Max Altitude after Diving (Scuba)

[3top]

Yes, me again!

I wonder if there is anyone on the forum who can answer a very specific question:

What would be an established altitude maximum for LOW LEVEL flights (500 ft, 1000 ft, 2000 ft,...) after diving. All I can find on the net deals with rest-times before airline travelling, military test, etc.
All these texts deal with cabin pressure alt of 5000 ft and more (8000 ft standard airline cabin pressure). But nothing on safe altitudes for flights IMMEDIATE after diving or few hours (1-4 hrs) rest-time.

Case at hand: I had/have to fly a set of divers to a search mission. Immersion times of 1 hour / 4 X day for a total of about 4 hrs - max depth about 75 ft or 20 m at any time possible.

They requested transport after diving at no more than 500 ft MSL (the search is done at sea level). Problem at hand is that I have to refuel at a location where I might scratch hills if I maintain 500 ft all the way....
Total flight time is about 2hrs.

Anyone flying with rescue-equipments that use divers?

I appreciate your help!

3top

:cool:

PS: As it is a medical question I will post a copy over at "medical", however there may people working with helicopters in exactly this environment.....

[Huron Topp]

2000 ft would be no problem at all.

[3top]

Huron Topp:

Thanks for the opinion - I though so too (actually I would even go to 3000ft, but for this case 1000 would do fine ...), when I was argueing with the divers (having been a volunteer rescue diver in Austria - cold lakes, at 400 to 1000m elevation, etc.) However they tell me to shut up, they are "professionals". Well I`ll fly them low then.
But I would like to have some proof - any reference from a rescue org. manual or so to show them that helicopter pilots can be "pro" in a different field too, besides you really never know when you have to fly these guys. Any idea?

3top

[Huron Topp]

I'll see if any of my manuals give a "definate" height. This is an excellent link though.
http://www.vnh.org/FSManual/01/09BubbleRelatedDisease.html

[[email protected]]

Our maximum altitude for a 'bent' diver is 1000' msl and frankly the lower the better en route to the hyperbaric chamber. I can understand why your professional divers want to stay low - any chance of the nitrogen expanding in the tissues (especially brain and nerve tissues) should be minimised. We have a Navy diver on exchange with us so I will ask his opinion and see what the RN position is on it.

[sycamore]

Would it help if they were to breathe oxygen en-route if you have to climb?

[Flying Boat]

4 hours total time is one hell of a time to build up Nitrogen in the body.
Ask them how long they plan to take for decompression stops, this should give you an idea about their saturation. The longer the more saturated.

I teach diving for fun, BS-AC, and we recommend no one flies or drives up high hills until at least a tissue code 'B'. That is at least 4 hours from your last dive (surfacing a 'G' with a small deco stop).

When I was in Saudi there were many cases where divers left Jeddah & drove into the mountains, 2-5,000ft, suffered from bad decompression illness and had to be rushed to the hyperbaric chamber.

I fully agree with crab, the lower the better.

Sycamore has a point, oxygen would help draw the Nitrogen out but if they are greatly saturated they could still suffer.

Once you have suffered from Decompression Illness, you are more susceptible to it, I would check to see if any have suffered before.

As you pointed out, they have said they are 'professionals' so tell them your planned height and get them to sign a waiver against any costs or damages resulting from decompression illness.

On the positive side, seeing as you said they were only going to 20m maximum, they might be diving on Nitrox, higher percentages of oxygen, so less Nitrogen to be absorbed, this still puts Nitrogen in the body though.

Good Luck

FB

[3top]

Thanks guys!

Great info coming. I found finally a table that gives 0 hours waiting times according to requested flight altitude versus Rest Nitrogen Letters. I just have one hell of a problem loading the chart (some trouble with power point here...).

Of course I agree with "as low as possible", but with 20m and 1000 ft there should really be no problem - If I remember right at 1000ft and the highest Letter - L - it was off the total immersion time table as it approached 400 min allowable or so. I will certainly check this out and post it when I am done.

Flying Boat:
They "seem" to be pro´s, on the other hand they are both overweight and at lunchtime they would stuff themselves with greasy chicken and fried rice!
I didn´t dive for a long time, but I do remember that we were urged to "refrain" from heavy food before diving.
They use regular air.

Crab:
As you said your max alt is 1000 for a "bent" diver, so the guy is already in trouble but you still can go to 1000.
My clients are not supposed to get themselves in deco troubles in the first place - the search is nothing for live or death, but scientific.


Keep it coming guys!

3top


:cool:

[crusty scab]

G'day 3top,

You might be interested in the table below? Although it was first produced in 1989 - shortly before the company in question went bankrupt. The company was the National Safety Council of australia - the NSCA.

They were a very large rescue orginasition in Australia who supplied fixed wing Pararescue, helicopter rescue, and hyperbaric retrivals.

The Parra-Jumpers - PJ's - of the Pararescue teams jumped with LAR-V diving equipment and had to train whilst on immediate standby with SCUBA as well as the LAR-V O2 set. The NSCA medical officers (trained in hyperbaric medcine) prepared the table so that 'on-shift' training could be conducted safely. The table was established using a mixture of Canadian and RN tables.

As an ex-RN Clearance Diver, and PJ, I found the company very proffesional. The fact that they employed diving doctors who were also trained as PJ's, and that the senior diving instructor was an ex RAN chief petty officer Clearance Diver, I believe, sums up the standard they operated to.

NSCA OPERATIONAL PROCEDURE FLYING AND DIVING

1. Allowable diving whilst maintaining immediate availability for operational flying.

a - LAR-V No Limit
b - Air diving 3meters 60minutes
6meters 30minutes
9meters 15minutes

2. Minimum required delay before flying or travelling to altitude after diving.

DIVING ACTIVITY UP TO 1000FT UP TO 3000FT

Up to 50% no deco
< 30m Nil Nil

Up to no deco limit
< 30m Nil 2Hrs

Repetitive dives
Deco diving
< 50m 2hrs 12Hrs

NOTE: Although we followed this table without incident - and indeed, that it extends to greater altitudes and depths, it was reasonably new. Due to the demise of the NSCA a long term study of it's effectivness wasn't undertaken, and should you ellect to use it I would suggest that you seek a current diving doctors opinion.

[3top]

Crusty Scab! ....what a name!

Thanks for all the advice! Just before the flight I did, I called a divemaster, however as he teaches "tourist"-diving he confirmed the extra careful way and prohibits flying for 12 hours anyway. Period. ....neverminf that coming back to the city they all climb above 500ft. .....but I could not fly there, go and figure.

AFTER the flight (to avoid any "professional"/professional discussions before the flight, I managed to stay below 500ft with a short excursion to 700 - less then 2 minutes...), I gave the divers (who according to them use USNavy tables....) the following list:

http://www.ndc.noaa.gov/pdfs/AscentToAltitudeTable.pdf

As it comes from NOAA it is some "official" table.
The rest of all the advice is very good and for me confirming my own opinion, but as long as it is not official in some way it proofs nothing to "professionals" (besides I do respect their request, as it is them who dive and it is their lives at stake...).
These two guys where out of the water for about 4 hours before getting on the helicopter and according to one off them where at repetetive letter J when completing the dives. The table mentions 1000ft as the first altitude level. I guess below that they will not consider it altitude at all...
This table pretty much confirms all the rest in here!

On the NOAA website one can find everything one needs to know as a pilot about diving+flying.

Thanks again,

3top
:cool:

[bugg smasher]

Quick question for the medevac types;

When evacuating a diver to a recompression chamber for treatment, what are the altitude restrictions, if any, so as not to aggravate the condition?

Many thanks

[griffothefog]

I remember a wessex from Chivenor made the news years back with a potential bends case by flying under the Tamar bridge on the way to Bovisands, utter bollocks :=

And before any mil types jump on that.... My info came from the actual doctor from that establishment who assured me that relative low level was preferable, but that meant flight levels :ugh:

[Mushroom_2]

I've done it in the past (mil) and was told "as low as possible". I'm no expert so I did what I was told.;)

[branahuie]

Max 500 feet if possible, quoted by the BSAC, several years ago..
a diver was flown from Stornoway to the chamber in Aberdeen via the Pentland Firth back in the 1980s by a Lossiemouth helicopter.
Did Bristows work out an overland route through the glens when they started with the CG in SYY?

[SilsoeSid]

I remember a wessex from Chivenor made the news years back with a potential bends case by flying under the Tamar bridge on the way to Bovisands,

Coming from that part if the country, I'd love to know where the diver was diving in order to warrant that particular route to Bovisand :suspect:

I was told, as part of a brief by the operators of a decompression chamber somewhere close to the Sulu Sea, that as air pressure decreases with height the lower the better, in an attempt to keep the gas bubbles as small as possible en route to the chamber.

[homonculus]

What a load of tosh

Divers dive in water. Helicopters fly in air. Different density. The pressure in water doubles in 33 feet but the pressure in air takes 5500 metres to drop by half.

Depressurisation in a fixed wing to 8000 feet might be an issue but flying at 500 instead of 2000 feet is just inexcusable. Might even be illegal.

What is important is early pressurisation and we now have portable chambers we can use in helicopters so the diver can be pressurised during transfer.

[TukTuk BoomBoom]

Well I don't know about flying under bridges but unless there's a fuel burn issue with a jet that can pressurize then the maximum altitude is 1000ft.
And homon if the guy is already bent to the point of a medevac flight then use your head, the pressure is already too low on the surface let alone at 2000ft.

Was diving in Micronesia along time ago an an Aussie diver got bent pretty bad and they flew him home in a Learjet at 1000 ft.
Thank god for DAN!

[Redland]

Sorry homonculus you are wrong please check before you say it is a load of tosh.

[bugg smasher]

Not the issue here homonculus, deco-chamber equipped heli units not available, under any circumstance.

This problem involves evacuating live-aboard divers in remote parts of Indonesia, possibly hours away, to a facility that can deal with life-threateneing recompression issues.

Once bent, what pilot guidelines do we follow?

[Te_Kahu]

I once talked about this with a Hyperbaric Medicine specialist. He said there were many factors at play and to consider in regard to the bends. However, the broadest rule was to stay low in non-pressurised aircraft.

TK

(edit to correct medical field)

[Myra Leese]

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.

[homonculus]

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

[Senior Pilot]

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 (http://www.ndc.noaa.gov) site has Required Surface Interval before Ascent to Altitude after diving (http://www.ndc.noaa.gov/pdfs/Rev_6_495.pdf) which obviously applies to 'normal' divers, but I've found nothing to refer to when dealing with divers needing transfer to a hyperbaric chamber?

[Redland]

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.

[Redland]

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.

[homonculus]

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.

[Redland]

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.

[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.

[SilsoeSid]

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/385712-sar-question.html


Helicoper forced to fly low in mercy dash for diver with bends - Daily Record (http://www.dailyrecord.co.uk/news/scottish-news/helicoper-forced-to-fly-low-in-mercy-980729)
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 (http://www.hyperlite.co.uk/services-08.html)

[SilsoeSid]

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.org/xmlui/bitstream/handle/123456789/5611/DAN_FAD_2002.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.

[Senior Pilot]

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/385712-sar-question.html

I'd suggest that both crab and Um...Lifting... gave answers, albeit without any direct reference:

crab@ (http://www.pprune.org/5136354-post9.html)

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... (http://www.pprune.org/5136397-post10.html)

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.

[homonculus]

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!

[[email protected]]

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?

[skadi]

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?

:ok::ok::ok:

skadi

[S76Heavy]

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.

[9Aplus]

Personally I am longer in diving (1980-es), than around helicopters-1996., therefore know a bit of both worlds. :cool:

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/download/Abyss-Manual.PDF (Eng. manual)

Page 30. contains part you are looking for ;)

Download (http://www.techdiving.com.br/download.htm)

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 :ok:

[homonculus]

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