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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.
"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.
Gernert has also banned diving with rebreathers from any of his vessels.
He made that announcement to his workers despite the fact that the two experts who examined Jones' Megalodon rebreather after his death found nothing wrong with it.
Jeffrey Bozanic was the first to examine Jones' rebreather, at the request of the medical examiner. Author of Mastering Rebreathers, one of the few books on the subject, Bozanic admits that he was actually not the optimal person to investigate Jones' gear. He has never used a Megalodon, and his impartiality isn't above question: He is friends with just about every rebreather manufacturer in the business.
Still, he's more qualified than most, and Jill Heinerth, a Megalodon user from North Florida, did her own independent evaluation several weeks later.
But there's still something unsettling about an industry so small, specialized, and tightly knit that few qualified, impartial people exist to evaluate equipment after accidents. The military would be ideal, but it simply doesn't have the time.
Military divers and professional underwater researchers have been using rebreathers for years. But most recreational divers are still new to the equipment. And they tend to be the most gung-ho and risk-taking.
"They're the pioneers," Bozanic says. "They're the ones blazing the path for people like you, who may decide they want to try these. This is a place where an average person with minimal investment $20,000 can get involved. You're part of the front edge of what's happening in the world, and there aren't many places you can do that anymore."
But those pioneers can pay a heavy price for their gusto. Bozanic and other experts say that rebreathers are practically infallible but that accidents occur because divers who consider themselves experts may become complacent about safety since they may feel too experienced to commit a lethal error. Bozanic believes that about 90 percent of rebreather deaths have been chalked up to human error. He admits he has heard of one or two in which the equipment failed, but he can't remember the specifics.