Where is this spelled out? I am only aware of a 1.5 ppO2 limit with no fO2 limit for deco mixes. My IANTD Standards document is from Aug 2007. Perhaps there is something newer?
Yeah, I tore apart my IANTD manuals last night looking for that because it didn't sound right to me either after I posted it, and I checked the IANTD website, and I couldn't find it spelled out in the Tek Lite manual or anywhere else. Since then, I have reconfirmed with my instructor that it is ppO2 of 1.5 at your deepest deco depth. Apparently I am told that it used to be 50% max O2 and then it was changed at some point. However, there is still the fo2 limit of 1.5; so I think it works out to about 93% or thereabouts to stay within the 1.5 fractional limit at 20fsw. It basically just means you can't deco with 100% O2 because your first stop is always going to be at least 20'. And so if you are going to do deco, unless you are using your back gas and it is Nitrox (I am assuming it is a suitable MOD) for your deco gas, then you will need to carry something less than 100% in your deco bottle to be at 1.5 or less at 20 fsw if you wish to switch at some point (and because you would like to take advantage of accelerated deco >50% ppO2). If you stay too long and you need to stop deeper than 20fsw, you'll be doing your first stop(s) on back gas too unless your MOD on the deco gas will let you start at a deeper depth, like 30 or 40 feet. So, while the max is not 50% O2, it is not 100% O2 either since you cannot exceed 1.5 ppO2 at your deepest deco stop.
I also had my instructor look up the extended range certs for all three, and they are:
IANTD extended range can take your cert to 180' (54m).
PSAI extended range can take your cert to 180' (55m).
TDI extended range can take your cert to 180' (55m).
These are the most recent standards. I have discovered it can be difficult to ascertain the most current information without an active instructor who has the latest info.
I don't have any TDI certs, but I am looking forward to continuing with PSAI for cave training and this summer for trimix.
Hope this clarifies the earlier post. Thanks for pointing that out.