Abstract
Cavity walls containing combustible insulation present an increased risk for fire propagation in a confined, concealed space. Damage to the building resulting from ignition of combustible insulation can be extensive; especially so, in the absence of horizontal and vertical fire-stops. Current codes and standards assess fire performance of exterior wall assemblies subjected to external ignition sources. However, test methods do not address the potential fire hazard resulting from ignition of combustible insulation within the wall cavity. A fire performance test has been developed that evaluates the fire propagation behavior of combustible insulation in a configuration that is representative of the actual installation. The test utilizes a full scale cavity wall assembly and offers fire performance evaluation of insulation of any thickness for either a 51 mm or 102 mm wide air space. A propane sand burner was selected as the ignition source; in addition to being reliable and repeatable, its heat output was carefully calibrated to be representative of potential ignition scenarios that may occur within a cavity wall. During the 15 minute fire performance test, the sample is continuously subjected to the propane sand burner exposure fire. An acceptable sample will produce a peak chemical heat release rate less than 100 kW and a maximum visible flame height less than 1.8 m. This fire performance test method is being incorporated into FM Approvals Standard for Cavity Walls and Rainscreens, Class Number 4411 [1] and is suitable for incorporation into other codes and standards. © Owned by the authors, published by EDP Sciences, 2016 Language: en
Highlights
Building trends are showing increased use of cavity walls and rain screens on exterior wall construction
Test results indicate that the proposed cavity wall panel test method is appropriate for evaluating the flame propagation characteristics of cavity wall insulation materials
The peak chemical heat release rates measured during the rigid extruded polystyrene tests were 835 to 1,630 kW while the peak chemical heat release rates measured during the sprayed polyurethane tests were below 100 kW
Summary
Building trends are showing increased use of cavity walls and rain screens on exterior wall construction. Cavity walls are primarily used to allow moisture that has penetrated the outer wall to drain down the cavity space where flashing directs the water to weep holes that remove the water from the cavity. These wall assemblies often contain insulation to increase thermal efficiency. Other combustibles such as air or vapor retarders could be present. Such fires would be difficult to locate and extinguish due to both sides being covered, and could result in fire damage, as well as extensive smoke damage
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