The reason this topic comes up again and again is that there is no "bright line" dividing no-decompression diving from decompression diving. There is just a gradual slope, where the likelihood of DCS from a direct ascent at the prescribed speed increases. Note that there are three variables involved in determining the safety of any given profile: Depth, time at depth, and ascent rate. The purpose of a safety stop is to slow the ascent rate, and it is placed shallow because the mathematics of the Haldanian/Buhlmann model suggest that decompression time, in the absence of a lower nitrogen decompression gas, is best spent shallow to push the gas gradient for elimination of nitrogen.
If you spend thirty minutes at thirty feet, your likelihood of DCS on ascent is vanishingly low. If you spent thirty minutes at 200 feet, your likelihood of DCS with a direct ascent is very high. For depths and times in between, the risk varies, but it is safe to say that as depth increases and time increases, the risk goes up as well. Thus the "required safety stop"; if it is truly required, it is a decompression stop, and you are doing staged decompression diving. This places the dive outside of normal recreational limits.
The fact is that the DCS risk for a controlled direct ascent is still going to be low, and most people would advise that you not return to the water to do an omitted safety stop. Omitting required decompression is another story.
The bottom line is that, if you are going to do dives that push the limits of the tables, you should have the skills to spend some stable time in the shallows as a safety precaution. If you don't have those skills, you're much better off staying much further away from the NDL limits.
If you spend thirty minutes at thirty feet, your likelihood of DCS on ascent is vanishingly low. If you spent thirty minutes at 200 feet, your likelihood of DCS with a direct ascent is very high. For depths and times in between, the risk varies, but it is safe to say that as depth increases and time increases, the risk goes up as well. Thus the "required safety stop"; if it is truly required, it is a decompression stop, and you are doing staged decompression diving. This places the dive outside of normal recreational limits.
The fact is that the DCS risk for a controlled direct ascent is still going to be low, and most people would advise that you not return to the water to do an omitted safety stop. Omitting required decompression is another story.
The bottom line is that, if you are going to do dives that push the limits of the tables, you should have the skills to spend some stable time in the shallows as a safety precaution. If you don't have those skills, you're much better off staying much further away from the NDL limits.
