Doc Wong Getting Bent in Monterey!

[Chuck Tribolet]

Just realized while replying to Chuck's post that even using the 80% EAD approximation, 75' on 32% has EAD of 60ft (it's where the approximation is spot on), so our misunderstanding does not stem from the 80% EAD approximation.
80' on 32% is about 64ft EAD, so Mark's above statement is correct as I said before, but if you want to get numbers for a 75' dive you get the EAD for 75' and then apply it to a table, rounding up only then if necessary. No need to round up to 80ft first when getting the EAD and then rounding up again when applying that EAD to a table. (If that was what you were doing.)

Paul, you are correct. I'm wrong.

 

[DocWong]

I ran the two dives on two different software programs, Deco Planner and HL Planner and they both came up within "No Decompression Limits" In both cases I still did a slow ascent and did stops anyway. So I believe these were recreational dives not requiring decompression.

I don't have the PADI tables, but if they were out of bounds for Dive 1 at 80 feet for 20 minutes, then a 2 hr surface interval, with Dive 2 at 75 feet for 47 minutes, I'd like to confirm that.

That said, all dives are decompression dives. In other words, all dives involve the absorbtion of nitrogen and the compression of the gas/air we breathe from our tanks into liquid form in our blood as we descend.

I think NDL or No Decompression Limits should be changed to Minimum Decompresson or slow ascents to 20 feet and 3 minutes at 20 and 3 minutes at 10 feet.

Thanks for the info Doc,


This is where semantics get confusing for those reading SB who are simple grunt recreational divers like me and not technical or decompression divers. Doc said he was doing recreational diving which should mean NO DECOMPRESSION DIVES, at least that's what I was taught. If I am reading my nitrox NDL tables correctly, this was not the case. According to the EAD NDL tables, the second dive alone exceeded recreational limits.

This was a decompression dive, all well and good. However, many rec diving readers can read the initial post and think "heck, can I do a 30 ft reef dive, lift a scooter and get bent?" In fact, this profile is beyond the majority of people who dive or read this board, I suspect. While it's true that DCS can occur after innocuous dives, Doc's case doesn't really fit, at least from the perspective of those of us weekend quarry/reef divers who live above 60 feet and never do decompression dives.

As for being silly for requesting the profiles, the profiles indicate a) this is not no deco recreational diving but decompression diving, a more advanced and inherently riskier art; b) there appears to be some debate as to how conservative this profile was (again, I am not being critical...I know nothing about decompression diving personally...I am just observing posts by people who do know something about it and there seems to be differences in opinion as to how the profiles were calculated indicating that there might have been some possibility of bumping against the limits).

Posts describing DCS should make it clear if the profiles were recreational or decompression dives. Otherwise, people doing NDL dives within limits will fear DCS more than they should.

Again, I may be talking out my rear end as I am wont to do, but many SBer's like me lack the knowledge to understand how an experience like Doc's should influence their own behavior. Avoiding exercise after two shallow reef dives may not be as critical as avoiding exercise after two dives like Doc's.

 

[TekDiveGirl]

Doc,

As a fellow sufferer of a dcs hit this past June, I'm glad that you are ok!

Dive safe!

Kimber

 

[paulwlee]

I don't have the PADI tables, but if they were out of bounds for Dive 1 at 80 feet for 20 minutes, then a 2 hr surface interval, with Dive 2 at 75 feet for 47 minutes, I'd like to confirm that.

Using PADI's table, after the first dive and surface interval, you are in group A.
For the second dive:
Using PADI's EAN32 tables,
you get 40 mins NDL for 80 ft and 54 mins NDL for 70ft, so following this table, yes, it was past NDL.
On the other hand, using PADI's Air table using 32% EAD of 60ft,
you get 49 mins NDL for 75ft.
(if you use the PADI EAD table, you get to round up twice and end up with the NDL for 70ft, which is 35min, but no need to use the EAD table if you can do the EAD calc yourself.)

So this dive does fit in PADI's definition of a no-decompression dive too, although for some ways of using the table the rounding errors (which is always towards the conservative side) push it off to decoland.

 

[limeyx]

Was that 47 minutes and then a 12 minute ascent? or 47 minutes including a 12 minute
ascent? If the the former, that seems like a long time. When I dive that area, usually
on a 34 mix, my computer hits the yellow at about 35 minutes, and I go up.

What about hydration?

Did you dive the day before?

At 60 feet, (EAD of 75 feet - 20%) you have approx 50 mins BT. So somewhat close to NDL, but definitely not over it.

 

[paulwlee]

Just to make it clear for people who are not familiar with the AG/JJT's Minimum Deco table, this table is different from PADI or NAUI tables in that it assumes a particular ascent profile that is different from the 30ft/min straight ascent with (sometimes mandatory, other times just suggested) 3 minute safety stop at 15ft.

That is why we are not discussing the gas loading from the previous dive 2 hours ago, as the required ascent profile adequately covers the offgassing requirement even with the gas load from the previous dive taken into account.

 

[shakeybrainsurgeon]

Doc

According to the PADI 32 EANx table which assumes a square profile, the second dive must be rounded to 80 ft, giving NDL limit 45 minutes, so 47 minutes does exceed this barely. This is as a single dive.

As noted above, a 2 h surface interval after the first dive put you in group A giving you 5 minutes of RNT, so your actual nitrogen bottom time was 52 minutes, even further out of of NDL of 45.

Thus, the PADI EANx 32 table says your profile exceeded table-calculated NDL limits. Other tables might disagree. Also, a nitrox computer taking into account the actual profile and not a square profile would likely show you were not beyond limits since the square profile, and rounding up, give much lower bottom times than the computer.

 

[Adobo]

Doc

According to the PADI 32 EANx table which assumes a square profile, the second dive must be rounded to 80 ft, giving NDL limit 45 minutes, so 47 minutes does exceed this barely. This is as a single dive.

As noted above, a 2 h surface interval after the first dive put you in group A giving you 5 minutes of RNT, so your actual nitrogen bottom time was 52 minutes, even further out of of NDL of 45.

Thus, the PADI EANx 32 table says your profile exceeded table-calculated NDL limits. Other tables might disagree. Also, a nitrox computer taking into account the actual profile and not a square profile would likely show you were not beyond limits since the square profile, and rounding up, give much lower bottom times than the computer.

PADI assumes a different ascent profile though. Neither GUE nor AG/JT/DM advocate the "ascend to 15ft and do a 3 to 5" approach.

Perhaps talking about the AG/JT/DM approach is even misleading as it was not the approach Harry modeled and applied for his dive.

Based on the 3 at 20 and 3 at 10 approach that Harry seems to be in favor of, it seems the table cut by Peter Steinhoff is the most appropriate to use for analysis on Harry's dive profile.

As a side note, I wonder if we are pointed in the right direction. No matter what table I look at, I have trouble finding any gross violations of any limits. The fact that Harry's ascent was slower and more conservative than even the already conservative standard GUE ascent should have more than mitigated any risks from slightly exceeding any limits on either the AG/JT/DM table or Peter Steinhoff's table.

Besides, it's not like you necessarily get bent by exceeding a limit by a minute. Similarly, there are no guarantees of not getting bent even if you obey the limits.

 

[shakeybrainsurgeon]

PADI assumes a different ascent profile though. Neither GUE nor AG/JT/DM advocate the "ascend to 15ft and do a 3 to 5" approach.

Perhaps talking about the AG/JT/DM approach is even misleading as it was not the approach Harry modeled and applied for his dive.

Based on the 3 at 20 and 3 at 10 approach that Harry seems to be in favor of, it seems the table cut by Peter Steinhoff is the most appropriate to use for analysis on Harry's dive profile.

As a side note, I wonder if we are pointed in the right direction. No matter what table I look at, I have trouble finding any gross violations of any limits. The fact that Harry's ascent was slower and more conservative than even the already conservative standard GUE ascent should have more than mitigated any risks from slightly exceeding any limits on either the AG/JT/DM table or Peter Steinhoff's table.

Besides, it's not like you get bent by exceeding a limit by a minute. Similarly, there are no guarantees of not getting bent even if you obey the limits.

There was no gross violation, perhaps no violation per se at all, but according to the PADI EAN 32 as I read it, the 2 dive profile exceeded the NDL limits by 7 minutes. My original point was that the lifting didn't precipitate the DCS, or if it did, it was because he was bumping into the limit somewhere so that the slightest perturbation might be enough to trigger bubble formation.

Question for dive medicine experts: if a diver comes in after knowing this profile with these symptoms, do you give him oxygen and send him home?

 

[pilot fish]

That was my question too: if somoene presents himself with DCS symptoms that are as clear as his was, do you just administer oxygen and send them home, or be more prudent and give them a chamber session, or two, along with oxygen? What could be the reason for not doing a chamber session? Cost? Diver had no ins? Puzzling.

There was no gross violation, perhaps no violation per se at all, but according to the PADI EAN 32 as I read it, the 2 dive profile exceeded the NDL limits by 7 minutes. My original point was that the lifting didn't precipitate the DCS, or if it did, it was because he was bumping into the limit somewhere so that the slightest perturbation might be enough to trigger bubble formation.

Question for dive medicine experts: if a diver comes in after knowing this profile with these symptoms, do you give him oxygen and send him home?