Off the chart on the dive tables

[gfaith]

Here is a link to you dive computer manual.

http://www.aqualung.com/us/technical_library/i550_R316.pdf

 

[blac86]

Hi Divers, I am new to the boards. I was certified in 1993 and dove about 20 times in the few years after that pretty much giving the sport up when kids came along. My youngest daughter just got certified at 16 and I have a renewed vigor for the sport with my new dive partner. forgive me, but I never really paid much attention to dive tables back in the day. All of my dives were single tank dives and my deepest back then was 86 feet. Now I am learning and calculating my times and I think I was off the chart on my last dive of the day. Here are my dives.

Dive 1: 30 minutes dive at a max depth of 51 feet, but most of the dive at 20 or 30 feet.
Surface Interval: 30 minutes
Dive 2: 30 minute dive at 60 feet with most of this dive at 60
Surface interval: 30 minutes
Dive 3: 30 minute dive with the majority of time at 90 feet. Safety stops at 60, 30, 15.

Done for the day or so we thought. The instructor says hey a guy just walked in wanting Enriched Air training. Want to get it also?

Surface Interval 2.5 hours
Dive 4: Nitrox Dive 32% to 90 feet. Maybe 20 minutes bottom time.

So, how does Nitrox work on the pressure tables after three regular air dives the same day? I saw no ill effects.

Ok, lets play good news bad news:
Bad news - your dives are wildly off tables
Good news - I ran them through my decompression planning software (using zhlc16 70/90)
Good news - your Nitrox dive was well within limits.
Bad news - your second dive already had you with a non negligible deco obligation.
Bad News - your third dive called for 30 minutes of decompression, which you did not do and are lucky you did not get hurt.
Good news - you survived

 

[flymolo]

Ok, lets play good news bad news:
Bad news - your dives are wildly off tables
Good news - I ran them through my decompression planning software (using zhlc16 70/90)
Good news - your Nitrox dive was well within limits.
Bad news - your second dive already had you with a non negligible deco obligation.
Bad News - your third dive called for 30 minutes of decompression, which you did not do and are lucky you did not get hurt.
Good news - you survived

Those are total dive times. Bottom time @Alligood was much shorter of course, we may have spent 15 minutes at 90. I do have a dive computer, but it was my first day with it. Darn Manual came on CD only.

Do you have logs? Can you post them?

 

[Neilwood]

Additional information will allow you to get more pertinent feedback.

I am going to make the assumption that you wore your computer and did not excede its NDLs. I am also going to assume that as part of the "nitrox course" your computer was set to reflect the Nitrox mix on your last dive. Please let us know if these assumptions are incorrect as they will guide feedback.

If my assumptions are correct, your set of dives is a great example of how hard it is to map a set of multi level dives back to tables - and to your perception of what you actually did on each dive. Tables assume a square dive profile. This is reasonable since in the old days the only reliable data post dive is the depth telltale on your mechanical depth gauge and the elasped time on your bottom timer. Limited reliable data means the tables are set up based on worst case scenario of a square profile. Doing multi level dives (which it appears you did) means you are further away from NDL limits than the table says.

Using a computer is whole different world. By computer your first dive is almost a non dive. Total dive time was 30 minutes, mostly above 30 feet but you did hit 50 feet. Lets assume 5 minutes at 50 feet. That is 5 minutes of 63 minutes allowed by the PADI table. By the table (30 minute square profile) you were almost half way to NDL, but by computer you would be less than 1/12. The rest of the dive was above 30 feet. Same dive, very different interpretation of your loading.

Can you confirm you used the computer and never went into deco?

Agreed - without the logs, we know nothing of how the dive was carried out so impossible to know how near to NDL the OP was. Tables work on absolute worst case scenario - descend to max depth immediately, stay there for the whole length of the dive and ascend to the surface (at a safe rate). As such, when faced with real world multi level dives tables become really restrictive.

If it was a bounce to 50ft, then the nitrogen uptake would indeed be minimal. I can only assume (as you did) that the computer was set correctly in the nitrox course for the mix. If that was done and the OP followed the computer and stayed within NDL on each dive, I don't see it being unsafe as such.

Personally I would prefer to see a lot longer surface intervals (30mins really is cutting things very fine).

To the OP, if you can post logs of the dives, it would help a lot in understanding the profiles involved.

 

[Neilwood]

Ok, lets play good news bad news:
Bad news - your dives are wildly off tables
Good news - I ran them through my decompression planning software (using zhlc16 70/90)
Good news - your Nitrox dive was well within limits.
Bad news - your second dive already had you with a non negligible deco obligation.
Bad News - your third dive called for 30 minutes of decompression, which you did not do and are lucky you did not get hurt.
Good news - you survived

Not sure how you can know these as facts unless you know the profiles. Ran on tables with no allowance for multilevel diving, they may be beyond deco planning software or table NDLs but going by a computer they may have been within NDL by a long way.

 

[blac86]

Not sure how you can know these as facts unless you know the profiles. Ran on tables with no allowance for multilevel diving, they may be beyond deco planning software or table NDLs but going by a computer they may have been within NDL by a long way.

I mean I can only work with the data that's given, and using that data constructed a four dive profile. If the data is bad of course the result is bad.

 

[Neilwood]

I mean I can only work with the data that's given, and using that data constructed a four dive profile. If the data is bad of course the result is bad.

I know what you mean and do not doubt the good intention but, given the forum we are in, it is better to give try to give a more balanced point of view than to jump to conclusions. Without logs or an idea of the profile, we are really in the dark.

I would agree though that those dives might not constitute the best series of dives (SI is way too short for my liking with any profile of dive - I try to go for 1hr as a minimum).

 

[sea_ledford]

I know what you mean and do not doubt the good intention but, given the forum we are in, it is better to give try to give a more balanced point of view than to jump to conclusions. Without logs or an idea of the profile, we are really in the dark.

I think he gave a perfectly well balanced point of view. The OP was diving tables because he didn't know how to use a brand new computer. The primary issue was a complete lack of planning of the dives. It sounds like this was more of the inst/DM than the OP, and likely the plan was "my boss told me I had to get all three of these dives done today, and I have nitrox class to teach this afternoon."

I don't think there was any jumping to conclusions, the dive times, depth and SI were provided. Sure we are in the dark about the actual profile, but that is true about every table dive. This is a perfect example of plan your dive and dive your plan not being followed.

Thanks to the OP for sharing this, I'm not meaning to dig on him at all! These posts are great to have in the Basic Scuba Diving forum. Just because you are diving with a "professional" it doesn't mean that they have your best interest in mind.

-Chris

 

[doctormike]

I know what you mean and do not doubt the good intention but, given the forum we are in, it is better to give try to give a more balanced point of view than to jump to conclusions. Without logs or an idea of the profile, we are really in the dark.

I would agree though that those dives might not constitute the best series of dives (SI is way too short for my liking with any profile of dive - I try to go for 1hr as a minimum).

I think that's sort of the point - if you don't have a logged profile, if you are doing table dives, you have to assume square profiles. All the people who come here and say that they don't need computers, and that they just dive tables, need to do calculations as if their maximum depth was their depth all through their bottom time (or that dive segment, if they are doing multi level). In fact, the main advantage of a dive computer is that it gives you credit for time above maximum depth.

If those were his dives, then he blew off deco. Now, he might have been physiologically safe because he really didn't spend much time at maximum depth, but there is no way of knowing that. From a dive planning and post dive analysis point of view, he blew off a lot of deco (I ran this through multi-deco as well, see below). That should be the take home message, and there is no need to sugar coat that just because we are in a green zone.


DIVE PLAN #1
Surface interval = 5 day 0 hr 0 min.
Elevation = 0ft
Conservatism = GF 30/70

Dec to 50ft (0) Air 60ft/min descent.
Level 50ft 29:10 (30) Air 0.53 ppO2, 50ft ead
Asc to 20ft (31) Air -30ft/min ascent.
Stop at 20ft 1:00 (32) Air 0.34 ppO2, 20ft ead
Stop at 10ft 1:00 (33) Air 0.27 ppO2, 10ft ead
Surface (33) Air -30ft/min ascent.

DIVE PLAN #2
Surface interval = 0 day 0 hr 30 min.
Elevation = 0ft
Conservatism = GF 30/70

Dec to 60ft (1) Air 60ft/min descent.
Level 60ft 29:00 (30) Air 0.59 ppO2, 60ft ead
Asc to 20ft (31) Air -30ft/min ascent.
Stop at 20ft 0:40 (32) Air 0.34 ppO2, 20ft ead
Stop at 10ft 3:00 (35) Air 0.27 ppO2, 10ft ead
Surface (35) Air -30ft/min ascent.


DIVE PLAN #3
Surface interval = 0 day 0 hr 30 min.
Elevation = 0ft
Conservatism = GF 30/70

Dec to 90ft (1) Air 60ft/min descent.
Level 90ft 28:30 (30) Air 0.78 ppO2, 90ft ead
Asc to 40ft (31) Air -30ft/min ascent.
Stop at 40ft 0:20 (32) Air 0.46 ppO2, 40ft ead
Stop at 30ft 3:00 (35) Air 0.40 ppO2, 30ft ead
Stop at 20ft 12:00 (47) Air 0.34 ppO2, 20ft ead
Stop at 10ft 37:00 (84) Air 0.27 ppO2, 10ft ead
Surface (84) Air -30ft/min ascent.

DIVE PLAN #4
Surface interval = 0 day 2 hr 30 min.
Elevation = 0ft
Conservatism = GF 30/70

Dec to 90ft (1) Nitrox 32 60ft/min descent.
Level 90ft 28:30 (30) Nitrox 32 1.19 ppO2, 73ft ead
Asc to 30ft (32) Nitrox 32 -30ft/min ascent.
Stop at 30ft 1:00 (33) Nitrox 32 0.61 ppO2, 21ft ead
Stop at 20ft 1:00 (34) Nitrox 32 0.51 ppO2, 13ft ead
Stop at 10ft 4:00 (38) Nitrox 32 0.42 ppO2, 4ft ead
Surface (38) Nitrox 32 -30ft/min ascent.

 

[KeithG]

...The OP was diving tables because he didn't know how to use a brand new computer. The primary issue was a complete lack of planning of the dives. It sounds like this was more of the inst/DM than the OP, and likely the plan was "my boss told me I had to get all three of these dives done today, and I have nitrox class to teach this afternoon." ...

I do not think the OP was diving tables. They are asking how to back track their dives to the tables. And the the posted profiles obviously exceed normal tables (and hence a pile of outraged peeps have their panty's in a knot).

As a computer diver, the profiles look fine to me - if I assume a conservative multi level dive profile. These were training dives after all. Has everyone assumed the instructor is a moron?

I believe the OP was naively doing "trust me" training dives while wearing a unfamiliar computer thingy and is now trying desperately to get some feedback on why they are not badly bent after radically exceeding their knowledge of the tables.

I could be wrong. The only way to discover the truth and provide sane feedback is for the OP to provide some clarification regarding their interpretation of the dives. Hopefully we have not scared the OP away.

If we have, I am happy to provide an alternate non square profile interpretation of the dives that makes the OPs day totally safe.