I generally enjoy Eric Douglas' column "Lessons for Life" in Scuba Diving magazine. But a recent one had me concerned. Maybe I am missing something...
This column is called "Pushing the Limits on a Liveaboard leads to DCI for this Scuba Diver", and it involves the risks of doing multiple dives on a vacation. Fair enough, good point. My concern is that the dive profiles that the author uses are so ridiculously OVER the "limits" that it actually affects the conclusion. The point should be that you can stay within your computer's NDLs and still get bent. But I can't imagine how he came up with these numbers...
These profiles are SO far into deco, the diver didn't have a chance of doing even one of them without major risk, let alone four. Using MultiDeco and a very aggressive gradient factor of 100/100, I get 20 minutes of deco for the first dive. And even if he DID that (which he didn't), he would have had over an hour of deco on his second dive. The article states that he did no deco at all. I guess they do state that they were "multi level" dives, so maybe the diver spent a lot of time at shallower depths. But they don't say that, and the way it is written you would really need to assume a square profile, otherwise the whole point is lost.
The problem with this is that a new diver will think that this is sort of in range but "pushing it", and not realize how way out of line this dive plan is. We often talk about the "sanity check" needed for computer generated dive plans. A diver doesn't have the ability to do these ascent profiles in their head, but they should at least be able to look at something and decide that it sounds like it's out of the ballpark.
This column is called "Pushing the Limits on a Liveaboard leads to DCI for this Scuba Diver", and it involves the risks of doing multiple dives on a vacation. Fair enough, good point. My concern is that the dive profiles that the author uses are so ridiculously OVER the "limits" that it actually affects the conclusion. The point should be that you can stay within your computer's NDLs and still get bent. But I can't imagine how he came up with these numbers...
The first day in the water, Heath made four multilevel dives while following his dive computer. It was set up to calculate his no-decompression limits based on the gas mix he was breathing. His first dive was to 106 feet with a total bottom time of 53 minutes. He had a surface interval of 1:49. Dive two was to 123 feet for 68 minutes, followed by 2:27 out of the water. Dive three was a dive to 91 feet for 75 minutes with a surface interval of 1:35. His fourth and final dive of the day was to 93 feet for 43 minutes. He finished up in time for dinner at 6:30 p.m. Heath didn’t experience any problems on the dives and performed a routine safety stop at the end of each one.
These profiles are SO far into deco, the diver didn't have a chance of doing even one of them without major risk, let alone four. Using MultiDeco and a very aggressive gradient factor of 100/100, I get 20 minutes of deco for the first dive. And even if he DID that (which he didn't), he would have had over an hour of deco on his second dive. The article states that he did no deco at all. I guess they do state that they were "multi level" dives, so maybe the diver spent a lot of time at shallower depths. But they don't say that, and the way it is written you would really need to assume a square profile, otherwise the whole point is lost.
The problem with this is that a new diver will think that this is sort of in range but "pushing it", and not realize how way out of line this dive plan is. We often talk about the "sanity check" needed for computer generated dive plans. A diver doesn't have the ability to do these ascent profiles in their head, but they should at least be able to look at something and decide that it sounds like it's out of the ballpark.