Thailand – Australia – United Kingdom

Rebreather Training in Thailand

Modified semi-closed rebreather diver course completed in Thailand

Koh Tao, Thailand – Big Blue Tech celebrates the graduation of Andrew Cavell from his TDI Semi Closed Rebreather Diver Course conducted over 4 dives around various dive sites on Koh Tao Island. The TDI Semi-Closed Rebreather Diver Course is designed to teach the student the safe diving and operation of a Semi-Closed Rebreather.

The semi-closed circuit rebreather (SCR) can be manufactured without the use of batteries or electronic components in a very reliable system. It’s only moving parts are the check valves in the mouthpiece and the demand valve override for deep inhalations. It can be simple, useful, and provide many of the benefits divers seek in rebreathers. With the use of Nitrox mixtures, the benefits of EAN use are retained with the added benefits of a properly designed SCR which includes:

  • Quiet, reduced bubble operation
  • Extended bottom time (due to efficient use of gas)
  • Lighter, more comfortable diving systems
  • All the physiological benefits of EAN (Nitrox)

Other advantages of the semi-closed circuit rebreather become obvious with use in each dives chosen environment. For example, the inspired air is moist, not-dry, helping to eliminate “cotton-mouth.” Also, the gas is warmer, reducing heat loss in cold-water diving. Buoyancy needs only be set once at depth. As the diver breathes, the system acts opposite to the lungs producing no change in buoyancy from inhalation to exhalation. This takes some getting used to for experienced divers.

Diving on the rebreather is a remarkable difference to normal open circuit scuba. Andrew’s first experience in the shallow training depths was commented as “that’s weird” when referring to the control of the buoyancy using your lungs. Because the unit uses a bag of air that you exhale and inhale from the exchange of gas from lungs to unit is different than experienced in normal scuba. In scuba diving when you exhale you descend and when you inhale you ascend. In a Semi-closed rebreather the movement is opposite.

During the open water dives do depths up to 30m Andrew found the marine life came much closer then ever before and that the air was not as dry as in normal scuba.

The rebreather which was used is a modified Drager Dolphin Semi-closed rebreather which has been adapted from it’s 4 litre tank which provided 69 hours of dive time to twin 6 litre tanks to get the increase gas and dive time while utilizing a full canister of soda lime. This rebreather also features the ability to bolt on a backplate and wing so technical divers can find it more comfortable and streamlined.


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