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Max Altitude after Diving (Scuba)

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Max Altitude after Diving (Scuba)

Old 8th Nov 2012, 19:42
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I was at Chivenor when the crew flew the bendy diver under the Tamar bridge; not my job but I did fly the reconstruction for the BBC 999 programme that followed. The diver had surfaced on the North coast of Devon, around Ilfracombe I think and the lowest route was planned which ended in the Tamar valley en route to Fort Bovisand where the cab landed on the chamber roof which was quite tight for a Wessex! The advice at that time was to stay as low as possible and everyone presumed 100 feet was a good height. As we now know that is not exactly required but the important thing is to try and maintain your chosen altitude but anywhere up to 1000' is now considered reasonable.
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Old 8th Nov 2012, 20:56
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Not sure why I am wrong. Avoiding significant altitudes is sensible but the difference between 500 ft and 2000 ft is negligible in terms of the partial pressure in the blood and so the amount of nitrogen that comes out of solution.

The partial pressure at sea level is 760 mm Hg and falls by 23 mm Hg per 1000 feet. This makes no difference. When we use a hyperbaric chamber in flight we pressurise to 1.5or 2 atmospheres ie an additional 760 mm Hg and we go up to 3 or more atmospheres when using hyperbaric therapy for other diseases

So flying at 2000 makes an academic but not a physiological difference and flying below normal rotary altitudes cannot be justified on flight safety grounds. Avoiding flying over a 10000 foot mountain is obviously a good idea

But heck I am just a doctor
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Old 8th Nov 2012, 21:21
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homonculus,

Do you have any reference tables that you use when flying a diver with the bends, that could be accessed by HEMS pilots or those involved?

The NOAA site has Required Surface Interval before Ascent to Altitude after diving which obviously applies to 'normal' divers, but I've found nothing to refer to when dealing with divers needing transfer to a hyperbaric chamber?
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Old 8th Nov 2012, 21:47
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I have seen the BSAC recommendations maybe 10 years ago and 500' was the recommended at that point maybe it has changed. However having bubbles of nitrogen increase in size by any further degree even if it is only by a 20th, may have a large impact on the severity of the condition. Also a decrease of aprox 1/20 of a bar will decrease the amount of nitrogen that is able to remain dissolved in the blood. So the effect would be greater than just the proportional increase in size of bubbles of the pressure change of 1/20.

I am just a diver not a doctor or a EMS/Rescue pilot, so happy to stand corrected.
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Old 8th Nov 2012, 22:02
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I have to say that the BSAC recommendations that I am referring to almost certainly did not take in to account the use of portable deco chambers, not sure how common they were then or are now though.
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Old 8th Nov 2012, 23:02
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Senior Pilot

No. The tables you refer to relate to depressurising to about 8000 feet a diver who has followed normal ascent tables. This is because the ascent tables have to balance perfection with the need to ascend at a reasonable rate for recreation and tank endurance. In other words you are ok if you remain at sea level but further decompression MAY be a problem.

This is different from a diver who has not ascended correctly and so has developed the bends. The correct policy is to start hyperbaric treatment as soon as possible to get the emboli back into solution in the blood. This is far more important than trying to navigate at 500 feet.

The problem arises from micro emboli in very small blood vessels so the size of the bubbles is pretty irrelevant.

So the current consensus is not to use fixed wing unless the patient is in a chamber or the aircraft can overpressurise, but rotary altitudes are acceptable.
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Old 8th Nov 2012, 23:11
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Homonculus, I am interested in DCI as a diver can you point me in a direction, for getting more info on this? As it does not seem to tie as nicely as it should to what I was taught many years ago.
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Old 9th Nov 2012, 00:26
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I used to dive to 30 metres in Seychelles, 40 mins or so, then drive home afterwards over a 1,000 ft mountain. Never did me any harm.
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Old 9th Nov 2012, 00:34
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Mmm, interesting that we have a doctor here telling us "Flying below normal rotary altitudes cannot be justified, on flight safety grounds." yet cannot point us in the direction of any black & white references.

No answers back in 2009;
http://www.pprune.org/rotorheads/385...-question.html


Helicoper forced to fly low in mercy dash for diver with bends - Daily Record
A Royal Navy Sea King helicopter from the rescue centre at HMS Gannet at Prestwick, in Ayrshire, was scrambled to airlift the woman to Aberdeen.

The crew were told by doctors not to fly above 300 feet and any changes in height had to be done "slowly" so any pressure change would not affect the patient.
I'm guessing that homonculus ("But heck I am just a doctor") wasn't one of those doctors!




Solution;
Helicopter Ambulance - SOS Hyperlite Portable Hyperbaric Chambers
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Old 9th Nov 2012, 00:54
  #30 (permalink)  

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I think homonculus might be confusing the recommended not flying above 2,000 feet after diving, with a flight involving someone that is already suffering with the bends.

http://archive.rubicon-foundation.or...pdf?sequence=1

Divers Alert Network
Flying After Diving Workshop Proceedings.

2002 Consensus Guidelines for Flying After Recreational Diving

The following guidelines are the consensus of attendees at the 2002 Flying After Diving Workshop.
They apply to air dives followed by flights at cabin altitudes of 2,000 to 8,000 feet (610 to 2,438 meters) for divers who do not have symptoms of decompression sickness (DCS).
The recommended preflight surface intervals do not guarantee avoidance of DCS. Longer surface intervals will reduce DCS risk further.
For a single no-decompression dive, a minimum preflight surface interval of 12 hours is suggested.
For multiple dives per day or multiple days of diving, a minimum preflight surface interval of 18 hours is suggested.
For dives requiring decompression stops, there is little evidence on which to base a recommendation, and a preflight surface interval substantially longer than 18 hours appears prudent.
Alert Diver, November/December 2002, page 7

Choppertop
I used to dive to 30 metres in Seychelles, 40 mins or so, then drive home afterwards over a 1,000 ft mountain. Never did me any harm.
1. You weren't suffering from the bends.
2. The route home was less than 2,000 ft.
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Old 9th Nov 2012, 01:43
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Originally Posted by SilsoeSid View Post
Mmm, interesting that we have a doctor here telling us "Flying below normal rotary altitudes cannot be justified, on flight safety grounds." yet cannot point us in the direction of any black & white references.

No answers back in 2009;
http://www.pprune.org/rotorheads/385...-question.html
I'd suggest that both crab and Um...Lifting... gave answers, albeit without any direct reference:

[email protected]

Having discussed this question at length several times and consulted the experts who run the hyperbaric chambers, the crucial issue is time to treatment. If you have a choice between a protracted low level transit and a quicker but higher level one, then the quicker option is the one to choose.

The sooner the casualty can be recompressed and given oxygen therapy the better the prognosis. I know it seems to fly in the face of common sense but that is what the experts recommend and by taking a long time to get the cas to hospital you can worsen, rather than improve, the situation
Um...Lifting...

Having run a chamber or two in my day, the treatment protocols are to get the patient back to depth as rapidly as possible, so crab is correct.

Depending upon the type of DCS (Decompression Sickness, Type I is simple pain such as joint pain, Type II involves neurological damage), tissue is busily dying the longer that gas not in solution (bubbles, essentially) is in the tissues. Recompression forces gas back into solution so that it can come out of solution via the alveoli in the lungs. Open a bottle of beer to see the process in reverse.

A common myth is that there is a requirement to go to a great depth to contract DCS. Not true. The final 3m in the water column to the surface are the most dangerous because of the steeper pressure gradient.
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Old 9th Nov 2012, 22:12
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Sillsoe Sid

This is exactly what I said. We are confusing the confusion

Sadly for pilots not everything in medicine has references. A reference would be hard to come by as you would have to do research involving perhaps 100 divers and the numbers don't exist. I think what you are looking for is a protocol but nobody has written it. That doesn't mean however that we don't know the pathophysiology of decompression which is why we can determine what we should and should not do.

As for a doctor telling you flying at 500 feet is not safe I can assure you we doctors in the back have as much self preservation as the next man

And some of us doctors also work in the front office on our days off!
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Old 10th Nov 2012, 08:29
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It depends if you think flying below 500' is safe or not - the military seem to have managed it quite reasonably for many years.

If you can achieve a quick transit to minimise time to treatment - and do so safely at low level, what is the problem?

Homonculus - I am guessing you don't fly professionally in the front office on your days off- ie HEMS, AA, SAR etc?
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Old 10th Nov 2012, 09:38
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It depends if you think flying below 500' is safe or not - the military seem to have managed it quite reasonably for many years.

If you can achieve a quick transit to minimise time to treatment - and do so safely at low level, what is the problem?

Homonculus - I am guessing you don't fly professionally in the front office on your days off- ie HEMS, AA, SAR etc?


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Old 10th Nov 2012, 10:40
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In my HEMS days (many moons ago) I had one of these calls.
A diver with the bends, ground ambulance called us because of the long road transit time.
I flew the guy at 200 ft AGL (clear of built up areas etc, flat open country, cavok and twin engine) to the nearest decompression unit which was just over half an hour away.

Later a discussion ensued with my CP about the chosen flight altitude. But due to lack of proper reference we agreed to disagree.
I had chosen my altitude based on my limited knowledge about decompression, with information from the doctor on board. I kept the flight as safe as possible for all, both airborne and on the ground, and as short as possible.

Unfortunately the diver did not make a complete recovery. Perhaps it would have been better in hindsight to get him going in the ground ambulance and either pick him up en route or drive him all the way; I don't know how much waiting for our arrival delayed his arrival in the hospital.
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Old 10th Nov 2012, 12:32
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Personally I am longer in diving (1980-es), than around helicopters-1996., therefore know a bit of both worlds.

Also good friend of mine is local legendary tech diver who
remembers akvalung and closed oxy units from day zero.
(Custeau / Emile Gagnan), therefore he sourced for us
Abyss SW from time of initial development stage.....

Flight after diving must be planed and included in decom
tables or calculations. Old US Navy approach with only 4 types of body tissues is not safe enough.

We are still using one old version of above SW, now unfortunately not supported any more,
to calculate safe margins.
In principle, when you need to fly after dive, that is technical
diving.
Therefore you must left behind all kind of guessing games.

Some old versions can be sourced for "free" from WEB here:
http://www.techdiving.com.br/Abyss/d...yss-Manual.PDF (Eng. manual)

Page 30. contains part you are looking for

Download

Tip is to use max flight level like starting point for calculations. Time on surface after diving is like part of
your calculation decom.
In that case your divers are on SAFE side.

If you have some more questions will invite above friend, to participate here too

Last edited by 9Aplus; 10th Nov 2012 at 13:09.
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Old 10th Nov 2012, 19:23
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Crab

The original question was is there a medical reason to fly at a low low level

The answer in helicopters is no in relation to the ground but to avoid high altitudes ASL

I would turn your question round and ask why you want to fly at the lower level when there is no medical advantage? Yes we all know the military are exempt from rules that apply to us mere mortals but why not fly at a more sensible altitude? apart from flight safety you would help avoid the ever present complaints from people on the ground, well documented in this forum, which continues to jeapordise the future of civilian flights.

I consider it a privilege to be able to fly and do my best to maximise safety and minimise nuisance. Most pilots do not have a photographic memory such that they can avoid individual houses on long distance flights. You may well be a better pilot than me but we are both proportionally safer at the higher altitude
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