Experimental study on temperature field of upward flame spread over discrete polystyrene foam

In this work, thermal analysis methods were used to obtain the temperature field of discrete flame spread across polystyrene (PS) foam inserted with incombustible barrier. The barrier length (L ₀) and the length (L) of PS below were changed to investigate their effects. The frontal temperature field (X–Z plane) showed that in cases where barrier prevented upward flame spread, the flame spread consists of three stages, namely growth stage, heating stage, and attenuation stage (or “upward spreading stage” for failed preventing case). During the heating stage, the area and the height of high-temperature zone (about 630–750 °C) in failed preventing cases were significantly larger than those in prevented cases, while the heating stage duration of the former was shorter. The maximum temperature was observed below the barrier. For XPS with lower length ratio (L/L ₀), the area of the high-temperature zone is larger than that of EPS with higher length ratio. The temperature field of the longitudinal section (Y–Z plane) revealed that the high-temperature zone was localized between −1 and 1 cm of the Y-axis. With the varying of L/L ₀ (L/L ₀ decreased for XPS while for EPS L/L ₀ first dropped and then rose), the vertical distance between the high-temperature zone and the unburned PS surface increased, while the area of the high-temperature zone and the temperature gradient decreased. Thus, the upward flame spread was prevented. These findings are helpful to reveal the mechanism of discrete flame spread.