives you the same chance of getting DCS as if you had dived to a mere 1.5 m greater depth, ie bugger all!
Essentially, the pressure loss in climbing to VFR heights is insignificant compared to the pressure change in surfacing from a decent depth, hence it is my opinion that the risk of getting DCS from VFR flights, or for that matter passenger flights, where the cabin altitude is I believe 6000 ish ft (?) is minimal.
I may well be wrong however, as there are complex phisiological factors associated with DCS that I dont know about but the above argument does make good sense.
Joined: Sep 2003
Posts: 1,198
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From: South Norfolk, England
Slight thread drift ... but "the bends" seem a very interesting subject when it comes to flight as well as diving. How high would you have to climb to unpressurised to possibly suffer in flight?
I worked for on a fishing vessel years ago where the skipper used to be an RAF diver (gunnery ranges out to sea) I mean the old type of frogman too ... like James bond in black rubber as it was in the sixties. He reckoned, whilst not impervious to the bends, that he had a high tolerance and had survived a bad episode with no ill effects when two collegues died
So I guess it can effect people differently?
SS
I worked for on a fishing vessel years ago where the skipper used to be an RAF diver (gunnery ranges out to sea) I mean the old type of frogman too ... like James bond in black rubber as it was in the sixties. He reckoned, whilst not impervious to the bends, that he had a high tolerance and had survived a bad episode with no ill effects when two collegues died
So I guess it can effect people differently? SS
Joined: Sep 2003
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From: UK,Twighlight Zone
It is not the alt that you climb to per se, it is the rate of change that you are subjected to. We have microbubbles in our body at the end of a dive even after having surfaced normally from either a correctly decompressed dive of from a no stop dive. These bubbles are expelled from our body over a period of time following the dive down to a back ground level. There is always a "background" of bubbles present, a doppler easily verifies this.
A rapid rate of change in pressure can cause the microbubbles to seed, essentially they all decide to wander off to a rave and make new friends. Little bubbles that did not cause problems suddenly grow in size and room has to be made for them. This happens in the form of tearing of tissue and nerve, blockage of veins and arteries etc which then presents as clinical DCI.
There is no such thing as an immunity to a bend, it comes down to carefull decompression and luck. The incidence of bends against time in water is pretty low if the basic rules are followed.
As BB points out his physics are correct on pressure changes. There are some complex issues around the subject as well along with some interesting spanners that can appear in the works PFO being one of them. They arguments continue to rage as to how many and what type of tissue compartments represent the human body. Haldanian, Buhlmaan, DSAT, Comex etc. At the end of the day they are just mathematical models.
AS I said before, the agencies recomendations are good, reduced liability etc. We make our own choice based on knowledge and experiance.
A rapid rate of change in pressure can cause the microbubbles to seed, essentially they all decide to wander off to a rave and make new friends. Little bubbles that did not cause problems suddenly grow in size and room has to be made for them. This happens in the form of tearing of tissue and nerve, blockage of veins and arteries etc which then presents as clinical DCI.
There is no such thing as an immunity to a bend, it comes down to carefull decompression and luck. The incidence of bends against time in water is pretty low if the basic rules are followed.
As BB points out his physics are correct on pressure changes. There are some complex issues around the subject as well along with some interesting spanners that can appear in the works PFO being one of them. They arguments continue to rage as to how many and what type of tissue compartments represent the human body. Haldanian, Buhlmaan, DSAT, Comex etc. At the end of the day they are just mathematical models.
AS I said before, the agencies recomendations are good, reduced liability etc. We make our own choice based on knowledge and experiance.
Joined: May 2000
Posts: 268
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From: uk
Baboon Boy
I see that in the 6 days that you have been a pruner, you have not only admitted to low flying over a built up area but you have also started posts on the following:
Questioning why no one will hire you a SEP for long solo overwater transits in Florida on the back of your 50 odd hours experience.
Asking what equipment you will need to fit to a C152 in order to tow a banner.
Aviation needs characters and I look forward to reading about "the further adventures of Baboon Boy". I just hope for your sake that its not in a CAA publication.
Something about old pilots and bold pilots????
I see that in the 6 days that you have been a pruner, you have not only admitted to low flying over a built up area but you have also started posts on the following:
Questioning why no one will hire you a SEP for long solo overwater transits in Florida on the back of your 50 odd hours experience.
Asking what equipment you will need to fit to a C152 in order to tow a banner.
Aviation needs characters and I look forward to reading about "the further adventures of Baboon Boy". I just hope for your sake that its not in a CAA publication.
Something about old pilots and bold pilots????
Joined: Oct 2006
Posts: 45
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From: Scotland
There are old pilots and there are bold pilots, but there are no old bold pilots right?
Baboon boy is recently qualified and is full of the joys of flying, and is enthusiastic about wealth of fantastic possibilities that are opened up by his "shiny new licence."
He also recognises his inexperience and the dangers of aviation.
Max contingency, the posts to which you refer result merely from idle musings aimed at satisfying his inquisitive mind, rather than a desire to "bite off more than he can chew" too early.
Aviation does need characters however do not think that the "crazy" nature of such people necessarily implies a haphazzard attitude and a lack of common sense.
Look at Murdoch off the A Team, clinically insane but arguably the greatest and safest pilot in history!
Baboon boy is recently qualified and is full of the joys of flying, and is enthusiastic about wealth of fantastic possibilities that are opened up by his "shiny new licence."
He also recognises his inexperience and the dangers of aviation.
Max contingency, the posts to which you refer result merely from idle musings aimed at satisfying his inquisitive mind, rather than a desire to "bite off more than he can chew" too early.
Aviation does need characters however do not think that the "crazy" nature of such people necessarily implies a haphazzard attitude and a lack of common sense.
Look at Murdoch off the A Team, clinically insane but arguably the greatest and safest pilot in history!
