Deco without deco training

[Web Monkey]

Just curious about peoples thoughts on doing dives that involved decompression, using a computer for guidance, without having the appropriate certification. By no means am I advocating or encouraging anyone to do this, so don't flame me. Just wanted to know if anyone did this either on purpose, or by accident (lost track of time staring at mermaids or whatever).

You should be fine following your computer, if your computer was designed to properly handle decompression dives and it doesn't fail and you can hold the required stops and have enough gas to do them.

Problems arise when things happen like:

• You have 40 minutes of deco and 5 minutes of gas remaning
• You have 40 minutes of deco and no gas
• You have 40 minutes of deco and decide that for some reason, you need to surface now

Deco training is nice, but the most valuable part of the class is learning how to plan your dive so that when there's a failure, you don't end up injured or dead.

Terry

 

[Blackwood]

I am not afraid to die, but I am absolutely terrified of being helpless. A CNS hit can leave you paralysed. That is why I stay within NDL's.

A few extra minutes underwater just can't possibly be worth the added risk.

Interesting. Think a few extra minutes on the bottom of what would otherwise be an NDL profile makes the difference between "ok" and "paralyzed?"

I suppose it may, but that's probably a coin flip.

 

[Sas]

Interesting. Think a few extra minutes on the bottom of what would otherwise be an NDL profile makes the difference between "ok" and "paralyzed?"

I suppose it may, but that's probably a coin flip.

Yea dives within the tables can leave you paralysed. Dives well outside the tables can do nothing at all. I know someone who had a problem on one of her deco stops not too long ago on a decompression dive to about 45-50m, did a rapid ascent and skipped over 20mins of mandatory deco. No worries, completely fine. A few years before this friend had been doing rec dives within the tables, and got bent. Deco theory really isn't very refined and doesn't have many absolutes...

 

[Diver Tim]

I got certified (PADI) July of '09, got tables with my book and spent quite a bit of time in class learning them. Personally, I wish they would have spent a little less time on tables and more on gas management.

 

[FritzCat66]

Looking forward to future computers that are not only air-integrated, but also blood-integrated. A strap-on venous ultrasound transducer continuously feeding back actual real-time blood microbubble data should really help the computer calculate remaining deco/non-deco times. :cool2:

 

[Amphiprion]

Or ideco for $0

I should have mentioned that. I have this app, but it requires either an iphone or an ipod touch. The cumulative amount is more expensive. Either way, these programs give a better comprehension of what a diver is in for doing planed deco.

The main issue is no matter what your computer tells you, it can't add gas into your tanks and you need to account for this. I always plan for total failure of my deco bottle as I almost had this happen once. If I can't do a square profile with back gas, then I don't do the dive.

 

[TSandM]

Having done some decompression training, this is my take:

It's not rocket science. You should have a much better understanding of what is known about the physiology of decompression than an OW diver, because you may be forced into situations where you have to make decisions on the fly that are not in your original plan. But it can be learned.

Buoyancy control can be learned, and mostly IS learned not from instruction, but from practice.

Anybody can buy V-planner and cut tables, and the program will give you the gas requirements, if you know your consumption rate.

Where training is really key is that, once you have entered into a decompression obligation, you can't surface to solve a problem. Therefore, you should know pretty well how to handle likely problems, and what your personal response is when things start to go thoroughly sideways. A good instructor serves you your head on a platter any number of times, until you really learn to think.

Can you learn, from the internet or books or whatever, how to execute an uneventful staged decompression dive? Sure you can. As long as it remains uneventful, it's no big deal. But when something inevitably does go wrong, I'm going to be glad I got the training.

 

[lamont]

Just curious about peoples thoughts on doing dives that involved decompression, using a computer for guidance, without having the appropriate certification. By no means am I advocating or encouraging anyone to do this, so don't flame me. Just wanted to know if anyone did this either on purpose, or by accident (lost track of time staring at mermaids or whatever).

You shouldn't do this by accident. That indicates a lack of situational awareness and that gets dangerous because you can get into a situation where you have a decompression obligation with insufficient gas to complete it.

Most technical divers were probably crossing the NDLs before they took technical training. But we're talking 40 mins @ 100 feet on 32% with maybe 5-10 minutes of mandatory backgas deco. That is still a long way from a 30 minute @ 150 foot dive on 21/35 with staged decompression using a 70 foot 50% bottle.

If you're asking if OW divers can just routinely blindly follow their computer into deco and be safe, then the answer to that is no. Even though the profiles that they dive may be less aggressive than the "pre-technical" diver above, the decompression will tend to be buhlmann-shaped and will run a higher risk of DCS. There's a difference between an OW diver with no idea what they're doing following their computer, and a diver with some exposure to the way of thinking about technical diving doing (somewhat mandatory) 1-2 minute stops from 1/2 their max depth up.

 

[MXGratefulDiver]

You shouldn't do this by accident. That indicates a lack of situational awareness and that gets dangerous because you can get into a situation where you have a decompression obligation with insufficient gas to complete it.

Most technical divers were probably crossing the NDLs before they took technical training. But we're talking 40 mins @ 100 feet on 32% with maybe 5-10 minutes of mandatory backgas deco. That is still a long way from a 30 minute @ 150 foot dive on 21/35 with staged decompression using a 70 foot 50% bottle.

If you're asking if OW divers can just routinely blindly follow their computer into deco and be safe, then the answer to that is no. Even though the profiles that they dive may be less aggressive than the "pre-technical" diver above, the decompression will tend to be buhlmann-shaped and will run a higher risk of DCS. There's a difference between an OW diver with no idea what they're doing following their computer, and a diver with some exposure to the way of thinking about technical diving doing (somewhat mandatory) 1-2 minute stops from 1/2 their max depth up.

What he's saying is that when a dive computer goes into deco it doesn't tell you that you should make any intermediate stops, or how fast to proceed on your ascent as you get closer to the surface. What most people read in the numbers amounts to something like "go to 10 feet and stay there for X minutes before surfacing".

That can get you bent if you follow the classic 30 feet per minute (or 60 feet per minute for some agencies) that you learned in your OW class. So you need to have a basic understanding of how an ascent affects your body once you've crammed it full of nitrogen, and "shape" your ascent accordingly.

You should begin your ascent at the recommended pace, make at least one (and preferably more than one) intermediate stop beginning at about half your deepest depth, and proceed to slow down as you go up. Deep divers tend to slow down to about 10 feet per minute, and make progressively longer intermediate stops as they get closer to the surface.

For the recreational diver, slowing your ascent progressively and making intermediate stops will cause your computer to "clear" ... meaning that you will no longer be showing a deco obligation ... by the time you reach your safety stop depth.

Also keep in mind that the distance from safety stop to the surface is the MOST IMPORTANT time to ascend slowly. Far too many recreational divers will religiously wait at safety-stop depth for the full three minutes ... and them surface WAY too fast. At 30 feet per minute, it should take you 30 seconds from the time you leave your safety stop till you surface. In practice, that seems glacially slow ... but especially if you've pushed yourself over your no-deco limits, it's the most important part of your ascent. Take it slow ... (tech divers often take up to five minutes to make that part of their ascent) ...

... Bob (Grateful Diver)

 

[waterpirate]

I agree with most everything that has been said, but would add this. Most people who stumble into a deco obligation are using computers that were never designed to handle a deco dive. In short they "punt" a solution and lock you out. Time and again I have witnessed the stumbler say " I do not know why my computer locked me out? I stayed at 10fsw for blank minutes like it said." Education is the key and gateway to safer diving, not simon says on my puter.
Eric