DIVING TIPS #1

Personal Dive Computers… the simpler and safer alternative

One of the many things that has distinguished Scuba Diving International™ as an innovative force in the scuba industry is our approach to non-decompression dive planning. To be specific, SDI divers MUST wear a personal dive computer to help track their decompression status and use it as their primary source of information for all sport-level dives; and as such SDI divers are not required to use printed ‘tables’ to plan their dives.

Unfortunately, setting the trend in any endeavor and promoting a change rather than following the status-quo opens one up to all kinds of flak and when we adopted this position (with the release of our first set of standards in 1998) some of the old guard opened up on us. Their argument essentially boiled down to “the old ways are better.” We disagreed because this was a similar argument to the one made against the adoption of the BCD, SPG and the backup second stage regulator.

For the most part, that particular issue has long passed and the industry as a whole is beginning to switch to the SDI way of doing things, and personal dive computers (PDC) are becoming universally adopted by divers from all agencies, not just SDI. However, there are some holdouts.

I recently received a message from a member of one of the many scuba-related forums out on the web. Apparently his girlfriend had signed up for an open water course and he was shocked to learn that his local dive store had switched affiliations and was now promoting, what his old instructor termed, “SDI’s superior program!”

My correspondent asked me what the differences are between the Open Water program he had taken through another sport diving agency and SDI’s. He explained that he was shocked to learn from his girlfriend that SDI promotes the use of PDCs rather than making students slog through calculations using tables.

He felt she was being short-changed and that not learning tables was dangerous. He actually said “if sport divers or occasional divers can’t familiarize themselves with the tables then should such an unsafe person be diving?” Wow… essentially, he was saying that ALL SDI divers are an accident waiting to happen. The stats prove otherwise, and all other pointers indicate that using a PDC as a part of a controlled decompression sickness management plan makes sport diving less risky. Let’s look at some facts.

SDI was created in the late 1990s by people who ran a technical diving agency; the biggest technical diving agency in the world, TDI. The men and women who helped put together its curriculum and developed its courses had the strongest background possible in diver education and diver safety, and the attendee list of those early brain-storming sessions read like a who’s who of recreational diving… both technical and sport branches.

Their primary concern was to create an open water course that made diving an adventure rather than a chore. As a group they had a sort of “sky’s the limit” perspective on diver education… after all, many of those early TDI/SDI instructors had experience exploring exciting spots around the globe that few divers had ever seen. The majority of them had been teaching people to dive in caves, and running diver programs to depths about three-times the “normal” sport diving limits. So their perspective on how far a student could progress was a mite broader than instructors from other backgrounds!

In part because of that, SDI’s approach to a sport diver’s progress and the way students are asked to present skills is a little more… progressive and less formulaic than some of the other options available. At those early meetings, when presented with the options of “what tables” SDI divers would use, lots of options were considered.

One piece of information had a great influence during those deliberations. Collectively, most experienced scuba instructors will agree that the single most difficult thing to teach open water students is how to plan repetitive dives using the old-fashioned printed tables. Working out the maximum allowable bottom time for a single dive is simple; but continuing the process for a second and third dive caused problems in the classroom. Time better spend actually discussing the physiology of diving and how to avoid “bubble troubles” was spent slogging through a process that lent itself to “user error.”

In fact there was plenty of feedback from students and experienced certified divers that fear of getting these calculations wrong, kept divers OUT of the water. This was (and is still) especially germane with ‘occasional divers.’ These are individuals who dive mostly on vacations, logging perhaps 10 to 30 dives a year. Working with tables was, they said, confusing for them and they felt restricted by this simple shortcoming. What it boiled down to was hating the thought of sitting on a dive boat trying to recall what step came next and looking like ‘a newbie.’

Coupled with that was the certainty that planning multi-level dives (either as single dives or as part of a day where two or more dives are carried out) are challenging working with traditional printed tables. Frankly, even some open water instructors have a problem with these multi-level dive calculations and have to ‘hit the books’ and revise the process before teaching it!

The answer for SDI was pretty obvious. PDCs had come a long way since the introduction of the first models in the late 1970s. Modern PDCs were reliable, affordable and packed with features that have real benefits for all levels of sport diver. Even the most basic model  can manage multilevel diving because it recalculates inert gas uptake in real time (updated every few seconds); it can track residual nitrogen following time on the surface greatly simplifying repetitive diving; and has a built in ascent rate warning to help divers make slow ascents, a huge help in DCS management. SDI figured that a dive computer makes simple work of the whole process of tracking, so SDI opted to promote PDCs as an essential part of every SDI diver’s kit!

Now let’s make no mistake here, a PDC is just a tracking device, and it is not quite plug and play. It IS necessary for a diver to read and understand the user’s manual that came with his PDC, and he has to take into account in his dive planning all the contributing factors that influence DCS management, such as hydration, tiredness and other stressors. And a PDC is not magic and does not do away with the need for a diver to have at least a basic understanding of the process of nitrogen uptake during a dive, and the elimination of that gas during ascent and surface interval. And finally it does not guarantee 100 percent risk-free diving; nothing can. But it is far superior to working with printed tables, even when the tables use the same algorithm as the computer.

Quite apart from anything else, even the most modestly priced models available today display the following information:

  • Current depth
  • Maximum depth reached on current  dive
  • No stop time with current mix, the time remaining at the current depth without the need decompression stops on ascent.
  • Dive time
  • CNS Oxygen Toxicity Status
  • Water temperature
  • Ascent rate

In addition, once the dive is over, computers can also provide information such as:

  • "Time to Fly" display showing when the diver can safely board an airplane.
  •  A log of key information about previous dives.
  • Maximum non-decompression bottom times for subsequent dives based on the partial pressure of the gases in the tissue.

No printed dive table can do any of that!

I guess in the end, there will always be someone who resists change, and to whom any "new fangled safety measure" is an anathema. But the simple truth is that tracking nitrogen loading with tables is out-moded and unnecessarily convoluted. PDCs do a better job and make diving both safer, more accessable, and more enjoyable.

Diver Tips is a regular feature of your newsletter. We have lots of ideas for future columns but we welcome your input. If there’s something you’d like to know more about or would like us to cover a specific aspect of diving (and it can be related to sport diving, technical diving or public safety diving), send your idea to godive@tdisdi.com.

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