The Fire Propagation test, BS 476, Part 6 was developed to assess a lining material's potential contribution to fire growth in an enclosure based on the material's notional k t release profile and is assessed by means of indices derived from measurements of the flue gas temperature. The apparatus was modified to include measurements of mass loss and oxygen consumption to enable calculation of heat release parameters. Air flows into the naturally ventilated enclosure systems were derived from exhaust gas measurements and variations in system combustion efficiencies were identified. Investigations reveal that the Fire Propagation test environment addresses crucial features of a wall lining's heat contribution to a dynamically changing fire environment in enclosures. The derived test performance indicators reflect in a single test, the fie response characteristics of the material with respect to the three generic material types tested, namely, plasterboards, fire retarded and untreated woods.