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Posted : February 16, 2007
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 PADI 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 you 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?
Based on their claim to be a 5 star PADI certified operator, I perhaps naively put myself in their hands and trusted that their knowledge was significantly greater than mine.
Your advice much appreciated.

Posted : February 17, 2007
Hi Simon, ok don’t ever do this again !!! Your training told you to use the RDP, it also should have covered the plan your dive then dive your plan. Don’t be mislead by more experienced divers into dives you shouldn’t be doing without further training and experience – even if they are an instructor – check with them even if that’s on the dive use good hand signals to say 18m is my floor, not going further… you get the drift and I’m not being square.

The dive you did – if you spent all 35mins at 29m (assuming direct decent to 29m) was a decompression dive and way beyond the RDP. You missed 20mins of decompression – that’s serious. I trust you didn’t get bad headaches, tingling, rashes, pain or felt very very tired after the dive.. if so contact Dr Jules Eden on the other forum and get yourself off to see a Diving Doctor ASAP. If you still have these symptoms go to A&E and tell them you missed 20mins deco on holiday and you then had a x hr flight…

What I think may have happened is you had a slow amble to 29m and you didn’t spend much time there (probably considerably less than 20mins) and then you went to successive shallower depths. Your instructors most likely didn’t put your health at risk, however this is a serious violation of PADI standards – Phone PADI 0117 300 7234 if you want to explore this further ask for the Training and Quality Management Dept.

The way you reconcile it on your RDP is you can’t. PADI have a stunning little course called the Multilevel Speciality (do your Advanced O/W course soon too). PADI have another dive planning tool called The Wheel and this allows you to plan and thence account for the PG after each stage or depth… with the right planning you can do 20 mins at 30m then go shallower and make a progressive move to the surface last three times this – SO LONG AS YOU DIVE THAT PLAN.

Don’t get into the habit as many have and do do and that is to forget the RDP and rely on your dive computer. I would guess the other divers were doing this for the second dive – or hopefully using the Wheel. Contact me via my own website and I’ll put you in touch with a good school near you to help with further training and get you diving with responsible divers.

I trust this is of help to you.
Answer provided by ADM Diving

Andrew Dawson-Maddocks
Additional Comment

Posted : February 17, 2007 by - Waggers
Thanks for your quick response - happily, I suffered no adverse effects at all. I do appreciate that my safety is my responsibility and will certainly learn from this experience.
The dive involved descent and ascent on the same fixed line to the sea bed / reef. We explored the reef for approx 30 mins before beginning our ascent. There was certainly no progress to shallower waters during the dive.
The more I think about the dive, the more it concerns me. I had visited the dive centre some 48 hrs earlier to book a dive. I told the manager when my flight was and reiterated that my OW qualification only permitted me to go to 18m. He told me that with an instructor, I could go deeper and that the site he had in mind was 29m. A discussion took place about the interval before my flight (18 hrs) and notes were made in their dive diary to the effect that a shallow dive would be appropriate. On the day, the instructor assured me that this depth (29m) was fine for me - in fact he even suggested that it would be safe to go to twice that depth! I also mentioned to him that on previous dives, I had got through my air rather fast. His solution : if that happened, so as not to reduce the dive time of the others in the party, I could share his air on the ascent if I ran out. He had left a spare tank on a line at 5m, but that seemed scant consolation.
Due more to luck than judgement, I was OK, but in a place like Tahiti, where divers have long flights to & from the island, it strikes me that adherance to the rules should be scrupulously observed. Others may not be so lucky.
Thanks again for your advice - I'll certainly let PADI know, because I fear that I'm not the only one daft enough to take the work of an 'expert'.
Additional Comment

Posted : February 17, 2007 by - ADM Diving
Hi Simon,

Well this isn't an expert issue.. The instructor looks like he took a commercial decision based on doing something interesting for the rest and something he felt he could look after you... not very wise nor a good move. Don't tar a lot of good instructors out there with this guys brush.

You possibly missed 10 mins deco look at this, which means he ran this dive on computer and waited until the computer said the NDL was nearly met and you then all asended. However a computer is personal and you can't share them, it is saying he was nearly into decrompression, however because of your actual profile and that of others it may have meant you were in deco. This is not a shining example that's for sure.

18hrs is very close, if you missed that amount of deco for real, then at the doors of the plane you had 5 theoretical tissue compartments (Bhulmann Tables use 16 compartments which are a deco set of tables, PADI tables uses 14), then during the flight these 5 tissue compartments would have put you back into deco or supersaturation...

In all likelyhood this was a close encounter for you.

A reminder PADI and the majority of tables define bottom time as the dive time from submerging to the point at which you directly ascend to the safety stop or surface, so in your case the RDP highlighted you as 10mins off the table (not to be confused with the time you missed in deco), not the original 35mins.

Some instructors teach you to work the PG out for the total dive time - that's inbuilding an extra safety margin for you. Bottom time is as I've put it for you in this reply - refer back to your manual you got with your O/W training.

I'm sorry you had this experience, don't let the instructor give you an experience like this, he was viiolating standards to do what he did and I'm glad you didn't get hurt by it. As i said contact me by my own website and i'll point you in the right direction for a good nearby school. When you phone PADI lead them to this Q&A and fill them in with more details as commercial judgements should not result in what happened.

As a good rule in the future for long haul flights do ensure you keep well hydrated with water after a few days diving and make the interval before flying more like 24hrs. If you are diving all week twice a day have a mid week break too.. I usually only do the mornign dive midweek, have the afternoon off, and the following morning and then resume that afternoon. This is very good pratice - take a look at go and read the safety tips page in full.

cheers Andrew.
Additional Comment

Posted : February 17, 2007 by - Waggers
Andrew -
I really appreciate the time you've taken to clarify things - it's a valuable lesson for the future.
All the best

Additional Comment

Posted : February 17, 2007 by - ADM Diving
Hi Simon,

No problem at all. Happy to help and its key to do things like this - Just ask as you have. It's a great sport and one which if done right can be very safe. I'm more than happy to help. Have fun progressing your diving. Take a peek at The Wheel some time and keep up with the diving, skills practice and further training like AOW and ML speciality.

Hey even after 3000+ dives I still use tables and table making tools and then dive to those plans. I'm sure those who I dive with will tell you how serious I am at this. All my past students, divemasters and instructor candidates will for sure!

The dive computer being a powerful guidance tool - & that's wise way to look at them as such. Some computers don't implement all of the Bhulmann or similar algorithms, some use a lot less 'tissue compartments or calculate less points'.

When you buy a dive computer go for a very good model - one that might be a stretch to acquire, but it's well worth it. However don't go for a model with loads of features your won't use or ever need. Make sure it has a good research base and very reliable pedigree. AND STILL USE TABLES/The WHEEL to plan your dive and then dive your plan.

Have fun and let me know if I can help in any other way. Safe diving. Andrew
The views expressed by the author are their own and the publishers accept no liability for the advice and views expressed by the author, or other users, which are provided as a general service to divers. Users are warned that secondary posts are the views of other users and may not be technically correct.
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