OK, this post is going to start with a far-flung analogy, but please stick with it.
I recently worked with some AOW students who had been taught by others in our shop, and I was asked to have a DMC join us so he could do some of his DM skills as well. He led the dive, starting with the 5 point descent. Under his direction and as the students had been taught in class, as one of the parts of the descent process, they all pointed to their wrists. When I debriefed him, I asked why. It's one of the 5 points he said --you are noting the time. I pointed out that since none of them were wearing watches, none of them were noting the time. I asked the purpose of noting the time. He had to think for a minute, and he realized it was so you could time the dive when using tables. I pointed out that they weren't using tables; they were using computers. He was baffled--he had no idea what to do in that situation.They were thus using incompatible processes--a descent procedure designed for watches and tables while instead using computers.
I think we are dealing with something analogous here--an uncomfortable blend of old procedures and new technology.
When recreational diving first came into existence, almost everyone used the US Navy air tables. They included deco stops for those who went deep enough and long enough to require them. Those tables were not very good for recreational divers, though, because the surface intervals were based on the 120 minute compartment, which led to very, very long surface intervals that made two tank diving a challenge. It didn't matter to the Navy, because their divers usually only did one dive a day, but it was a problem for divers like you and me. Because of that, PADI did extensive research on the kind of diving being done by typical recreational divers so that they could create a system that would enable recreational divers to enjoy multiple dive days. The result was the PADI Recreational Dive Planner, which shortened the first dive NDLs, used the 60 minute compartment for surface intervals, and made more pressure groups to decrease rounding. This new process completely changed the way recreational diving was done, and even if you did not use the PADI tables, you were doing something very similar. That became the norm upon which probably 90% of the today's divers were trained.
In order to make that work, though, they had to take decompression out of the tables. Most modern dive tables do not have any information for decompression stops in them, and the assumption is that you simply won't go into deco. If you do go into deco while using most dive tables, you have literally gone "off the charts," and the table does not know how to deal with your situation. The consequences for going off the charts are draconian. If you exceed the NDL by one minute while using the PADI tables, you must do an 8 minute stop and stay out of the water for 6 hours. Exceed it by 6 minutes and you must do a 15 minute stop and stay out of the water for 24 hours. This leads to the strong warning that you MUST NOT exceed your NDL! It leads to the situation where I once had a dive buddy suddenly bolt to the surface in absolute terror because his computer indicated he was getting close to his NDL. He was sure he was having a near death experience.
This is another case of people using table procedures for computer dives. If you exceed your NDL by one minute with any modern recreational dive computer, it will clear deco during a standard safety stop, and you will be back in the water after a normal surface interval. If you exceed the NDL by one minute with a tech computer like a Shearwater, it will require a one minute stop only. If you are taking the computer version of the PADI OW course, you are taught that if you exceed the NDL with your computer, you should follow the computer's directions for appropriate decompression. That sounds a lot like what people are advocating here. Eventually something like that will become the norm and we will not be having threads like this one.
I recently worked with some AOW students who had been taught by others in our shop, and I was asked to have a DMC join us so he could do some of his DM skills as well. He led the dive, starting with the 5 point descent. Under his direction and as the students had been taught in class, as one of the parts of the descent process, they all pointed to their wrists. When I debriefed him, I asked why. It's one of the 5 points he said --you are noting the time. I pointed out that since none of them were wearing watches, none of them were noting the time. I asked the purpose of noting the time. He had to think for a minute, and he realized it was so you could time the dive when using tables. I pointed out that they weren't using tables; they were using computers. He was baffled--he had no idea what to do in that situation.They were thus using incompatible processes--a descent procedure designed for watches and tables while instead using computers.
I think we are dealing with something analogous here--an uncomfortable blend of old procedures and new technology.
When recreational diving first came into existence, almost everyone used the US Navy air tables. They included deco stops for those who went deep enough and long enough to require them. Those tables were not very good for recreational divers, though, because the surface intervals were based on the 120 minute compartment, which led to very, very long surface intervals that made two tank diving a challenge. It didn't matter to the Navy, because their divers usually only did one dive a day, but it was a problem for divers like you and me. Because of that, PADI did extensive research on the kind of diving being done by typical recreational divers so that they could create a system that would enable recreational divers to enjoy multiple dive days. The result was the PADI Recreational Dive Planner, which shortened the first dive NDLs, used the 60 minute compartment for surface intervals, and made more pressure groups to decrease rounding. This new process completely changed the way recreational diving was done, and even if you did not use the PADI tables, you were doing something very similar. That became the norm upon which probably 90% of the today's divers were trained.
In order to make that work, though, they had to take decompression out of the tables. Most modern dive tables do not have any information for decompression stops in them, and the assumption is that you simply won't go into deco. If you do go into deco while using most dive tables, you have literally gone "off the charts," and the table does not know how to deal with your situation. The consequences for going off the charts are draconian. If you exceed the NDL by one minute while using the PADI tables, you must do an 8 minute stop and stay out of the water for 6 hours. Exceed it by 6 minutes and you must do a 15 minute stop and stay out of the water for 24 hours. This leads to the strong warning that you MUST NOT exceed your NDL! It leads to the situation where I once had a dive buddy suddenly bolt to the surface in absolute terror because his computer indicated he was getting close to his NDL. He was sure he was having a near death experience.
This is another case of people using table procedures for computer dives. If you exceed your NDL by one minute with any modern recreational dive computer, it will clear deco during a standard safety stop, and you will be back in the water after a normal surface interval. If you exceed the NDL by one minute with a tech computer like a Shearwater, it will require a one minute stop only. If you are taking the computer version of the PADI OW course, you are taught that if you exceed the NDL with your computer, you should follow the computer's directions for appropriate decompression. That sounds a lot like what people are advocating here. Eventually something like that will become the norm and we will not be having threads like this one.
Books, most of which include specific disclaimers in the front cover that say this is no substitute for training?
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