The fact that some of us could do a nice safe ascent with 400 psi is irrelevant. The diver in question was an air hog. If he was down to 400 psi that quickly I really doubt that his ascent would suddenly show a slower air consumption. I had an instabuddy a few weeks ago. He seemed ok in the water but had warned me he was an air hog. He was right. He was down to 1000 psi within 15 minutes at 55 ft. I seriously doubt that he could make it up from depth and do a safety stop on 400 psi. Especially since getting low would make him breath even faster.