Using liquid sodium at high temperatures in test facilities requires defining rules specific to this technology to ensure that operations are safe and reliable. Such facilities can be operated under optimal safety conditions when a certain number of safety principles are adopted as early as the design phase. The purpose of this document is therefore to explain the safety rules to be incorporated by the designer during the definition of a project to build a facility implementing sodium at high temperature. These design rules are applicable to the various functions that the facility must provide under the best possible conditions of safety; for this reason, rules pertaining to construction or system operations are not covered in this document.