Flammability of Polymer Foams

The wide acceptance of polymer foams in construction has led to the necessity of developing such materials of low combustibility often combined with a low smoke evolution during fire. Their characterisation from the point of view of fire safety is a very complex task because of the fact that such materials can potentially be exposed to a large variety of ignition sources and circumstances and the environment influences their performance in a fire. 

A relatively large amount of unfavourable publicity has appeared in the media related to their flammability, smoke and toxicity aspects. Examples are the major fire in 1992 at a vegetable processing facility in Yuma (Arizona, USA), in 1996 at the international observatory in Hawaii, in 2002 in nightclubs in Chicago, Rhode Island and Bali. Producers of polymer foams have made determined efforts to demonstrate that these products do not present an unacceptable fire hazard when properly installed and maintained [153,154]. 

The fire behaviour of polymer foams is largely dependent on their exposure to air and is dominated by the characteristic low thermal inertia which permits the surface to respond very rapidly to any imposed heat flux and consequently ignition maximum rates of burning can be achieved very quickly. Approaches toward reducing the flammability of polymer systems, in general, can be grouped in several categories [25,142,155-176]  

Flame retardant additives operate in several ways. The minerals are resistant to fire and absorb heat. Due to the fact they are likely to be good heat conductors, they carry heat rapidly away from local hot spots, thus preventing or delaying the possibility of the temperature rising to the ignition point. For example, hydrated alumina whose decomposition retards the raising of temperature until the water evapourates. Aromatic 

Phosphorus containing flame retardants are used as phosphates, phosphonates, phosphines and phosphinic oxides. Halogen-containing phosphate esters such as bromine and chlorine in the form of tris (halogen alkyl) phosphates are popular [33]. The effects of phosphorus and brominated additives on flexible PU foam were compared [179]. Melamine has broad utility as a flame retardant additive in flexible PU foams [180]. 

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