Another flying after diving Q

[EFX]

So I am planning a dive trip weekend. Wanted to see if anyone could help with some off gassing info. I am planning a 2 tank dive with EAN to no more the 80' without getting into deco. Followed by another day of 2 tanks using EAN to 70' or so not getting into deco. Then followed by an early morning dive to 15' MAX but need to be on a plane 12 hrs later. I know the risks but what is a dive to 15' really going to do?

I compared your profile with another profile with the same ending N2 load. I chose dive times that would result in 5 minutes of NDL before ascending. All descending and ascending rates were equal: 60 ft/min descent, 30 ft/min ascend to stop, 20 ft/min stop to surface. All dives were done using Buhlmann ZH-L16 algorithm (16 compartments). Starting pressure at the surface was assumed to be sea level for all dives. For reference, the inspired surface pressure (subtracting out the water vapor pressure in the lungs) at sea level is 24.5 fsw (feet of sea water). Here's what I got using my spreadsheet:

Your profile (all dives on EAN32):
Day 1: 80 ft for 42 min, 15 ft for 3 min, 80 min SI, 80 ft for 40 min, 15 ft. for 3 min.
Day 2: 70 ft for 69 min, 15 ft for 3 min, 80 min SI, 70 ft for 60 min, 15 ft for 3 min.
Day 3: 15 ft for 90 min, 12 hr SI.
After 12 hours compartment 16 had the highest N2 load at 25.4 fsw.
Compartments 1-9 have cleared.

To get the same N2 loading of 25.4 in compartment 16 for one dive on air:
70 ft for 32 min, 15 ft for 3 min, 12 hour SI.
Compartments 1-8 have cleared.

Based on this comparison would you fly out 12 hours after a 32 minute dive to 70 ft on air?

Note: the spreadsheet used a GF-Hi of 100% and does not add conservatism for multiday diving.

 

[Lorenzoid]

Here's a previous thread that may be of interest: Diving to maximum 30 feet and Flying the same day?

 

[Rhone Man]

So I am planning a dive trip weekend. Wanted to see if anyone could help with some off gassing info. I am planning a 2 tank dive with EAN to no more the 80' without getting into deco. Followed by another day of 2 tanks using EAN to 70' or so not getting into deco. Then followed by an early morning dive to 15' MAX but need to be on a plane 12 hrs later. I know the risks but what is a dive to 15' really going to do?

I have certainly done similar things many times, and for whatever it is worth, I'm still here.

Kind of depends on how long your flight is. On the hop from Little Cayman to Grand Cayman I wouldn't even think about it. If I was flying Sydney to London, that might make me a tad more cautious.

 

[EFX]

I also want to piggy back on this thread (not hijack) and ask for info on this... would be curious to learn a bit more about the WHY behind this in more detail, and at what point it does become a factor and how much so.

For example, the OP asks if diving only 15' before flying will be a big deal. Likewise, I am wondering if diving to 60 feet and then staying at lodging that evening which is a bit elevated - say 700' above sea level - and then coming back in morning and diving again the next day, then going back to the same lodging, would be a problem. And if so, why, and what's the "safe" threshold and how does that risk factor work and relate to dive depth, time, etc.?

I don't think you have anything to worry about. The pressure change going from sea level to 700 ft is the equivalent pressure equal to 1.3 fsw (feet of sea water). Interestingly, if you were diving anywhere between 1,000 and 2,000 ft above sea level the PADI altitude table would call for 62 ft. for an actual 60 ft dive. This is a 2 fsw pressure difference. If you are concerned, using tables round the dive up to 70 ft. My Mares Puck dive computer added no conservatism for altitude until the dive was at 1,000 ft. or higher. My Perdix computer measures the current atmospheric pressure automatically taking into account dives at altitude, or after a dive off-gassing will be adjusted as one ascends in altitude.

The off-gassing rate of pressure change is what's important. A 10 ft/min ascent rate in the water is very conservative. This is equivalent to 1.3 ft per 7.8 seconds. There is no way you can drive fast enough from the dive site to your lodging in 7.8 seconds. Besides, you'll be on the surface for a while off-gassing before you drive back.

 

[EFX]

I compared your profile with another profile with the same ending N2 load. I chose dive times that would result in 5 minutes of NDL before ascending. All descending and ascending rates were equal: 60 ft/min descent, 30 ft/min ascend to stop, 20 ft/min stop to surface. All dives were done using Buhlmann ZH-L16 algorithm (16 compartments). Starting pressure at the surface was assumed to be sea level for all dives. For reference, the inspired surface pressure (subtracting out the water vapor pressure in the lungs) at sea level is 24.5 fsw (feet of sea water). Here's what I got using my spreadsheet:

Your profile (all dives on EAN32):
Day 1: 80 ft for 42 min, 15 ft for 3 min, 80 min SI, 80 ft for 40 min, 15 ft. for 3 min.
Day 2: 70 ft for 69 min, 15 ft for 3 min, 80 min SI, 70 ft for 60 min, 15 ft for 3 min.
Day 3: 15 ft for 90 min, 12 hr SI.
After 12 hours compartment 16 had the highest N2 load at 25.4 fsw.
Compartments 1-9 have cleared.

To get the same N2 loading of 25.4 in compartment 16 for one dive on air:
70 ft for 32 min, 15 ft for 3 min, 12 hour SI.
Compartments 1-8 have cleared.

Based on this comparison would you fly out 12 hours after a 32 minute dive to 70 ft on air?

Note: the spreadsheet used a GF-Hi of 100% and does not add conservatism for multiday diving.

If any of you are interested here is a link to the spreadsheet I used to calculate the EAN32 dive profile. I opened another copy of the spreadsheet and entered the profile for the 70 ft. dive.

 

[Shotmaster]

I had a very good friend in my Army unit. We dove all weekend at 30-40 fsw, he did a HALO jump at 12,500 on Monday and got bent so bad it almost killed him. His recovery of the physical disabilities took 10 years and was a slow process, it ended his career in Special Forces instantly.

 

[drobertsca]

Not just cabin depressurization you need to worry about. Remember, commercial airliners typically only pressurize their cabins to 6000 - 8000 feet above sea level.

We are all trained not to push our NDL limits while diving, since no model can account for all physiological factors at any given time. And cheating the no-fly time is just another way to push the limits of the model. However, it will work every time but the last

 

[DFDubb]

I had a very good friend in my Army unit. We dove all weekend at 30-40 fsw, he did a HALO jump at 12,500 on Monday and got bent so bad it almost killed him. His recovery of the physical disabilities took 10 years and was a slow process, it ended his career in Special Forces instantly.

Ummm, can I ask why? I would think just about anyone with the slightest knowledge of diving would've seen that one coming.

 

[Shotmaster]

It was right at 24 hours from time of last dive to his jump time, he thought 24 hours was sufficient time to off gas. He didn't take into account the unpressurized jump at altitude. He only had about 30 dives worth of experience and PADI training. None of us knew he was scheduled for a high altitude jump following the weekend.

 

[Altamira]

I would have thought 24 hours between diving and flying was a sufficient surface interval because that is what the Air Force requires, and I thought those regulations took into consideration the possibility of no pressurization or loss of cabin pressurization. Perhaps there were other complicating circumstances, or more likely, we do not know all there is to know about off-gassing. Regardless, I think all divers need to hear about situations like this. The issue of how soon you can fly after diving pops up periodically, a thread usually started by someone looking for "permission" to bend or violate established dive/fly guidelines, or have some other diver alleviate their concerns. Unfortunately, divers that are not in the aviation business usually do not have sufficient knowledge of the potential myriad of aircraft problems that can put their planned, and sometimes shaved, dive/fly times in the toilet, and they do not think about the fact that they probably are not going to have any control over that situation.