This standard specifies the test gases, test pressures and categories of appliances relative to the use of gaseous fuels of the first, second and third families. It serves as a reference document in the specific standards for appliances that fall within the scope of the Council Directive on the approximation of the laws of Member States concerning gas appliances (90/396/EC). The standard makes recommendations for the use of the gases and pressures to be applied for the tests. The full procedure will be given in the corresponding appliance standards. NOTE The test gases and the test pressures specified in this standard are in principle intended to be used with all the appliances in order to establish conformity with the corresponding standards. However, the use of some test gases and test pressures may not be appropriate in the following cases: appliances with nominal heat input greater than 300 kW; appliances constructed on site; appliances in which the final design is influenced by the user; appliances constructed for use with high supply pressures (notably direct use of the saturated vapour pressure). In these cases, the specific appliance standards may specify other test conditions in order to establish compliance with their requirements.