Experimental Investigation of the Effect of Heat Flux on the Fire Behavior of Engineered Wood Samples

Round 1

Reviewer 1 Report

The comments to my previous four comment given in an attached file have not been included in the revised manuscript as far as I can see.

Author Response

Dear Reviewer,

Thank you for your valuable comments and suggestions. I have presented below answers to questions: 

(Point 1): Good idea, but the relevance to use IR to simulate fire is not shown.

Response 1: We agree with reviewer’s remark. The Introduction section was revised. The relevance of using IR thermography methods to study combustion processes was shown.

(Point 2): Cited literature is limited to certain parts of the world.

Response 2: We agree with the reviewer’s comments. Information has been added to the paper.

(Point 3): The results are not compared to other studies and show large differences, e.g. in charring rates.

Response 3: We agree that the comparison of presented results in the article is inaccurate in its present form. The section with the results and conclusions was significantly revised. In particular, the obtained results on charring rates were compared with the articles of other authors (Aseeva, R.M. et al., 2012; Pope, I. et al., 2019; Bartlett, A.I. et al., 2019). The results of assessing the surface temperature at the samples’ end during heat exposure were compared with the results of other authors, which included the presence of fire retardant processing. Information added to the article.

(Point 4): The role of fire retardants are overemphazised, they show even higher charring rates than untreated wood.

Response 4: We carefully studied the information available in scientific publications and reports on the behavior of fire retardants under thermal exposure, with regard to the task of processing wood and wood-based materials. The article provides a justification for the obtained temperatures on the surface of the samples processed by fire retardant. The comparison was made in terms of the charring rates of materials processed by fire retardant.

It should be emphasized that surface impregnation provides a layer of fire protection on the surface, which do not exceed 2 mm. As the result of carried-out work, one can conclude that the standard brush impregnation recommended by the producer does not provide the required fire protection (fire protection consumption is 0.3 – 0.5 kg/m²). Such uncharacteristic behavior of fire retardants requires further additional investigations of the penetration depth of the fire retardant into a sample, the chemical properties of the active component of the fire retardant, and the gas composition of pyrolysis products.

Currently, we are conducting experiments to study the effect of vacuum impregnation of wood on fire characteristics. The main advantage of deep impregnation over other processing methods is the penetration depth of the protective compounds. It can be from 5 to 50 mm, depending on the type of wood [Goreshnev, M.A., Kazarin, A.N., Lopatin, V.V. et al. Combined Timber Drying Method. J Eng Phys Thermophy 86, 336–339 (2013). https://doi.org/10.1007/s10891-013-0838-7]. Preliminary results show that the use of vacuum impregnation contributed to the high fire resistance of wood in the entire range of heat flux 10-40 kW/m² from the standard emitter. This results in a decrease of carbonization depth by more than two times in comparison with a similar material with a processed surface. It was found that after processing material by fire protection, the temperature range of the active pyrolysis stage shifted without occurring of flame combustion, which affected the ignition time.

Reviewer 2 Report

In the abstract, the authors use the wording “Time ignition rate”. This wording seems unknown for me. Ignition rate or Ignition time are two wordings that are well known but not Time ignition rate. What is the definition of it?

Introuction:

First sentence: “The A huge amount” should be modified

 

In the table 1, the rate of charring seems to be higher when using 2 fire retardants (ZOTEKS and Fenilaks) for Plywood and OSB, and all 3 fire retardants have the same effect for the Chipboard. But the authors do not conclude anything on this result which can seem surprising. The same surprising result can be observed for the final char depth (d char i.e. not explained in the text).

In the table 2, the ignition time for chipboard without fire retardant (considered as untreated) is 24 s, 23 s for Plywood and 35 s for OSB.  And line 236, the authors mentioned that the time to ignition (and not time ignition as in the text) of untreated chipboard is 30% higher than for plywood and OSB. How authors can conclude like this?

The table 2 should present also the results of the fire-retardant impregnation in terms of ratio between time to ignition with and without fire retardant. It will be clearer and permit authors not to make mistake in presentation of results.

In the conclusion, authors explained that fire retardants increase the time to ignition by 30%. This conclusion must be modified and should fit the results of the table 2 (some fire retardants on some type of wood delay the time to ignition).

 

This article presents a new method to investigate the effect of heat flux on wood and fire retardant. The new method seems really promising but the current state of the study is not mature enough. Results are really scattered and conclusions given by the authors are sometimes not aligned with the results.

Author Response

Dear Reviewer,

Thank you for your valuable comments and suggestions. I have presented below answers to questions:

(Point 1): In the abstract, the authors use the wording “Time ignition rate”. This wording seems unknown for me. Ignition rate or Ignition time are two wordings that are well known but not Time ignition rate. What is the definition of it?

Response 1: We made a mistake in the the term. It is correct to use "time to ignition" in the context of this article.

(Point 2): Introuction:

First sentence: “The A huge amount” should be modified

Response 2: The authors agree with the remark. The article "the" was removed.

(Point 3): In the table 1, the rate of charring seems to be higher when using 2 fire retardants (ZOTEKS and Fenilaks) for Plywood and OSB, and all 3 fire retardants have the same effect for the Chipboard. But the authors do not conclude anything on this result which can seem surprising. The same surprising result can be observed for the final char depth (d char i.e. not explained in the text).

Response 3: Indeed, the obtained results make it possible to judge the controversial contribution of fire retardants in improving the fire-retardant properties of presented wood construction materials. This requires additional arguments. The description of the obtained results was added to the article.

(Point 4): In the table 2, the ignition time for chipboard without fire retardant (considered as untreated) is 24 s, 23 s for Plywood and 35 s for OSB.  And line 236, the authors mentioned that the time to ignition (and not time ignition as in the text) of untreated chipboard is 30% higher than for plywood and OSB. How authors can conclude like this?

Response 4: We made a mistake in describing the total contribution of fire retardant into time to ignition values. Corrections were made in the article.

(Point 5): The table 2 should present also the results of the fire-retardant impregnation in terms of ratio between time to ignition with and without fire retardant. It will be clearer and permit authors not to make mistake in presentation of results.

Response 5: We agree with the remark. This presentation of the results would be clearer. Table 2 was modified.

(Point 6): In the conclusion, authors explained that fire retardants increase the time to ignition by 30%. This conclusion must be modified and should fit the results of the table 2 (some fire retardants on some type of wood delay the time to ignition).

Response 6: We agree with the comment. The conclusions based on the data in Table 2 was revised.

(Point 7): This article presents a new method to investigate the effect of heat flux on wood and fire retardant. The new method seems really promising but the current state of the study is not mature enough. Results are really scattered and conclusions given by the authors are sometimes not aligned with the results.

Response 7: The text of the article, experimental methodology, and conclusions were revised. Discussion of the obtained results was added, as well as comparison with the results of other authors.

Reviewer 3 Report

Experiments are good, but introduction needs work as this part is sloppy.

 

Reference 1, and 9 are wrong. I think correct one for reference 1 is Fireline intensity.

Alexander M.E., Cruz M. (2019) Fireline Intensity. In: Manzello S. (eds) Encyclopedia of Wildfires and Wildland-Urban Interface (WUI) Fires. Springer, Cham. https://doi.org/10.1007/978-3-319-51727-8_52-1

Reference 9 is describing ember generation in forest. Not related to wood products.

 

Figure 1 is hard to understand. Needs entire image of those.

 

Table’s significant number is too many. Really sure?

 

Mixed usage of fire intensity and fireline intensity bothers me a lot. I think they do not understand term correctly.

Author Response

Dear Reviewer,

Thank you for your valuable comments and suggestions. I have presented below answers to questions:

(Point 1): Experiments are good, but introduction needs work as this part is sloppy.

Response 1: The introduction of the article was broadened.

(Point 2): Reference 1, and 9 are wrong. I think correct one for reference 1 is Fireline intensity.

Alexander M.E., Cruz M. (2019) Fireline Intensity. In: Manzello S. (eds) Encyclopedia of Wildfires and Wildland-Urban Interface (WUI) Fires. Springer, Cham. https://doi.org/10.1007/978-3-319-51727-8_52-1

Reference 9 is describing ember generation in forest. Not related to wood products.

Response 2: Indeed, there was a citation error. Reference 1 is incorrect. The term "fireline intensity" was discussed in Byram's concept. The link presented by the reviewer is correct.

Reference 9 was also incorrect. We had in mind the results of experiments described in the work of

Grishin, A. M.; Filkov, A. I.; Loboda, E. L.; Reyno, V. V.; Kozlov, A. V.; Kuznetsov, V. T.; Kasymov, D. P.; Andreyuk, S. M.; Ivanov, A. I.; Stolyarchuk, N. D. A field experiment on grass fire effects on wooden constructions and peat layer ignition. Int. J. Wildl. Fire. 2014, 23 445–449. https://doi.org/10.1071/WF12069.

Corrections were added to the references.

(Point 3): Figure 1 is hard to understand. Needs entire image of those.

Response 3: Figure 1 was updated. The blackbody model and the carriage are shown in Figure 4, excepting that the sample is installed instead of the SGB01 heat flux sensor.

(Point 4): Table’s significant number is too many. Really sure?

Response 4: We presented the results of statistical processing of the obtained multiple measurements. We agree with the remark, the table was changed.

(Point 5): Mixed usage of fire intensity and fireline intensity bothers me a lot. I think they do not understand term correctly.

Response 5: We used the term “fireline intensity”, which is the rate of heat transfer per unit length of the fireline (kW / m).

Reviewer 4 Report

It should be useful to include a description of the composition of the wooden materials (Species, type of glue (phenolic, melamine, urea, etc))

I suggest to use other type of CONSTRUCTION wooden materials that could have better correlation with HARDWOOD/SOFTWOOD, for example CLT, LVL, GLULAM, etc.

Cone calorimeter study (At different heat flux 25-75 for example) with the measurement of heat and smoke parameters in the vertical configuration of the equipment should be a very interesting and complementary study. 

Author Response

Dear Reviewer,

Thank you for your valuable comments and suggestions. I have presented below answers to questions:

(Point 1): It should be useful to include a description of the composition of the wooden materials (Species, type of glue (phenolic, melamine, urea, etc))

Response 1: Description of the wooden materials composition, density, moisture content and thermal conductivity were added to the article.

(Point 2): I suggest to use other type of CONSTRUCTION wooden materials that could have better correlation with HARDWOOD/SOFTWOOD, for example CLT, LVL, GLULAM, etc.

Response 2: The authors are grateful for the essential comment. In future studies, we are planning to investigate composite materials, such as «layer of wood-based material + heat-insulating layer + layer of wood-based material» in a similar setting, as well as to consider vertical combustion along the material surface.

(Point 3): Cone calorimeter study (At different heat flux 25-75 for example) with the measurement of heat and smoke parameters in the vertical configuration of the equipment should be a very interesting and complementary study.

Response 3: We are familiar with the works [1-4], which are aiming at studying the energy characteristics of wood samples exposed to a heat flux of various intensity. However, the experimental scheme used in our work differs from the most common one, where the effect of a heat flux occurs over the entire area of the sample.

We are planning to carry out a series of experiments to study the vertical combustion wave on the surface of various materials using IR thermography methods.

 

1. Hao, H., Chow, C. L., & Lau, D. (2020). Effect of heat flux on combustion of different wood species. Fuel, 278, 118325. doi:10.1016/j.fuel.2020.118325;
2. Osvaldov L.M., Kadlicova P., Rychly J. Fire Characteristics of Selected Tropical Woods without and with Fire Retardant, Coatings, 2020, 10(6), 527; 10.3390/coatings10060527;
3. Ira, J., Hasalová, L., Šálek, V. et al. Thermal Analysis and Cone Calorimeter Study of Engineered Wood with an Emphasis on Fire Modelling. Fire Technol 56, 1099–1132 (2020). https://doi.org/10.1007/s10694-019-00922-9;
4. Hasburgh, Laura E.; White, Robert H.; Dietenberger, Mark A.; Boardman, Charles R. 2015. Comparison of the Heat Release Rate from the Mass Loss Calorimeter to the Cone Calorimeter for Wood-based Materials. In: Proceedings Fire and Materials 2015, 14th international Conference and Exhibition, 2-4 February 2015, Hyatt Hotel, Fisherman's Wharf, San Francisco, USA; 2015. pp. 116-126.

Round 2

Reviewer 1 Report

The authors have still not answered my original comments:

• Good idea, but the relevance to use IR to simulate fire is not shown
• The results are not compared to other studies .... "

The effects of fire retardants are low and do not motivate publication.

Reviewer 2 Report

Table 1: For the chipboard and OSB, the thermal conductivity is missing (urea glue is mentioned instead)

 

Authors did a really nice work on updating and improving the quality of the paper.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Overall, the paper provides interesting information on charring behavior of wood-based products with and without fire-retardants. The methodology is however lacking of precise details and relevancy. There are numerous existing and simplier test methods for evaluating charring rates. It would be interesting if the authors can provide a discussion justifying their choice of testing.

Below are comments related to the paper, as presented:

Line 133: "CO2", 2 should be as subscript. Lines 139-141: It is unfortunate that the thicknesses are not the same as it may affect the thermal penetration into the specimens.
Also, what were the density and moisture content of the specimens? Moisture also affects combustion properties, namely its time to ignition. How many replicates per products? Can the authors provide further information/characteristics about the 3 tested products and specimens? Figure 3: It is unclear how the specimen is mounted to the holder. Was it backed with insulation? What was the material for the holder? The boundary condition behind the specimens will have an impact on the heating rate, and thus the charring behavior. Please provide further details on the mounting method. Figure 6: What is the "approximation" shown in the figure? Please provide information and details about the equation used for this approximation. Line 193: 37.5 kW/m² is very low for a heater at 1100 deg C. Can the authors provide more information on how the incident heat flux is determined? Line 194: this range of 32-37.5 is well below the incident heat flux of an element exposed to the standard ISO 834 fire. Please elaborate further with respect to the chosen heat flux levels and how it compares to a standard fire exposure. Figure 8: As mentionned previously, the backing of the specimens will have an impact on heat transfer. Further explanations and discussion is needed for fully capturing the heat transfer occuring through the specimens. Line 221: This seems to be a farily long frequency. Can you explain why 100 s was chosen? It would have been valuable to have data at shorter time periods. Table 1: Unfortunately, this is difficult to correlate to literature as there are no indications about the density and moisture content of the specimens. Also, the data suggests that using fire-retardants have no effects on charring rates (or very little). Can you explain further these results?
The discussion of the results is much too short and not enough in-depth. Please review and analyse data in more details. Line 231: What do you mean by this "maximum temperature..."? You further mention that non-treated products are 650 C while treated products are at 820 C. Is this the ignition temperature? Is it the surface temperature while sustained combustion, thus including heat generated by the combustion in addition to the incident heat flux? Please elaborate further as it is unclear what your are trying to prove or demonstrate with these numbers. Ignition temperature of wood products is typically much lower than 650 C. Lines 234-235: That is somewhat strange as many textbooks have published values for charring rates of various wood and wood-based products. Line 242: The layered may have some influence, but the main parameters affecting ignition are density, thermal conductivity and specific heat. What was the species used for the plywood? What was its density? Line 266: delete "he". Line 287: The toxicity and VOC emission during the service life also need to be considered. Typically, using fire retardants chemicals generates more soot and smoke, and more CO, CO2, thus are more hazardeous for life safety of occupants.

 

Reviewer 2 Report

Good idea, but the relevance to use IR to simulate fire is not shown.

Cited literature is limited to certain parts of the world.

The results are not compared to other studies and show large differences, e.g. in charring rates.

The role of fire retardants are overemphazised, they show even higher charring rates than untreated wood.