In a rebreather system exhaled breathing gas is collected in a counterlung and can be inhaled again after a recycling process, where CO2 is removed and metabolised O2 is replaced. Rebreathers are used by rescue services (fire fighters, smoke divers, miners), in medicine (anaesthesiology, O2 rebreathers for emergency treatments) and in diving. The ability of a closed circuit rebreather to provide a life sustaining gas depends on the correct function of each component. The main bottlenecks in present rebreather units are O2 sensing (electrochemical sensors) and the chemical CO2 removal. The scientific objectives of this proposal address on the one hand the research and prototyping of a novel paramagnetic microfabricated silicon O2 sensor. On the other hand an innovative and reusable nano technology based CO2 filter (nano porous fibres, polymer nanofibres) will be developed. Based on these components a prototype of a rebreather unit will be designed and characterized. The proposed work will be carried out at Imego, Sweden. Arne Sieber will receive intensive training in the fields of: - silicon micofabrication, MEMS design, fabrication and characterization - nanotechnologies, especially application and treatment of nano propos hollow fibres/polymer nanofibres Furthermore it is envisaged that he will be able to enhance his management, leadership, teaching and presentation skills.