**4. Discussion**

The test of a model of a ventilated facade made of two different external claddings showed significant material differences. Large-slab ceramic tiles very quickly, in the first few minutes or so, were destroyed by high temperatures, then their degradation does not deepen. The course of events in the part made of fiber cement boards looks different. In the initial stage of the fire, the panels show high resistance—the first few minutes or so. About 11 min, the first signs of degradation of fiber cement boards are visible (Figure 4c). Then the state of the degradation was deepened until the final destruction. Fiber cement boards have exhausted their load-bearing capacity during high temperature exposure. They were held on the structure only by perforated steel tapes. The authors wanting to refer the results from large-scale test to testing on samples by Szymków [1], had to specify the method of reference of the results. The temperature in the large-scale test was much higher than in Szymków's research [1], the time function will be not representative. The authors determined that as the most reflecting value will be function of integral.

The integral corresponding to the temperature function from time was determined for all thermocouples. The following results were obtained:


These results are shown in Figure 8 together with temperature diagrams for all thermocouples: TE1, TE2, TE3, TE4. In this graph we can observe a linear growth pattern of the integral for TE3 and TE4 thermocouples (thermocouples placed in a part of the cladding made of large-slab ceramic tiles). In addition, in the part with ceramic sinters the fire force was much higher. The maximum temperature for TE3 was 862.7 ◦C and for TE2 thermocouple measuring the temperature in the area of fiber cement boards it was 735.5 ◦C. The much higher temperatures in the large-slab ceramic tiles area were caused by the much faster destruction of this material, the "release" of access to the thermocouples. The falling-off of large-slab ceramic tiles made easier way to burn mineral wool, this allows maintain higher temperature. In addition, it was likely that ceramic sinters insulate thermocouples much worse than fiber cement boards. The temperature course for TE1 and TE2 thermocouples contains much more disturbances and significant faults. In addition, the integral function has a visible refraction in 34th and 39th minutes for TE1 thermocouple and 42nd and 48th minutes for TE2 thermocouple.

**Figure 8.** Temperature measurement results for thermocouples and the increasing integral for the temperature-time function.

Szymków in [16] carried out tests to identify the degree of destruction of fiber cement boards under high temperatures. He analyzed the influence of temperature 400 ◦C in a given unit of time. Di fferent samples of 20 mm × 100 mm fiber cement boards were subjected to high temperature influence in 1 to 15 min. The samples di ffered in technical parameters, composition, production technology and area of application and were tested at di fferent times. Characteristic parameters of individual sample series given by the manufacturer are presented in Table 1.



For the purposes of the articles, selected test results from [16] were used. Fracture energy *Wf* and modulus of rupture *MOR* were analyzed. The results are presented in Table 2.

**Table 2.** Aggregate summary of averaged values of fracture energy *Wf* and modulus of rupture MOR for panels, under the influence of high temperature 400 ◦C from 1 to 15 min [1].


As the results shown in the study [16] show, for fiber cement boards at high temperature of 400 ◦C, the fracture energy increased in the initial phase. In case of B, C, D series boards, the fracture energy increased from 2% to 9%. Then a decrease in the fracture energy was visible for all types of fiber cement boards. The same was true for modulus of rupture *MOR*, which increased from 3% to 20% in the initial period and then decreases. Table 3 shows the aggregate summary of the temperature function integral from the maximum time that a sample could be tested for the A–E series of boards.


**Table 3.** Aggregate summary of the temperature function integral from the maximum time [1].

For the purpose of further analyses, the average value of the function integral for all series was assumed to be 3800 (◦C × min). The average value of the function integral for all series corresponds to the increasing integral for TE1 thermocouple in about 20.5 min and the increasing integral for TE2 thermocouple in about 12.75 min. This is reflected in Figure 6; Figure 8. The time of 12.75 min approximately coincides with the point of significant fault in the temperature graph for TE1 thermocouple. This corresponds to the beginning of the destruction in 11th minute of the tested model (Figure 5). Fiber cement boards detach into parts, probably obscuring the TE1 thermocouple. Then the fiber cement panels were continuously destroyed until the end of the test. This corresponds to integral 42,686.2 (◦C × min). The tests shown in [16] end with the integral value of 6000 (◦C × min). The results obtained during the test in question indicate identical tendencies to the behavior of the samples presented in [16].
