How long you can hold your breath has nothing to do with the depth of a CESA. Standard naval submarine escape training starts much deeper than you are talking about, and they are required to exhale fully before beginning the ascent. In experiments conducted by the British navy a half century ago, successful emergency ascents were made from hundreds of feet, again after exhaling. A quick Google search will show you videos of this.I am wondering where I argued self reliance is bad. I am pointing out equipment reliance is not making things better. If every scuba diver could free dive half of their certified depth, how would that effect their self reliance and confidence. It is only 15m for an AOWD, anyone can hold their breath for 30 seconds. I often get average depth of 15 meters when doing recreational diving even max was 30-40m. This means in average I am within the range of the surface..