max altitude after diving (scuba)

[3top]

Hi all!

I am visiting from "Rotorheads" some down the forum line.

I wonder if there is anyone on "Medical" 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 (in a helicopter) 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

[slim_slag]

I haven't got a clue, but "back of the fag packet" calculations say that the pressure difference between 500ft and 1000ft is around 0.5 inch of mercury which is 1/60th of the atmosphere.

One atmosphere is 33ft of water, 1/60th of this is around 6 inches of water. So the pressure difference on a human when you fly at 1000ft as opposed to 500 ft is less than the height of a small wave your divers have been swimming under. The lawyers may see it differently.

[RodgerF]

Hi 3top

I have found this link. It discusses dive profiles which you might want to dicsuss with your passengers.

http://faculty.washington.edu/ekay/altitude.html

[mad_jock]

If you want to know to the n'th degree whats happening with decompression subscribe to this mailing list. (scuba-uk)

http://www.drogon.net/scuba-uk-ndg/

Some of the people on the list design decompression software and are 100% up on the tissue half life algorithems. Funny gas mixes etc so will be able to tell you about breathing nitrox to help etc.

Biggest problem with deco is it is all based on statistcal curves and there are quite alot of cases of people getting bent inside the tables.

And if it helps I have dived similar profiles and we drove back over the Rest and be Thankful which is well over 1000ft with no probs felt. This dosn't mean I didn't get a brain bend which most pilots get at some point in their career but can't feel it.

Which is why commercial divers always play safe and want to stay as low as possible

MJ

[3top]

THanks guys for all the advice!

Made the flight today at average 400 ft with one short excursion to 650 ft. No complaints. I found a table that would have placed them at 2000 ft without problems.....

I will work at this to find a safe solution for fast diver (non bent accident flights) transfer after diving if necessary.

3top

:cool:

[slim_slag]

I was talking to my flight nurse 'missus' about this last night and they only ever need to worry about transporting divers from lakes which are higher than the closest hyperbaric chamber. She said they would keep as low as possible, but obviously not too low that they hit wires and kill four people. If she thought she had a problem she would patch into the docs at the chamber. She did say that a helicopter transport would only take around 30 minutes, where if you sent them by ground it would take several hours. So in an emergency situation I guess you also want to consider the risks/rewards of leaving them at a lower altitude but for a far longer period of time.

[3top]

SLim:

Thanks for the note. Actually if the lakes are HIGHER than the location of the chamber, any transport to a lower altitude than the lake surface will help already, as ambient pressure increases with lower altitudes.

I got the 2 divers back okay at average 400 ft, though it needed some "interesting" flying.

These 2 were diving according to US Navy tables which are quite tight. I found a table which gives information on saturation letters versus altitude versus rest time at sea level. Tomorrow I should have some time to verify this and post the results!

3top

[mad_jock]

US navy tables are a nightmare.

They were designed years ago off the british tables which were created by killing goats in a chamber.

I think the bend hit rate is 1 in 10 000 dives inside tables.

MJ

[slim_slag]

Try and find:

Bennett PB, Dovenbarger JA, Bond BG, and Wacholz CJ: Flying after Diving: 1987 Accidents, Alert Diver 5(1):1, 1989

Kiser KW: Disorders of the deep, Emergency Medicine (June 30) 18-58, 1984.

Apparently they says keep below 1000ft, but I don't have the actual texts.

These references came from

Flight Nursing Principles and Practice, Lee, Genell. ISBN 0-8016-6138-2. Page 466

[mad_jock]

Why don't give these peeps a ring

http://www.demon.co.uk/hyperbar/

They are very pleasant and are more than willing to help, explain things so they don't have to help people.

They also have no problems showing you around the facilitys.

The standby emergency blokes are top lads who actually managed to survive diving in the north sea in the 70's.

MJ

And I just found this which is proberly more than you wanted on the techie side of things

http://www.emedicine.com/emerg/topic790.htm