big PADI mistake

[Diver0001]

Se7en once bubbled...

I'm sorry Diver0001, but if you actually did this dive - 75 min at 18m on an AL 80 full of air, you are an idiot.

I'd want at least 15min at 5m after that time/depth. If you did it on Nitrox 40, then you are fine, with a slow ascent and safety stop.

To do that dive, assuming you sucked every psi out of your tank, you'd need a sac of <11 litres per minute. I doubt I will ever meet anyone with a sac of <11 for a whole dive, who would not have enough clues to not do the dive above. Actually, I doubt I will ever meet anyone who uses a SAC of 10 to plan a whole dive...

A normal diver would do more like 40 minutes at 18m, and know (especially if not tracking time), to be conservative with air, and to do a reasonable safety stop. An idiot would drop to 40m, and stay there until they ran out of air, and then bolt for the surface. You can't stop idiots, but you can suggest that some activities are safe enough for people who can still think for them selves.

Se7en

I stand corrected. Indeed the maximum depth was 18m on the dive in question. I used my computer and remained within the NDL's. I obviously didn't make that clear. My SAC on that dive was under 10 litres/min. It often is when I dive in the tropics.

In any case my point was that the person who said that you don't need a watch on an 18m dive is a little off base. Someone with decent air consumption will be able to bend themselves.

R..

 

[Se7en]

Diver0001 once bubbled...

In any case my point was that the person who said that you don't need a watch on an 18m dive is a little off base. Someone with decent air consumption will be able to bend themselves.
R..

My point when I said it was that anyone with half a clue would also be able to make sure they didn't bend themselves.

Even with your great air consumption, you didn't spend enough time at 18m to bend yourself.

Assuming an 80 cuft tank, and assuming you return to the boat with 15 cuft, you have 65 cuft of air to breath. Lets say you use 5 cuft on you descent and your slow ascent - leaving 60 cuft to breath at 18m. From memory, you have around 55 minutes on the PADI rdp before you hit NDRs. (although a safety stop is recommended if you approach the NDR)

therefore 60 cuft of air for 55 minutes - you have 1.1 cuft of air per minute. However, you are at 2.8 atm of pressure, so you actually only have 0.4 cuft per minute... which is your 10 litres / minute SAC.

So you are right. Someone who is relaxed enough underwater to have a 10 l/m SAC, holds exactly 18m for as long as their air lasts, and dumb enough not to do a decent safety stop, or to do multiple dives back to back, would be at the limit of PADI tables...

And as we all know, you get bent as soon as you exceed PADI tables.

So to any idiots out there with great SACS:
DO NOT DIVE WITHOUT A TIMING DEVICE!

I must either have a few clues or a lousy SAC, 'cause I've done a couple of hundred dives with no timing device. Sometimes I even manage to do it wearing twins. Lucky I guess.

Se7en
Note - I'm not American, so there is sarcasm in the above. Look it up.

 

[sheck33]

Se7en once bubbled...


And as we all know, you get bent as soon as you exceed PADI tables.

no you dont. If that is true i would have been bent a few hundred times by now.

 

[MikeFerrara]

Some people do

 

[sheck33]

MikeFerrara once bubbled...
Some people do

I should have been more accurate:

Exceeding the PADI tables does NOT GARANTEE you get bent, which is what he said.
BUT staying within table limits doesnt garantee you DONT get bent either

 

[Se7en]

Read for context...

Se7en once bubbled...

And as we all know, you get bent as soon as you exceed PADI tables.
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.
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Note - I'm not American, so there is sarcasm in the above. Look it up.

It was sarcasm! Of course I don't believe that you get bent as soon as you exceed a RDP NDL. Nor do I believe you are guaranteed safe within them. I was trying to suggest that applying some common sense was more important than using a watch to make sure you stick to the exact limits of the tables!

Personally I treat every dive as a deco dive. the last dive I did was 6m for an hour - I still spent 2-3 minutes on a slow ascent from 4m. I treat it just the same as the 20min at 40m profile I'm doing tomorrow - work out a deco schedule and stick to it. (Only real difference is that I'll take a watch on the deeper dive )

Se7en

 

[cold kiwi]

if there is a miss under standing on what to do its the instructors fault ....not the system....although i do think that some of the factors about safety should be more pressed ...and not worry about a open water diver sh.itting them selves and not wanting to be a diver for example air embolisms more on barotrauma and d.c.s

 

[coliseum]

Again... why are we using the table to do a Multi level dive in Miguel's example?