How Long Should I Wait Before Driving Up To 6000ft?

[Tuby]

Hi guys,

I did some search on the forum regarding driving after diving but i'm still confused. There are numerous techniques mentioned, but what I would like to know is after doing multiple dives for three (3) days, how long would I need to wait before I drive to a town with an elevation of 6000ft? I'm not sure if it relates, but PADI recommends not less than 18 hours after doing multiple day dives before taking a flight...

 

[Blackwood]

Driving to 6000 feet is basically the same thing as flying in a commercial airliner (without the potential for a sudden loss of cabin pressure in the case of the former).

16 hours represents fully clearing 30 minute (and faster) tissues. I'm not sure where the 18 is coming from.

 

[Tuby]

Blackwood,

I got the 18 hours from the notes section of the PADI Rec Dive Planner which applies for repetative or multi-day dives. Will the use of a dive computer give a more accurate surface interval time before flying (especially those with NO FLY feature)?

 

[Scott]

More details might be helpful.
What elevation are you coming from to get to 6000 ft? Sea level, 5000 ft?
How soon after diving will you start your elevation change?

 

[Blackwood]

Blackwood,

I got the 18 hours from the notes section of the PADI Rec Dive Planner which applies for repetative or multi-day dives.

I just meant I don't know what their basis is, but I was having a blond moment.

PADI uses a compartment-based tissue model (buhlmann), theorizing that various types of tissues load and unload inert gas at varying rates. They conceptualize them as having half-life exponential growth and decay.

Most people consider either 5 or 6 half lives as being fully saturated (or desaturated, depending on what you're looking at it).

18 hours is 6 cycles of a 3 hour compartment (i.e. after 3 hours that tissue has offgassed 50%, after 6 hours it has offgassed 75%, ..., after 18 hours it has offgassed 98.4%).

Will the use of a dive computer give a more accurate surface interval time before flying (especially those with NO FLY feature)?

I believe some computers simply count down 18 or 24 or 48 hours. Others count down until the slowest compartment (48 hours = 6 cycles of an 8 hour compartment) is considered to be completely offgassed.

I don't necessarily see one being better than the other, or either being better than a wristwatch.

 

[Mr Carcharodon]

There is not a simple answer without knowing the depths and times of all the dives. Worst case assumptions would say ~50 hours. That assumes a saturation dive which is pretty silly for recreational diving. All the computers I have used have a no fly time on surfacing. But different computers make different assumptions and come up with very different times. Most of the assumptions have never been validated so we do not know if they are correct or not.

12-18 hours are typical recommendations and are reasonable for generic undefined dives. Deep, stressful multiple dives or being cold should push you the longer end of the recommendations.

 

[Hatul]

This question has been asked before. It's not the same as flying. One conservative way of dealing with this is to set your computer to 6000ft altitude and dive within the restricted profile. Then there's no need to wait before driving back.

Adam

 

[fire_diver]

It should only take as long as your need to pack up your gear in your car.

Think about it.... You spend minutes dropping your surrounding psi from AT LEAST 28psi (33 feet deep) to 14 psi at the surface. Then it's going to take you a lot longer to go from that 14 psi to 12 psi. Did you worry about the bends when making your surface? Why should you worry about driving to an elevation that is a fraction of what you have already done.

I can see MAYBE having some concern if you are diving on the edge of a coastal mountain, then driving straight up in a few minutes. If it's going to take you a half hour or long to reach that hight, don't worry.

 

[lamont]

They're actually basing that off of chamber studies where participants were taken to 60 feet for 60 minutes, with a 60 fpm ascent and no stop, following by a 2 hour(?) SI and another dive, and then taken to 6,000 ft altitude after a variable SI. The last case of DCS occured after an 11 hour SI, so 18 hours was judged to be safe.

I have all kinds of issues with how this study was carried, out, but if you've got divers doing multiple recreational dives, blowing off stops and ignoring repetitive diving residual nitrogen completely, then they should probably not fly or ascend to altitude for 18+ hours. Definitely. IMO, the problem there is that you shouldn't fly right after you've bent yourself, you'll only get worse.

If you do clean deco that seems overly conservative since it does wait until the 3 hour compartment is fully cleared. A 5-6 hour recommendation to clear the 1-hour compartment would seem to be more than enough. Since you're going to be hard pressed to get out of the water and get into a plane in quicker than 3 hours, and I think that's more than enough, I'd say the flying-after-diving guidelines can be largely ignored.

But again, that means you treat your recreational dives like deco dives and don't blow off stops.

Oh, and if you're worried about the plane having decompression at 30,000 feet you might want more 1 ata deco time... Depends on your tolerance for risk there...

I just meant I don't know what their basis is, but I was having a blond moment.

PADI uses a compartment-based tissue model (buhlmann), theorizing that various types of tissues load and unload inert gas at varying rates. They conceptualize them as having half-life exponential growth and decay.

Most people consider either 5 or 6 half lives as being fully saturated (or desaturated, depending on what you're looking at it).

18 hours is 6 cycles of a 3 hour compartment (i.e. after 3 hours that tissue has offgassed 50%, after 6 hours it has offgassed 75%, ..., after 18 hours it has offgassed 98.4%).



I believe some computers simply count down 18 or 24 or 48 hours. Others count down until the slowest compartment (48 hours = 6 cycles of an 8 hour compartment) is considered to be completely offgassed.

I don't necessarily see one being better than the other, or either being better than a wristwatch.

 

[fire_diver]

Lamont, re-read the OP's first post. Asking about driving to altitude.

I can understand the need for the conservatism if flying. Even though you may be out of the water for a few hours before takeoff (assuming the worst disciplined diver), it only takes seconds for that plane to climb above the 7000 foot mark that the cabin is pressurized to. If you take the chance of catastrophic pressure loss, then you would instantly jump from 7000 to 35,000 foot in pressure. That is serious concern for DCS.