Plastics are macromolecular organic compounds produced synthetically or by modification of natural materials. The structure and shape of these macromolecular materials, produced by polymerizational, polyadditional or polycondensational reactions, will strongly influence their properties. The chain molecules of thermoplastics (polyamides, polycarbonates, polyesters, polystyrene, polyvinyl chloride, polymethyl-metacrylate, etc.) are linear or branched, the elastomers (neoprene, polysulphides, isoprene, etc.) are lightly cross-linked, while thermosetting plastics (duroplastics: polyalkydes, epoxy resins, polyurethanes, etc.) are densely cross-linked. Natural caoutchouc is used as raw material by the rubber industry, and after being vulcanized, rubber is produced. The artificial caoutchoucs, the structure of which is similar to that of natural chaoutchouc, are polymers and co-polymers of butadiene. The range of products from plastics and rubber used in nearly all fields of everyday life is steadily widening. Use of the large variety and excellent technical properties of this group of materials results in items such as various building structures, furniture, clothes, commodities, parts for vehicles and machines.
Typically, as organic materials, plastics and rubber also are considered to be combustible materials. For the description of their fire behaviour, a number of parameters are used that can be tested by special methods. With the knowledge of these parameters, one can allocate the fields of their application (determined, pointed out, set), and the fire safety provisions can be elaborated. These parameters are combustibility, ignitability, ability to develop smoke, inclination to produce toxic gases and burning dripping.
In many cases the ignition temperature of plastics is higher than that of wood or any other materials, but in most cases they ignite more easily, and their burning takes place more rapidly and with higher intensity. Fires of plastics are often accompanied by the unpleasant phenomena of large quantities of dense smoke being released that can strongly restrict visibility and develop various toxic gases (hydrochloric acid, phosgene, carbon monoxide, hydrogen cyanide, nitrous gases, etc.). Thermoplastic materials melt during burning, then flow and depending on their location (if mounted in or on a ceiling) produce drops which remain in the burning area and might ignite the combustible materials underneath.
The improvement of burning properties represents a complex problem and a “key issue” of plastics chemistry. Fire-retardant agents inhibit combustibility, ignition will be slower, the rate of combustion will fall, and flame propagation will slow down. At the same time, the quantity and optical density of smoke will be higher and the gas mixture produced will be more toxic.