Abstract
In semi-closed-circuit breathing apparatus, there is a relative decrease in the oxygen content in the breathing space compared to the oxygen content in the premix supplied to the breathing space, caused by the mixing of regenerated gas with fresh gas. This process can be modelled similarly to other ventilation processes (Kłos R., 2007). In an apparatus with bags placed one inside the other, such a decrease is relatively significant. This article provides an introduction to decompression planning for the CRABE apparatus.