The cone calorimeter with the controlled atmosphere compartment was used to control the fire air ventilation and to simulate the behaviour of materials in compartment fires, with rich burning under post flashover conditions. The standard cone calorimeter with controlled atmosphere design has to be improved, by compartment wall insulation, to reduce heat losses which reduced the fire temperature. Heat losses from the test section to the water cooled load cell were shown to be significant and the test specimen was insultated from the support. A chimney was added to the cone outlet to enable the measurement of the mean composition of the raw discharge gases. A method was developed for determining the mean gas sample and to prevent back flow of external air. This improved design was used to create under ventilated fires with pine wood where the equivalence ratio was controlled by the air flow into the compartment. These modified procedures for the cone calorimeter greatly extend its usefulness in material testing to conditions close to those encountered in post flashover compartment fires
