Threshold heat exposure for establishing sustained flames in a particleboard cavity

During a compartment fire, flames may vent externally through windows. After sufficient exposure to these flames, combustible ventilation cavity walls in a facade system may ignite, sustaining flames even after the initial fire source is extinguished. These sustained flames can ignite wall surfaces above, allowing fire spread upward. This experimental study investigates the minimum heat exposure duration needed to establish sustained flames in a cavity consisting of a particleboard wall and an inert wall, across cavity widths from 2 cm to 7 cm. A narrow cavity leads to more re-radiation between cavity walls but lower oxygen availability, having opposing effects on sustained flames. A 3 cm cavity width required the shortest flame exposure duration, 120 s. Reducing the width to 2 cm or increasing it to 4 cm raised the required exposure duration to 160 s and 145 s, respectively. The elevated temperature above the cavity also suggests an increased potential for fire spread to upper regions of a facade when the cavity width is close to 3 cm. This critical cavity width falls within the range of cavity widths commonly used in facade systems.