In prescriptive regulation of Japanese Building Standard Code, combustible material can be used as for interior finish when sprinkler system and smoke exhaustion facility is installed in the building. But, in performance based code, it is general that design fire source of interior finish is not considered the fire suppression effect by water application such as sprinkler system. One of the reasons is that the evaluation method for evaluation method of burning behavior of interior finish corresponding to fire suppression effect by water application is not established.
On the other hand, flame propagation speed is characterized with flammability and ignitability of interior finish, according to the results of previous research1). Authors supposed an estimating equation to calculate the heat release rate corresponding to heat of pyrolysis and heat of combustion of the combustible material and water delivered density2). However there is little quantitative knowledge regarding the effect of water application on the ignitability.
A series of experiments was carried out to comprehend the effect of delay of pyrolysis and ignition owing to water application in the present research. Particularly, this research mainly focused on the condition that pyrolysis and ignition of combustible materials occur even though water droplets hit on the material's surface.
The small-scale specimens were installed at 50mm opposite side from electric heater. The water spray (manufacturer: Ikeuchi corporation, model number: JJXP010) was installed at unexposed side of electric heater. Water droplets from water spray were supplied through the hole of electric heater (see Fig. 1).
Two types of specimen were used in the experiments. First is thin steel plate (35mm×35mm×2mm thickness) in order to grasp the heat absorption effect and attenuation effect of radiation owing to water application. Second is PMMA (φ50mm×30mm thickness) in order to comprehend the effect of water application on time to pyrolysis and ignition. Main parameters of the experiments are radiative heat flux (20~40 kW/m2) and water delivered density (0~6 g/s.m2) onto the specimen surface. Pilot burner was used only in second experiment using PMMA.
As the results of first experiments, estimated incident heat flux onto steel plate, which is based on the heat balance of steel plate by using experimental data of the steel plate temperature, is approximately the same as the external heat flux minus sensible heat and latent heat of water (qex–w·Lw) when the supplied water onto specimen completely evaporated. Then, in this case, the attenuation effect of radiation by water droplets was negligible because temperature measured by pyrometer was almost the same as temperature measured by thermocouple.
On the other hand, as the results of second experiments, time to pyrolysis and ignition increased as increasing water delivered density at each external heat flux. Whereas, specimen surface temperature at time to pyrolysis and ignition are 250 C and 350 C, respectively, regardless of external heat flux and water delivered density. According to the results of comparison of external heat flux and inverse square root of time to pyrolysis 1/√tp, it is confirmed that time to pyrolysis with water application can be estimated by using correlation between external heat flux and time to pyrolysis without water application when irradiance with water application is regarded as the external heat flux minus sensible heat and latent heat of water (qex–w·Lw). On the other hand, calculated value of time to ignition by using same method is shorter than actual value. One of the reasons is thought that the pyrolysis gas was prevented oxidation reaction by water droplets and water vapor.
