Assessment of the thermal conductivity of intumescent coatings in fire

• Predictive method for intumescent coatings under different fires.
• Simple and accurate quantification of the intumescent coating thermal conductivity.
• Accurate calculation of intumescent coating protected steel under different conditions.

This paper presents the results of the detailed assessment of a method that can be used to predict the intumescent coating behaviour and thermal conductivity under different conditions (changing steel section factor, intumescent coating thickness and fire condition). The basis of this method is the analytical solution of Amon and Denson (1984) [1] for predicting bubble growth under pressure under an idealised condition, which has previously been extended by the authors to non-uniform temperature field and temperature-dependent viscosity of intumescent melt. This paper demonstrates the accuracy of the predictive method to quantify the expansion process of intumescent coatings under different fire conditions, by comparing the temperatures of intumescent coating protected steel plates under different fire conditions with the fire test results of Zhang et al. (2012) [18]. The method is then applied to assess how the intumescent coating expansion and effective thermal conductivity are affected by changing the coating thickness, the steel thickness and the fire condition including smouldering fire. The results indicate that the expansion ratio of intumescent coating decreases, and hence the effective thermal conductivity increases, as the rate of heating increases. Therefore, the intumescent coating thermal conductivity obtained from the Standard fire exposure can be safely used for slower realistic fires, but would produce unsafe results for faster fires.