A typical Self-Contained Underwater Breathing Apparatus, or scuba gear for short, usually consists of a tank containing compressed air and a mouthpiece used to regulate the flow of air from the tank into the lungs. But breathing air in this manner is extremely inefficient, especially while considering the applications of this particular apparatus. This is because the air you breathe out still contains a fair amount of oxygen.

Modern scuba gear use rebreathers to filter out the exhaled carbon dioxide gas and gather the oxygen, to recirculate it until it is consumed. By doing so, the underwater breathing process becomes more efficient, allowing professional divers to remain submerged for a longer time.

Basically, a rebreather has three roles. One is to remove the carbon dioxide gas from the exhaled air. This is done by pumping it through a chamber containing sodium hydroxide, which reacts with the carbon dioxide and forms calcium carbonate. Secondly, the rebreather must complement the amount of consumed oxygen with fresh one from the tank. The oxygen tanks may contain either pure oxygen or oxygen mixed with either nitrogen or helium.

Alternatively, the rebreather must control the oxygen concentration inside the breathing loop after the exhaled oxygen is combined with fresh oxygen, for an optimal oxygen delivery sequence.

Types of rebreathers:

Currently, there are three types of rebreather systems commercially available - oxygen rebreathers, semi-closed circuit and closed circuit ones. The oxygen rebreathers make use of pure oxygen tanks as the only source of breathing gas. They are generally disadvantaged by the facts that they cannot be used in decompression depths and may pose oxygen intoxication risks.

Semi-closed circuit rebreathers on the other hand, carry tanks containing oxygen mixed with another gas - nitrogen, helium - and enable divers to surpass decompression depths without any risk of suffering from oxygen intoxication. Closed-circuit rebreathers are a combination between the two, using both pure oxygen and oxygen mixed with various gases.

Besides being highly efficient in making use of the gas carried by a diver, rebreathers are also lighter than any other conventional scuba gear. The normal concentration of oxygen inside the atmospheric air is about 21 percent, while that of nitrogen is 78 percent. Since nitrogen is not as critical as oxygen, almost three quarters of the gas carried in conventional scuba tanks is dead weight. Also, less nitrogen is circulated through the system with the help of rebreathers, thus the effects of decompression are reduced to minimum.

Because they recycle oxygen and carbon dioxide is filtered through sodium hydroxide, very little or no gas is ever pumped into the water to produce the characteristic bubbles.

Source

Technical Diving International™ recently announced an agreement with Poseidon Diving Systems, to offer certification on its revolutionary Cis-Lunar Mk VI aCCR, and is offering active CCR instructors the opportunity to upgrade their teaching credentials to cover the automatic, sport-level unit. Instructor upgrades scheduled for NEC Birmingham Dive Show, and DEMA.

“The process is as simple as the unit itself is to operate,” says vice-president of training and membership services, Sean Harrison. “Any active, Closed-Circuit Rebreather instructor can attend the one-day workshop and earn his or her Discovery [Cis-Lunar Mk VI] instructor certification.”

Harrison explains that the unit is aimed at a whole new market and is quite different to ‘mainstream’ closed-circuit rebreathers.

“Poseidon’s Discovery is a remarkable design,” Harrison says. “And the design is the key to our members currently teaching CCR to be able to upgrade to teach it with a minimum of fuss.”

The Mk VI offers all the features of CCR over open-circuit – extended dive times, quiet operation, warm, humid breathing gas, and delivery of ideal gas mixes during all phases of the dive. But the real attraction of Poseidon’s Discovery CCR centers on its ease of use and automated pre-dive tests and operations. It is the simplification and automation of the unit prep and operation that will appeal to sport divers; people who have considered CCR diving but have been put off by their perception that it is complex and not worth the effort for dives within sport diving limits.

The pre-dive procedures for Poseidon’s entry into the CCR market is no more complex than preparing open-circuit gear, due to the pre-packed canister and the Mk VI’s ability to perform all pre-dive tests automatically; from checking gas volumes and loop pressure tests, to calibration of its redundant oxygen sensors. Procedures during the dive are equally simple due to automated operation and no option to “fly the rig manually.” In the unlikely event of any failures in the automated systems, the unit bails out to open-circuit mode.

“The unit promises to bring all the benefits of CCR diving to the avid sport diver, someone who is interested in new concepts in diving but who is less focused on the technical side of things than the average CCR diver has been up to this point. We feel the Discovery will help to open up the CCR market more than any other unit on the market today.”

TDI will be offering upgrades through hands-on workshops to active CCR instructors and instructor-trainers at NEC Birmingham Dive Show, DEMA and other shows and special events in the coming months.

For the past 14 years, photographer and filmmaker Jill Heinerth has been exploring underwater caves around the world, from lava tubes off the coast of North Africa to icebergs in the Antarctic. Wired.com recently caught up with Heinerth to talk about some of her most exciting cave diving moments, as well as the recent technological advances that have made cave diving easier, safer and more accessible to recreational divers. This gallery showcases some of Heinerth’s best underwater images and includes captions adapted from our conversation with her.

Above: “My Neighborhood Cave” in High Springs, Florida

Heinerth snapped this photo of herself as she descended through the tannic water of the Santa Fe River into her neighborhood cave in High Springs, Florida. The swirling orange blaze above her comes from the mixing of river water, stained red by decaying cypress trees, with crystal blue spring water flowing from the cave. The giant black mask she’s wearing is connected to a special diving tank called a rebreather.

“Basically, it does the same thing as a space suit,” Heinerth said. “In normal scuba gear, you’re inhaling gas and exhaling a column of bubbles into the water. But in a rebreather, you’re actually recycling your air, with carbon dioxide getting scrubbed out of the mixture and oxygen getting added back in. With an electronic rebreather, you can tune the gases that you’re using, so that in deeper water you can use helium and other gases to get the optimal mixture of breathing gas for deep water.”

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From Mares via Press release

Dear Customer,

Please be informed that we have discovered a quality issue on the O-ring assembled on the Nemo Air
Quick Connector.

Under certain circumstances the O-ring can fail and consequently Nemo Air may start leaking through the
Quick Connector. As a result, there is a continuous, albeit slow, loss of breathing gas.

This situation could potentially lead to an accident, hence Mares has decided to issue a product recall. The solution already exists in the form of an O-ring of different material and hardness which can be retrofitted onto the Quick Connector of your current Nemo Air.

Please note that the event of an uncontrolled loss of breathing gas from the high pressure hose is regulated
by the EN250 Norm, which requires a 0.3mm opening in the high pressure fitting. As a result, the loss of breathing gas is very slow and a diver should always be able to complete a dive safely,

NONETHELESS FOR YOUR PERSONAL SAFETY AND TO AVOID POSSIBLE DANGEROUS ACCIDENTS:

STOP DIVING WITH A QUICK CONNECTOR SUBJECT TO THIS RECALL UNTIL THE EXISTING O-RING IS REMOVED AND SUBSTITUTED WITH THE NEW ONE.

• Affected products and codes are:

1. Finished goods
414158 – DIVE COMPUTER NEMO AIR
414159 - DIVE COMPUTER NEMO AIR W/COMPASS NO

2. Spare parts
44200771 – HP HOSE W/QUICK CONNECTOR NEMO AIR
44200770 – QUICK CONNECTOR ASSY. FEMALE NEMO AIR

PLEASE CONTACT THE NEAREST AUTHORIZED MARES SERVICE CENTER TO SCHEDULE THE REPLACEMENT OF THE O-RING IN YOUR QUICK CONNECTOR.

NEMO AIR QUICK CONNECTOR O-RING MUST BE REMOVED AND SUBSTITUTED WITH THE NEW ONE.

More information will be published on: www.mares.com