The rebreather is an alternative to the conventional compressed air cylinders for scuba diving. What is special about it: The device processes your breathing air so that you can continue using it. Thereby, a lot of the devices use pure oxygen or are semi-closed systems with variable oxygen percentages. In comparison to conventional diving with compressed air cylinders, there are two advantages:
You can stay longer under water.
Less dangerous bubbles are formed in the air due to the processing.
In order to compare how much deeper you can dive here, there is the special measuring unit “Equivalent Air Depth” (EAD).
What is the danger of a rebreather?
A lot of diving organisations recommend to dive only up to 7 metres with this device. The reason is that the devices are very dependent on the functions of their individual components. While you can return to the surface unharmed with a compressed air cylinder, for example when the regulator fails, with this variant every mistake can have severe consequences.
In addition, you have to handle the filter particularly carefully: If you remove it when it is still wet, it may possibly not function anymore for the next dive.