The piloted transition to flaming in smoldering fire retarded and non‐fire retarded polyurethane foam

Abstract

The piloted transition from smoldering to flaming, though a significant fire safety concern, has not been previously extensively studied. Experimental results are presented on the piloted transition from smoldering to flaming in non-fire retarded (NFR) polyurethane foam and the fire retarded polyurethane foam Pyrell ® . The samples are small blocks, vertically placed in the wall of an upward wind tunnel. The free surface is exposed to an oxidizer flow and a radiant heat flux. The smolder product gases pass upwards through a pilot. The experiments on NFR foam show that the smolder velocity and peak smolder temperature, which increase with the oxygen concentration and heat flux, are strongly correlated to the transition to flaming event, in that there are minimum values of these parameters for transition to occur. The existence of a minimum smolder velocity for ignition supports the concept of a gaseous mixture reaching a lean flammability limit as the criterion for the transition to flaming. To compensate for the solid-and gas-phase effects of the fire retardants on the piloted transition in Pyrell, it was necessary to increase the oxygen concentration and the power supplied to the smolder igniter and the pilot. The piloted transition is observed in oxygen concentrations above 17% in NFR foam, and above 23% in Pyrell. The results show that although Pyrell is less flammable than NFR foam, it is still susceptible to smoldering and the piloted transition to flaming in oxygen-enriched environments, which is of interest for special applications such as future space missions.

Radiant Ignition of Polyurethane Foam: The Effect of Sample Size

“…The error in the spread rate is estimated to be ±25% due to the uncertainty of ±2.5 mm in the thermocouple placement in the foam. The spread rates measured for smouldering are in agreement with the work of Anderson et al [5] using a similar experimental set-up but are higher than those generally found for unassisted smouldering [3,17]. The higher spread rate could be explained by the energy assistance provided by the heater.…”

“…Putzeys et al [17] found that a minimum heat flux between 8 kW m À2 and 8:75 kW m À2 will result in the transition from smouldering to flaming of a 50 mm 9 50 mm 9 125 mm sample of PU foam with internal forced flow and sample sides heated to 200°C by external means. This value is much lower than that measured here for 50 mm size ð45 kW m À2 to 48 kW m À2 ), but the heating of the samples in [7] sides and the increased air flow dramatically enhance the smouldering combustion, increasing the likelihood of transition to flaming.…”

“…Transition is a complex phenomenon which, though significant in fire safety, has received relatively little study. Putzeys et al [17] found that the smoulder velocity and peak temperature are strongly correlated to the occurrence of transition from smouldering to flaming. The transition has also been observed to occur when pores are formed in the region behind the smouldering front [18].…”

Onset of smoldering in cotton: Effects of density

“…. In comparison, Putzeys et al and Torero and Fernandez-Pello used open cell, non-fire retarded polyurethane foam with density 26.5 kg/m 3 , porosity 0.975 and permeability 2.76•10 −9 m 2 in their experiments on smoldering ignition and propagation[70,84].…”

Apparatus for the vertical orientation cone calorimeter testing of flexible polyurethane foams

“…Flexible polyurethane (PU) foam presents some unique fire threats in the modern home because it is not only a high heat release material when it burns but also because when it burns it collapses into a pool of burning material that can lead to rapid flashover events should beds or upholstered furniture catch fire . Of course, ignition source intensity and the presence/absence of flame retardants (FRs) will affect fire growth from burning PU foam , but even then, most flame retarded flexible foams still drip and flow upon exposure to flame as most of the existing FRs in commercial use for flexible foams are designed to reduce heat release and inhibit ignition and flame spread, not necessarily to prevent dripping . For a FR to be effective in flexible foams, multiple mechanisms of action can be utilized to provide satisfactory performance in a regulatory fire test.…”