Blackcrusader
Contributor
Hello. I am not deco trained. I might be one day but that’s currently not the case. My OP was about Nitrox but not as opposed to air for safety. However, your posts tend to make me think that diving without planning for deco is not safe.
What you could say Dody is that doing dives without planning are not safe. Let's take the vacation diver. They do not plan their gas or most likely even know what their air consumption is. They do not understand about SAC rates. I've met many they are decent divers but do not have the knowledge as the dive plan is simple, follow the guide do not exceed a certain depth and and are told not to exceed NDL in fact most DM's will tell people to ascend when they get to 5 minutes to NDL.
Now do I plan my gas usage for a max depth 30m dive when diving on air or nitrox and not exceeding NDL. No I don't. Most of these dives the vacation divers are not capable of staying at 30m for long on air as NDL is not far away and also they need to ascend to shallower depths to make sure they have enough air for an hours dive. They normally follow the guide. If I am buddied up with an instabuddy then I monitor their air and bring them shallower to get them to have a longer dive for say an hour.
So lets take a sac rate of 25l/min which BSAC recommends for a new diver planning a dive. A vacation diver will have less than 50 bar after 20 minutes staying at 30m on an AL80. So they would not be able to stay deep enough even on air to get to NDL. Your sac rate was 20l/min before and is better now but it changes with your dives as some are less comfortable than others. So the vacation diver who stays deep sometimes gets a very short dive 25 minutes. If shallower say 40 minutes.
Deco diving is not dangerous, what is dangerous is people who are not trained thinking it's OK to exceed NDL and not understand the required air to do the deco stop and safely complete the dive. Also my dive computer is setup to give me longer times to NDL than the default on most computers. A lot of divers are on the default settings and that's a good thing as well. So I have to be careful also not to let my dive instabuddy exceed NDL on their dive computers as sometimes they just tag along not looking at the NDL properly.
I know you are planning your dives on your sac rate but that too is a risk when you sac rate varies a lot. Some of us the sac rate does not vary so much. That's just experience and skills. You are doing fine for someone with 50 or 60 dives since November. A lot of new divers would never have asked the questions or tried to understand things the way you have.
No internet back when I was taught so did not have the ability to just get information as you can today. For your original question, using nitrox is better for multiple back to back dives even if you set your computer to 21% as normal and do not exceed 34m depth. Better if you say stuck to max at 30m if on nitrox 32%. If you use nitrox 32% on your computer you will have longer times to NDL. So then as you are gas planning for yourself and your wife you can decide do you want to do a dive at 25m for a longer time to NDL then ascend to shallower depths or even end the dive.