KITTED-UP
6 . The modern rebreather
It ’ s a surprise to many that closed-circuit diving has been around far longer than open circuit . Early experiments found that the carbon dioxide levels soon built up in bag-style systems making breathing uncomfortable ( and dangerous ), so simple absorbing pads made from straw soaked in lime were used to absorb the CO₂ , still dangerous as lime becomes caustic when wet , but at least the diver didn ’ t suffocate .
The military have used rebreathers extensively - the attraction of no bubbles and a simple design made them ideal for sneaking under ships to affix mines . These were pure oxygen rebreathers so had the problem of limited depth as below around 10 metres , divers would convulse . The oxygen needed to be diluted down but this introduced a complexity of not really knowing what was in your breathing gas , so a level of gas measurement and control was needed .
Commercial rebreathers were developed in the late 1980s and early 1990s , with the AP Inspiration being the first commercially available CE marked rebreather on the market . The Classic is a relatively simple piece of equipment – it doesn ’ t even know it is underwater ! The one thing it does do well is monitor the oxygen levels in the breathing loop , and squirts a bit of oxygen in to keep it near a “ set point ”. Early adopters of rebreathers had to pioneer their use
and they had a bit of a reputation of being dangerous until the training and use protocols were fully developed . Since the Classic , rebreathers have been further engineered adding fancier electronics that monitor your dive profile , measure other gases such as CO₂ and helium and have secondary displays so your buddy can see how your loop is doing .
7 . The next step ...
Predicting what happens next with a diving crystal ball is always a challenge . Lots of manufacturers have talked of the ‘ recreational rebreather ’ where divers miss out the open circuit noisy bubbly bit . If they can get the cost down then that ’ s a real possibility , especially if solid state gas monitoring comes into the mainstream .
The increasing scarcity of helium is already putting a real dampener on deeper diving – blowing upwards of £ 100 on a fill for a twinset is today ’ s reality , so closed circuit is becoming the only affordable option .
Whatever happens , you can ’ t get away from the fact that you ’ re dropping a shaved monkey into a cold , unbreathable environment that needs care to survive . The development of new and exciting kit will hopefully keep us exploring .
ILLUSTRATION : IAN LEGGE
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