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8 The PCB Magazine • March 2015 Abstract This article takes a critical look at all aspects of fire retardancy, starting with the need for fire safety. The function of a flame retardant is exam- ined and reactive and additive flame retardant classes are contrasted along with their chemical and physical effect mechanisms. Major flame retardant compounds, both halogen and halo- gen free, are examined in detail. Toxicology and Environmental impact are examined with particular emphasis on Tetrabromobisphenol-A which is the most widely used flame retardant in PCB materials. European legislative directives are also considered. by Alun Morgan EurOpEan InSTITuTE Of prInTED CIrCuITS I. What are flame retardants? Flame retardants are compounds, which when added to materials during or after man- ufacture, inhibit or suppress the combustion process. They interfere with combustion at various stages of the process, e.g., during heating, de- composition, ignition or flame spread. Their primary function is to suppress the spread of fires or delay the time of flashover so that peo- ple can escape. Flame retardants used in plastic materials fall broadly into two categories, namely ad- ditive and reactive. Additive flame retardants are incorporated and dispersed into the plastic prior to, during, or most commonly following polymerisation. If they are chemically compat- ible with the plastic they act as plasticisers oth- Feature