This study addresses the safety issue for the realization of a CO2 heat distribution system in the NEST research and innovation building. It is based on consideration around the concept of CO2 network developed at LENI/IPESE-EPFL and takes advantage from the realization of an experimental CO2 network. The concept of CO2 system in building extends the approach developed by the refrigeration industry by giving access of the CO2 network to the floors of allegedly inhabited buildings and neighbourhoods. The main implication on safety results from the larger amount of pressurized working fluid and the presence of people living or working in the vicinity.