Question about diving at altitude

[Charlie99]

So let me ask everyone something. Let's suppose a diver was to travel to altitude (6,200'), do a dive to around 170' without waiting 12-24 hours or worrying about altitude calculations and then drive home all within 6-7 hours...what do you think would happen to that diver?

6,000' of altitude increases the effective depth about the same percentage as EAN32 decreases it.

In other words, your increased risk of DCS would be about the same as doing the same dive on air at sea level while using an EAN32 table. One might assume that this is a very great increase in risk, but in reality, it's not much more than the difference between the PADI table and the old USN table.

DCS is a relatively low probability event, so even if you have increased your risk by a factor of 10, more likely than not you would be able to repeat that dive hundreds of times before experiencing a DCS hit.

Charlie

 

[seavonj]

Waiting 12-24 hours to do an altitude dive is just a waste of time.
Give me a few days and I along with BoomX will attempt such a dive, we will drive from Sacramento to Tahoe and as soon as we get there dive to 170' do deco get back into our truck and drive back down the mountain. What could possibly go wrong???!!!
I'll even video the whole thing....

 

[boomx5]

6,000' of altitude increases the effective depth about the same percentage as EAN32 decreases it.

In other words, your increased risk of DCS would be about the same as doing the same dive on air at sea level while using an EAN32 table. One might assume that this is a very great increase in risk, but in reality, it's not much more than the difference between the PADI table and the old USN table.

DCS is a relatively low probability event, so even if you have increased your risk by a factor of 10, more likely than not you would be able to repeat that dive hundreds of times before experiencing a DCS hit.

Charlie

Great...now everybody is going to ask for their money back on their altitude specialty cards...you know what that's going to do to the dive industry around here!? By the way, I'm going to be back in Maui in December if you want to get a couple of dives in again, let me know.

 

[boomx5]

Give me a few days and I along with BoomX

Hey Sport...what happened to the "5". The funny thing is, that's a mornings worth of diving for us. We usually leave around 5-6 am and are back by lunch time and are back at work by 1 or 2 in the afternoon....what else are you supposed to do if you have 6-7 hours to burn?

 

[Charlie99]

Great...now everybody is going to ask for their money back on their altitude specialty cards...you know what that's going to do to the dive industry around here!?

I don't think it'll hurt the altitude certs anymore than it would the nitrox certs . Just as I don't dive air using nitrox tables, I wouldn't dive at 6,000' altitude using sea level tables. And newer dual phase models, such as RGBM, actually have bigger compensation for altitude than do the neo-haldanian models.

Most divers don't seem to recognize just how fuzzy or gradual the DCS risk increases. While I wouldn't purposely plan to increase my risk by ignoring altitude, the overall fuzziness of deco does make me very willing to blow off several minutes of deco if needed in an emergency situation.

Charlie

 

[Kriterian]

No, wrong direction. As they drive back, pressure increases.

Ok, I'm not being a smart arse, just curious. I thought your ears popped while driving up a mountain because the air pressure was increasing. Although the air seems thinner up there, so that makes sense that it's decreasing as you rise. So why do you have to equalize when going up in a plane or on a mountain?

 

[JeffG]

So let me ask everyone something. Let's suppose a diver was to travel to altitude (6,200'), do a dive to around 170' without waiting 12-24 hours or worrying about altitude calculations and then drive home all within 6-7 hours...what do you think would happen to that diver?

He would die a gross and disgusting death...unless of course he employed some tic tac toe deco to get himself out of a tight spot.

 

[Fishlips_1]

Not really sure about all the driving/diving/driving. But as far as the altitude dive goes, first off you need too count 2 pressure zones for each 1000' you rise in elevation. What is your email and I will scan you a copy of the altitude tables. By the way, Cultis is very clear right now, I was just certified there last month. 40 degrees @ 20'. That is where we dive as a club, so, if you find any float hooks please leave them. We've had some taken. I guess it takes all kinds.
Have a great dive,
Lips

 

[DA Aquamaster]

At altitude you have to take into account theoretical depth. To grossly simplify things, you have to do this as you are really concerned about the multiple increase in atmospheric pressure at the dive site, not the depth. So at altitude with lower atmospheric pressure, it takes less than 33 ft of water to create another ATA worth of pressure.

E.R Cross developed a theoretical depth correction table to take the math out of the process. At 30 ft and 40 ft the theoretical depth is only 35 and 47 ft respectively, no the difference will not be that great. For deeper depths though it can begin to get significant and a 170 ft dive at 5000 ft would be equivalent to a 199' dive at sea level so you would need to use a 200' deco schedule rather than a 170' schedule for a 170' dive at 5000'.

You also would want to decrease your ascent rate by about 20% and, as indicated above, you need to figure your pressure group and residual nitrogen time from the "ascent" up the hill to the lake as well as your "surface interval" after arriving at the lake.

A computer simplifies the process as, provided the computer takes altitude into consideration, it will adjust your NDL's based on atamospheric pressure at the dive site.

 

[Mad_diver]

So let me ask everyone something. Let's suppose a diver was to travel to altitude (6,200'), do a dive to around 170' without waiting 12-24 hours or worrying about altitude calculations and then drive home all within 6-7 hours...what do you think would happen to that diver?

If you're diving Air at that altitude and go THAT DEEP, I'd be willing to bet you'd be bent befor you hit the surface.

To identify the risk, we need to know HOW long you were at that altitude before you made the dive. (There is a certain amount of off gasing that happens when you arrive). Also we'd need to know how long you stayed at that depth and what breathing gas you were using.

Driving home isn't any big deal (assuming you make to the surface) as long as your house is at a lower elevation than the dive site.

This is ALL covered in the PADI Altitude course.