For those reasons and more, the concept of rebreathing of reusing the air that comes from the lungs never went away. As early as the 19th Century, inventors were aware that they could reuse the precious oxygen in a diver's apparatus only if they came up with a way to absorb the carbon dioxide in a closed system.
In the 1930s, Italian spear fishermen were having luck with a system that filtered exhalations through soda lime, a caustic, white, powdery substance made from quicklime that had been treated with lye. That technology became popular in World War II with frogmen who wanted to dive without releasing telltale bubbles to betray their location.
Soda lime filters and scrubbers made from a similar compound, lithium hydroxide, have become standard equipment in closed breathing systems ever since such scrubbers keep air breathable in submarines and spaceships, for example, and the military is still the rebreather's best customer. In the past decade, however, commercial rebreathers have grown dramatically in popularity with serious recreational divers.
Except for the lack of bubbles, however, a diver using a rebreather looks essentially the same but with more tanks on his or her back. Carbon dioxide and other toxic gases exhaled in rebreather systems go through a large scrubber canister containing soda lime. After filtration, automatic sensors test the amount of oxygen in the system and add more according to a level the diver sets to match his depth. Pure oxygen is added from one tank, and oxygen combined with other gases called diluent is added from another canister.
In other words, rebreather users today carry a virtual chemical laboratory on their backs and must be mindful of the gases passing through the closed apparatus of tanks and hoses.
As a diver adjusts his depth, it's crucial that he monitor his oxygen level in that bubbleless system. Too much oxygen and he can go into convulsions. Too little and he will lose consciousness. In either case, he's likely to die.
For that reason, divers are very particular about the mix of gases in diluent. One popular combination is called tri-mix, composed of helium, nitrogen, and oxygen, which helps with decompression and allows for deeper and extremely long dives using tri-mix with a rebreather, eight-hour dives are possible.
For serious divers, already the most gear-conscious people on Earth, rebreathers may be the ultimate impulse buy. About 5,000 of the units exist, and new ones can cost $20,000.
And none of them has quite the cachet of the gleaming unit built by a man named Leon Scamahorn.
After a career in the Army's Special Forces as an expert in combat diving, Scamahorn, 42, saw the potential for commercial rebreathers and, in 1998, purchased a company called InnerSpace Systems. Determined to leave his mark on the field, he designed the most rugged and militaristic unit on the market, naming it after a giant prehistoric shark the Megalodon.
"The Meg" weighs 45 to 85 pounds and costs $8,000 to $15,000. Because of its supposed indestructibility, it has developed something of a cult following.
Eight divers, however, have died using Megalodons, and Scamahorn himself says that people should think twice before buying or using them. Three times in one phone conversation, Scamahorn warned, "The rebreather is like a parachute. If you don't pack it right, you die."
One of the Megalodon's admirers was Zak Jones.
On a recent Tuesday night at the Treasure Trove, a Fort Lauderdale bar, Zak Jones' presence is almost palpable, but no one will discuss it with a New Times reporter.
From Hawaii, however, former Pro Dive International employee Shannon Cunningham says that Jones practically used to own the Trove.
"He had almost a Chris Farley comedic presence," she says. "He was always trying to make somebody laugh. Typical Zak would be going to the Trove after work and drinking beers. No matter what the day was like, he'd find humor in it."
On Tuesday the legendary taco night the Trove brims with the salty people of the sea. The deck hands, the divers, the fisherman, the lifeguards, and, as usual, Pro Dive instructors have come to unwind.
They say they wish they could talk to a reporter, because there are rumors going around about Jones' death that they want to correct. They want somebody to get it right. And they say they want to prevent more deaths. But Pro Dive CEO Frank Gernert has forbidden them to talk about the incident. Not even about their affection for Jones.