The phosphorus oxidation state has also recently been reported to influence flame retardancy . It was shown that by increasing the phosphorus oxidation state, the condensed phase mechanism could be favoured by the accumulation of a carbon layer, resulting in retardation of flame propagation. Secondary dissociation reactions were shown to be primarily facilitated by the phosphorus oxidation state. It was also demonstrated that the presence of oxygen in such HFFR systems favours the cleavage of P-C bonds, offering different FR mechanisms that could influence the flame spread.