Technology is opening all sorts of places to human exploration, including areas of the sea previously too remote to spend much time lingering in. I had occasion to reflect on whether this is a good or a bad thing when I went scuba diving with a rebreather in the Caribbean last summer. Rebreather technology, though new to me, has been gaining popularity among technically inclined recreational divers — enabling them to dive deeper and for longer periods than with comparably sized, traditional open-circuit scuba systems.

When you inhale using a traditional system, compressed air or nitrox (a blended gas containing more oxygen and less nitrogen than ordinary air) is drawn from a tank to a regulator to your lungs. When you exhale, the air — now containing less oxygen plus carbon dioxide — bubbles out into the water.

Though robust, reliable and inexpensive, open-circuit systems have significant drawbacks. For one, the waste of all that perfectly good oxygen. Inhaled air is about 21 percent oxygen; when you exhale, the oxygen level is still about 15 to 16 percent. In addition, those noisy bubbles can scare fish. (They also make military divers conspicuous when they'd rather not be noticed.)

Rebreathers, in contrast, employ a closed or semiclosed circuit; instead of releasing exhaled air into the water, the system forces it through a chemical scrubber that removes the carbon dioxide. The scrubbed air is then supplemented with oxygen from a small tank, bringing it up to the 21 percent concentration that is easily breathable. Because gas gets compressed as a diver descends, diluent (often ordinary air or trimix, a mixture of nitrogen, oxygen and helium) from another tank maintains the gas volume in the rebreather circuit.

While the concept isn't entirely new — primitive rebreathers have been around for more than a century — modern technology has made the system much safer and more capable. (Nevertheless, the label on the unit I used read, "DANGER: This device is capable of killing you without warning!") The development of sensors that provide reliable and accurate measures of oxygen was a major breakthrough. Though rebreathers are a long way from becoming as widely used as open-circuit scuba gear, they have gone from being the exclusive equipment of military and scientific divers to a staple of sophisticated, committed recreational divers.

Wanting to see for myself how the technology has progressed, I contacted Divetech on Grand Cayman Island and asked to be taken on a familiarization dive using the KISS Sport rebreather system.

Several divers told me that most people who go from open-circuit scuba systems to rebreathers find it to be a shock — and the more skilled the diver, the harder the transition. This was certainly true for me. I felt very awkward at first, as many techniques used by experienced open-circuit divers — such as controlling buoyancy by breathing deeper or shallower, depending on whether you want to go up or down — didn't work with a rebreather. I did get better, though, as the dive progressed.

Frequent diving with a rebreather demands a considerable investment in time and energy — one that I'm not sure I'm ready for, at least right now. Among other things, rebreathers require more maintenance than regular scuba gear because the technology is more complex. The KISS system is a respectable unit that's been out for a couple of years. It works fine, but looks to me like it was put together as a shop project. The Inspiration system, used by Nat Robb, my instructor at Divetech, is much more sophisticated. It is fully computerized, and its innards look more like a fighter jet's than a vacuum cleaner's. It costs $10,000 (compared to $5200 for KISS). But over the coming years, the growing popularity of rebreather diving will no doubt result in falling prices, improved capabilities and, most important, better safety.



My experience with the rebreather got me thinking about the many technological improvements that have made scuba diving safer and more accessible than in the Sea Hunt era. Because of better buoyancy- control devices, regulators, spare-air devices and, especially, dive computers that track nitrogen uptake and bottom time to help divers avoid the bends, more divers are taking up the sport than ever before.

Some people assume that's a bad thing. All those new people, they figure, will ruin it for everyone. But I'm not so sure. Yes, some sites are overdived, but the big picture is probably more positive. In his recent book, Sprawl, historian Robert Bruegmann notes that interest in preserving the environment took off at about the same time that people began flooding into the suburbs — and getting a little closer to nature.

And ocean explorer Jean-Michel Cousteau, in his foreword to Cathy Church's book, My Underwater Photo Journey, wrote that if more people were exposed to the beauty and complexity of the undersea world, they'd be much less likely to pollute and destroy it. People who have seen a coral reef up close tend to care more about reefs than people who haven't.

The instinct of many people who spend time in nature is to wall it off from the great unwashed masses. But I wonder if we would be better off encouraging people to appreciate it. Underwater, at least, advances in technology are doing just that.