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, 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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Notes

  1. 1.

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

Abbreviations

c p :

Specific heat capacity (J kg−1 K−1)

erfc:

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)

c:

Characteristic

conv:

Of convection

cr:

Critical

e:

External/incident radiation

ig:

Of ignition

P:

Of pyrolysis

r:

Of radiation

s:

Of the surface

T:

Total, considering convection and radiation

∞:

Of ambient

CHF:

Critical heat flux

CO:

Carbon monoxide

CO2 :

Carbon dioxide

DTG:

Differential thermo-gravimetric analysis

EPS:

Expanded polystyrene

LOESS:

Locally weighted scatterplot smoothing

O2 :

Oxygen

PIR:

Rigid polyisocyanurate foam

PF:

Rigid phenolic foam

SW:

Stone mineral wool

TGA:

Thermo-gravimetric analysis

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Acknowledgments

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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Keywords

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