Flying after diving if computer shows all compartments cleared?

[NDonahue]

I am familiar with the DAN guidance on flying after diving. My question is why ones dive computer, if it shows the theoretical tissue loading by compartment, isn’t sufficient to determine safe time to fly?

For example, the image below shows the modeling of my tissue loading 8 hours after a relatively shallow dive this morning.

Thanks in advance for the explanation.

 

[Duke Dive Medicine]

The DAN FAD recommendations are based on extensive research done at Duke. If you stay within them, you're all but assured of safety. I'm not saying your computer is wrong, and if you fly based on what your computer says, you might be perfectly safe. But, as you said, it's a computer model of your tissues. The DAN FAD recommendations are based on peer-reviewed empiric research.

Best regards,
DDM

 

[lowwall]

You will have to make your own call on this. There have been zero studies on flying after mild diving profiles. All we have are rules of thumb based on limited observations of dives to NDL, leavened with a healthy dose of safety padding.

FWIW, I'd do it faced with your stated situation.

 

[Divin'Papaw]

Another point to consider. Your computer is showing tissue loading at sea level. A commercial airline is pressurized but not to sea level. Under lower atmospheric pressures, the tissue loading calculations change. DAN FAD guidance also accounts for potential pressurization issues in flight I believe (but not certain).

 

[lowwall]

FWIW, here's DAN's own summary of their study that led to their FAD recommendations:

"Because little human experimental data could be found that was relevant to flying after recreational diving, DAN funded a series of trials at the Duke University Center for Hyperbaric Medicine and Environmental Physiology that were conducted from 1992-1999. Dry, resting volunteers tested nine single and repetitive dive profiles that were near the recreational diving no-decompression limits. [Emphasis added.]

The dives were followed by four-hour simulated flights at 8,000 feet (2,438 meters). In 802 trials, there were 40 DCS incidents during or after flight. For single no-stop dives to 60 fsw (feet of sea water; 18 msw, or meters of sea water) or deeper, there was no DCS for surface intervals of 11 hours or longer. For repetitive, no-stop dives, DCS occurred for surface intervals of less than 17 hours."

 

[LFMarm]

I know many who push well beyond recommendations (less than 24h before flying after long and deep deco dives) but are taking additional precautions like extra long stop at 6m on O2 and additional O2 breathing after surfacing. I have not heard about problems during flights but nobody doing these practices knows how close to DCS.

 

[Sascha314]

Two things should be considered:

On a normal flight you are pressurized to about 2400m above sea level. Thats about 75% of the pressure at sea level. In this regime there is litte experience to model. You need to offgas to be safe at this pressure (about 0.75 bar), which can be mathematically calculated. But you should add some safety margin as it is unknown territory.

Next is, there could be a sudden loss of cabin pressure. In this emergency situation you want to have the safety margin to be ok in this event.

 

[inquis]

Your SurfGF is a decent proxy for tissue loading, and at sea level it is perhaps 1-2% at that 8 hr mark based on that graph. However, at the 8000 ft equivalent pressure altitude for most commercial flights, surfGF goes up because it's based on the ambient pressure. In the Duke study previously mentioned, when the SurfGF(0 ft) was at or a bit below 0, the SurfGF(8k ft) was about 38% and 8% of the divers got bent -- not great odds.

The hard data shows that a non-zero surfGF at sea level is a long way from being safe to fly, and the 12/18 hr (single/repetitive NDL diving) guidelines from DAN have been proven to be pretty safe. Sure, you might get away with less, but do you really want to be that guinea pig?

 

[lowwall]

Next is, there could be a sudden loss of cabin pressure. In this emergency situation you want to have the safety margin to be ok in this event.

I wouldn't take loss of cabin pressure into account. First, it's exceedingly rare for commercial flights. Second, the immediate response to a loss of pressure is an emergency descent to no more than 10,000'. This should be completed within a few minutes. Third, the masks that drop down provide 100% O2 for 10-15 minutes. So free O2 to help wash out those last bits of N2

 

[tursiops]

In the Duke study previously mentioned, when the SurfGF(0 ft) was at or a bit below 0, the SurfGF(8k ft) was about 38% and 8% of the divers got bent -- not great odds.

?? Were not these chamber tests done before SurfGF was invented?