What's the latest on no-fly times for multiple trimix dives over several days ?

[AJ]

On the surface it seems this practice may risk filling up the tissues that fill and release gasses more slowly, beyond their M value. Obviously a lot will depend on the number of repetitive dives as well as the depth / time of those dives.

It all depends on what 'excessive deco' and 'something shallow' means. Breathing Oxygen would speed up off-gassing. The question here is: how much and is it enough?

 

[1atm]

With oxygen at 6m you will actually exit the water desaturated (at least for some tissues). That means you’ll be on-gassing on the surface. Granted, this its probably not feasible to desaturate slow tissues, but you can bring down the tension considerably with a pO2 of 1.6

Re the OP question, for trimix dives in the 45-50m range with 50% deco gas, with 1 dive per day over several days, I usually take a 6h+ surface interval, and have not had any problems. But thats my private opinion.

 

[kensuf]

With oxygen at 6m you will actually exit the water desaturated (at least for some tissues). That means you’ll be on-gassing on the surface. Granted, this its probably not feasible to desaturate slow tissues, but you can bring down the tension considerably with a pO2 of 1.6

This.

If you haven't been diving in the past 24 hours, but you've been at sea level the whole tme, the internal partial pressure of inert gas in your tissues is going to be around 0.79BAR. If you sit on a couch and start breathing pure oxygen, you will begin off-gasing and the internal partial pressure in your tissues will drop.

 

[LiteHedded]

I'm generally ok flying the next day

 

[RyanT]

I do a trip like this once or twice a year. I fly home the next day and the interval between my last dive and flight is usually about 22 hours. Of course this is a little under the recommended 24 hours, but it seems to work for me. I wouldn't do a shorter interval.

 

[beester]

To be honest I think the recommended intervals are unnecessary conservative. 24h-48h are in my opinion more driven by liability of airlines than real empiric evidence.

My shortest interval between getting out of the water and flight was about 9 hours (this after a T2/ full trimix dive), and I know others who have done less (you could say... their hair was still wet when boarding). Same with going from sea level to 2000m (which amounts to the same as an international flight, since cabine pressure is kept at a max of 2400m or 8000ft on international flights).

Of course this is also not driven by real study... so your milleage may vary.

 

[RyanT]

To be honest I think the recommended intervals are unnecessary conservative. 24h-48h are in my opinion more driven by liability of airlines than real empiric evidence.

When you're (de)pressurized to 8,000 feet, it's a little less than a 1/3 atmosphere reduction. That means that getting on a plane after (say) a 12 hour surface interval would be like ascending an additional 10 fsw. It seems like that would similar to a 12 hour safety stop, then ascending 10'. @beester, I agree, it's hard to imagine that the pressure reduction would make a huge difference after a decent surface interval. But... with that said, there was a doppler study done by DAN recently that showed fairly substantial bubbling in divers on airplanes, even after substantial surface intervals. I was surprised. The 24 hour recommendation seems excessive, but I'm not really willing to use myself as a crash test dummy, so I do like to at least get closer to the 24 hour mark.

 

[michael-fisch]

This thread is about no fly times for multiple trimix dives over several days.
Why is almost everybody's response geared only to the the same thoughts that we learned in AOW regarding air? Is it because we've lost the ability to read, or is it because we want to respond but lack the ability to understand what happens during trimix diving?

The Helium in Trimix goes into the tissues very quickly.
If you dive to, and stay at 200' for longer than 150 minutes, it doesn't matter how much longer you stay at that depth - you are saturated, the deco will be the same for that dive as it would be for a 4 day dive at that depth.

Luckily decompression, from the helium in the gas mix, is also accomplished much faster than with air, somewhere on the order of 2.5 times faster.
A 12-18 hour break after the last trimix dives before flying, is as conservative as the the usual 24-48 hour wait after decompression air dives.

Thats one of the advantages that trimix divers have in addition to keeping a clear head, ease of breathing and enjoying our dives.
Believe me, it isn't free - the gas, extra gear and training costs a fortune - but for many of us, it is worth it.

Michael

 

[fsardone]

Couple of thoughts here.
First nobody has studied bubbling by non divers flying.
Second the danger is aircraft decompression. Sudden aircraft decompression to 20,000 ft (which is done in chamber for all military personnel who will fly jets) is known to have bent subjects who never dove.

So the question is kind of interesting but hardly answerable with the available data so agencies throw a 24-48 hours blanket on everything.
I did fly immediatly after surfacing. Pilot was a friend and I asked him to set the max cabin prussure differential. So we had more than an atm (1100 millibar) in the cabin, the aircraft actually depressurised upon landing.

Do not try this at home

cheers

 

[1atm]

We have a commercial airline pilot in the local diving circle here. He routinely gets on the plane with the hair still wet from the dive (probably not quite due to briefing times etc but you get the idea). Similar story as what fsardone described ... know that so long as the cabin doesnt depressurize it probably isnt an issue, if it does you have an entirely different order of issue at hand, and as the pilot you get to have a proper oxygen mask straight away ;-)

Something probably not worth recommending, but an indication that the 48h surface interval procedure might be a tad on the conservative side. In the absence of big scientific studies, and with DANs homebase in world champion country of litigation, its no surprise ;-)