Fire Safety Science Digital Archive

An operator independent method for measuring the time to ignition is presented. Ignition occurs when the 2nd derivative of mass loss vs. time curve reaches its peak, i.e., when the mass loss rate increases most rapidly due to applied heating. Prior to evaluating the 2nd derivative one smoothes the data using the 4th order Savitski-Golay method. The technique is demonstrated for a wide variety of polymers (PMMA, POM, FRPP, Polyisocyanurate foam, PVC, CPVC and PVDF) to examine their ignition behavior in ambient air as well as in 40% oxygen. The 2nd derivative and the observed ignition times are compared. In all cases, the times are identical in 40% oxygen. The two times are also identical for ordinary polymers in air. However, for the halogenated fuels, PVC, CPVC and PVDF, the observed ignition is both intermittent and delayed. For halogenated fuels, enhanced ambient oxygen accelerates gas-phase combustion, but has negligible effect on initiation of mass transfer. In most cases, the agreement between observed and 2nd derivative ignition times in air and in 40% oxygen is quite remarkable, confirming that the operator independent 2nd derivative ignition method is both reliable and consistent.