The Tewarson apparatus is a combustion calorimeter developed by Factory Mutual Research Corporation in the USA in the 1970s. A modified and computerized version of this calorimeter is used at the Rhone-Poulenc Decines Centre to study the combustion of plastics, fabrics, chemicals and pesticides on 30 g samples in a 0.1 m diameter glass dish. The combustion of up to 100 products has been Studied in this experimental set-up and-he following thermal data obtained: mass of product;burnt, experimental heat of combustion, combustion efficiency, burning mass flux, ratios of convection and radiant heat, flame height, flame temperature. The on-line analysis of combustion gases provides the following chemical data: production of CO2, CO, HCN, NO2, NO,-SO2, HCl,HF, HBr, chemical yield for the combustion of carbon, nitrogen, sulphur, chlorine, fluorine, bromine. The thermal data obtained are input to the POOL 2:0 computer code to estimate the thermal effect of chemical pool fires. The combustion chemical data obtained are input to atmospheric dispersion codes to estimate; the toxic effects of chemical pool fires. The correlation of experimental data obtained using the Tewarson apparatus, based on the sample chemical formulae, helps provide the missing combustion data. As an example, a correlation is given for the combustion characteristics of chlorinated organic chemicals.