There is nothing to fear about accidentally going into deco as long as you know what to do when it happens.
Simon is the best-selling author of Scuba Confidential – An Insider’s Guide to Becoming a Better Diver and Scuba Professional – Insights into Scuba Diver Training & Operations. Both books are available from Oceanic Ventures. Simon has also just published a new book for divers-to-be and absolute beginners called Scuba Fundamental – Start Diving the Right Way.
There is a very good reason why instructors tell their students not to go into deco and why dive computer manuals repeat the warning time after time.
Chances are that the cylinder on your back is usually your only air source when you dive. If you run very low on air or if you suffer a rapid loss of air supply, perhaps because of a regulator free flow or a split hose, then the best option you have is to make a slow controlled ascent directly to the surface.
Yes, an alternative option is to share air with an alert, calm and capable diver around who is carrying more air than they need and is both equipped and willing to share it. But you can’t depend that someone like that will be nearby when you need them.
If you stay calm and you are not in deco, that is to say, if your computer is not showing required decompression stops, you will make it safely to the surface. You will probably not be able to make a safety stop on the way up but that is not going to be health threatening. After all, a safety stop on a no-decompression-stops dive is a luxury rather than a necessity.
On the other hand, if you do have required decompression stops, then going straight to the surface and missing those stops is definitely a health risk! That is the main reason why divers are told, “don’t go into deco!”
But Divers Do It All The Time
You may not be surprised to hear that divers accidentally go into deco every day. This is because they are only human, they have fun diving and they tend to get distracted. If it has not yet happened to you, it certainly will, so it is useful to know what to do when it does!
Because they have heard the warning so often, divers tend to panic when they find themselves accidentally in deco. There is no need for anxiety. Going into deco will not hurt you. Going to the surface when you are in deco, however, may well hurt you.
Know how your computer works and what it looks like when you go into deco. Do not be the diver who gets back into the boat moaning about a “broken” computer that is actually functioning perfectly. It is just telling the diver that they should still be underwater waiting until their deco stops clear.
The first thing you notice when you go into deco is that your computer screen suddenly looks different. A new depth reading appears, usually 10ft or 20ft, and a new time display. The depth is your new ceiling; you must not go shallower than this. The time is either your decompression stop time at the ceiling or an indicator of the minimum time it will now take you to reach the surface taking into account both your ascent time and the decompression stop time.
Every brand of computer is different. There is no industry standard. You must know how yours works. I know the manual looks boring but take the time to study it. Trust me, if you see your computer’s deco screen for the first time deep down at 100ft with your brain befuddled by narcosis, you will have no idea what it is saying to you.
Run The Clock Down
So what do you do next? First, look at your pressure gauge. If you still have plenty of air left, relax; you have nothing to be concerned about. Start ascending gradually, keeping an eye on your computer until the deco/ascent time figure stops growing. When the figure starts to drop, continue your dive at that depth but do not go deeper again. Eventually, the deco will clear and you will see your usual no decompression screen display again with plenty of minutes remaining.
Finally, end the dive a little earlier than originally planned to make sure you have plenty of air left to do an extended safety stop of eight or ten minutes before you surface.
Remember
1. Going into deco is nothing to panic about.
2. Know what your computer screen will look like when it happens.
3. Do a long safety stop at the end of every dive where you accidentally go into deco.
The issue is what to do when you are in deco and your tank is almost empty. For instance, if your computer tell you to make two stops with a total time of 10 minutes and you only have air for 6 or 7 minutes, is it better go directly to 15 feet and breath all the air? Or make the deeper stop and then do incompletely the shallow one?