When ever this topic is discussed there is always a conflict of what narcosis is. Whether it is just plain stupered or and issue of coordination or retention of short term memory. Most timnes i hear the depth range is below 100 ft and has been as little as 50-60 ft, though rare. I have seen pics by divers in the 100 ft area that dont recall taking the pic why they took it. "WOW look at that fish" "I dont remember that or even taking the picture" I want to say its a region of 80-100 to as shallow as 60 from most literature including SSI that i have read.