Flying after diving math.

[cavemanxxx]

Hypoxia at that level would take place quite quickly, but by that time our fly boys would have their Oxy mask on( at least, thats what the passengers would hope ).

Great stats on deco. at alt. Question still remains, has any one donw the maths on the effects of going to 8000ft directly after i.e. multi days diving. What is the limiting factor ?

 

[Dr Deco]

Dear Readers:

Altitude and Diving

As has been mentioned, this particular problem has not yet been fully evaluated. It should be possible to put some algorithm into a dive computer, but this is not done because of the cost of the research. Unless manufacturers get together and fund such a study, it will not be done by one company. This is because, after going to the expense, any deco meter program would simply take the results and program something very similar into their device for little additional cost. [Back calculating is very simple.]

If you really wish to see the effects of flying following many days of diving, you must actually perform many days of chamber dives. It is obvious that this begins to become very costly.

Altitude Decompression

The question of further decompression following a loss of cabin pressure is very troublesome for a diver. The plan is to descend within a few minutes so that DCS is not encountered by the passengers. What would happen to a diver is anybody’s guess.

The normal; restriction of 8,000 feet applies to the cabin pressure. This would not be a problem to non-divers as they never get the bends on an airplane. A diver, with additional dissolved gas and tissue microbubbles, could be an entirely different story.

Dr Deco :doctor:

 

[DIR Tec Diver]

The previous information is extremely informative and very precise however one of the big issues has been skipped. The airlines in attempts to save money do not keep the cabin pressure at acceptable levels, and these levels may not be standard between airlines. It costs a lot of money to pressurize the cabins to normal levels, and since most passengers are non divers, there is no big push or need for the appropriate pressurization. This leaves us divers at a higher risk of DCS, thus why we need to be conservative and err on the side of caution in regards to flying after diving. It is true that DAN and the NEDU (Navey experimental diving unit) have research on going, but no matter the results as long as the airlines try to trim costs and make short cuts, we are at a higher risk unless we take extra time to ensure proper off gassing.

 

[Charlie99]

DIR Tec Diver once bubbled...
The previous information is extremely informative and very precise however one of the big issues has been skipped. The airlines in attempts to save money do not keep the cabin pressure at acceptable levels, and these levels may not be standard between airlines. It costs a lot of money to pressurize the cabins to normal levels, and since most passengers are non divers, there is no big push or need for the appropriate pressurization.

Could you be more specific? Which airlines? Which countries?

While in US airspace, or flying on a U.S. based carrier the FAA rules require a cabin altitude no higher than 8,000 feet (about 2,400 meters) under normal conditions. The requirement is in FAR25. I have heard unconfirmed rumors, but never seen anything definitive about some European countries allowing a slightly higher altitude.

Another altitude limit is just over 10,000 feet, where a cabin altitude alarm and activation of emergency oxygen system occurs. I found out about this limit on a flight from Maui about 16 hours after my last dive. Shortly after takeoff I began to feel lightheaded, but was relieved to find out that other passengers were feeling the same symptoms. In a few minutes the captain announced that we were diverting to Honolulu because of an "open cargo door" alarm, and that if we were feeling faint it was because the cabin altitude was now at 10,000 feet, just short of tripping the oxygen system. The captain kept cabin pressure at 10,000 feet altitude (to provide inward pressure on the door) all the way through the landing, and then dropped it to sea level in about 2 minutes while taxiing to the gate -- some of the non-divers onboard had significant difficulties with the unusually rapid pressurization.

 

[cavemanxxx]

the price of pressurization is not such an issue, rather the stresses on the hull. A lower cabin alt would reduce the life span of the hull.............

I am still quite sure that the normal 8000 feet cabin alt would in it self not be harmfull to divers, but of course an explosive decompression at 39,000 will most likely be a bubbly event

 

[Charlie99]

caveman once bubbled...
I am still quite sure that the normal 8000 feet cabin alt would in it self not be harmfull to divers, ....

Wrong, wrong, wrong. .:wacko: The fly after dive limitations are specifically due to the 8000 ft cabin altitude, and are in no way related to accidental depressurization.

Caveman, your statement seems to be the second most common flying misconception, after the mythical "unpressurized cargo hold".

If anyone wants to work out the math, simply calculate the loading in your long halftime compartments, then using Buhlmann a and b values, figure out the allowable loading at 0.78ATA or whatever altitude you wish to ascend to

 

[cavemanxxx]

Thanks, always glad to hear I am wrong, you stay alive longer that way.

 

[chrpai]

DIR Tec Diver once bubbled...
This leaves us divers at a higher risk of DCS, thus why we need to be conservative and err on the side of caution in regards to flying after diving. It is true that DAN and the NEDU (Navey experimental diving unit) have research on going, but no matter the results as long as the airlines try to trim costs and make short cuts, we are at a higher risk unless we take extra time to ensure proper off gassing.

Funny, I've seen one of your GUE/DIR instructors post that its perfectly fine to do the deco cleanup posted earlier and drive straight to the airport after a dive.

 

[BigJetDriver]

When it comes to aircraft presssurization, most of the new generation aircraft can hold a cabin altitude better (i.e. lower) than 8000 ft msl. If your computer will read ambient pressure, take it with you in the cabin and check it at cruise altitude.

The notion that airlines keep a higher cabin altitude to save money stems from a lot of reasons, but most of them come under the heading of "urban myth". I am not knocking anyone's ideas here, it is just that the physics (and the reality) of the problem leads to different conclusions.

To try to boil it down to a thumbnail sketch is difficult. In the short version, however, as you may already know, any aircraft only remains pressurized because the pressurization system pumps more into the hull than the amount constantly leaking out through all the little holes that are already there. One could stand in the aisle, fire off a full magazine of handgun ammunition through the hull, and the end result would only be a lot more wind noise. Gert Frobe would not fly down the aisle and out the window as he did in one James Bond movie. (You understand I am not recommending this as an experiment!)

An aircraft pressure hull CAN be made which will hold 1 ATM, but the weight required to do so will seriously restrict payload. This is not to say it can't be done, but if you think ticket prices are bad now....

The FAD recommendations are conservative, as has been noted. DAN is doing an excellent study on this, and they really are looking for participants. Contact them at: <http://www.diversalertnetwork.org/medical/research/index.asp>
for more information.

BTW: We really do train to get our masks on in seconds if there is a problem. The new ones look like the "face-hugger" creature in the movie "Allien"! It WILL take more than a few seconds to get the beast down from 35,000+ feet to 10,000, even at max rate. So, hang onto your hat!