"Altitude" Diving When Already Living at Altitude

[BFRedrocks]

I was re-reading my computer manual in the section about making sure to change the setting based on your altitude (essentially change it from default if you are diving at an elevation >1000 ft). The manual also says to acclimate yourself when you dive at altitude. Which leads me to my question...

If I live at altitude already (elevation of about 1200 ft), and then I dive at altitude (roughly the same 1200 ft elevation), should I still be changing the "altitude" setting on the computer? IOW, would it make a difference, not in the calculations, but in how my body reacts to being at altitude, making the computer settings overly conservative? Obviously I shouldn't have to acclimate once I arrive at the dive site because I live at the same altitude. So is the computer making adjustments for a person who normally lives at sea level but is diving well above the altitude their body is used to?

Just curious...

 

[eponym]

The short answer to all three questions is "No."

Acclimating to altitude is not the reason we adjust dive times/depths when diving at altitude. The reason is that you're surfacing to a lesser surface pressure. It has to do with the ratio of the pressure of the nitrogen dissolved in your tissues versus the pressure of nitrogen in your lungs once you're at the surface. An altitude diving course will help a great deal.

I'm not sure why your computer maker advises you to acclimate, although I can think of some reasons. I look forward to hearing some thoughts on this.

 

[BFRedrocks]

Thanks for the reply...so the short answer is "yes" to always basing your computer settings on the actual altitude of the dive, regardless of the altitude you live at or come from.

I think the manual says to acclimate just as a general rule like was taught in the AOW class (altitude "specialty") that if you're driving "up" to a dive site, your body has excess nitrogen so you should let your body acclimate for a few hours.

 

[beanojones]

I'm not sure why your computer maker advises you to acclimate, although I can think of some reasons. I look forward to hearing some thoughts on this.

They say acclimate because it is too much trouble explaining that once one arrives at altitude they have already been 'diving' for a long time at a deeper elevation, and they need some surface interval to get rid of residual nitrogen. (usually, though not in the OP's circumstance).

But that's just about the surface interval before the dive.

As far as the no decompression limits for the dive, once one has had an adequate surface interval, something very different is at play:

OP think of it this way. If you were staying in a hotel at 66 feet underwater (3 ATA), you could do dives to 165 feet (6 ATM) for as long as 205 minutes without needing to decompress. Once that idea makes sense then what your computer is actually doing at altitude might make more sense.

 

[windapp]

They say acclimate because it is too much trouble explaining that once one arrives at altitude they have already been 'diving' for a long time at a deeper elevation, and they need some surface interval to get rid of residual nitrogen. (usually, though not in the OP's circumstance).

But that's just about the surface interval before the dive.

As far as the no decompression limits for the dive once one has had an adequate surface interval, some thing very different is at play:

OP think of it this way. If you were staying in a hotel at 66 feet underwater (3 ATA), you could do dives to 165 feet (6 ATM) for as long as 205 minutes without going needing to decompress. Once that idea makes sense then what your computer is actually doing at altitude might make more sense.

What a great idea. Maybe some of us should get together and open a saturation diving hotel.

 

[DivemasterDennis]

I live at 5400 feet and dive a lot at about 5000 feet and occasionally at higher altitudes. I don't think sea level to 1200 feet will impact your "shortness of breath factor" too much. but 5000 feet and up clearly does, as anyone who has gone hiking in the Rockies (or lesser Mountains) can attest. As to computer settings, some (mine) actually adjust for altitude. via a built in feature. If yours does not, then absolutely set it for the altitude at which you are diving. Of course, I am sure we all have our altitude tables from our AOW class or altitude specialty to allow us to calculate the ndl and plan our dive profile at any altitude!
DivemasterDennis

 

[kaerius]

I was re-reading my computer manual in the section about making sure to change the setting based on your altitude (essentially change it from default if you are diving at an elevation >1000 ft). The manual also says to acclimate yourself when you dive at altitude. Which leads me to my question...

If I live at altitude already (elevation of about 1200 ft), and then I dive at altitude (roughly the same 1200 ft elevation), should I still be changing the "altitude" setting on the computer? IOW, would it make a difference, not in the calculations, but in how my body reacts to being at altitude, making the computer settings overly conservative? Obviously I shouldn't have to acclimate once I arrive at the dive site because I live at the same altitude. So is the computer making adjustments for a person who normally lives at sea level but is diving well above the altitude their body is used to?

Just curious...

The reason for the rules with altitude diving has nothing to do with aclimatization. Only with the physics of gasses.

For a deeper understanding of the subject, the reason for this is called Henry's Law.

Basically, the lower atmospheric pressure at altitude affect offgasing of nitrogen dissolved in your body, putting you at greater risk of a DCS hit. Gas coming out of solution more easily and faster can more easily form bubbles.