In the literature, several other types of HFFR are also reported. For example, phosphate-based flame retardants (PFR) are reviewed by Levchik and Shen ; P-N based by Klatt , and mineral based by Sauerwein The literature shows that PFR additives used as HFFR have different chemical structures and compositions. PFR combinations acting in both the gas and the condensed phase are very suitable for effective FR systems, according to both Camino and Schartel. Reduced combustion efficiency by using HFFR is usually accompanied by an increase in CO and smoke production, according to Schartel . The main source of heat generation causing more burning is the conversion of CO to CO2 by oxidation with the OH-radicals present in the flame. This suggests that PFR combinations, generally favoured, should minimize CO oxidation and should result in higher CO yields.