Safety stop on Oxygen or Nitrox

[Crowley]

... But in your first post just half an hour ago you said, quote "Practically speaking, for recreational diving, 18m(60ft) per minute is fine... " unquote. Now you are saying quote, "I doubt you'd find any diver these days prepared to risk an 18m/min ascent." unquote. If I asked you let's say tomorrow how fast would it be?

In String's defence, it was me that said that 18m/min is fine - not him

Do I ascend a this rate? No - I do what my computer tells me to, and the Suunto RGBM model suggests that microbubble formation on ascent limits the ascent rate to 10 metres per minute. I stick to that.

In the area I work, the diving we do is almost ridiculously conservative - 1.4ata, no deco, etc. - and this is for our own safety as much as it is for others. We keep it conservative because we are almost permanently fizzy, and this is what our customers expect of us, because they want safe, enjoyable dives floating about with the fish.

If people want to push limits - whether diving or racing motorcycles, this is fine, but it's not for the average diver, nor the average biker. 150mph through heavy traffic is indeed possible, (I know, because I've done it) but just because it's possible doesn't mean it should be advocated. You adapt your riding to the road conditions just in the same way you adapt your diving to what you are doing at the time.

Different computers will tell you different things - but for all I might know, or whatever people on this forum tell me, I'm not going to argue with a company that's invested millions of dollars in research over 30 years, however conservative their computers are.

Stay safe

C.

 

[String]

In the area I work, the diving we do is almost ridiculously conservative - 1.4ata, no deco, etc. - and this is for our own safety as much as it is for others. We keep it conservative because we are almost permanently fizzy, and this is what our customers expect of us, because they want safe, enjoyable dives floating about with the fish.
.

That is a big thing. The current tables and models fall down in particular when dealing with short surface intervals and long periods of repeat/multiple diving such as you get when working.

2-3 dives a day, 7 days a week for sometimes weeks on end is going to put you far more on the edge of the model than someone doing 2 dives a day for 3 days then going home.
Its (relatively) unusual to see an instructor get bent even on these schedules. That said i know of 3 instructors with perforated ear drums in the last 4 months now!

 

[Den7]

In String's defence, it was me that said that 18m/min is fine - not him

Do I ascend a this rate? No - I do what my computer tells me to, and the Suunto RGBM model suggests that microbubble formation on ascent limits the ascent rate to 10 metres per minute. I stick to that.

In the area I work, the diving we do is almost ridiculously conservative - 1.4ata, no deco, etc. - and this is for our own safety as much as it is for others. We keep it conservative because we are almost permanently fizzy, and this is what our customers expect of us, because they want safe, enjoyable dives floating about with the fish.

If people want to push limits - whether diving or racing motorcycles, this is fine, but it's not for the average diver, nor the average biker. 150mph through heavy traffic is indeed possible, (I know, because I've done it) but just because it's possible doesn't mean it should be advocated. You adapt your riding to the road conditions just in the same way you adapt your diving to what you are doing at the time.

Different computers will tell you different things - but for all I might know, or whatever people on this forum tell me, I'm not going to argue with a company that's invested millions of dollars in research over 30 years, however conservative their computers are.

Stay safe

C.

Thank you for your comments, Crowley. I appreciate.

What surprises me the most was that none of my instructions told me that the safest maximum ascend rate would be about 10 meters / 33 feet per minute. In fact, my computer's manual says it is even 9m/30ft per minute. They all for some reason kept on insisting that 18 meters / 60 feet per minute was the maximum safe limit. The same data (18/60) is also written in my PADI textbook. I never push the limits though but to find out that the recommnded limit is actually twice as less... came out as a big surprise to me (when I bought my new computer) which is also contrary to what the PADI OW textbook says. Thanks goodness I always sticked to much slower ascend rates.....

That's why I asked the initial question (just an idea that crossed my mind) if twice as less or twice as much the other way around would not jeapordize my safety limit which in both cases would get all down to 18m/60ft per minute only... It looks like I was wrong and my idea did not prove to be right...

 

[Blackwood]

The same data (18/60) is also written in my PADI textbook.

That's because their model is based on a 60fpm ascent rate. Slower is considered 'safe' (longer time decompressing than the model predicts is necessary), faster is considered 'unsafe' (shorter time decompressing than the model predicts is necessary).

No ascent rate per dissolved gas models is 'unsafe' in and of itself. But when you are diving to limits computed using a specific ascent rate, that rate becomes important. One could just as easily construct a 120fpm table as a 60fpm table.

Regarding the PADI/DSAT model, it may 'work better' at 60fpm than 30fpm (higher offgasing gradient). In either case, you should be both theoretically and statistically okay if you abide by all the limits in the model (including ascent rate).