Ascension after diving.

[raybo]

There have been a couple of threads open recently regarding diving at altitude, and obligation of agencies that train a ta altitude. SMKChef actually post this one Altitude, cold, & DCS in this forum.

A number of has carried on a discusion related to it. the gist of the somewhat unresolved question is about ascension to altitude after diving.

I live in a mountainous state, and it is virtually impossible to get make a day trip and not have to ascend and descend over terrain elevation differences in the 1000-3000 ft range, or even more..

I found this Altitude Dive Tables It appears to inidcate it is a safe and practical matter to simply use the highest anticipated elevation expected after diving and use that elevation for planning purposes. It would foloow that this would work for any of the major tables in use in recreational diving today.

Is this the correct method for safely planning dives that require ascension after diving when logistics prohibit the standard NO Fly times recommended?

Is it safe to interpret this to also indicate this would not require any surface interval prior to departure.

If this is the correct method, for those rare cases where travel is required over a mountain pass where the elevation will exceed the max recommended elevation for diving,of 10,000 ft, can the formulas in B.R. Weinkes book on diving at altitude be used to determine the theoretical depth, and then that be applied to the tables in planning?

And finally, in those situation where the requirements of the diving activity and time constraints dictate that the actual dive site elvation be used in planning dives, is there a concise reletively simple to use method to determine an appropriate surface interval prior to departure.

 

[Dr Deco]

I have no experience in this area of altitude decompression. Responses from others would be appreciated.

Dr D.

 

[rmediver2002]

The navy dive manual addresses this senario, a table is provided on page 9-53 (table 9-5)

Basically for altitudes less than 10,000 you would have a minimum surface interval before you ascend.

Using the examples you gave: (altitude listed is from sea-level,

1000 - if your repet group designator is I or less no interval is required, the max interval listed would be for a Z diver and they would have to wait 8 hours and 17 minutes.

2000 - Less than H no interval, Z = 9 hours and 54 minutes

3000 - G repet group or lower no wait, Z 11 hour and 42 minute interval required...

When using this table you select the highest repetative group designator obtained within the last 24 hours.



These intervals are recommended to decrease the chance of DCS.

You could work your normal profiles specifically or target the highest RNT designator you can safely have without an interval being required and work it into your dive plan...

Hope this was some help to you,

Jeff Lane

 

[raybo]

Guess I should have known the place to get it would be the Navy Dive Manual.

Weinke's book on altitude diving lists references to it.

I ordered one in an electronic format. Hopefully be here in a few days. I have a lot of questions~ not just altitude ~ that I figured I could get from it.

Thanks guys.

 

[Diver0001]

raybo once bubbled...
<snip>

I found this Altitude Dive Tables It appears to inidcate it is a safe and practical matter to simply use the highest anticipated elevation expected after diving and use that elevation for planning purposes. It would foloow that this would work for any of the major tables in use in recreational diving today.

You're confusing two things. Diving at altitude requires finding adjusted NDL's to suit the altitude you're diving at, which is what this table is for, *and*, finding the appropriate surface interval before increasing your altitude after a dive, for which you need something more.

For the first part (the table you found), you need to adjust the depth on your tables because your gauges don't read accurately at altitude. This happens because gauges are designed for use at sea level with an ambient atmospheric pressure at the surface of 1 ATA. At altitude this ambient pressure is less than 1ATA (this should be obvious) and your gauges read inaccuratly. In fact you will be deeper than your gauge indicates. This table makes the necessary adjustment to your depth to compensate so you find the correct NDL and repetative group for planning. You can use this adjustment with any agencies tables. [note: Most, if not all, modern computers will adjust automatically for altitude so you don't ordinarily need this table with a computer. Refer to your user's manual for more details.]

For the second part you need something else, which is a table to tell you how long of a surface interval you need after your last dive before you can change altitude. More correctly, before you can ascend to a higher altitude than where you finished your last dive. You didn't say which table you have but you should look for an altitude table sanctioned by your certification agency. People often refer to the U.S. Navy altitude table in the forums but this table corresponds to the Navy dive tables, which uses a 120 min 1/2 time for surface intervals. Other tables (PADI, for example) use other 1/2 times for surface intervals so using the Navy altitude tables in combination with the PADI RDP (especially after repetative dives) is a bit of a crap shoot due to the difference in how surface intervals are calculated. You'd be much better off looking for a DSAT equivalent if it exists (I'm sorry to give you a 1/2 answer. I understand the theory but I don't dive at altitude and I've never taken the specialty so I don't know which resources are out there). PADI (and others, I'm sure) have a specialty for altitude diving and in your situation it would be highly advisable to take it.

Is this the correct method for safely planning dives that require ascension after diving when logistics prohibit the standard NO Fly times recommended?

The straight answer is NO. You're best off checking with your LDS for a specialty course in your situation.

Is it safe to interpret this to also indicate this would not require any surface interval prior to departure.

Again the straight answer is NO, but that should be obvious by now.

If this is the correct method, for those rare cases where travel is required over a mountain pass where the elevation will exceed the max recommended elevation for diving,of 10,000 ft, can the formulas in B.R. Weinkes book on diving at altitude be used to determine the theoretical depth, and then that be applied to the tables in planning?

Again NO.

And finally, in those situation where the requirements of the diving activity and time constraints dictate that the actual dive site elvation be used in planning dives, is there a concise reletively simple to use method to determine an appropriate surface interval prior to departure.

The answer to this is YES tables exist. However I'm not 100% sure if appropriate tables exist for your situation so I will refer you to your LDS once again for a specialty course.

Cheers,
R..

 

[raybo]

or at least I haven't been able to fine them yet.

I was origiginally trained with Navy tables, and am in the process of getting them in my hands again.

If you go to the link I provided, it read as thought the answer to the questions I asked would be yes. that jsut didn't seem right, Hence the questions.

Thanks again.

 

[Diver0001]

raybo once bubbled...
or at least I haven't been able to fine them yet.

<snip>

If you go to the link I provided, it read as thought the answer to the questions I asked would be yes.

<snip>

Well......that *is* what it says. If you understand the tables, the deco theory and how your equipment works it pretty obvious that using your highest altitude for the coming 24 hours would work for planning purposes. The down side is that you would sacrifice bottom time for lack of a method by which to work out the required surface interval before ascending to a higher altitude ......

But ok. Bottom time notwithstanding it's probably safer than using the U.S. Navy tables, and clearly safer than combining Navy altitude tables with tables from who-knows-where........

And it should be clear that all bets are off if you dive with a computer.

R..

 

[GreenDiverDown]

Diver0001 once bubbled...


You're confusing two things. Diving at altitude requires finding adjusted NDL's to suit the altitude you're diving at, which is what this table is for, *and*, finding the appropriate surface interval before increasing your altitude after a dive, for which you need something more.

For the first part (the table you found), you need to adjust the depth on your tables because your gauges don't read accurately at altitude. This happens because gauges are designed for use at sea level with an ambient atmospheric pressure at the surface of 1 ATA. At altitude this ambient pressure is less than 1ATA (this should be obvious) and your gauges read inaccuratly. In fact you will be deeper than your gauge indicates. This table makes the necessary adjustment to your depth to compensate so you find the correct NDL and repetative group for planning. You can use this adjustment with any agencies tables.

Well...yes and no...

The Theoretical Depth at Altitude Table gives theoretical depths.

Gauge correction gives actual depths.

Bourdon tube gauges read shallower than actual depth at altitude and therefore will require adjustment. If the gauge is nonadjustastable you can easily do some simple math to figure the actual depth. 1 plus 1 for every thousand feet. For example, if you are diving at 5420 feet with a nonadjustable Bourdon gauge and it is reading 25 feet, your actual depth is 32 feet 1+1(6)= 7 Add 7 to 25 and you have your actual depth. Remember to round up fractions of 1000 feet.

You would then use this actual depth and go to your TDA table to figure your theoretical depth to use with your RDP. On the TDA table, rounding up to 6000 feet, an actual depth of 32 feet gives you a theoretical depth of 50 feet. (Remember to round up your actual depth...in this case you would round up from 32 to 40.) You can now take this depth to your RDP.

Remember, theoretical depth is a sea level equivalent depth and not gauge correction.

Of course you can avoid the issue entirely with a capillary gauge which reads deeper than actual depth and will give you the theoretical depth directly.

SA

 

[roakey]

Is the fact that a capillary depth gauge always reads theoretical depth! No conversion necessary!

Of course they're quite hard to get an accurate reading beyond about 40 feet or so...

Roak

 

[raybo]

Diver0001 oce bubbled...

PADI (and others, I'm sure) have a specialty for altitude diving and in your situation it would be highly advisable to take it.

I'm taking a PADI altitude course. Like most PADI courses, here's the book. Any questions? Working through the dive planning is fairly straightforward. I have a reaonable amount of formal secondary physics and science education, and grasping the conversions aren't that difficult. I'm taking several other specialties as well. S&R, deep, and just decided to do Ice. Have Nitrox & Dry. We're meeting tomorrow night to get the logistics planning for the Ice O/W in Colorado in 2 weeks. I really want to do a lot of local diving other than the Blue Hole. That's going to entail a lot of this kind planning. Mountains here aren't as high as Colorado, but they're still here.

The info is out there, I'm just going to have to find it.

Diver0001 oce bubbled...

But ok. Bottom time notwithstanding it's probably safer than using the U.S. Navy tables, and clearly safer than combining Navy altitude tables with tables from who-knows-where........

I completely agree with the assertion that tables of different organizations shouldn't be used, but I'm curious as to why you consider (at least that is what the implication appears to me) that the Nay table swould be unsafe to use in this situation. I'll have to confirm my understanding, but I thought the Y tables were exactly the Navy tables except for a couple slight NDL & P-group changes in the +100 ft.

Another question for Walter?