Have you ever heard someone complain or discuss major narcosis at 20ft no matter what the breathing gas?I guess my real question is, if oxygen is narcotic, why is there no discussion about it when talking about accelerated deco? Or is it not a significant factor when shallow? And if it isn't a significant factor when shallow, why should it be an issue at depth?
Narcosis doesn't factor into even the most conservative dive planning at 0-90ft(ish) depth. Very few divers are doing deco deeper than that so until you start doing 250-300ft dives and starting your deco below 100ft its not an issue.