Question Diving before flight

[tursiops]

Except that isn't the one that DAN currently gives, despite the more recent research you noted. Unless there is inconsistent information on their website, DAN has had this posted for years:

Guidelines for Flying After Diving

The recommendations for flying after diving come from a DAN study — read all about the study workshop and conclusions.

dan.org

Many of us do use a 24-hour rule of thumb for flying home after our dive vacations, but as far as I can determine, DAN did not say that is their rule of thumb.

24h is the DAN-Europe recommendation, although you'd be hard-pressed to find that information on thier website, or any mention of ANY delay before flying!

Don't you find it wonderful that DAN-US and DAN-Europe don't agree on this?

 

[boulderjohn]

Don't you find it wonderful that DAN-US and DAN-Europe don't agree on this?

I have been told by someone with supposedly inside information that their leadership hates each other, and that DAN Europe specifically has made decisions primarily because they are different from DAN Americas. If that is true, it's pretty sad. I can think of two and possibly three specific decisions that suspiciously seem to support that idea, and one is their 24-hour flying after diving policy.

1. DAN Europe does indeed say 24 hours, and they recently published a report of a study that they said proved it. It was a downright maddening study that seemed designed to support their policy. They used doppler bubble imagining to test people immediately after diving and then test them 24 hours later. When the people were bubble free in 24 hours, they said it proved that 24 hours was a "sufficient" time period to wait. "Sufficient" is not the same thing as "necessary." Why the heck didn't they also test them at 12 hours or 18 hours? They went bubble free before 24 hours, but we have no idea when they went bubble free. What if they had tested them after a week and said that a week was a sufficient time to wait? Would we all be waiting around for an extra week at dive locations before setting off for home?

2. About 20 years ago, during the height of the deep stops in decompression diving mania, people began to study deep stops in recreational, NDL dives. A couple (yes, two) studies seemed to suggest they were helpful, but later on people noted flaws in the methodology of the studies, and neither is highly regarded now. Shortly after that, DAN Americas published a discussion with several experts (including Simon Mitchell and David Doolette, and they said there was no evidence of a benefit to deep stops in NDL diving. That is still the recommendation of DAN Americas, but DAN Europe recommends deep stops for NDL dives.

3. About a decade ago, the deep stops philosophy started to be generally abandoned, and by 4-5 years ago that bubble had burst. I somehow got on a mailing list that included DAN Europe representation, and my sense of what was going on was that they were doing what they could to support research efforts designed to reverse that trend and prove the value of deep stops in decompression diving. As mysteriously as I got on that list, I just as mysteriously got off of it, so I don't know how those efforts are progressing.

 

[L13]

Lets do some math! (actually, I did the math in a spread sheet, I'm only showing the results).

This is more advanced diving concepts, if you want skip to the bold conclusions.

After day 1 (two 1 hour dives to 60ft) and 48 hour surf interval (the evening dive presumably starts on day 3 at a time later than the time the afternoon dives end on day 1) the total nitrogen above normal in the tissues will be ... 0!!

(actually there will still be 0.1 fsw in tissue 15 and 0.2 fsw in tissue 16, and zero in all the others)

Now we do dive 3, 1 hour at 60 ft. Max Surf GF ~= 80%.

17.5 hours after dive 3, tissues 1-9 will be at 0 nitrogen above normal, tissue 10 will have 0.1 fsw up to tissue 16 with 0.8 fsw nitrogen above normal (all GF's 0%, at sea level it takes 6 fsw to get GF > 0%).

After 4 hours of flying tissues 1-10 will have degassed to below normal at Denver (5,000ft), tissue 10 will have 0.5 fsw up to tissue 16 at 3.2 fsw nitrogen above normal. 3.2 fsw is a GF of 0% (at 5,000 ft it takes 5 fsw to get a GF > 0%).

In other words, dissolved nitrogen in the blood stream at Denver is a non-issue!

The real issue is bubbles already in your blood stream from when you first surfaced (it takes a while for them to re-absorb) suddenly growing by ~35% when you go to 8,000 cabin pressure and migrating to somewhere damaging. Each surfacing after a dive produces another burst of bubbles, which is the primary reason for the longer wait after more dives. Landing at Denver will re-compress the bubbles making things better, your fast tissues being sub-saturated will absorb bubbles faster though not as much in Denver as they would at sea level.

For practical purposes, this is flying 18 hours after a single mild dive. Well within the DAN guidelines, and Denver as a destination has negligible effect.

In this case the GF when first arriving at 8,000 ft cabin pressure jumps to ~22%, and if the cabin were to depressurize to 25,000 feet it would jump to 101%. With more and bigger dives dissolved nitrogen can become a problem, that initial drop in pressure and jump in GF can also produce new bubbles just like after the dive. With big dives or enough smaller dives that initial GF jump at 8,000 feet can easily exceed GF = 100%.

 

[rick00001967]

i love when the DAN recommendations come up in discussion and no one ever points out that the 12 and 18hr rules are "minimum" recommendations. i ry not to do anything to minimum standards in my life if i can avoid it.
if there is any question about your plan, why not just scrap the day off idea and do two days on a row instead with your last day off?

 

[inquis]

The nearly 18 hr SI is well above the "minimum" recommendation of 12 hrs for a single NDL dive.

 

[rick00001967]

The nearly 18 hr SI is well above the "minimum" recommendation of 12 hrs for a single NDL dive.

yes i agree.
i just find in general, when it comes to discussing this topic, most people interpret the 12 and 18hr rules as hard and fast rules when we know they are just guidelines and cannot guarantee anything.
that is why they are minimum requirements.
i find it troublesome (especially with new divers) that they may believe nothing bad can ever happen to them as long as they follow these rules.
"if i dive 10 times in 5 days then i can get out of the water at 12pm and fly out at 6am."...... well maybe you can, but maybe you shouldn't. it may depend on a number of factors.
nothing is guaranteed. if it was, DAN would remove the word "minimum".
holidays are about more than just diving. go dive. enjoy. but why not leave the last day open to try something new. then any concern about trying time your flight down to the last minute is removed from the equation.
just my opinion. but it is 24hrs for this guy after multiple dives. i dont remember ever having to decide after doing only one dive, but if i did do only one dive, i cannot see me ever flying within 12 hrs of the dive.
i may be wrong but i have taught some pilots to dive, and i seem to remember they were required to wait 24hrs after breathing any compressed gas. even if it is in the pool. stricter standards i guess.

 

[iointerrupt]

The details matter, and in this case, the proposed dive plan is already extremely conservative.

Once the drive to the airport becomes more risky than the dive, cranking in more conservatism is counter-productive.

You can always crank in so much conservatism that you never get in the water. At some point you have to say "the risks here are known and acceptable, I'm jumping in". The point is to get wet, in the end.

 

[L13]

Lets do some math! (actually, I did the math in a spread sheet, I'm only showing the results).

@inquis pointed out a few errors in my calculations. most are essentially unchanged.

The only significant difference is that the GF at first reaching 8,000 ft would be ~12% not ~22%

 

[Cavevixen]

All the research presumes the diver is returning to sea level at the end of the altitude excursion.
You are playing with fire if you fly to Denver instead of sea level.
Wait 24h, at least.

Lol, okay.

 

[tynanpatrick]

I always want at least 24 hours, but I'm also very over-cautious about it. I usually want 36 hours if I can get it. I know that's way beyond the recommendations, but I have trouble with my ears, so I like to give them some time to stabilize and I always figure better safe than sorry.