First let us understand how burning during a fire happens: burning requires fuel, oxygen, and flame. Without oxygen, burning cannot sustain or continue. Flame retardants use different mechanisms to cut the oxygen supply, since without continuous oxygen supply flame cannot spread.
Two major prevention mechanisms are: Removal (absorption) of oxygen from air which surrounds the flame (or ignition point). The other is forming a condensed layer of material around the flame (carbonaceous) to prevent oxygen flow.
Halogens (chlorine, fluorine etc) are chemicals which readily combine with oxygen or react with oxygen to form a by-product. Hence, if halogens are introduced into a flame, they remove or absorb oxygen. PVC uses both the mechanisms of flame retarding and when introduced into a flame, emits chlorine, which reacts with oxygen around the flame, thereby enabling removal/absorption of oxygen. PVC also swells to form a condensed layer, which obstructs the free flow of oxygen. Hence, the material burns until the oxygen depletes within the condensed layer and the depletion of oxygen is through reaction with halogen.
In order to explain the behaviour of PVC and other chlorinated polymers like PVDC in the fire, we need to look at their chemical structures and existing elements. In a fire event, PVC first flashes intermittently and after some time burns steadily, in both ventilated (abundant oxygen) and vitiated (limited oxygen available). Poor combustion of PVC is mainly due to the presence of chlorine element in its chemical structure which greatly disturbs the burning process, resulting in HCl and many other compounds. These burning products (HCl and other Cl compounds) act as flame retardant agents, extinguishing the flame.
Therefore, we term PVC as a flame-retardant material. Wood that once catches fire is difficult to control for its speed of spread. And if there is wind blowing, then one cannot control the spread and fire will rapidly cover the surrounding area as well.
Nowadays, incidences of fire in multi storeyed buildings are on the rise, where fire expands rapidly because of the wooden furniture in the homes. Hence, we strongly believe that use of WPC boards should be encouraged more and more to prevent fire and save human lives and assets.
