Dive plan

[Shiran]

Hello everybody!

I was discussing about a certain dive plan in another SCUBA diving board.
The dive would be to the depth of 40m with NITROX 32%. As you can tell, that would make the PO2 exactly 1.6.
The dive conditions at the area are very good and no special physical effort will be required.
By looking at the NOAA NITROX I table and my ANDI Complete SafeAir User guide the dive plan seems fine.
So far so good, however, in the other SCUBA diving board I was confronted by other members who refered to my plan as suicidal and ensisted that I should go through a Technical Diving course before performing such dive.
I would like to know your opinion on that matter.

Thanks in advance,
Shiran.

 

[O-ring]

At least use EANx28 to get the ppo2 down to a reasonable level...

 

[Scubaroo]

1.4 is considered a safer PPO2 limit. A PPO2 of 1.6 is typically used during decompression, where there is no real physical activity. By planning to dive with a PPO2 of 1.6, you allow yourself no margin of error if you should encounter a deeper depth. What if your mixture is really 32.8%? Suddenly you're diving at 1.64 PPO2. "Look ma, I'm dancing!" "No son, those are oxygen convulsions. Try and shoot a lift bag before you drown so we can salvage your gear!"

Do you have training or experience of diving to that depth? 40m is a deep dive for recreational divers. Do you have redundant air sources? Are you diving with a buddy who has the training or experience?

 

[MechDiver]

Shiran once bubbled...
Hello everybody!

I was discussing about a certain dive plan in another SCUBA diving board.
The dive would be to the depth of 40m with NITROX 32%. As you can tell, that would make the PO2 exactly 1.6.
The dive conditions at the area are very good and no special physical effort will be required.
By looking at the NOAA NITROX I table and my ANDI Complete SafeAir User guide the dive plan seems fine.
So far so good, however, in the other SCUBA diving board I was confronted by other members who refered to my plan as suicidal and ensisted that I should go through a Technical Diving course before performing such dive.
I would like to know your opinion on that matter.

Thanks in advance,
Shiran.

I wouldn't say it is suicidal by any means, but not the best planned either. You give no idication of how long your dive would be, what type of equipment you are using, or what the purpose of the dive is. I have done deco dives to 130 ft on 30% EAN and have no problem doing that. That said, I will only go to 1.6 during deco as a matter of course, and that during a planned dive.

I see no reason to push to 1.6 for a rec dive when alternatives are available.

 

[O-ring]

...only yours was better worded. Blow some more air in those tanks to knock down the ppo2 and then read the Aussie's post...mate

 

[Shiran]

Yea, I will probably use a lower oxygen rate in my mixture. I only asked about 32% because it's the maximum within the NOAA table limits.
The dive would be a recreational dive to a certain site.
I have the training and experience in dives to 30m, but I didn't get to 40m yet.
I will be diving with my usual diving partner who has the exact amount of experience that I have.
The equipment is a regular SCUBA diving gear.

 

[Scubaroo]

How are you handling gas planning?

I guess if you're talking about "regular SCUBA diving gear" and not being more specific, you'll be diving with the common 80cf aluminum (or do the Israelis use aluminium?) tanks. Which are usually 77.4cf, not 80cf. Have you calculated your SAC and used that to plan your bottom times and ascent times?

Assume your buddy has a problem at 40m, and you need to abort the dive, while sharing air. A safe (metric) rate of ascent is 10m per minute, plus a 3 minute safety stop at 5m (this is a recreational dive, so this is the minimum safety stop you would do). Assume that you and your buddy are both mildy perplexed by the situation, and have a SAC of 1cfm (slightly confusing, I'm mixing cubic feet and metres, but stay with me on this one). You have a single tank (your buddy's is empty because his regulator freeflowed), so the effective SAC against your tank is now 2. So for both of you to get from 40m to 5m, at 10m a minute, you're going to consume *roughly* 26cf of air, plus another 9cf at the safety stop. That's 35cf of air to safely abort the dive if there is a problem at depth. If you've got a standard 3000psi / (207bar?) tank, your turning pressure will have to be around 93 bar, just to (barely) make it to the surface. And that's with a conservative SAC of 1cfm - which could quite easily jump to 2 or 3 if you're stressed. If you both have a SAC of 2, your turning pressure (the point at which you must being your ascent to the surface) will be 185bar! You won't even have reached the bottom before having to turn back, in order to have sufficient air remaining for a safe ascent in the event of a problem.

There's a world of difference between diving from 30m to 40m.

 

[MikeFerrara]

Never push your ppo2. I keep it below 1.4 and would rather have it about 1.2.
Is 40m too deep for recreational equipment? I think so.

When I do 40m I have a seperate deco gas and redundancy in my bottom gas. I plan on some decompression time and have plenty of gas. When I go to 40m I have plenty of time and can relax and enjoy the dive. Time pressure is among the worst kinds of presure.

 

[Arduous]

I agree with O-ring & MechDiver.

You mentioned should you take additional training, such as a technical coure. No amount of training can teach you how to cope with a CNS hit. Unless that training is teaching you to keep your ppo2’s below 1.6, avoiding CNS hit all together.
( We would hope )

…………………………..Arduous

 

[Rick Murchison]

I know of no documented CNS hits at an exposure of 1.6 or below within NOAA's single exposure limits where 1.6 has not been previously exceeded. I know of no documented CNS hits at an exposure of 1.4 or below within NOAA's single exposure limits regardless of previous exposure.
If any of you know of a verifiable CNS hit within those exposure limits please cite it.
Thanks,
Rick