Northwest Dive Club

What impact, if any, does living at altitude (say, 3000 feet) have if you want to dive Puget Sound on the weekends?

I know some folks refrain from diving if they are planning to drive over Snoqualmie Pass within a certain timeframe, but what if you live in Snoqualmie Pass full-time?

lizard0924 wrote:What impact, if any, does living at altitude (say, 3000 feet) have if you want to dive Puget Sound on the weekends?

I know some folks refrain from diving if they are planning to drive over Snoqualmie Pass within a certain timeframe, but what if you live in Snoqualmie Pass full-time?

Don't sweat it Liz. It's utterly silly to worry or adjust your diving based on such a small altitude change. If you do the math, the change from sea level to Snoqualmie is equivalent to an in-water depth change of about 4 feet (at the surface). If you can't do the equivalent of a 4ft ascent over the course of the 40 minutes it takes to get from the waterfront to Snoqualmie you were already bent to start with. That's my opinion. I'm not an altitude diving expert, but I do cross Snoqualmie every time I go diving, and I have done the math (for fun).

Edited to add: I hope the tone of my post didn't sound snotty or curt. I meant it with a lighthearted "don't worry about it" and a smile.

Unfortunately it isn't as simple as looking at the relative pressure difference - more important is the ratio of absolute pressures from the depth at which you loaded nitrogen to the altitude at your destination. People have experienced symptoms of decompression illness simply by getting on a plane and flying to 8000 feet above sea level - no diving involved. Odds are low, but still - regulations say that commercial airlines have to pressurize cabins to 8000 feet above sea level or better. If you're ever injured diving, necessitating air transport, they'll likely fly at or below 1000 feet. So, I would say that driving to an altitude of 3000 feet after diving should give you cause for concern, especially if you've had a long weekend of heavy-duty underwater fun. There are lots of guidelines for this stuff, but these tables are probably your best reference:

http://www.ndc.noaa.gov/dp_forms.html

http://www.ndc.noaa.gov/pdfs/AscentToAltitudeTable.pdf

First of all no one Knows the exact answer as differentiated from Apparently Reasonable Guesses and Protocols. In that respect you are your own test pilot.

I'm sure there are people who take the situation you are in with a Me Worry? attitude and others who blanch at the prospect and would spend time at lower altitude before going home.

I bounce back and forth to Colorado fairly frequently so I've done a bit of research and have a bit of experience. If it were me I'd take seriously the atltitude difference. I'd do some research on what the locals do on Maui, for example. Tourists are warned not to dive and go to those altitudes but I don't know what the locals do. I'd also check to see how fast a person loses their altitude acclimatization. That is important because part of that acclimatization is more red blood cells for more effective oxygenation of the body.

Me? If it were just a day's divng of maybe 3 or 4 dives with no extended deco and using appropriate EAN mixes I'd just have dinner before driving home and then make it home to sleep in my own bed. If it were a weekend of heavy diving or lots of deco I'f probably make sure I spent the night at close to sea level and drive home on Monday morning. But that is just me and not necessarily an example to be followed.

Whatevah, I'm not buying it. I don't think talking about injured divers comes into this equation. We aren't talking about someone who is already bent. Look at it this way: If I do a no-deco dive to 100ft and then surface and drive to Snoqualmie it's roughly equivalent to a 104ft dive with a long safety stop at 4ft (however long it take to pack up) and then a gentle 40 minute ascent from 4ft to the surface (sea level to Snoqualmie). THAT is not going to get me bent.

I'm tired. I need Richard or Lamont to take over.

I blow it off. In fact I fly after diving too (shudder). If you are already bent, subclinically or clinically, ascents will make it worse. If you are not already bent, ascending up the pass won't bend you. Nor will flying actually. Existing bubbles will grow. Dissolved gas is not going to come storming out of your tissues due to a 3 to 6ft water equivelant difference and bend you. I don't consider a 102ft dive any different than a 99ft dive.

Most divers have such poor ascents and ascent skills they finish their dives subclinically bent. And hence need to further decompress at sea level and offgas some existing subclinical bubbles for awhile. If you are riding the ragged edge, living at the pass is slightly better since you have a tiny tiny bit less dissolved gas in your tissues in the first place. So after a 20min air dive at 100ft the sea level living diver has a smidge more dissolved gas than the altitude living diver - assuming an instant descent from altitude to 100fsw. But really the whole "altitude" thing is splitting hairs, what you do in the water has vastly more influence on your dissolved & bubble gas loadings and whether you're gonna get bent.

Acclimatization, red blood cell volume, etc are completely irrelvant to DCS.

For me, the most important part is the ascent profile.

I do the deco in the water. Meaning, I want to get out of the water "clean". I've done many dives where I've left the dive site and essentially drove right over the pass.

I've also done dives and got on an airplane while the gear was still dripping wet (I'm not advocating anyone do this). Why? Because I took care of the decompression in the water, not part of it in the water and part of it on the way home.

Ditto -- I have no problem doing a decompression dive and hopping on a plane because I am confident that my deco schedule and cautious ascent will leave me without subclinical bubbles on the surface.

I also don't buy the ratio change argument -- the ratio of change from 5 ft to the surface is higher than the ratio of change from the surface to this altitude, and even cautious divers do that in less than a minute (a far cry from the 40 min drive). If you're worried about it, then just tack a few minutes onto your safety stop and/or do a 3 minute ascent from 10ft.

Thanks for everyone's input! I was researching this concept and came across this information:

http://faculty.washington.edu/ekay/altitude.html

The "Altitude Exposure Recommendations" table of data was what triggered my query in the first place. It seems to suggest that there is a window of possible (maybe not likely, but possible) concern in the 3K ft. elevation range, especially if one does multiple, high-stress dives.

Of course, for me personally, this is probably all theoretical, since I rarely do multiple dives per day here anyway.

It seems that I should be able to knock out one regular dive (usually less than 90 feet in depth) with a super slow, cautious ascent, grab a bite to eat and then head back home to the mountains, without too much fear of DCS setting in.

lizard0924 wrote:Of course, for me personally, this is probably all theoretical, since I rarely do dives here anyway.

fixed that for you.

spatman wrote:

lizard0924 wrote:Of course, for me personally, this is probably all theoretical, since I rarely do dives here anyway.

fixed that for you.

Hardy, har, har. I've just been busy lately. I do dive here, I really do.

airsix wrote:Whatevah, I'm not buying it.

I provided links to guidelines that are provided by folks who've done the studies, and who've collected data on incidents. I don't necessarily adhere to those guidelines myself, but I think the OP has a valid concern and should form her own judgement. I know what my own experience has been, but that's not nearly as large a sample size as NOAA, DAN and the various dive certification agencies are working with.

airsix wrote:I don't think talking about injured divers comes into this equation. We aren't talking about someone who is already bent.

Injured is not necessarily bent. The recommended 1000' foot ceiling is a precaution because they don't know about the diver's loading history - just as I don't know what the OP's diving history is going to be each time she drives back up to 3000' of elevation. Even if I did know, I also know that the decompression theories are imperfect. The key is, some people who write the books and the protocols consider it a significant factor.

whatevah wrote:

airsix wrote:Whatevah, I'm not buying it.

I provided links to guidelines that are provided by folks who've done the studies, and who've collected data on incidents.

And if you read that data you'll see that an air diver in any group 'G' or below can do a direct ascent to 3,000ft. You could be an 'I' group diver at the end of the dive and if you only took 30 minutes to pack and start up the pass you could do a direct ascent. Now look at the air tables also on that page and see the profiles you'd have to pull to get to group 'I'. Use those tables and construct a realistic scenario (single dive or repetitive) that gets a recreational diver into a group higher than 'I'.

airsix wrote:And if you read that data you'll see that an air diver in any group 'G' or below can do a direct ascent to 3,000ft. You could be an 'I' group diver at the end of the dive and if you only took 30 minutes to pack and start up the pass you could do a direct ascent. Now look at the air tables also on that page and see the profiles you'd have to pull to get to group 'I'. Use those tables and construct a realistic scenario (single dive or repetitive) that gets a recreational diver into a group higher than 'I'.

You use the highest group designator achieved in the prior 24hrs. Assuming over an hour and a half between exiting the water from your last dive and reaching 3000', the table suggests sticking at or below Group H in the prior 24hrs. I have no idea what kind of diving the OP might be doing in the 24hrs prior to departing sea level for 3000'.

Two forty minute dives to 50fsw separated by a one hour surface interval is not unrealistic.

There are plenty of "confident" individuals on this board willing to testify as to their own anecdotal evidence, but I think it's best to give the person asking the question some information they can use to become confident in their own conclusions.

Too much math for me.

The NOAA tables say any interval more than 12 hours is not a repetitive dive.

Edited to add: My bad. I missed the footnote about highest group in past 24hrs.

CaptnJack wrote:Too much math for me.

Haha! You weren't the one asking the question though...

After all this I'll bet you wish you hadn't asked, eh? This illustrates that different folks have different opinions and, like preachers, can quote chapter and verse to support their opinion. In the end, as I hope I said in my earlier post, it is up to you because it is your body and your risk tolerance.

Bests

i got bent ... Over a Lap one time and spanked ... Never do that again

H20doctor wrote:i got bent ... Over a Lap one time and spanked ... Never do that again

Those male strippers can be rough eh?

Not to continue picking the scab, but another thing to remember about those NOAA tables is they refer to commercial aircraft flight. A typical commercial jet climbs at a rate of over 4,000 feet per minute. That is a much faster "rate of ascent" than a 40 minute drive up Snoqulamie.

H20doctor wrote:i got bent ... Over a Lap one time and spanked ... Never do that again

you liked it and we all know it :luv: