These pages show the collection of semi-closed rebreathers. The distinction is made by country. Different semi-closed systems occur in each country. Besides the active semi-closed rebreathers, we also know more special types such as passive breath-controlled depth compensated systems. Each rebreather has its own page where the operation is explained as much as possible. Semi-closed systems are the oldest systems for underwater use. Long before electronic systems came on the market, semi-closed systems were already in use. The reason why semi-closed systems came into being is basically the fact that oxygen can only be used for diving at depths of 6-10 metres. At that depth, oxygen will become toxic and people will become unconscious due to hyperoxia. By diluting the oxygen, we can breathe a nitrox mixture that allows us to dive much deeper. However, the nitrogen constantly injected into the breathing loop is not absorbed by the body and must therefore be released to the environment. So gas will occasionally be released to the environment today called the semi-closed system. Besides systems that work with ready mixed gas, we also know of mixing systems and even systems that make the oxygen from liquid oxygen gaseous. Enjoy reading the pages ahead! Countries with an thumb-icon in the button already have content, the others are temporary placeholders