Accumulated 02 following a large number of repetitive Nitrox dives over 3 days.

[Astran]

This seems to be a theme with you. If you don't and won't listen to your computer or advice you don't like, what exactly is your purpose on this thread? Your questions have already been answered. I am very curious as to where, when, and from who you learned nitrox

My questions were answered, thank you very much. I don't have any further need to post until and unless further posts, primarily those directed towards me and my diving style, or contribute to the topical content of this thread, merit a response.

My credentials and certifications are none of your business, they are irrelevant and are clearly meant to be antagonistic and are nothing more than harassment. No different then yelling at someone who pulls a bonehead move while driving and you yell "where did you get your license, mail order?".

Consider yourself lucky I took the time and effort to even respond.

 

[tursiops]

according to the DAN article, a diver has up to 300 minutes per day maximum exposure

You are not reading that article correctly.
Table 4 is applicable to Nitrox.
AT PPO2 (not PO2) of 1.3, the single-exposure limit is 180 mins; the 24h limit is 210 mins; and the exceptional exposure (NOT appropriate for recreational, non-combat divers!) is 240 mins. NOWHERE does it say 300 minutes!

I stated earlier I was at 1.03 when my computer's 02 alarm activated and rapidly dropped to .95.

You keep saying this, and it keeps being irrelevant. Even at PPO2 of 1.03, you are accumulating dosage. That's when you (according to your computer) crossed the line and got the alarm.

The DAN article (about 16 years old) quotes NOAA for its information; the most recent NOAA Diving Manual and Diving Safety Manual mandates NO use of Exceptional Exposure tables. The NOAA tables now use a 2h half-time for O2 washout; 6 half times is thus 12h, so NOAA says your clock starts anew after 12h of no diving. Section 4.3.3.3 in the Diving Manual 5th Edition, Tables 4.4-4.7 and Figures 4.22-4.24 are your more modern information sources.

 

[DBPacific]

My questions were answered, thank you very much. I don't have any further need to post until and unless further posts, primarily those directed towards me and my diving style, or contribute to the topical content of this thread, merit a response.

My credentials and certifications are none of your business, they are irrelevant and are clearly meant to be antagonistic and are nothing more than harassment. Consider yourself lucky I took the time and effort to even respond.

 

[Astran]

You are not reading that article correctly.Even at PPO2 of 1.03, you are accumulating dosage. That's when you (according to your computer) crossed the line and got the alarm.

If the daily limit is P02 1.3 is 210 minutes and yet for a good chunk of those minutes I'm at 1.03 then sure, I'm accumulating 02 but not at a rate that exceeds the recommended limits.

In other words 233 minutes (my total dive times sans safety stops) of repetitive diving at 1.03 is safe according to the tables in the (16 year old) article. 233 minutes of diving at P04, is not ok. Hard or impossible to calculate but I'm somewhere in between those ranges. I wasn't anywhere close to "exceptional exposures" (whatever that means in regard to safety) even if you figure that I was at the high end of the range.

I get that the Oceanic, with it's ultraconservative algorithm that doesn't account for half-life of 02 especially during long overnight surface intervals, alarms when it determines an unsafe exposure limit has been reached and it does not account for the 12 hours of no diving which occurred prior to the dive during which the Oceanic alarmed me to unsafe 02 levels.

I don't know anything about the newest NOAA manuals and recommendations, I clicked on your supplied link but those manuals are not available for reading unless purchased.

 

[tursiops]

If the daily limit is P02 1.3 is 210 minutes and yet for a good chunk of those minutes I'm at 1.03 then sure, I'm accumulating 02 but not at a rate that exceeds the recommended limits.

And, yet, your alarm went off. So you DID exceed the limits (as sued in that computer).

300 minutes is considered "exceptional exposure"

I do not know where you are getting this 300 mins you keep using.

I don't know anything about the newest NOAA manuals and recommendations, I clicked on your supplied link but those manuals are not available for reading unless purchased.

The Diving Safety Manual is free. It is linked to.
The Diving Manual is now in its 6th edition. I was referencing the 5th edition. The 4th edition, with pretty much the same material, is available on line. See section 3.3.3.3. I am providing this material because you appear to like original sources; so read this. Everything else is derivative from this, including the Navy Dive Manual.

 

[Astran]

And, yet, your alarm went off. So you DID exceed the limits (as sued in that computer).

Yes. I definitely exceeded safe P02 limits, as per the Oceanic's ultraconservative algorithm that does not account for 02 half-life especially during the 12 hours between dives during sleep. I think we covered this earlier?

I do not know where you are getting this 300 mins you keep using.

I don't either. I see the maximum daily 02 limit for exceptional exposure is 240 minutes at P02 1.3. I thought the 300 minutes was in a table from that article, maybe it was another one. I've been looking at a lot of tables in the last few hours. Either way my maximum dive time sans safety stops was 233 minutes, at something less than P02 1.4 and at times as lower as .95 or even lower.

The Diving Safety Manual is free.

Cool. I'm going to check it out and if I find anything in there that supports my side of the argument, I'll be sure to post back!

 

[tursiops]

I'm going to check it out and if I find anything in there that supports my side of the argument,

There is no argument. it is like Climate Change; there is no argument, there is no controversy. There are some who choose not to accept the science. One does not "believe" science, one accepts it or not.

 

[GJC]

I think you guys are mixing up O2 minutes and OTUs.

An OTU is 1 min on 100% O2 for 1 min at sea level

1 min at 1.4 O2 pressure is 1.4 OTU
That would be 32% at 111 ft

240 min at 1.4 is close to 300 OTU. I know 300 OTU is the daily limit mentioned as the max 24 hr exposure in the NOAA dive manual.

More on how they arrived at 300 later when I have more time.

 

[Astran]

@tursiops

The newer manual uses the same tables as the old one, it just drops the "exceptional exposure" tables.

I went back and manually calculated my exposures for the most dive intensive 24 hour period including the dive that my Oceanic alarm indicated I was at an unsafe level.

I realized I needed to add a 7th dive to the total since it was within 24 hours.

Dive times are -3 minutes (safety stop), depth is average but pretty accurate.

Dive 1 10:07 AM 40 minutes depth 80' EAN 34 P02 1.2
Dive 2 1:54 AM 34 minutes depth 80' EAN 34 P02 1.2
Dive 3 3:20 pm 38 minutes depth 80' EAN 32 P02 1.1
Dive 4 5:00 PM 34 minutes depth 85' EAN 32 P02 1.1
Dive 5 6:30 PM 54 minutes depth 60' EAN 32 P02 .9
Dive 6 7:40 AM 30 minutes depth 90' EAN 35 P02 1.3
Dive 7 9:39 AM 20 minutes in, depth 65' , Alarm went off. EAN 35 P02 1.1 (as per table, but dive computer indicated 1.03 then dropped to .95)

250 minutes total over 7 dives within 24 hours at a P02 of about 1.1 is within the limits of the NOAA table in the newer manual which allows for 270 minutes at P02 of 1.1

Even if you round up and say "well his average P02 over those dives is closer to 1.2" then at most, I'm about 10 minutes over the recommended NOAA normal limit, but these seven dives are including times to ascend and descend which are at least 10 minutes that can be adjusted downward as far as P02 values go.

 

[tursiops]

@tursiops

The newer manual uses the same tables as the old one, it just drops the "exceptional exposure" tables.

I went back and manually calculated my exposures for the most dive intensive 24 hour period including the dive that my Oceanic alarm indicated I was at an unsafe level.

I realized I needed to add a 7th dive to the total since it was within 24 hours.

Dive times are -3 minutes (safety stop), depth is average but pretty accurate.

Dive 1 10:07 AM 40 minutes depth 80' EAN 34 P02 1.2
Dive 2 1:54 AM 34 minutes depth 80' EAN 34 P02 1.2
Dive 3 3:20 pm 38 minutes depth 80' EAN 32 P02 1.1
Dive 4 5:00 PM 34 minutes depth 85' EAN 32 P02 1.1
Dive 5 6:30 PM 54 minutes depth 60' EAN 32 P02 .9
Dive 6 7:40 AM 30 minutes depth 90' EAN 35 P02 1.3
Dive 7 9:39 AM 20 minutes in, depth 65' , Alarm went off. EAN 35 P02 1.1 (as per table, but dive computer indicated 1.03 then dropped to .95)

250 minutes total over 7 dives within 24 hours at a P02 of about 1.1 is within the limits of the NOAA table in the newer manual which allows for 270 minutes at P02 of 1.1

Even if you round up and say "well his average P02 over those dives is closer to 1.2" then at most, I'm about 10 minutes over the recommended NOAA normal limit, but these seven dives are including times to ascend and descend which are at least 10 minutes that can be adjusted downward as far as P02 values go.

I definitely appreciate your effort here, but I'm afraid you can't use average depth....you need to use actual depth...which is what your computer does. The reason you can't use average depth is because the rate of accumulation of OTUs or time on the oxygen clock is not linearly proportional to depth (or equivalently PPO2). It's the same problem with calculating NDLs; you can't use average depth....so you either use max depth with tables or actual depth with a computer. If you use max depth on each of these 7 dives, you'll be greatly overestimating your oxygen exposure, but at least you won't be introducing an error other than conservatism. By using average depth, the error you introduced tends to underestimate your oxygen exposure, due to the shape of the "ongassing" curve.
Note the footnote to Table 3.5 in the NOAA Dive Manual, 4th editiion. "The oxygen clock runs more than three times as fast at 1.60 atm than at a PO2 level of 1.40 atm." Non-linearity is insignificant at low PPO2 levels, but gets noticeable and important at the higher levels, where you are working.