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


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, rigid phenolic foam, rigid expanded polystyrene foam and low density flexible stone wool. 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 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 to 6.5 × 103 W2 s K−2 m−4.

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  1. 1.

    Thermal conductivity of ceramic paper: 0.08 and 0.11 W m−1 K−1 at 600°C and 800°C, respectively.


c p :

Specific heat capacity (J kg−1 K−1)


Error function

h :

Heat transfer coefficient (W m−2 K−1)

k :

Conductivity (W m−1 K−1)

L :

Thickness or length (m)

\( \dot{m} \) :

Mass flow (kg s−1)

\( \overline{\text{Nu}}_{L} \) :

Nusselt number (–)

\( {\text{Ra}}_{L} \) :

Rayleigh number (–)

t :

Time (s)

\( \dot{q}^{\prime\prime} \) :

Heat flux (W m−2)

T :

Temperature (K or °C)

x :

Space (m)

α :

Absorptivity (–)

ρ :

Density (kg m−3)

κ :

Thermal diffusivity (m2 s−1)

σ :

Stefan–Boltzmann constant (W m−2 K−4)




Of convection




External/incident radiation


Of ignition


Of pyrolysis


Of radiation


Of the surface


Total, considering convection and radiation


Of ambient


Critical heat flux


Carbon monoxide

CO2 :

Carbon dioxide


Differential thermo-gravimetric analysis


Expanded polystyrene


Locally weighted scatterplot smoothing

O2 :



Rigid polyisocyanurate foam


Rigid phenolic foam


Stone mineral wool


Thermo-gravimetric analysis


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The authors would like to gratefully acknowledge funding contribution from Rockwool International A/S towards the Ph.D. studies of Juan P. Hidalgo. Alastair Bartlett is gratefully acknowledged for his contribution with the Cone Calorimeter experiments. Michal Krajcovic is gratefully acknowledged for his precious lab assistance on the performed experimental programmes.

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Correspondence to Juan P. Hidalgo.

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Hidalgo, J.P., Torero, J.L. & Welch, S. Experimental Characterisation of the Fire Behaviour of Thermal Insulation Materials for a Performance-Based Design Methodology. Fire Technol 53, 1201–1232 (2017). https://doi.org/10.1007/s10694-016-0625-z

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  • Insulation materials
  • Fire hazard
  • Pyrolysis onset
  • Performance-based design
  • Critical temperature
  • Fire performance
  • Flammability