18 replies to this topic

[shadragon]

Not that I was holding my breath...but I was glad to use one of the Cochran computers from WW on my last dive trip. I kept thinking I was going REALLY slow up as I ascended, but tried to stay in the safe range all the way up. I've since learned that the ascent rate I knew from 12 years ago of 60 ft per minute has been changed to 30 ft per minute. My scuba review didn't bring that to my attention. When did this change?

60 or 30 those are maximums. Slower the ascent the better. The 3 minute safety stop is another one. You can do one 5 - 8 minutes or longer as long as you have air. Does not hurt anything.

[shadragon]

Similarly, the PADI tables say that you're clear of excess nitrogen 6 hours after any recreational diving no matter how intensive, whereas most computers still penalise you up to 24 hours and some go to 48 hours or even longer.

No. Sorry that is simply not correct. The PADI tables show that if you dive to 35' for up to 205 minutes then after a 3 - 6 hour SI you are back in pressure group A for subsequent dives. This means you add 3 - 10 minutes Residual Nitrogen Time to your expected bottom time of your next dive as based on the depth of your subsequent dive. This in effect decreases your bottom time for any subsequent dive. This is consistent with dive computers which do exactly the same thing. The advantage of DC's is they track actual nitrogen exposures based on your profile(s) over multiple dives. However, they use different numbers of compartments and even different algorithms in some cases. So it is apples and oranges. Not sure what you mean by 'penalize'. After a 6+ hour SI my computer does not restrict my dives by any noticeable amount.

It is possible the conservancy factor in the tables makes 6 hours the tipping point in the calculations, where N2 is so small it cannot be accounted for effectively. However, no where on the tables does it say you are clear of N2. Hence the 12 hour (single dive) and 18 hour (multiple dive) no fly warning on the back side of the tables.

[peterbj7]

Regardless of your pressure group, the surface interval table shows you "clear" after a period not exceeding 6 hours.

[ScubaTex]

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