Thailand – Australia – United Kingdom

TDI CCR (Rebreather) Mod 1 course in Thailand

Technical divers study the delicate art of closed circuit rebreather diving

Koh Tao, Thailand

Big Blue Tech celebrates the successful graduation of Nick Amidy, Tony Alba and Thomas Hallstrom from their TDI Mod 1 ISC Megalodon CCR course conducted over 5 days on Koh Tao Island in the Gulf of Thailand. This course was also attended by Ben Reymenants, Simone Reymentants and Kris Harrison.

The CCR Mod 1 course is the first certification level for divers wishing to learn the safe assembly, use and diving of a closed circuit rebreather issued through technical diving certification agency TDI (technical diving international)

Military, photographic, and recreational divers use a CCR (closed circuit rebreather) because they allow long dives and produce no bubbles. Closed circuit rebreathers generally supply two breathing gases to the loop: one is pure oxygen and the other is a diluent or diluting gas such as air or trimix.

The major task of the fully closed circuit rebreather is to control the oxygen concentration, known as the oxygen partial pressure, in the loop and to warn the diver if it is becoming dangerously low or high. The concentration of oxygen in the loop depends on two factors: depth and the proportion of oxygen in the mix. Too low a concentration of oxygen results in hypoxia leading to sudden unconsciousness and ultimately death. Too high a concentration of oxygen results in hyperoxia, leading to oxygen toxicity, a condition causing convulsions which can make the diver lose the mouthpiece when they occur underwater, and can lead to drowning.

In fully automatic closed-circuit systems, a mechanism injects oxygen into the loop when it detects that the partial pressure of oxygen in the loop has fallen below the required level. Often this mechanism is electrical and relies on oxygen sensitive electro-galvanic fuel cells called “ppO2 meters” to measure the concentration of oxygen in the loop.

The diver may be able to manually control the mixture by adding diluent gas or oxygen. Adding diluent can prevent the loop’s gas mixture becoming too oxygen rich. Manually adding oxygen is risky as additional small volumes of oxygen in the loop can easily raise the partial pressure of oxygen to dangerous levels.
The course started with a session in the swimming pool where students starter to learn the fundamental skills related to all rebreathers before progressing on to open water diving.

The successful completion of the Mod course signals the start of Mod 2 where all the students progress on to decompression diving on a ISC Megalodon CCR


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