The Effectiveness of Horizontal Barriers in Preventing Fire Spread on Vertical Insulation Panels Made of Polystyrene Foams

Expanded polystyrene (EPS) and extruded polystyrene (XPS) foams are both excellent exterior thermal insulation materials for buildings. However, their flammability also induces high fire hazard. Current regulation in China requires horizontal fire barriers with a minimum height of 30 cm when polystyrene foams are used as the external insulation. The present work evaluates the effectiveness of such barriers in inhibiting fire growth in insulation walls. The walls were made of B2 grade EPS and XPS foams without protective coatings but with mineral wool as horizontal barriers. Altogether six combinations of fire positions and barrier positions were tested for both EPS and XPS. The heat release rate (HRR) of the fire and the temperature distribution on the wall were recorded and analyzed. The results indicate that, without a barrier, fire starting at the middle of the wall generated higher peak HRR than that starting at the bottom, which was in turn higher than that starting at the top. When the insulation panel below the barrier was 1 m high, the upward fire spread from the bottom could be stopped by 40-cm, but not 30-cm, barriers. However, when the insulation panel below the barrier was 2 m high, even the 40-cm barriers failed. Lastly, the downward fire spread from above could not be stopped by 40-cm barrier due to dripping of burning plastics. The study highlights the limitations of horizontal fire barriers in preventing the vertical fire spread over exposed B2 grade polystyrene insulation and establishes protocols for further investigations.