Performance of Intumescent Fire Protection Coatings in Non-Standard Heating Scenarios

Background Theory: Brief Literature Review

Numerous research studies have been carried out to establish the thermo-insulation properties of intumescent coatings by experimental testing usually in combination with some form of numerical analysis and modelling. Experiments include both bench-scale cone calorimeter tests, small-scale furnace tests on coated plates (Bartholmai, 2003, 2006), and furnace tests on cellular beams (Bailey 2006).

Bench-scale studies have examined typical water-based and solvent based intumescent systems (Bartholmai 2003) and also an epoxy resin containing boric acid and phosphate-based intumescent coating (Batholmai 2006). The results from the former show a considerable slow down in the rate of temperature increase, between 200-300°C, due to the intumescence process, the subsequent  insulating char development and also peripheral energy absorbing processes. Temperature influences during the latter tests also resolved a damping effect at 150°C due to the endothermic reaction of boric acid, which releases water. Mesquita (2007) concluded that stable or damping effects occur at low temperatures. 

Mesquita (2007) performed full-scale experimental fire resistance tests, bench scale experiments and subsequent  numerical analysis based on steel plates coated with intumescent coating subjected to a radiant heat flux inside a cone calorimeter. The insulating char thickness and steel temperatures which were measured experimentally have been used in the non linear inverse numerical analysis to assess the intumescence surface temperature and the effective thermal conductivity. It was found that at lower heat fluxes the intumescence becomes more stable, but for the higher heat flux it continues to increase. In terms of our proposed research, which tests intumescent in slow heating curves, the stable nature at lower heat fluxes would suggest that intumescence growth is dependent the time taken for temperature rise.

Han (2010) performed experimental analysis for evaluated thermal shielding efficiency of intumescent coatings using a cone calorimeter as heat source. The relationship between heat flux, distance to cone heater, coating thickness, sample size, edge effect and heat insulator were analysed. It was found that significant relationships between these parameters and the thermal insulating effect of the intumescent coating were evident. Non-standard fire scenario parameters have a greater influence as the heat flux  is varied and as a result trial tests will need to be carried out to ascertain any possible errors which may arise.  There do not appear to be significant differences in using a pin or plate thermocouples, which corresponds with previous research. It was found that results obtained by the cone calorimeter are comparable with large scale furnace tests.