how long can i stay down on dive 3

[danreind]

Could someone explain to me what the "bend a friend" tables are? I've never heard of them.

As for the question of how to "reality check" a dive computer, probably the best way is with desktop dive planning software. I would usually have a rough multi-level profile planned out which gave me some intuition as to whether my dive computer was in the ballpark or not.

While such software is primarily intended for mixed gas decompression diving, it can certainly be used for testing multi-level no-deco profiles. These are available both commercially and as shareware (GAP and ZPlan being the most well known). Heck, the Buhlmann algorithm is so easy you can even do it on a spreadsheet if you wanted to.

WARNING: Just because one has access to a decompression schedule doesn't mean one knows everything one needs to do decompression diving - training is vital! Like flying a plane, it's very easy until something goes wrong.

Cheers,

Dan

 

[Dr Deco]

All decompression systems [virtually] utilize NDLs and halftimes of compartments. All of these can be handled simultaneously with a dive computer.

However, when a table format is utilized, there is a need to produce a “one size fits all” for the repetitive dive situations. If the table designer's initial conditions are placed into a PC, the necessary dive and decompression times are calculated exactly. In a table format, it becomes necessary to abridge this to reduce the whole system to a single card.

The USN tables were designed for surface-supplied, decompression diving and needed different constraints on repetitive diving than for SCUBA divers. Naturally, rec divers are not surface supplied and do not load gas as much.

Thus, you can find considerable differences in USN tables and rec diver tables. This was one purpose of the PADI RDP.

 

[octodiver]

Great input! I'm impressed... here's another angle...

Here's how to make "every" table/profile a conservative one:
Along with the various tables (and much much more great info) John Lippmanns,
"Deeper Into Diving" also discusses the predisposing factors to DCS that are
just touched on in training manuals. Why aren't we teaching divers - by example,
and in the manuals - to be responsible and conservative and follow a prescribed
method/formula for dealing with these factors? Why not teach divers to take
Lippmann's advice and take 10% off the NDL's for every predisposing factor they have:
(age, gender, weight, temperture...) thereby creating a PERSONAL SAFETY LIMIT
for every diver... Maybe this would take out some of the "mystery" as to why some
folks get hit while diving a profile while others on that profile didn't...
AND, ultimately help reduce the numbers of "undeserved" hits!!

 

[Rick Murchison]

A point of clarification. The SSI tables are the Navy tables, truncated (not modified) to reflect doppler NDL times. Indeed, until recently, the SSI tables simply applied a red line on top of the Navy tables along the doppler limits - today they just leave off that portion of the Navy tables that falls outside the doppler limits.
Rick

 

[Walter]

Rick,

Correct me if I'm wrong (I do not have a copy of the SSI tables), but isn't is risky to leave the NDL's unchanged without giving repetitive group info for the additional time from where the tables were truncated and the NDL. How would one deal with accidentially exceeding the NDL's if using the SSI tables?

Danreind,

There are no tables named the Bend a Friend tables. That's merely a loving nickname applied to the most liberal tables I've seen in use today.

Dr. Deco,

You state, "The USN tables were designed for surface-supplied, decompression diving and needed different constraints on repetitive diving than for SCUBA divers. Naturally, rec divers are not surface supplied and do not load gas as much.

Thus, you can find considerable differences in USN tables and rec diver tables. This was one purpose of the PADI RDP."

This may be, but this was not the way it was presented to the diving public. The RDP was presented as a more conservative table. It was part of PADI's plan to combat lawsuits and bad publicity in the late 1980's. There were some product liability lawsuits from PADI selling PADI Dive Tables which were, in fact, unmodified US Navy Tables. People pushed them, got bent and sued PADI. PADI unveiled the RDP as the new safer, more conservative table, it clearly is less conservative than US Navy tables as modified by NAUI, YMCA and probably other agencies as well.

Walter

 

[Rick Murchison]

No, it is less risky.
All SSI has done to the Navy tables is to lop off those NDLs that fall outside the Doppler limits - so, for example, where the Navy NDL for 50' runs out to 100 minutes, the SSI table ends at 70. So, if your repetitive group is "H" (Navy/SSI table) at the end of a dive, your RNT for a subsequent dive to 50' starts at 66 minutes - if you then wanted to make a 40 minute dive to 50', on the non-doppler table (which allows a TBT of 100 minutes) you'd need a surface interval of only 37 minutes (RNT 56 minutes + 40 minute ABT), where the doppler limit (70 minutes TBT) requires a surface interval of 2 hrs 24 minutes (RNT 29 minutes + 40 minute ABT). For recreational no-decompression diving the result is a much more conservative table.
Rick

 

[Dr Deco]

Dear Readers:

The RDP is more conservative with respect to the NDLs for a single square dive, or multilevels within that single dive. If one goes to repetitive dives, the surface interval will be less with the RDP than with the US Navy tables because of the way in which residual gas loads are calculated. They are based on the loading of the sixty-minute compartment rather than the 120-minute compartment.

The conservatism is thus based on the NDLs that were reduced in accordance with research from Doppler bubble detectors. These tables will usually be more conservative than a dive computer, except for the first, square dive.

Conservatism in diving should not necessarily be based on dive tables since these are for a large population on individuals. Instead, one should attempt to modify your personal dive habits to include those factors that are not in deco tables (or computers). These have been discussed in various postings of the FORUM and would be:
[sp][sp]:bolt:

• take a safety stop, and move your arms and legs at the stop to promote the flow of blood;
• avoid those straining activities that promote the formation and growth of micronuclei in tissues (e.g., climbing ladders will full gear, and lifting heavy tanks and weight belts)
• avoid remaining sedentary during the surface intervals(do not sleep) but rather remain seated but move arms and legs to promote the flow of blood.
• avoid physically strenuous activities during the surface interval and following the dive, do not run (strenuous), for example, for several hours post surfacing.
• remember to stay well hydrated as this promotes perfusion (= blood flow) and increases the surface tension of the bodies fluid to as high a value as possible.
  
  Possibly it is true that, the more you know, the longer you live.
  
  Dr Deco :doctor:

 

[Walter]

Dr. Deco,

While you contribute a great deal to our collective education with regard to decompression issues, the first part of your post is misleading.

You state, "The RDP is more conservative with respect to the NDLs for a single square dive, or multilevels within that single dive."

If compared to the unmodified US Navy tables that is true for most depths (they have identical NDL's at 130 ft). However, when compared to the tables of other agencies, it's not true. I made some comparisons of NDL's of several tables for 10 depths from 40 ft to 130 ft. Compared were:

PADI's RDP, NAUI's tables, YMCA's tables, DCIEM tables, and the Michigan tables.

PADI's RDP has the longest <3>(or tied for the longest <3>) NDL at 6 of the 10 depths. At none of the depths did it have the shortest (nor did it tie for the shortest) NDL.

DCIEM tables had the shortest <4>(or tied for the shortest<4>) NDL at 8 of the 10 depths, although it does have the longest NDL at 40 ft.

YMCA tables tied for the shortest NDL at 4 of the 10 depths, it tied (with the RDP) for the longest at 50 ft.

The Michigan Tables tied for the shortest NDL at 4 of the 10 depths, it tied (with the RDP) for the longest at 90 ft.

NAUI tables were alone with the shortest NDL at 40 ft, but also had the longest <3> (or tied for the longest <3>) at 6 of the 10 depths.

At no depth was "The RDP is more conservative with respect to the NDLs for a single square dive, or multilevels within that single dive." Therefore, the statement is misleading.

I wholeheartedly agree with the second half of your post.

Rick,

You did not answer my questions.

I asked: "........isn't is risky to leave the NDL's unchanged without giving repetitive group info for the additional time from where the tables were truncated and the NDL."

You used an example of 50 ft. You are correct, the US Navy tables have an NDL of 100 minutes, but IF SSI's tables are truncated and not modified US Navy tables they still have the same NDL's. They will show an NDL of 100 minutes at 50 ft, but are lopped off at 70 minutes. How do you account for the time between 70 minutes & 100 minutes?

I also asked: "How would one deal with accidentially exceeding the NDL's if using the SSI tables?" Emergency decompression proceedures should be available.

I'm curious. I do have several sets of tables, but not SSI's.

Walter

 

[Walter]

I did not place them there. I don't care for them, I don't use them and if I did, I certainly would never put them where I was making a serious point. More importantly, how can I get them out?

Walter

 

[BillP]

Hi Walter:

I agree with you on the "smilies". This board software automatically changes certain punctuation based emoticons to the animated smilies. I would guess that something like the "greater than" sign followed by a closing parenthesis or a closing parenthesis followed by a period makes the winking smilie. There is an option at the bottom of the field to type a reply to "Disable Smilies in This Post". It is also available in the edit message field. Go back and edit your message selecting that option and see if the smilies don't disappear.

HTH,

Bill