I think some people here are misunderstanding the reasons for the decompression stops; they are to prevent nitrogen (for recreational diving) from coming out of solution and forming bubbles In the various tissues of the human body. The no-decompression limits mean that the diver, in a majority of situations (over 80%) can ascend to the surface without having those bubbles form. We in the 1970s started using the term, the “knife edge” of the no-decompression tables, to tell people that at that point, there was a higher probability of bubbles forming, as new research had shown that “micro bubbles” were forming when people came close to the no-decompression limits. They used a doppler instrument to actually listen to those micro bubbles go by. The micro bubbles were asymptomatic, but were there. So we cautioned against getting close to that “knife edge” of the no-decompression limits. Now the deeper you go, the more likely you were to get into a situation where you were close to the “knife edge” of the no-decompression limits.
If you want to get an idea sometime, get into a 50 meter pool, and start at the 10 meter area in the shallow end, dip under the water and swim to the other end as if you were descending on a dive. It will take you longer than you thing. I wrote earlier that at 130 feet (40 meters) you have 8 minutes of no-decompression diving. But that starts on the descent. So when you get to the other end, you probably have less than 5 minutes to tool around before you must ascend in order to stay within the 8 minute bottom time for no decompression. But is that really 8 minutes? I originally wrote “5 minutes,” as that was the next figure over and we always used that figure to stay away from that “knife edge” where 80+% of healthy, young male divers (Navy divers) won‘t get bent.
Now, I am still healthy, but not young by any means, so I won’t come close to the no-decompression limits on any of my diving. The “stops” of decompression diving are ways of stopping to off-gas excess nitrogen from the blood stream, in order not to produce those bubbles that accumulate in weird places to give the symptoms of “the bends,” or decompression sickness. When decompression stops are necessary, they form a barrier to the diver coming directly to the surface, and therefore fall into the “technical diving“ category in that special procedures and precautions are necessary to prevent that bubbling of nitrogen.
This has nothing at all to do with scuba police, or even the ”recommendations” of national training agencies (NAUI, PADI, etc.) or even the U.S. Navy. It has to do with an accumulation of studies, experiences, and deaths from decompression sickness over the last 100+ years. So pay attention, and stop this useless wrangling over terminology.
SeaRat
PS, one of the studies:
Cited by
Undersea Biomed Res
. 1976 Jun;3(2):121-30.
Gas phase separation during decompression in man: ultrasound monitoring
T S Neuman,
D A Hall,
P G Linaweaver Jr
Abstract
During two dive series, one to 132 fsw and one to 210 fsw, Doppler ultrasonic bubble detectors were used to monitor venous gas bubbles in divers during decompression and for 30 min thereafter. Various decompression schedules were used. Bubble scores were evaluated by independent listerners to tape recordings in a blind manner. A significant increase in bubble scores throughout the stages of decompression and postdecompression was demonstrated as well as a statistically significant relationship between bubble score and decompression sickness. A reduction in mean bubble score was found in divers who made an additional deep decompression stop that was unrelated to the extension of the decompression time. The implications of these findings are discussed.
