After comparing the overall fire protection effect, we compared the fire protection effect of various materials via classification.
3.3.1. Different Brands of IFC
After comparing the data for case 2 and case 3 in
Figure 8, it was obvious that brand B IFC (W) was better than brand A IFC (W).
Figure 11 shows the specimens of case 2 and case 3 after the fire test. It could be seen from the observation that the fire-retardant coatings of case 3 still adhered to the tray after expansion, while the coatings of case 2 had poor adhesiveness, and a large amount of the coatings fell off at the bottom and side of the tray. The adhesion effect shown here was consistent with the adhesive strength of this two coatings in
Table 2.
The coatings of case 2 and case 3 after the fire test were taken for thickness measurements, and the data was recorded in
Table 5. It could be seen that the expansion ratio of case 3 is larger than that of case 2. Hence, we could conclude that the adhesive property and the expansion effect of the brand B IFC (W) were better than those of brand A.
By comparing the temperature curves of case 2 and case 3 in
Figure 9, it could be inferred that the low expansion ratio of case 2 resulted in a larger temperature rise, and the slope of the case 2 temperature curve suddenly became larger at about 1200 s, which might have been caused by the coating shedding of case 2.
At the same time, we also considered the char structure produced by different kinds of coatings after heating. Taking the coating of case 2 and case 3 respectively, we found that the char structure of case 3 was more compact in appearance, as shown in
Figure 12.
Further, we observed the microstructure of char by SEM (scanning electron microscope) at 100 times, as shown in
Figure 13. It could be found that the char of case 2 had a porous and loose structure, while the char of case 3 was compact, and the gap between cells was closed. According to the discussion of Puri, R.G. et al. [
38], the fire protection effect of char structure like case 3 was better.
Therefore, before selecting IFC for large-scale projects, we can heat the coated plate and compare the expansion progress, cohesiveness and char structure of coatings to select a better one.
3.3.3. Different Thickness
After comparing the data for case 3, case 4, case 5, and case 6 in
Figure 8, it was found that the thicker the coatings were, the better the fire protection effect was. After observing the coatings of these four cases, the expansion effect for each case of coatings was found to be good, and there was essentially no shedding phenomenon. The coatings of these four cases after the fire test were taken for thickness measurements, and the data were recorded in
Table 7.
From the table, we could find two phenomenon:
The expansion ratio of the coatings decrease with the increase of the coating thickness.
The final coating thickness of case 4 after expansion was similar to that of case 3, but the failure time was very different.
According to the principle of IFC in
Section 2.4, shielded by the upper char layer (closer to fire), the lower layer might be in the last three stages without full expansion, so it seemed unreasonable to take it as a conclusion directly. We took the upper char layer and the lower char layer after the experiment, and found that the color of the lower char layer was lighter, as shown in
Figure 14, which further indicated that the lower char might not fully expand.
In order to find out the reason of these two phenomenon and draw a reasonable conclusion, we did a simple supplementary experiment. We put the plates coated with 1.5 mm and 2.5 mm brand B IFC (W) under the condition of pool fire and heated it fully until the char no longer expanded, as shown in
Figure 15. In the experiment, the coatings near the center of the fire source foamed first, the coating thickness was recorded every minute.
The thickness of the fully expanded coating was measured and recorded in
Table 8.
The coating thickness curve is shown in
Figure 16.
From
Table 8 and
Figure 16, we could see that the expansion ratio of the same kind of coating had nothing to do with the initial coating thickness. After the complete expansion, the expansion ratio was basically the same, and the expansion speed gradually slowed down with time. However, the coating with thicker initial thickness always had thicker thickness in the whole process of expansion, so this might be the reason why the temperature rise of 2.5 mm specimen was slower than that of 1.5 mm specimen in
Figure 9.
Further observation of the temperature curve displayed in
Figure 9 showed that the initial stage of the temperature curve of case 3 was a downward convex curve, while the initial stage of the temperature curve of case 4, case 5, and case 6 was an upward convex curve, which indicated that the initial temperature rises of the latter three cases were faster. According to the analysis of the supplementary experiment, it was speculated that this might have been because the coating thickness was thinner during the heating process due to the thinner initial thickness, and when the coating were expanding, a large amount of heat was transferred to the tray at early stage. Even after the coating completely expanded, the temperature rise rate decreased, but because the temperature in the tray had reached a high value, the cable still failed quickly. Therefore, when IFC were used to protect the cables in the trays, a certain initial thickness of the coatings was necessary.
For case 8, case 9, and case 10, brand C NFC were used, and the thicker the coating was, the better the fire protection effect was. The initial temperature rises for these three cases were relatively slow, and the temperature rise rate slowly increased with time.
For case 11 and case 12 using brand D FC, the thicker the material was, the better the fire protection effect was. The initial temperature rise rate of these two cases was low, but in contrast to that of NFC, the temperature rise rate in the medium-term increased quickly, resulting in a rapid temperature rise, which made the fire protection effect less than that of NFC with the same thickness.
3.3.4. Different Fireproof Materials
In the experiment, the three kinds of materials that met the fire protection requirements were brand B IFC (W), brand C NFC, and brand D FC. In order to compare the fire protection effect of the three materials, we counted the failure time data of some cases, as shown in
Table 9.
By comparing case 3 and case 12, we found that although the material thickness of case 3 was much less than that of case 12, the failure time was later than that of case 12. Considering that the fire protection effect of the three materials was positively related to the thickness, so it could be inferred that the fire protection effect of the Brand B IFC (W) was better than that of the brand D FC for the same thickness condition.
By comparing case 8, case 9, and case 11, it was found that the material thicknesses of cases 8 and 9 were less than that of case 11, but the failure times were later than that of case 11. It could be inferred that the fire protection effect of the brand C NFC was better than that of brand D FC for the same thickness condition. This result was consistent with the thermal conductivity of this two materials in
Table 2.
By comparing case 3 and case 10, it was found that although the failure time of case 3 was earlier than that of case 10, the difference was not significant. Additionally, considering the fact that the material thickness of case 3 was far less than that of case 10, we could speculate that the fire protection effect of the brand B IFC (W) was better than that of the brand C NFC for the same thickness condition.
For the selection of these three materials, there were the following considerations:
The IFC (W) had thin thickness, a good fire protection effect, and a beautiful appearance, but the construction was more complex, and the material price and the construction cost were larger than those of NFC and NFC. The water resistance and the durability of the coating were worse than those of the NFC, but the water resistance and the durability could be improved by brushing the topcoat.
The NFC had strong durability, the material price per square meter was the lowest among the three materials, and the fire-retardant effect was good, but the good fire-retardant effect was obtained with the thickness. The coating was thick, heavy, rough, and not beautiful enough, but it could also be brushed with a topcoat to make it more beautiful.
The construction of FC was relatively convenient, and the price was moderate. It could be wrapped with high-temperature glue or iron wire winding. The thickness was large and the fire protection effect was general. It could easily be soaked by rain outside, so the surface could be waterproof and beautified with a tarpaulin or aluminum sheet.
It could be seen that the three schemes had their own advantages and disadvantages, and they needed to be selected according to the actual needs.