Experimental Characterisation of the Fire Behaviour of Thermal Insulation Materials for a Performance-Based Design Methodology

Abstract

A novel performance-based methodology for the quantitative fire safe design of building assemblies including insulation materials has recently been proposed. This approach is based on the definition of suitable thermal barriers in order to control the fire hazards imposed by the insulation. Under this framework, the concept of "critical temperature" has been used to define an initiating failure criterion for the insulation, so as to ensure there will be no significant contribution to the fire nor generation of hazardous gas effluents. This paper proposes a methodology to evaluate this "critical temperature" using as examples some of the most common insulation materials used for buildings in the EU market, i.e. rigid polyisocyanurate foam (PIR), rigid phenolic foam (PF), rigid expanded polystyrene foam (EPS) and low density flexible stone wool (SW). A characterisation of these materials, based on a series of ad-hoc Cone Calorimeter and thermo-gravimetric experiments, serves to establish the rationale behind the quantification of the critical temperature. The temperature of the main peak of pyrolysis, obtained from differential thermo-gravimetric analysis (DTG) under a nitrogen atmosphere at low heating rates, is proposed as the "critical temperature" for materials that do not significantly shrink and melt, i.e. charring insulation materials. For materials with shrinking and melting behaviour it is suggested that the melting point could be used as "critical temperature". Conservative values of "critical temperature" proposed are 300 °C for polyisocyanurate, 425 °C for phenolic foam and 240 °C for expanded polystyrene. The concept of a "critical temperature" for the low density stone wool is examined in the same manner and found to be non-applicable due to the inability to promote a flammable mixture. Additionally, thermal inertia values required for the performance-based methodology are obtained for PIR and PF using a novel approach, providing thermal inertia values within the range 4.5-6.5 •10 3 W 2 •s•K-2 •m-4 .

Fire performance of closed‐cell charring insulation materials in plasterboard‐insulation assemblies

“…12,14 Noting the concerns regarding a potential inadequate extrapolation of the fire performance of these specific products to the performance of generic material groups, 23 the polyisocyanurate and phenolic foam used within this work are hereafter denoted as foams A and B, respectively. 12,14 Noting the concerns regarding a potential inadequate extrapolation of the fire performance of these specific products to the performance of generic material groups, 23 the polyisocyanurate and phenolic foam used within this work are hereafter denoted as foams A and B, respectively.…”

“…12,18 Given that the plasterboard is placed at the surface of the insulation, it is expected that pyrolysis gases may not be able to establish a flame at this surface but be released by cracks or gaps from the assembly. The use of thermocouples is essential to determine the instant at which the insulation starts pyrolysing ("critical temperature") and therefore establish a conservative primary failure mode consistent with previous work.…”

“…[5][6][7][8][9][10][11] Recently, Hidalgo et al 12 presented thermogravimetric analyses (TGA) and an assessment of flammability parameters (critical heat flux for ignition and thermal inertia) through cone calorimeter testing 13 for the specific materials studied within their research framework. Characterisation of the thermal decomposition experienced by several types of polyisocyanurate and phenolic foam insulation at high temperatures has been pursued by several authors.…”

“…12 The general issues associated with sample identification and results generalisation have recently been highlighted in a letter regarding materials identification sent to fire journal editors. 12 The general issues associated with sample identification and results generalisation have recently been highlighted in a letter regarding materials identification sent to fire journal editors.…”

“…12 The general issues associated with sample identification and results generalisation have recently been highlighted in a letter regarding materials identification sent to fire journal editors. 12 The work presented herein provides an expansion of the framework for the fire safe use of insulation materials. Additionally, the formulation of these materials is generally confidential and not publicly accessible.…”