Tables on a Chip

In the October issue of In Depth, under the title "Computing Your Way into Trouble?" we published excerpts from the 1995 publication of a computer workshop sponsored by the Underwater Hyperbaric Medical Society. Bret Gilliam, who participated in that session, took issue with a number of points and submitted an article in response. Gilliam is currently CEO of UWATEC (a dive computer manufacturer) and vice chairman of NAUI's board of directors.

In 1988 I was vice president of Ocean Quest International, which operated a 500-foot cruise ship catering to sport divers. We carried ten 32-foot dive boats and offered four dives a day plus a night dive to our 160 or more divers. Before we began operating, we were interested in the role computers might play in eliminating human error in record keeping for repetitive diving. We spent considerable effort chamber- and field-testing various models. Ultimately we settled on Dacor's MicroBrain, which combined a very small instrument with Buhlmann's conservative P-3 algorithm and a reliable immersion switch.

We purchased over 200 units and supplied them to guests and staff. Out of nearly 80,000 computer and table dives, we only had seven cases of DCS -- less than half of one percent incidence across the entire diver population.

But of those divers who used our computers -- more than half -- we had zero incidents of DCS. I produced a paper on our experience that was published by the American Academy of Underwater Sciences and the South Pacific Undersea Medical Society and widely reported in various media (including Undercurrent and In Depth). My intent was not to shill for the manufacturers but to share our success with the rest of the industry who were conducting similar aggressive resort programs.

Dr. Edmonds (who has opposed dive computers since their introduction) doesn't seem to like the results of my report, since it suggested that his "gloom and doom" predictions were not valid. He may want to shoot the messenger, but there is no disputing the facts that we recorded.

Edmonds conveniently ignores that much of the theoretical scenarios he offers as proof that computers might allow a threatening exposure also apply equally to dive tables! It is both simplistic and inaccurate to compare modern electronic dive computers to the navy tables, which he holds aloft as sacred scripture.

Every decompression model incorporated into today's dive computers is more conservative for "square profiles" than the navy tables. And this is the only possible valid comparison, since tables were not designed for multi-level use.

Dive computers are active calculating instruments that are specifically designed to record and analyze the diver's exact profile and not penalize him for "maximum depth for total time" as tables do. But it is important to understand that their algorithms are also designed to handle this type of multi-level function.

We now see ascent and descent rates built into computers that are substantially slower than navy tables; many models incorporate audible alarms to warn divers if they exceed those parameters. At UWATEC, we have introduced computers that will actually modify the decompression model based upon the diver's work load (breathing rate), predicted skin temperature based on the surrounding water, and ascent rate. This is about as close to a customized computer as today's technology allows.

Edmonds makes the absurd claim that manufacturers are knowingly promulgating unsafe computers and then standing behind "clauses for lawyers" and "small print in the manual." That's a rather naive view. Computer manuals contain suggested safety guidelines and cautions that are prudent in a litigious environment where persons sue McDonald's over coffee they spilled in their own lap.

As manufacturers, many of us are committed to extensive testing protocol for our models and are further cooperating in DAN's ambitious dive data projects, where we provide computers and software to monitor and download profiles for their ongoing studies.

Other parts of the article suggest, without valid data, that DCS is on the rise. What is really happening is that education has lifted the stigma of guilt from reporting symptoms, so more divers are coming in for evaluation. In the past, divers didn't report problems for fear of being rebuked or ridiculed by "holier than thou" types who branded them as screw-ups.

Are we "computing our way into trouble" as Edmonds claims? I very much doubt it. Computers have largely eliminated mathematical and record-keeping errors by divers since the data are now automatically calculated by instruments far more accurate. I don't know of anyone, with the possible exception of Edmonds, who suggests that the navy tables of old were a standard to which we should subscribe forever.

Dive computers now enjoy such a widespread acceptance in the sport that tables are becoming almost an historical footnote in the market. Let's not confuse occasional diver errors or lapses in reasonable common sense with condemnation of a reliable and valuable technology. Otherwise, we'd all still be earthbound creatures in the first place.