A relatively large laboratory-scale sample of a commercial type of PVC material usually used in building, flooring, home furnishings, clothing, etc., is thermally decomposed under carefully controlled conditions. Dehydrochlorination of PVC material at high temperature (up to 600 degreesC) has been studied. The results show that dehydrochlorination beginning at the temperature of 150 degreesC can be divided into three stages: low-temperature moderation in the temperature interval 150-180 degreesC, medium-temperature acceleration in the interval 180-250 degreesC, and high-temperature moderation in the interval 250-280 degreesC. The release of chlorine as HCl from PVC materials, at the same temperature, is highest in oxygen, and it increases with an increase of oxygen content. The release of chlorine as HCl is higher by about 5-10% in hydrogen than in nitrogen. In addition, the effect of additives such as dioctyl phthalate (DOP) and calcium stearate (CaSt(2)) on dehydrochlorination of PVC is studied. The release of chlorine as HCl is markedly reduced by additives.