EOBA Oxygen rebreather

World’s most compact semi-closed rebreather

The Japanese EOBA (Enriched Oxygen Breathing Apparatus) is in fact a semi-closed system. This is because the mix in the mini cylinders contains 80% oxygen and 20% Nitrox. The reason for this is that you can dive a little deeper and the less pure oxygen forms a smaller risk of oxygen poisoning. The unit built in the 1990s is of a special concept because the counter lungs are missing. This role is fulfilled by the expanding hoses. Together with a mini rubber and mini bottles, this is a special device which, according to the manufacturer’s specifications, can be used safely down to 5 metres diving depth with a diving time of 10 minutes.

Nippon Sanso K.K developed this compact semi-closed underwater breathing apparatus, the eOBA. It consists of a mouthpiece, manifold with a purge valve, two spring-loaded flexible tubes, a small CO2 absorbent canister (net wt. = 190g), and two compact high pressure bottles (50ccx2: 190kg/cm2: 80%O2, 20%N2) with a regulator which supplies the gas at the constant flow rate of 1.5 l/min and lasts for 10 min. Thus, a counterlung is not incorporated. However, spring-loaded tubes act as a counterlung since its volume increases to 3.5 l when fully inflated. Dives to a depth of 5m are also recommended because of no bypass valve. This new eOBA was tested using the mechanical breathing machine and CO2 supply system to the circuit. For the various combinations of tidal volumes (0.5-2.5 l) and respiratory rates (10-20 breaths/min), the pressure at the mouthpiece, respiratory volume and the CO2 level were continuously monitored. The CO2 absorption rates were then calculated. The thin sloping P-V loops demonstrate that the eOBA is a flow dependent type of apparatus. It was found that the external work of breathing (0.1 kg.m/l at 30 l/min) were allowable. The CO2 absorption rates were sufficient when minute ventilation increased to 30 l/min. Thus, results show that the eOBA must be suitable for shallow and short dives.

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