1.1 This part of ISO 182 specifies a method for the determination of the thermal stability at elevated temperature of compounds and products based on vinyl chloride homopolymers and copolymers (in the following text abbreviated as PVC) which undergo dehydrochlorination (the evolution of hydrogen chloride). 1.2 The method may be used as a quality control test during manufacture and conversion of PVC compounds. It may also be used for the characterization of PVC compounds and products, especially with regard to the effectiveness of their heat-stabilizing systems. It is suitable for coloured PVC compounds and products where a discolouration test under the action of heat may be unsatisfactory. 1.3 The method is recommended for compounded PVC materials and products only, although it can be used for polymers in powder form under appropriate conditions, to be agreed upon between the interested parties. The method is not recommended for PVC compounds in the form of dry blends, since such materials may not be sufficiently homogeneous. 1.4 PVC compounds and products may evolve other decomposition products, in addition to hydrogen chloride, at elevated temperatures. A limited number of these decomposition products may affect the conductivity of water when they are absorbed into it. Compensation for this effect is not within the scope of this part of ISO 182, and therefore care is necessary in attempting to compare results for dissimilar compounds and products. In this case a method suitable for the determination of chloride ion (Cl-) in the absorbing solution shall be used (see ISO 182-4). 1.5 The method may also be applied to other plastics materials which can evolve hydrogen chloride or other hydrogen halides when heated under the conditions prescribed by the relevant specifications, or as agreed upon between the interested parties.