Why must you have nitrox knowledge to dive rebreathers?
The basic gas mixture breathed in any rebreather to depths of 40 m will be Nitrox and therefore the diver must understand the considerations of using Nitrox for recreational diving. Explain the basic differences between closed and semi closed circuits SCR units such as the Drager Dolphin and the San-o-Sub Azimuth use a pre-selected, constant flow, Nitrox mix that is chosen to match the MOD of the planned dive. Venting of excess gas occurs periodically during the dive and ascent. Closed Circuit Rebreather (CCR) units dynamically mix 100% oxygen with a diluent to form a breathable gas mix. For entry-level rebreather diving, the diluent used is air and this combines with 100% oxygen to form a Nitrox mix. For deeper dives the diluent gas may be heliox or trimix, depending on the rebreather manufacturers recommendation. This mix varies continuously with depth to maintain a pre-selected PO2 set point. Venting of gas only occurs on ascent due to expansion.
