As some of you may be aware, the Inter-connected Compartment Model (ICM) described in my published journal article now goes by the name of “SAUL”. This is not entirely, or even primarily, an ego trip. Rather, it’s an attempt to avoid the unnecessary use of jargon – particularly when it results in unpronounceable acronyms. While ICM is an appropriate and relevant way to describe the model’s properties in a scientific context, in the context of diving, it becomes less meaningful, less directly relevant and, of course, less easily remembered.
“SAUL” – for Safe Advanced Underwater algorithm – is a more relevant description from a diver’s perspective.
As I’ve mentioned before in this blog, “SAUL” is completely different from current algorithms, being probability-based rather than based on the Haldane model. This may raise two different questions in the minds of divers: 1. Is “SAUL” tested to the same extent as other models? and 2. Would I have to learn a whole new way of interacting with my dive computer with “SAUL”?
Is “SAUL” tested to the same extent as other models?
The short answer to this question is “yes”. The most extensive body of research on dive profiles and decompression sickness was done and compiled by the U.S Navy, together with the (British) Royal Navy and the Canadian Navy (currently “DRDC”). All diving algorithms have (in a rough sense) been “tested”, either directly or indirectly, against the Navy data. This is because they are usually tested against the PADI recreational dive planner data, which is a more conservative form of the US Navy tables. While new dive computers do undergo testing, this is not a test of the accuracy of the algorithm, but a check primarily of being not too inconsistent with other popular algorithms in current use. I have access to the Navy data and believe that “SAUL”, for both decompression and no-decompression diving on air or nitrox, for both single and repetitive dives, provides a better fit to the Navy data than does any other algorithm. This is why SAUL, but not any other algorithm, can account for the beneficial effect of safety stops and slow ascents. This, in turn, explains why SAUL accounts for DAN’s Project Dive Exploration (PDE) data for air and nitrox, far better than any other algorithm.
Would I have to learn a whole new way of interacting with my dive computer with “SAUL”?
The short answer here is “no”. Even though “SAUL” is probability-based, during a dive, you would still have the familiar “time remaining” to go by and your ascent would include a 3-minute safety stop at 15 feet (for recreational dives). What would be different would be how that function is calculated, and what additional information you would have. Before the dive, you would select the maximum probability of decompression sickness that you are prepared to accept. (Of course, we would all prefer a zero probability of DCS – except, unfortunately, a) zero probability of DCS is not really feasible in diving, and b) the lower the probability of DCS, the more limited your dive will be in length and/or depth.) The “time remaining” that you see during the dive would be calculated to correspond to your chosen probability of DCS, together with the dive profile you have done so far. In addition to “time remaining”, you would also see two other functions: the probability of DCS if you were to begin your ascent right then, including a safety stop , and the probability of DCS if you were to begin your ascent right then but omit the safety stop. These three functions would be continually recalculated during the course of the dive.
The above description is what you would see during recreational diving. (Before the dive you would have selected either recreational diving or decompression diving.) During decompression diving, what you would see would be very similar, except that, instead of only one safety stop, you would have one or more decompression stops. You may be wondering why recreational diving and decompression diving are calculated separately instead of being merged as one. It is because the model parameters (i.e. the constants in the equations of the model) for the two are different, and can’t be switched on the fly. In any event, if you’re on a recreational dive but have seriously overstayed your maximum time remaining (a seriously bad idea), there’s no point in directing you to do a proper decompression stop if you don’t have enough air left to do it. If you do overstay your maximum remaining time, the “time remaining” function will, of course, tell you to ascend immediately, but, unlike with other computers, it will not shut you out. The functions indicating your probability of DCS on an immediate ascent, with and without a safety stop, will continue to provide you that information.
I do intend to put a dive planner online, but can’t say exactly when that will happen. It may take some time because I have a number of other professional commitments that I am working on at this time.