Ok, we talk about OC diving. Max PO2 of 1.4 at bottomphase is the max in most agencies. 1.6 during deco. I always advice to lower the PO2 to 1.3 or maybe 1.2. Some divers want to use 1.0 or 1.1 at dives in full trimix range. You can do, but this means a longer deco, need more gas. Maybe it is not a lot, but consider it in your plan, look if all aspects fit.
END is a personal choice too. Some hold stricktly to 30m, others say 40 or 45m. Most agencies will say max END of 40m. For me personally I don't see any need to use a 30/30 at 30m, even not in currents. Somewhere between 40 and 50m I will add some helium to my mix. The 'deep air' courses go to 55m, and some divers will say I cannot deal with the narcoses, so it is too deep for them. I don't teach that courses as I am responsible as instructor, then will say take the normoxic trimix course. But I teach adv. nitrox to 42m.
More helium in your mix will give you longere decotimes too. There are some studies done that say there is no 'heliumpenalty', but use 'what works works'. So for me I accept that more helium will give me a longer decotime. More deco is not a problem as long as you have enough gas.
On CCR this means for me that I use on trimixdives 6/72 as diluent. This gas I have used up to 135m depth. A CCR gives you a constant PO2, so it works in a wide range. On OC it is not the best gas. If you believe in icd, more helium will make you maybe have to use helium in your first decogas too.
You can use on oc (even some on ccr) 'standardgases'. You don't have to do best mix calculations (which are not difficult), END always max 30m. The easy blend argument as it is helium+ean32 is most times ******** as trimix is made by partial blending mostly from what I see. But you can see it as advantage (poormansmix, heliair has the same advantage then). And you lower the ICD risks if they are there. But mostly you use a lot of helium. And helium is rare and expensive.
Here a nice example for people who believe in standardgases and DIR and say all other gases are wrong.
Go to 55m depth, use 18/45. PO2 ->OK, END=20.4-> OK. Plan with ratio deco. And you will have a nice dive.
Then you want to save some money, here it will be around 15 buck for a twin12. Take an 18/35, same depth:
PO2->OK, END=28->OK, still in the 30m range. Plan with ratio deco (you will be 1 or 2 minutes more conservative with this gas instead of 18/45 if you use a decoplanner, and ratio deco still can be used here), so still OK.
The only thing I will say with this example: be a thinking diver. 18/45 is not wrong, 18/35 is not wrong. And some other combinations of O2 and helium are not wrong either.
If you are afraid of high CNS load, take an ean80. This almost lowers the CNS half instead of pure oxygen. It seems that pure oxygen makes your more cold as the small capillairies will 'close', and EAN80 does not. If someone has proof for this, I am interested. This would mean that pure oxygen is maybe not as effective as some think (pure oxygen is theoretically the most efective decogas as the gradient are max). On dives to 100m, there is no difference in decotime if you use ean80 instead of 100% (1-2 minute differnce or so).
Think outside the box. If you only think in ean50 and 100% as decogases, you can be limited in bottomtime. Using for example 40% and 80% as decogas can mean you have 1 minute more bottomtime if you stay within reserves. And the bottomphase is the most worthly phase of the dive, that is the part of the fun. If you go for a 60m dive and you can do 21 minutes instead of 20 minutes, that can make a difference as such dives are not cheap.
Ok, my comments have mostly nothing to do with ICD, but I will say there are a lot of personal aspects to make a choice or make another choice. And all choices can be safe. Be a thinking diver, and are not afraid of thinking outside of the box. Dive safe.
