Flying @ 1500 ft after shallow dives

[Superlyte27]

Help me find where the Navy Tables give you a repetitive group for EAN32 deco. I can see where accelerated deco on nitrox might put you in an acceptable repetitive group for flight to altitude. I just can't find it.

Also don’t forget a 30/70GF

 

[Asteve]

Diving with the computer set to 2,000 feet (which many computers cannot do) will give you slightly shorter NDLs. According to the US Navy tables, if I did a 45 foot dive for 125 minutes, I would be in pressure group N and would have to wait 5:32 before ascending 2,000 feet. I can't be perfectly sure, but let's say that I cut that time a little short because I had a computer set to 2,000 feet altitude. In that case, I would be in pressure group M, and I would have to wait 4:28 before I could ascend to 2,000 feet.

When we have discussions on ascent to altitude discussions, many people advocate setting the computer to the altitude of the coming ascent and thinking this clears them to ascend to that altitude. I have no idea where that belief started, but it is quite common. I have never seen it even mentioned in any resource on altitude diving.

I guess what I was thinking is that if I am diving at 2000 ft I could return to 2000 ft without getting bent. I guess it makes a different since I am start at 0 ft even if the computer is set for 2000 ft??? so have to wait 4:28 hours.
Thanks

 

[rsingler]

I guess what I was thinking is that if I am diving at 2000 ft I could return to 2000 ft without getting bent. I guess it makes a different since I am start at 0 ft even if the computer is set for 2000 ft??? so have to wait 4:28 hours.
Thanks

Think of it this way. If your reference altitude is 2000', then not only are you doing your NDL dive, you are preceding it with a saturation dive equivalent to about 2 ft of sea water depth. All your tissues have ~7% of an atmosphere already loaded, compared with 2000'. Therefore, after your dive, you need to offgas some portion of that extra so that the leftover nitrogen from your dive PLUS your sea level saturation doesn't exceed what the tables think is safe for ascent.
A few hours gets rid of most of that, so that all you're left with is your sea level saturation (plus a bit) when you ascend "back" to your reference altitude of 2000'.

 

[justinthedeeps]

You are preceding it with a saturation dive equivalent to about 2 ft of sea water depth. All your tissues have ~7% of an atmosphere already loaded, compared with 2000'.

Life: the perpetual saturation dive :kungfumaster:

I don't altitude dive (yet?) but do people take this into account? For example if you drive up to 5000' from sea level in less than an hour and jump right into an altitude lake dive, that is quite different from living at 5000' with respect to the saturation status of the "slow tissues" (model)

Or what about hopping off a 12 hour flight ('~8000ft') and diving immediately, is there an undersaturation 'bonus' or are you just giving yourself a bigger ppN2 hit?

 

[rsingler]

Sounds like it's time for you to get your Altitude Diver Specialty! I really enjoyed mine. The dive is just a dive. Your computer keeps your safe. But all of your questions are answered there. Yes, there are tables for how long you need to be at altitude to offgas your sea level nitrogen. But, no, there's no nitrogen hit from being "undersaturated."
The theory is fascinating! It gets pretty complicated and @boulderjohn is probably one of our best experts on this forum.

 

[maj2]

I had a similar experience with a low altitude flight after diving about 10 years ago in South Africa.

The safari lodge that my family was at offered a day of diving at Sodwana Bay that I wanted to do. They flew us out in the morning, did our dive, had a quick lunch, and was back on the plane a couple of hours after diving. Even encountered a whale shark on the way out to the dive site for some extra unplanned time in the water.

Plane was a bush plane, about 4 to 6 seats total (including the pilot).

Dive was to max 45ft and total dive time right around 60min.

My pre-flight briefing for the flight home was pretty cool. The pilot was also a diver. He felt the altitude to under 800ft for the flight back to the lodge and put me in the "copilot" seat so I could communicate any possible symptoms to him (there were none). He had the luxury of that low altitude since there was nothing but bush on the flight path. The flight out in the morning had been at between 1000ft and 1500ft.

I had checked the day's plan with DAN before we even left Canada for the trip and was comfortable with the plan after that consult.

Fun day of diving!

 

[duke dive medicine]

Life: the perpetual saturation dive :kungfumaster:

I don't altitude dive (yet?) but do people take this into account? For example if you drive up to 5000' from sea level in less than an hour and jump right into an altitude lake dive, that is quite different from living at 5000' with respect to the saturation status of the "slow tissues" (model)

Or what about hopping off a 12 hour flight ('~8000ft') and diving immediately, is there an undersaturation 'bonus' or are you just giving yourself a bigger ppN2 hit?

The US Navy Diving Manual Revision 7 also provides guidance on this, duplicated below:

 

[drbill]

I wouldn't. We had a local instructor who had done two training dives in shallow water, then drove up over our hills (~1,600 ft) and got bent.