The U.S. Bureau of Mines performed experiments to determine if primary gas toxicities that evolve during the early (approx. 300 Deg c) and later (> or = 400 deg c) combustion stages of polyvinyl chloride and chlorinated brattices could be predicted by a smoke particle characteristic, which could be used as a simple and inexpensive test parameter. The experiments were conducted in an approximately 20-l furnace at set furnace temperatures of 250 deg and 1,000 deg c, for 14-min duration, with an airflow through the furnace of 10 l/min. The variables studied, as a function of time, were the hydrogen chloride (hcl) and carbon monoxide (co) concentrations, sample and furnace temperatures, the sample mass weight loss, the average smoke particle diameter (dg) and number concentration (no), and the product of the average smoke particle diameter and concentration (dgno). Results show that the inverse of the smoke particle diameter-concentration (l/dgno) correlates directly with the primary gas toxicities evolved during both stages of combustion.