**4. Fire retardancy of flammable materials**

Typically, the flammable materials are easily combustible and rapidly growing in a fire (reaction-to-fire), in terms of the spread of fire or propagation of fire, up the stage when flashover occurs in a compartment. Flashover can occur quickly in seconds or slowly depending on the speed of fire growth rate. Wood is the most frequently used combustible products in addition with polymers (plastics and rubbers), foams, textiles, cables, and fire reinforced composites. Three different kinds of methods, such as clear or transparent varnish paints, pigmented intumescent reactive coatings, and surface impregnations are utilized in wood to enable the restriction of growth and/or spread of fire. The European fire classification for reaction-to-fire is based on fire growth rate index (FIGRA), which indicates the time to reach flashover in the standardized reference test as per BS EN 14390. Other test methods, the single burning item (SBI) test (BS EN 13823; 2002), radiant panel test for flooring (EN ISO 9239-1; 2002) and either the small flame test (BS EN 11925-2; 2002) or the bomb calorimeter (BS EN ISO 1716), are also relevant to the fire retardant system in Euro-class [8]. Two standards, such as fire propagation test (BS476, part 6:1989) and surface spread of flame test (BS476, part 7:1987), were applicable to the fire test methods in the UK for flammable materials. The BS476, part 6 test method is intended to provide a comparative measure of the contribution to the growth of fire of a product. The test result is expressed as fire propagation index (I) and three sub-indices, i1, i2, and i3. The higher the fire propagation index means the greater the growth of fire. On the other hand, the BS476, part 7 measures the lateral spread of flame along the surface of a specimen, which is mounted at right angles to a high intensity radiation panel. The extent and rate of flame spread of specimen are used to determine the classification, which can range from Class 1 (the best) down to Class 4. The ASTM E 84, 2010 and ISO 5660 are most commonly used in USA and International standards for testing of flammable materials. The factors influencing the performance of coating systems are thickness, density, substrates, composites, and panel type. Each type of product shall be evaluated and representative specimens shall be tested to ensure that the effect of each variable parameter is considered.
