What's the best way to deal with accidental deco?

There is a good reason why instructors tell their students not to go into deco and why dive computer manuals warn you about it in bold CAPS.

Like most sport divers, you probably only carry one air source when you dive, the cylinder on your back. If you run out of air or suffer a rapid loss of air supply, for example because of a regulator free flow, a blown o-ring or a split hose, then, unless you have an alert, calm and capable diver nearby who has enough air and is both equipped and willing to share it with you, the only survival option you have is to make a slow controlled ascent directly to the surface.

And, if you have not exceeded your no-decompression limits, you should be able to make it. You will not be able to make a safety stop on the way up but that is not going to be life threatening. After all, a safety stop on a no-decompression dive is a luxury rather than a necessity.

On the other hand, if you have gone into deco and your computer is showing required decompression stops, then going straight to the surface and missing those stops is definitely a health risk.

That is why you are told not to go into deco.
However, divers accidentally go into deco every day. This is because they are only human, they are having fun 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 happen.

Rule number one is - Don’t Panic.

The first thing an unaware diver usually does when they glance at their computer and see that they have accidentally gone into deco is get very anxious and head quickly for the surface. This, of course, is the worst thing you can do. A fast uncontrolled ascent can easily get you hurt.

Run The Clock Down

So what do you do? First, look at your pressure gauge. If you still have plenty of air left, relax you have nothing to be worried about. Move gradually to a shallower depth, keeping an eye on your computer. When the deco/ascent minutes required number stops increasing and starts to drop, continue your dive at that shallower depth but do not go deeper again.
Eventually, the deco will clear and you will see your usual computer dive 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.

Ignorance

Arguably, ignorance is even worse than panic. It is common to hear divers on a boat complain after a dive that their computer is broken. On examination, it turns out that their computer is working perfectly. It is just flashing a warning about missed decompression stops. On the dive they just completed, they obviously went into deco without noticing and then ascended without understanding what their computer was showing them and ignoring their required deco stops.
So, as well as remembering to stay calm and move slowly to a shallower depth when you accidentally go into deco, you also have to know how your computer works.
When you go into deco, your computer screen changes. A new depth appears, usually 3m (10ft) or 6m (20ft), and there is a new time display. The new depth is your decompression ceiling you must not go above this depth until the reading disappears or changes to a shallower depth.
The time displayed is either your decompression stop time or an indicator of the minimum time it will now take you to reach the surface taking into account both ascent time and stop time.

Every make of computer is different (as you can see in the two images below). There is no industry standard. You must know how to interpret your deco screen. Study your computer manual, look at the relevant images or graphics and memorise them.

This is time well spent. Trust me, if you see your computer’s deco screen for the first time when you are at depth with your brain befuddled by narcosis, you will have no idea what it is saying, nor will you be able to work it out quickly.

Remember

1. Accidentally going into deco is nothing to panic about.

2. Make sure you know what your computer screen will look like when it happens.

3. At the end of any dive when you have accidentally gone into deco, make a long safety stop before surfacing.