PAST RESEARCH 



Effects of Flame Retardants 



Generally speaking, flame retardants de- 

 crease the maximum rate of combustion and 

 increase the production of char, which is a 

 portion of the airborne particulate from wood 

 fires. Another source of particulate is proba- 

 bly the tar fractions. A retardant that en- 

 hances char and tar production will produce 

 more particulate if it does not in some way 

 also enhance the more complete combustion 

 of the char by glowing. Past work has shown 

 that most flame retardants increase CO, C0 2 , 

 and H 2 produced from the pyrolysis of wood 

 and cellulosic fuels. 1 



The pyrolysis and combustion of cellulosic 

 fuels can be graphically expressed as involving 

 two competitive pathways. The low energy 

 pathway, which occurs at temperatures 

 around 270° C. or less for cellulose, produces 

 char and relatively large amounts of water and 

 carbon dioxide. The char usually sustains 

 glowing combustion. The high energy path- 



1 F. Shafizadeh. Pyrolysis and combustion of cellu- 

 losic materials. P. 419-474, in: Advances in Carbo- 

 hydrate Chemistry. R. Stuart Tipson, Ed., Vol. 23. 

 New York and London: Academic Press. 1968. 



way, which occurs at 340" C. or higher for 

 cellulose, produces flammable volatiles; these 

 support flaming combustion and produce little 

 char or residue. 



The effect of most pyrolytic flame retar- 

 dants is to emphasize the low energy pathway 

 at the expense of flaming. This is generally 

 characterized by the lowering of the tempera- 

 ture of pyrolysis and an increase in char. The 

 enhancement of the "glowing" mechanism at 

 the expense of "flaming" does not mean there 

 will be a decrease in residue following the fire. 

 There may be a relative increase in energy re- 

 leased by way of the low energy pathway, but 

 the total energy released may be decreased be- 

 cause of the residue produced. Whether the 

 residue sustains glowing or not depends upon 

 the chemical composition of the retardant 

 used and the environmental conditions. This 

 is not readily apparent if one considers only 

 pyrolysis. When combustion is included, the 

 picture becomes complicated by the possibil- 

 ity of a retardant catalyzing the glowing com- 

 bustion of the residue as compared to another 

 equally effective retardant that might alter 

 some other combustion phenomenon. 



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