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Waggers
posted : February 16, 2007 Post subject: Can anyone explain...
Hi - I'm after some advice, if anyone can help. I'm a fairly recently qualified Open Water diver and have just come back from Tahiti. While there, I went on a dive with a certified instructor and a couple of fairly experienced divers.
We went down to a depth of 29m for 35 mins and stopped for 3 mins at 5m on the ascent.
Can anyone please explain how I square this with the maximum that my RDP shows for a 30m dive, which is 20 mins? Also, the other divers in the party were intending to do a second dive later that morning. How would they have calculated their pressure group after dive 1, when the RDP doesn't go beyond 20 mins?
Am I going bonkers?!
Thanks for any advice
Simon

 
Chris.S.
posted : February 16, 2007 Post subject: Can anyone explain...
Ahh yes! The good old 'international heros of the deep' tables. Beware-these tables can lead to an untimely death!
As a commercial saturation diver and offshore air diving supervisor, I can only really comment on the tables that I use. The least conservative of these being the U.S.Navy tables. This dive would have put you on a '100/40' table, giving you a 10ft stop for 15 mins. That would be running very close to the mark, so for safety we would add something like '4+4', i.e. 4mins onto the bottom time and 4 foot onto the depth, putting you on a '110/40' table requiring a 2 min 20ft stop followed by a 21 min 10ft stop!! The PADI table (I am fairly unfamiliar with-we don't use it) for 100/40 i believe would also require a 15 min stop at 10ft, thus putting you in group 'k', making it fairly pointless to do a repet to a similar depth. Out of interest, Generally speaking, the offshore industry does not repet, certainly not after a dive requiring decompression.
Anyway, my point being that this is bad! In recreational diving, you are very much responsible for your own safety. It is definitely worth working these things out before the dive and adding in your own safety factors. Don't just follow the 'heros of the deep', 'cause most of them are dead!

 
Dan
posted : February 16, 2007 Post subject: Can anyone explain...
Hi Simon, we have an expert on the site that can answer all these questions for you. Just go to the Technical diving section and visit the Q & A's section with Andrew Dawsion Maddocks. He will tell you what you need to know.

Dan

 
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