This is a question I get asked a lot. In almost every single technical course I teach I am asked by the student which gradient factor should they set their computer to. The next question : What gradient factor do you dive? I hate this question for a couple of reasons. First what I am comfortable diving is not necessarily right for that diver. From a liability standpoint if I tell a diver to run 35/85 and they take a DCS hit I don’t want to be morally or legally liable. The only gradient factor I can suggest is the factory default. But I am getting ahead of myself. Which one is right?
First people need to understand what those numbers are doing and I will put it in basic layman terms since that is the best way for us to understand it. If you hold a technical degree and know more than I do and can expand in a way I will be able to understand I would love to hear from you. You have a line, and that line is basically the point at which the vast majority of divers should be able to get out of the water and not have DCS problems. Notice I say vast majority, not all. That is that second number, in this case 85 if we are running 35/85. So imagine that as a margin of safety at 15 since that is what is left when we assume 100 is that line. Now the first number. That 35 is going to dictate your first stop with 100 being the point to which you could ascend to and again most likely not have issues. Keep in mind after a 300 foot dive that line that is the 100 may start at 150 feet. So what we have is a low starting point and a merger up through your stops until that 85 is 0 feet of depth. Now the diver needs to understand 2 things. First there are many factors that play into decompression. Your stop depths and times are only two of them. Dehydration, mental, and physical stress, warmth, ascent rate, and general physical variants can all cause these profiles to work better or worse depending on the day. The second is that this code and the various tables and computers used by divers are not all coming from a single source and a single code writer. The author must create a starting point and incorporate the code and theory he has chosen into a useable format. I will give an example. I once did a dive on Open Circuit to 175 feet for 1 hour of bottom time. I had two mixed gas dive computers from mainstream reputable companies. With the exact same gradient factor on that dive I had a 20 percent difference in the decompression obligation between those two computers. I continued to dive them both, not necessarily together, and had no significant decompression related issues from dives performed with either one.
Now here is the important part. I have known divers who got bent using gradient factors I would consider to be VERY conservative. No I won’t say what they were. I have also known divers who for various reasons aborted deco and suffered no decompression hit. I have also completed my deco 25 minutes sooner than other team members on the exact same dive using the exact same gasses, gotten out of the water and was fine while they got bent bad. So we are left with some very real facts. First; stops and times are important but equally as important is the “Art of Diving”. Ascent rate, hydration, relaxation at deco, staying warm. These are all in my opinion as important as your stop depths and time.
Next let’s look at risk. Having told you that divers I know have gotten bent while using in my opinion quite conservative gradients do you still feel comfortable diving a gradient factor that leaves almost no conservatism and brings you up very quickly? Are you diving it just because your instructor is diving it? I have no problem doing deco. I am much more comfortable in the water than in a dry chamber with IVs hooked up. I have no problem doing a little extra deco. So why am I writing this? First I want people to seek out education for themselves, not just blindly follow what someone else does because that very experienced diver may have 20 years of doing things a certain way, and that certain way might not be correct for you or even them for that matter. I want people to evaluate the dive, assess the risk they can accept in terms of their dive profile and dive safely. I have evaluated the risks and chosen my dive planning. Have you? Or have you just plugged in numbers someone told you to use on the internet or in that video you watched about an exploration project. Oh but if you are diving 100/100 or something very close to that, believe me you are wrong. Safe Diving. -Jon B.