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A diver emerges from a clear river in Florida and swims toward shore. When he reaches shallow waters he stands, streaming, to reveal a sleek, compact device seated at chest-level.
It’s easy to see that he’s wearing a rebreather, a closed-circuit breathing device that helps him dive without producing the bubbles we normally see with the more common open-circuit scuba.
Where many of us who began diving in the ‘70s, ‘80s or even longer ago might have gaped at this device and then swooped in for a closer look, more and more sport divers are seeing – and participating in – diving with rebreathers.
If you dive with rebreathers, you already know how they work. But have you considered their history? Or are you a sport diver who’s considering taking rebreather training?
Here’s how to whet your appetite: DAN has developed a short presentation that outlines the principles, operations and history of the rebreather.
Did you know that the first rebreather, created in the late 17th century, was composed of two bladder valves and an air-cleaning device that was made of flannel impregnated with calcinated potash?
And that near the end of the 18th century, another scientist showed that the carbon dioxide produced by breathing could be removed by bubbling the expired air through limewater?
Scientists first created the rebreathing apparatus to filter out contaminants topside. A century later, in 1880, they applied that same thinking to breathing underwater when a diver used an oxygen rebreather to perform a heavy lifting job underwater: he closed a jammed door, thereby helping clear a flooded tunnel.
This was the proverbial first step into a rapidly developing technology that has leapt through history. Following its use to administer 100 percent oxygen to divers undergoing decompression in submersible decompression chambers before World War II, WWII divers in the Italian Navy employed rebreathers to plant mines.
Tracing the history as it moves from the Normandy coast where British and Canadian Forces landed on Sword and Gold Beaches, divers from the Landing Craft Obstruction Clearance Units (LCOCU) cleared obstacles using oxygen rebreathers.
Then Dr. Christian Lambertsen developed a closed-circuit oxygen rebreather for use by the Operational Swimmers of the U.S. Office of Strategic Services, who became the forerunners of the U.S. Navy Underwater Demolition and SEAL divers.
The presentation reviews key factors relating to rebreather design and safety. There are three basic types: closed-circuit oxygen, semi-closed circuit mixed gas, and closed-circuit mixed gas. It also covers issues concerning design and testing, including work of breathing, respiratory pressure and their standards.
Gas consumption and oxygen control can vary widely with depth, diver workload, and rebreather type. Carbon dioxide removal and CO2 scrubber design include as much art as science. Dive times are extended and decompression times reduced by the high oxygen partial pressures used in electronic rebreathers. The eye can be affected by oxygen toxicity at these sustained oxygen partial pressures, however, even though pulmonary and CNS oxygen toxicity are not problems.
Many laboratories, companies, and people provided information and pictures for this presentation, and their assistance is gratefully acknowledged.
Want to know more about the fascinating history? Go to
http://www.DiversAlertNetwork.org/Research/Rebreathers where DAN Members can read more about the rebreather.
And if you’d like to share with students or friends, you can download a copy of the presentation for free. Don’t forget to look at the PowerPoint Notes pages where a description and background of each slide is given.
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