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I live about 20 minutes from the beach, but its somewhat steep so my house is at about 2500' elevation. Should I be concerned about driving home soon after getting out of the water? I've been told that it should be ok, but I've also read recommendations to stay lower than 1000' (or is it 500') after diving.
I would love to spend 3-4 hours on the beach after every dive trip, but one of the drawbacks of living close to where you can dive means that sometimes you do have schedules to keep...
So far I've assumed that if I don't push close to the NDL limit that I shouldn't have to worry much. However there have been a few dives where after I get home I'm unusually fatigued - which could also be due to the fact that I'm a new diver and don't have the best technique yet.
I recently got a cobra2 computer and was thinking about using the altitude diving setting. I know its intended for lakes or whatever that are at elevation, but would it also work similarly for returning to a higher elevation after diving? The A1 setting is for 1000-5000 feet elevation which would certainly cover my trip home.
Depending on depth, staying away from NDL may or may not be sufficient, since you could still be saturating the faster tissue compartments enough to be an issue.
One resource you may want to look into is the NOAA Ascent to Altitude table. Note that you have to use the letter groups from one of the NOAA tables (air or Nitrox, depending on what you're diving) and not letter groups from some other table.
From my own experience, you should definitely stay near sea level for a few hours, especially if you have any condition that leaves you more prone to DCS. I found I was last year due to a PFO, so this is just my experience, my wife was fine during this.
After two dives (long dives, but within computer limits) in Kona ending by early afternoon, we drove to Waimea for dinner, about 2500'. This was at least 3+ hours after the last dive. In the restaurant I started feeling a bit strange, and upon leaving an hour or so later, I got hit with transient vertigo and double vision walking to the car. Went away within a minute or two, but it got my attention. Took the short way down to the coast and all was fine after that, but no way will I go above 1000' again until I have had more than just a few hours after long, deep dives like that. Had the PFO fixed, but I ain't taking chances with what hearing I have left.
bleeb - Thanks for the tables, that was exactly the information I was looking for that I hadn't seen anywhere else. I'm going to print those and keep them with me from now on. It looks like for most cases I'll need 1.5-3.5 hours which isn't bad, and for more aggressive dives I'll have to amuse myself at sea level for a while. Could be worse!
Lopaka - I read your post and had to look at my profile again - even though I hadn't entered my location when I registered that is exactly the case I'm talking about. I live on the dry side of Waimea and dive most often down around Puako or up the Kohala coast.
Interesting. I just ran some of the numbers and its not what you might expect. If you stay shallow and dive close to the limits, you end up with more required surface time before you can ascend to 3000'. For deeper dives you reach the NDL before you require much surface time. Must be the slower tissue compartments that dominate here.
Also interesting is the comparison of the Suunto Cobra2 to the NOAA tables - I had heard it was more conservative but hadn't seen numbers. Also, it seems that using the A1 alititude mode doesn't protect for long, shallower dives so sounds like I'll just stick with the standard P0/A0 mode and check the NOAA tables before I head home.
The below is for air assuming a post-dive ascent to 3000'. Units are feet and minutes, with NOAA groups.
Depth Max time Group interval for 3000'30 405 N 60840 200 N 60850 100 L 46660 60 J 29770 50 J 29780 40 I 20090 30 H 91100 25 H 91110 20 G 0
Cobra2 P0/A0 limits:
Depth Max time Group interval for 3000'30 -- - ---40 120 K 38550 69 I 20060 50 H 9170 36 H 9180 28 G 090 22 G 0100 17 F 0110 13 E 0
Depth Max time Group interval for 3000'30 160 I 20040 86 I 20050 56 H 9160 38 G 070 29 F 080 23 F 090 18 F 0100 14 E 0110 11 E 0
There's no question in my mind if the "Cobra data" is valid. Just to be clear, the diver group and time to ascend to 3000' from the "Cobra data" is actually from the NOAA tables. I just calculated those values based on the NDL times from the Cobra manual for the Suunto algorithm. That's the max time I'll stay down when using my Cobra and so that dive profile gives me the longest time I'll need to wait before heading home.
For example, the NDL at 60' according to the Cobra is 50 minutes, so that's the maximum time I'd stay at 60' when diving with my computer. If I look at the NOAA tables, a 50 minute dive at 60' makes me an H diver, and an H diver needs a surface interval of 91 minutes before ascending to 3000' elevation.
I'm not trying to directly relate what the Cobra says to NOAA Diver groups - effectively I'm just picking a dive depth and length and comparing what answers different tables give.
I plan on using my computer during the dive to make sure I stay within the NDL, and then after the dive getting the max depth and duration from my computer and using the NOAA tables to find how long I have to wait before driving home.
A few years back a local instructor got bent. Based on her word and her computer, all her dives were very conservative. The only thing they could come up with was that she had driven to her boyfriend's a the other side of the island and reached a maximum elevation of about 1,600 ft.