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

[Nasser]

I'm wondering are there any new advisories for no-fly times for multiple trimix dives in the 75m-90m range over about 5-7 consecutive days (one/day)? Last time I checked there was at least a 24hr interval recommended before flying for multiple dives over several days, referring more to live aboard type diving (3-4 dives per day NDL dives) but nothing specifically on these types of dives.

Anyone have any updated info. on this?

Thanks.
nas

 

[rjack321]

I'm wondering are there any new advisories for no-fly times for multiple trimix dives in the 75m-90m range over about 5-7 consecutive days (one/day)? Last time I checked there was at least a 24hr interval recommended before flying for multiple dives over several days, referring more to live aboard type diving (3-4 dives per day NDL dives) but nothing specifically on these types of dives.

Anyone have any updated info. on this?

Thanks.
nas

"substantially more than 18hrs"
What is Decompression: Flying after Diving — Medical Dive Article — DAN | Divers Alert Network

On the other hand you can crank up the deco on the last dive, plus potentially add tons of helium (which has a far better gas gradient at the surface and for all practical purposes there's no such thing as a residual helium load), and shorten that time as much as you want.

 

[kensuf]

I do a trip or two like this annually and make my last dive day something shallow and do excessive deco, then fly home the next day.

 

[michael-fisch]

Helium goes out much faster than nitrogen and is almost always the limiting gas for decompression unless you are doing WKPP style saturation dives.
If helium is the limiting gas a 12 hour seperation between the last dive and the flight should be equivilant to much longer than the day usually reccomended for nitrogen.

Michael
who is not a doctor, not even a doctor of divinity, and will have to say, if you got bent, that you shouldn't have heeded my freely given advice

 

[decompression]

Dives like that I'll ensure a nice relaxing 24 hours..........

 

[NAM001]

Just asking here but would an accurate time be based on the mix. Im not sure whether there would be much of one. You have deco mix to speed purge the N2. So if you did a really long last dive 20 ft O2 leg then your pressure group should be rather low with little N2 to off load on a SI compared to air.

 

[atdotde]

I believe this is largely unknown. Just looking at tissue loadings you would probably be fine with a 24 hour interval, possibly shorter. You could try to run this thru a planner and look at the saturation after some surface interval and compare it to m-values at altitude (e.g. in Subsurface). The problem with that approach is that you tend to get much shorter times than the recommendations by agencies like DAN. So this might not be the full story.

One thing to consider is that sometimes DCS symptoms don't show immediately after the dive but only a few hours after the dive. At that point, it's worse if you are on a plane than on the ground (independent of the question if the symptoms were prompted by the plane or would have show even without flying).

I have written up some facts about flying after diving from a deco perspective in my blog: Can we calculate no-fly-times? – The Theoretical Diver

 

[michael-fisch]

Helium caused DCS comes on fast and hits hard. if you are getting the niggles 6hrs later helium didn't cause it.
Usual times for onset of symptoms caused by excessive helium supersaturation seldom exceed 45 minutes, sometimes as long as 90 minutes.

Michael

 

[Nasser]

Thanks for the feedback. There's an interesting article in Tech Dive Mag by Asser Salameh (the Dec 2010 issue) on accelerating no-fly times using surface 02. While there is an improvement in reducing the time using surface 02, it's not as much as I would have thought, especially when comparing no-fly times for air dives to trimix dives. Although in general, those diving on mix had a much shorter no-fly time compared to diving air (without the use of surface 02). but since we're talking about deeper dives here, the comparison is not as relevant but interesting to note.

I'm in the habit of padding my shallowest stops and breathing a rich mix on the surface for about 15 min., but more for an added safety precaution rather than in an attempt to accelerate no-fly times. It was also interesting to note in the article that one of the interviewees in the article mentioned padding the 12 meter stop on subsequent dives "in order to gain more efficient off-gassing of denser tissue compartments that don't respond as effectively at 6 meters". The article was from 2010 though so maybe there's some newer up to date information.

I guess for the time being I'll continue to pad my shallow stop, breath a rich mix on the surface for a few minutes as an added safety precaution, and give at least 24hrs prior to flying.

 

[HKGuns]

I do a trip or two like this annually and make my last dive day something shallow and do excessive deco, then fly home the next day.

A little knowledge is dangerous and I'm a newbie, so this is a question.

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.

As you are in instructor appreciate the theory behind how this works.