Driving to altitude after diving at altitude

[Zef]

Theoretically speaking one can breath high concentrations of O2 before and during the drive home to increase the off-gassing of N2 accumulated in the body.

Even with O2, I would recommend the longer drive at the lower altitude.

-Z

 

[tursiops]

The SSI table in my logbook. We dove to 50ft (altitude adjusted to 60ft) for 20 minutes. Resurfaced as a D diver. An hour & 10 minutes later I've moved to C and 2:40 since surfacing I'm a B.

Well, I'm confused now. You say you were using SSI tables, but quoting NOAA altitude limits?
You say you went to 50 ft at 4600 ft altitude but called it 60 ft? Don't the table say 70 ft?
That all seems quite inconsistent, probably not correct, and perhaps dangerous.....
You can certainly use the NOAA procedures, which are based on the Navy procedures, or the Navy procedures, but you need to use just one set of tables, not mix them up, and use them correctly. It doesn't sound like that is what you are doing.
I assume you have not taken an altitude diving class?

 

[boulderjohn]

I am not SSI, but I believe that the SSI tables are based on the US Navy tables. At least, that is what is says on the tables. The PADI table pressure group letters definitely do not correspond to the Navy/NOAA designations.

Of course, the real problem with using the tables for this purpose is that once certification is over, pretty much no one uses the tables these days. I have written in the past that the time that I tried to calculate one of my first dives after certification was the only time in my life that I have seen anyone try to use tables outside of training dives. If you are doing a multi-level dive, any attempt to assign yourself to a table pressure group afterwards is a guess.

Here is a warning, I have seen many ScubaBoard posts over the years in which posters claim to be using the US Navy tables (and by extension SSI or NAUI) when they are diving. What they describe is NOT really using the tables; it is both wrong and dangerous. What I have seen described is people using mnemonics or simply memory to recall their first dive table limits, waiting for the typical surface interval provided by a dive operator, and then using the same limits for the second dive. They are using that simple mnemonic rather than using the full table procedure. Here is why that is wrong.

1. By going back to first dive limits after a typical dive operation surface interval, divers are not taking residual nitrogen into account. Their second dive should be shorter than the first dive, depending upon the length of the surface interval.
2. The US Navy (NAUI, SSI) surface intervals are very long, primarily because Navy divers typically only do one dive a day. This made recreational 2-tank dives difficult.
3. That lengthy surface interval was one of the reasons that PADI did the research that resulted in the PADI tables. That research indicated that surface intervals of that length were not necessary for typical recreational dives. In order to make sure dives with shorter intervals were safe, PADI shortened the NDL limits for first dives while also shortening the surface intervals by a significant amount.
4. Computer algorithms are generally pretty consistent with the PADI surface intervals.
5. Dive operations schedule 2-tank dives with surface intervals consistent with PADI and computer algorithms. They are close to half the required surface intervals of the US Navy tables.
6. If you are diving near the limits of the US Navy tables for your first dive, then doing a PADI-length surface interval before going back to US Navy first dive limit, then you are not using your tables. You are more likely diving roughly the same depths and times as everyone else and trusting that it will all work out for you. If you stay well within limits and adhering to dive operation schedules, you will probably be OK anyway, but you are not diving in accordance to the tables.

 

[Edward3c]

BSAC sell altitude tables providing dive tables from sea leaver to 3,000m, they include how to adjust surface codes accordingly. BSAC has surface codes A to G (G is after mandatory deco).

For example, moving from 4,600ft (1,400m), which is level 3, to 7,000ft (2,130m), which is level 4, then back to 5,000ft (1,520m), level 3. Starting with a surface code at level 3 of B which at level 4 remains B and stays at B when returning to level 3.

If you’d been moving from, or to, sea level the results would have been different; starting with B at level 3 going to a D at level 1 then remaining D when returning to level 3.

Revisiting this. I didn't do it right.

Diving at 4,600ft (1,400m) is at level 3, you would have surfaced on a code D from the BSAC tables. Leaving around 2 hour 30 minutes later would have you give you code C. Moving to an altitude of 7,000ft (2,130m) changed the code to D. Descending again to 5,000ft (1,520m) would result in you staying on a code D. Which gives 9 hours to clear back to an A code.

Good to get some real world practise in.

 

[shurite7]

Hi! I couldn't iagine that Hindi and Bolivian military had interesting material... Is it in english? Can you give us some links?

The articles are in English. At the moment I am in the process of a move and all my stuff is in boxes. I found the material through my uni’s ILL. The articles probably can be found online; start with rubicon’s or research gate’s website. The reason I read the articles was to obtain more knowledge to teach the high elevation class, and more significantly I was driving over passes after diving.

 

[CycleCat]

Well, I'm confused now. You say you were using SSI tables, but quoting NOAA altitude limits?

That's the only tool for what I'm trying to learn that I'm aware of right now.

You say you went to 50 ft at 4600 ft altitude but called it 60 ft? Don't the table say 70 ft?
That all seems quite inconsistent, probably not correct, and perhaps dangerous.....

I dove to 50 feet. Altitude required it to be adjusted as if it was 60 feet. I don't know where you got 70 feet.

I was taught add 4% for every 1000 feet. We dove at 4600', rounded up to 5000 for safety, that's 20%. Twenty percent of 50' is 10'.... equals 60.

I assume you have not taken an altitude diving class?

I have.

I am not SSI, but I believe that the SSI tables are based on the US Navy tables. At least, that is what is says on the tables. The PADI table pressure group letters definitely do not correspond to the Navy/NOAA designations.

Of course, the real problem with using the tables for this purpose is that once certification is over, pretty much no one uses the tables these days.
...

Here is a warning, I have seen many ScubaBoard posts over the years in which posters claim to be using the US Navy tables (and by extension SSI or NAUI) when they are diving. What they describe is NOT really using the tables; it is both wrong and dangerous. What I have seen described is people using mnemonics or simply memory to recall their first dive table limits,

Before you even posted this, I compared my dive and SI to the Navy and NAUI tables and they jived exactly. I wouldn't do any of this by memory because it's all still new to me. I go through all this mental exercise with the tables because I'm striving to understand. I was the kid who destroyed many electric toys trying to learn how they worked.

 

[tursiops]

That's the only tool for what I'm trying to learn that I'm aware of right now.

You can get the current (v7) Navy dive manual online for free.

I dove to 50 feet. Altitude required it to be adjusted as if it was 60 feet. I don't know where you got 70 feet.

Both the NOAA and Navy manuals would say 70 feet, not 60. They provide tables.

I was taught add 4% for every 1000 feet.

This sounds like something somebody made up because they didn't have the actual tables.

 

[boulderjohn]

This sounds like something somebody made up because they didn't have the actual tables.

What Tursiops means is there is a table giving altitude adjustments to create a theoretical depth. Mine does have 60 feet as the theoretical depth for a 50 foot dive at Santa Rosa. A 60 foot dive would have a theoretical depth of 72 feet, which you would then have to round to 80 feet.

 

[tursiops]

What Tursiops means is there is a table giving altitude adjustments to create a theoretical depth. Mine does have 60 feet as the theoretical depth for a 50 foot dive at Santa Rosa. A 60 foot dive would have a theoretical depth of 72 feet, which you would then have to round to 80 feet.

Interesting. I have a table (no source on it) that also shows 60 foot theoretical depth for a 50 foot dive at 5000 feet (rounded up from 4600).
But the current NOAA and Navy tables show 70 ft. Here is the current Navy table:

 

[CycleCat]

This sounds like something somebody made up because they didn't have the actual tables.

Interesting. I have a table (no source on it) that also shows 60 foot theoretical depth for a 50 foot dive at 5000 feet (rounded up from 4600).
View attachment 617688

I guess it is a method to figure altitude diving when you don't have the tables (or don't want to buy them). When were you certified? I have just been working through cert in the last 2.5 months. Maybe the 4%/1000 is a new thing.

I brought up the v.7 Navy dive manual and am going through it now.