flying in unpressurized aircraft after diving

[rs86]

Hey everybody,

I live on an island that can only be reached by small twin otter airplane with a non pressurized cabin cruising at 3,300 ft. It takes about 20 mins to get to the next island.

Many people who dive here think that it's okay for them to make a dive just hours before flying, because "the plane doesn't fly that high."

I am not an expert, but I've calculated (please correct me if I'm wrong) that during these flights, people are exposed to a pressure of about 0.9 atm, while in a pressurized aircraft people are exposed to pressure about the equivalent of 8,000 feet altitude, or about 0.77 atm.

Even though the unpressurized plane doesn't fly that high, passengers (people who dove just a few hours before) experience a decline in ambient pressure, which means a higher risk of DCS.

Does anybody know if this small decline would significantly contribute to a higher risk of DCS? If so, does anybody know of any studies that have looked into this?

Many people ask me if it's okay to hop on the small plane just after a dive. I always tell them it's not the smartest idea. Others tell them it's no problem. I would like to back my advice up with some scientific proof.

Thanks very much for any information!

 

[boulderjohn]

Here is the NOAA ascent to altitude table. http://www.ndc.noaa.gov/pdfs/AscentToAltitudeTable.pdf

It indicates when you can ascend to that altitude after diving, using the S Navy tables pressure groups. As you can see, for modest dives, you don't have to wait much at all. THe DAN study said that ascents to 2,000 feet were not considered enough to merit consideration.

 

[SailNaked]

part of your proof is that people do it without experiencing DCS,
if lots do it a lot then the % risk would seem to be low.
that said .1atm of difference is what it is, there is potential every time you lower the pressure on your body that you will not be able to compensate. it is also relavant what is the difference over time, does then plane ascend gradually or fast?

my $.02 (redemption value $0.00)

 

[oldschoolto]

As a skydiver I always went by the rule of 24hrs from scuba diving to sky diving.... but We'd go to 13,500 + agl .... It was a good safety margin... Just like the rule of 24hrs for pilots of Bottle to Throttle....

jim...

 

[DivemasterDennis]

While the risk is low, the risk is present. 3300 is more than 2000 feet, hence it is of significance. I would allow at least and 8 hour interval fter diving, and feel better about a 12 hour interval. Remember, individuals susceptibility to DCS varies greatly. Older people are more susceptible as are overweight people, people with certain health conditions, etc. Also, the number, frequency and duration of your dives are all conrtibuting factors. I love a challenging dive, and will take risks within reason. But why risk serious illness or death for "one last dive? " Hence the opinion I have given about at least an 8 hour interval, more if other risk factors are present.
DivemasterDennis

 

[CoopAir]

Being a private pilot myself flying piston singles, I've been very interested in this sort of thing.

I'm still at a loss to figure out why the guidelines are 12-24 hrs even when ascending to 8000 ft.

The reason I think this is because I saw the deco profile for some guys who were diving ridiculously deep (700 fsw) on trimix and at the end, even their longest deco stop at 10 fsw was about a bit over 2 hrs. (Their 20' stop was about half as long if I remember correctly)

Certainly, if it took these guys just 2 hrs of deco to have a 10 ft ceiling increase (mind you, the most critical 10 ft--with a 25% reduction in psi from 10' to surface) after having dove to 700', with a huge amount of inert gas loading of course, then why would anyone diving within recreational limits with no deco obligation be in danger to fly after 2 hrs which is again, another 25% reduction in ambient psi (which is what you have from the surface to 8000')

 

[Griffo]

Being a private pilot myself flying piston singles, I've been very interested in this sort of thing.

I'm still at a loss to figure out why the guidelines are 12-24 hrs even when ascending to 8000 ft.

The reason I think this is because I saw the deco profile for some guys who were diving ridiculously deep (700 fsw) on trimix and at the end, even their longest deco stop at 10 fsw was about a bit over 2 hrs. (Their 20' stop was about half as long if I remember correctly)

Certainly, if it took these guys just 2 hrs of deco to have a 10 ft ceiling increase (mind you, the most critical 10 ft--with a 25% reduction in psi from 10' to surface) after having dove to 700', with a huge amount of inert gas loading of course, then why would anyone diving within recreational limits with no deco obligation be in danger to fly after 2 hrs which is again, another 25% reduction in ambient psi (which is what you have from the surface to 8000')

To start with that 2 hours would be on pure O2. And the return to the surface would reduce the pressure gradient which would then slow-down the rate of off-gasing. Even more-so if you you just breathing air.

 

[CoopAir]

To start with that 2 hours would be on pure O2. And the return to the surface would reduce the pressure gradient which would then slow-down the rate of off-gasing. Even more-so if you you just breathing air.

Oh, I certainly realize that the shallow stops are done at 100%, but even if these guys had switched to air instead, I doubt the 10' stop would be longer than 3 or 4 hrs...........still far less than 12-24 hrs

And again, this is for a crazy deep dive so I chose an extreme example. It just seems hard to believe that even a fairly aggressive recreational diver (say 75% of NDL limits) would not offgas enough on the surface in 3 hrs for a 25% reduction in ambient pressure.

I used that extreme tech dive to illustrate my point vividly.

Not trying to argue, just trying to understand.

 

[Superlyte27]

I have a friend who cave dives on sunday and teaches helicopter lessons on monday. He's been doing this for years.

 

[Hatul]

Being a private pilot myself flying piston singles, I've been very interested in this sort of thing.

I'm still at a loss to figure out why the guidelines are 12-24 hrs even when ascending to 8000 ft.

The reason I think this is because I saw the deco profile for some guys who were diving ridiculously deep (700 fsw) on trimix and at the end, even their longest deco stop at 10 fsw was about a bit over 2 hrs. (Their 20' stop was about half as long if I remember correctly)

Certainly, if it took these guys just 2 hrs of deco to have a 10 ft ceiling increase (mind you, the most critical 10 ft--with a 25% reduction in psi from 10' to surface) after having dove to 700', with a huge amount of inert gas loading of course, then why would anyone diving within recreational limits with no deco obligation be in danger to fly after 2 hrs which is again, another 25% reduction in ambient psi (which is what you have from the surface to 8000')

You left out one detail. Diving from sea level and then flying is like saturation diving from 8000 ft to sea level, then making the actual dive, then an ascent to 8000 ft, having been saturated at sea level. The guys who do deco diving are never saturated.