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

Freediving is any of various aquatic activities that share the practice of breath-hold underwater diving. Examples include breathhold spear fishing, freedive photography, apnea competitions and, to a degree, snorkeling. The activity that garners the most public attention is competitive apnea, an extreme sport, in which competitors attempt to attain great depths, times or distances on a single breath without direct assistance of self-contained underwater breathing apparatus (scuba).

Recent interest in this sport has caused dive schools to look at this side of diving as a great alternative to traditional underwater interaction. A recent article in the Times about Freediving in Koh Tao reviewed the sport, the island and the local leaders in free diving; Apnea Total. In the article Guyan Mitra says:

By the end of the two-day course, I was comfortable at 20 metres, a depth that had sounded inconceivable 48 hours earlier. Plus, I was able to dive Ko Tao’s newest underwater site. A boat had recently sunk — without casualty, thankfully — creating a modern wreck around which a kaleidoscope of tropical sea life was investigating.

Using my new-found skills, I was able to probe and glide in and around the wreck, just like my fellow fish. Not quite a merman, but getting there… definitely getting there.

That article in its entirety can be found here

Additional interest was generated from the inflight magazine for Bangkok Airways; “Fah Thai” where photo journalist and fellow technical diving enthusiast Ayesha Cantrell reports about the growing trend of breath hold diving growing on Koh Tao. In the report Ayeasha says:

Go scuba diving around Koh Tao in the Gulf of Thailand and you may encounter a mermaid. Propelled by her monofin to depths of 50 metres on a single breath of air, Monica Ganame is the nearest you’ll get to meeting one of these mythical creatures underwater.

The Argentinian-born professional free diver wears no air tank or other bulky scuba gear - instead, Monica can hold her breath for up to six minutes and explore the underwater world in its truly natural state. The absence of dive equipment not only allows Monica to interact much more closely with marine life, but also to feel a part of the ocean herself.

Ayesha is referring to Monica Ganame who is co-owner of Apnea Total on Koh Tao, that article can be found here

One of Apnea Totals protege’s is Jeroen Marteens who became a freediving instructor through their school. Jeroen is your typical freediving instructor; Tall, slim and appears to be someone who likes his yoga and perhaps a bit of incense. Jeroen join the Big Blue Family to start our Big Blue Freediving department and has been very busy ever since. With maximum 3 people per course.

Jeroen will be taking out members of the Big Blue Tech team for their freediving course later this month, although there were grumblings between wearing 6 cylinders or none at all it is a fringe and extreme side of scuba diving so technical diving and freediving have quite a lot of similarities.

You can find more details about these courses: Freediver Basic and Freediver Advanced