*3.7. Reaction to Fire*

The thermal properties and results of the cone calorimeter tests are presented in Table 8 and Figure 7.

**Table 8.** Results of the test calorimeter cone for WCSP and GB in accordance with ASTM E1354-17 (from start of test +15 min).


The WCSP with a SP replacement rate of 15% was tested for comparison with GB. Test results in Figure 7a indicate that the heat release rate (HRR) of GB increases very quickly and reaches a maximum at about 65 s, due to burning of the overlay paper occurring at about 57 s (Table 8). The WCSP showed very low HRR throughout the 20 min duration. The peak of heat release is not obvious as no combustion took place (Table 8). The HRR of WCSP varied from <sup>−</sup>2 to 16 kW/m2 and also varied from <sup>−</sup>4 to 12 kW/m2 in the case of GB after the ignition. Such variations are related to the accuracy of the cone calorimeter for materials exhibiting low combustibility characteristics, such as a THR less than 15 MJ/m2.

The National Building Code of Canada (NBCC) states that a material can be used in non-combustible construction provided that, when tested in accordance with CAN/ULC-S135 [25] at a heat flux of 50 kW/m2, the total heat release is no more than 3 MJ/m<sup>2</sup> and the total smoke extinction area is no more than 1.0 m2.

Figure 7b shows that WCSP behaves similarly to GB with respect to mass loss. Indeed, the remaining mass of GB after 15 min is 81% while the WCSP is 78%. The average total smoke production for 15 min recorded for both materials are less than 1 m2 (Table 8). Their average total heat release (THR) exceed in each case 3 MJ/m2 (Figure 7 and Table 8). While CAN/ULC-S135 slightly differs from ISO 5660, the results suggest that WCSP would most likely fail these requirements due to its average THR exceeding 3 MJ/m2. Given the low value threshold of 3 MJ/m2, very few products consisting in whole or in part of combustible materials will pass this test [26]. It is unclear from the NBCC as to how this threshold value was determined.

In Japan, based on the performance during a cone calorimeter test when subjected to an irradiance level of 50 kW/m2, the reaction to fire of interior finishing materials are classified as being non-combustible, quasi-non-combustible or fire retardant [27]. Neither WCSP nor GB actually meet the Japanese criteria of a non-combustible material: THR <sup>≤</sup> 8 MJ/m2 and peak rate of heat release <sup>≤</sup>200 kW/m<sup>2</sup> after 20 min of exposure. It is noted that the Japanese THR threshold of 8 MJ/m2 is much less severe than the Canadian value of 3 MJ/m2. They would however both meet the criteria for a quasi-non-combustible material: THR <sup>≤</sup> 8 MJ/m2 and peak rate of heat release <sup>≤</sup>200 kW/m2 after 10 min of exposure.

Flame-spread, which is used to describe the surface burning characteristics of building materials, is one of the most commonly tested fire performance characteristics for limiting fire growth in the early stage of fire development. The results generated in this study show that the surface of WCSP is still not burnt after 20 min. The surface color barely changed and neither fractures nor burnt surface could be observed in Figure 7d). The side face of the specimen became dark due to direct contact with the metallic specimen holder and the aluminum wrap, while the surface of the GB burned completely (Figure 7e). The side face of the sample shows that the GB burned and became dark (Figure 7f) across the thickness, while the 3 mm surface layer of the WCSP almost did not change color (Figure 7g) and did not burn. However, the wood particles on the inside and back face of the WCSP became dark

due to the high temperature and large porosity (Figure 7g,h). It may explain why the HRR of WCSP (−2 to 16 kW/m2) was slightly higher than that of GB (−4 to 12 kW/m2) after the end of ignition of GB (Figure 7a).

**Figure 7.** Cone calorimeter measurements: (**a**) Heat release rate (HRR). (**b**) Relative mass. (**c**) Total heat release (THR). (**d**) Front face of WCSP before (**left**) and after (**right**) testing. (**e**) Front face of GB before (**left**) and after (**right**) testing. (**f**) Side face of gypsum specimen before and after testing. (**g**) Side face of WCSP before (**left**) and after (**right**) testing. (**h**) Back face (**left**) before and after testing (**right**) of WCSP.
