Question about the PADI Dive Table

[911_abuser]

Speaking in hypotheticals, if dive X has a limit of Y do i have to be on the surface by Y or do I only need to start my ascent at Y? Also does Y include time needed for a safety stop.

 

[Walter]

Bottom time is from the time you begin your descent until you begin an uninterrupted ascent (safety stops are not considered an interruption of your ascent). Ascent time and safety stops are not part of your bottom time.

 

[glbirch]

bottom time - variable definition; in square wave diving, the time between descending below the surface to the beginning of ascent. In multi-level diving, the time between descending below the surface and beginning the safety stop. (Other definitions may apply depending on the specific type of diving.)

There also seems to be some variance between different agencies, but this appears to be the more common opinion.

 

[scubatoys]

Keep in mind the history of this... In the "good ole days" bottom time started at descent, and ended when your head hit the top... Then guys would look at their tables and watches and say "Gee... Were at 100 feet, and we have to be back at the surface in 1 minute... Let's hurry up!

Turns out that ascent rate is a more critical factor in DCS than time at depth. More people get bent within table limits that outside table limits. So don't hurry the ascent... you can make a nice slow ascent with multiple safety stops - and it is doing more help than harm. A popular safety stop system now is go to half your depth, stop 2-3 minutes then again and again until you get to your 10-15 ft stop... ie

Diving 100 feet... slow ascent to 50 ft, stop there 2 minutes, slow ascent to 25 ft, stop there for 2 minutes, slow ascent to 12 (10-15ft) stay for 3-5 minutes and slow ascent to the surface. This procedure would add 10 minutes to your dive if you included it in bottom time - But this type of procedure will make you much safer that hurrying to the surface to make sure your bottom time wasn't too long...

 

[Dr Deco]

Hello Scuba Board Readers:

Ascent

Scubatoys has some sage advice here when he speaks about the slow ascent. This will prevent the Boyle’s law expansion of tissue micronuclei and is more import than an ascent that hopes to prevent further on-gassing.

When it comes to nuclei, there are two very import “rules of the road” that put the control of DCS firmly in the hands of the diver.

• The first is the slow ascent that was mentioned. This is equivalent to the slow release of pressure from a carbonated beverage when the cap is slowly untightened. No, you are not releasing the dissolved gas slowly (what is normally meant by “decompression”), rather you are preventing the Boyle’s law expansion of nuclei on the bottle wall. It is very clear in this case!
• The second is the prevention of the formation of tissue nuclei by not straining when entering the boat and during the surface interval.

This puts the “ball in the diver’s court” so to speak.

Meters

I get the definite feeling from this Forum that most divers wish to put their trust in the meters. They will go and purchase the latest in a decompression gizmo even though most divers get the “bends” while within the tables. That will not really be prevented by a decompression meter (when doing normal, recreational diving profiles). :nonono:

Nucleation from physical activity is a very real phenomenon that is easily observed in the laboratory. It gives us big headaches here at NASA in our EVA program.


Dr Deco :doctor:

 

[hockeyplay]

Scubatoys wrote "This procedure would add 10 minutes to your dive if you included it in bottom time - But this type of procedure will make you much safer that hurrying to the surface to make sure your bottom time wasn't too long..."

So I guess my question is: Should I count it in my bottom time or no? I assume no because these are 1) safety stops and 2) at shallower depth than the table column I'd be using when charting my pressure group.

Of course, I'd rather not find out in the field that I was wrong....

 

[Uncle Pug]

Be sure to take along enough gas to do the slow ascent with stops.

 

[chrpai]

Speaking in hypotheticals, if dive X has a limit of Y do i have to be on the surface by Y or do I only need to start my ascent at Y? Also does Y include time needed for a safety stop.

Y is your NDL limit (max bottom time) for a diven max depth. You start counting the moment you start your descent and you must start your ascent at no more then 60fpm by the time reach Y. Also if you come within 3 pressure groups of Y your safety stop becomes mandatory.

Others may disagree with this and offer information on deep stops, slow ascent rates ectera, but this is officially how you use the PADI RDP.

 

[Spectre]

Bottom time is from the time you begin your descent until you begin an uninterrupted ascent (safety stops are not considered an interruption of your ascent). Ascent time and safety stops are not part of your bottom time.

Provided that the ascent rate is within reason. Obviously if you ascent at a rate of, say, 1 ft per minute from 90 feet.... that's going to effect your bottom time. e.g. if you start ascending from 90 feet at 23 minutes, at 1 ft/min you'll be at 80 at 33; where the NDL for 80 w/ padi tables is, I believe, 30 minutes.

That's not a hard and fast rule, it's just an example to show that steady ascent assumes a reasonable rate.

 

[miguel sanz]

I think it´s important for new divers that when someone talks about deep stops or veryslow ascent rates, it has to be carefully performed so you don´t start ONGASING WHILE ASCENDING