Improvement in Fire Resistance and Smoke Leakage Performance for Existing Polyvinyl Chloride Pipes Passing Through Walls

Response to Reviewer 1 Comments

1. Summary

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files. [This is only a recommended summary. Please feel free to adjust it. We do suggest maintaining a neutral tone and thanking the reviewers for their contribution although the comments may be negative or off-target. If you disagree with the reviewer's comments please include any concerns you may have in the letter to the Academic Editor.]

2. Questions for General Evaluation

Reviewer’s Evaluation

Response and Revisions

Does the introduction provide sufficient background and include all relevant references?

Yes

[Please give your response if necessary. Or you can also give your corresponding response in the point-by-point response letter. The same as below]

Are all the cited references relevant to the research?

Yes

Dear Sir/ Madam,

Thank you for the review and affirmation!

Is the research design appropriate?

Yes

Dear Sir/ Madam,

Thank you for the review and affirmation!

Are the methods adequately described?

Yes

Dear Sir/ Madam,

Thank you for the review and affirmation!

Are the results clearly presented?

Yes

Dear Sir/ Madam,

Thank you for the review and affirmation!

Are the conclusions supported by the results?

Yes

Thank you for the review and affirmation of the review committee.

3. Point-by-point response to Comments and Suggestions for Authors

Comments 1:

Manuscript is well written and presented

Response 1:

Thank you for the review and affirmation of the review committee.

4. Response to Comments on the Quality of English Language

Point 1:

The English is fine and does not require any improvement.

Response 1:    (in red)

Dear Sir/ Madam,

Thank you for the review and affirmation!.

5. Additional clarifications

[Here, mention any other clarifications you would like to provide to the journal editor/reviewer.]

Response to Reviewer 1 Comments

1. Summary

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files. [This is only a recommended summary. Please feel free to adjust it. We do suggest maintaining a neutral tone and thanking the reviewers for their contribution although the comments may be negative or off-target. If you disagree with the reviewer's comments please include any concerns you may have in the letter to the Academic Editor.]

2. Questions for General Evaluation

Reviewer’s Evaluation

Response and Revisions

Is the work a significant contribution to the field?

[Please give your response if necessary. Or you can also give your corresponding response in the point-by-point response letter. The same as below]

Is the work well organized and comprehensively described?

Is the work scientifically sound and not misleading?

Are there appropriate and adequate references to related and previous work?     

Is the English used correct and readable?

3. Point-by-point response to Comments and Suggestions for Authors

Comments 1: [Paste the full reviewer comment here.]

Response 1: [Type your response here and mark your revisions in red] Thank you for pointing this out. I/We agree with this comment. Therefore, I/we have….[Explain what change you have made. Mention exactly where in the revised manuscript this change can be found – page number, paragraph, and line.]

“[updated text in the manuscript if necessary]”

Comments 2: [Paste the full reviewer comment here.]

Response 2: Agree. I/We have, accordingly, done/revised/changed/modified…..to emphasize this point. Discuss the changes made, providing the necessary explanation/clarification. Mention exactly where in the revised manuscript this change can be found – page number, paragraph, and line.]

“[updated text in the manuscript if necessary]”

4. Response to Comments on the Quality of English Language

Point 1:

Response 1:    (in red)

5. Additional clarifications

[Here, mention any other clarifications you would like to provide to the journal editor/reviewer.]

Response to Reviewer 2 Comments

1. Summary

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files. [This is only a recommended summary. Please feel free to adjust it. We do suggest maintaining a neutral tone and thanking the reviewers for their contribution although the comments may be negative or off-target. If you disagree with the reviewer's comments please include any concerns you may have in the letter to the Academic Editor.]

2. Questions for General Evaluation

Reviewer’s Evaluation

Response and Revisions

Does the introduction provide sufficient background and include all relevant references?

Yes/Can be improved/Must be improved/Not applicable

[Please give your response if necessary. Or you can also give your corresponding response in the point-by-point response letter. The same as below]

Are all the cited references relevant to the research?

Yes/Can be improved/Must be improved/Not applicable

Yes, For more information, please read my journal

Is the research design appropriate?

Yes/Can be improved/Must be improved/Not applicable

Yes, For more information, please read my journal

Are the methods adequately described?

Yes/Can be improved/Must be improved/Not applicable

Yes, For more information, please read my journal

Are the results clearly presented?

Yes/Can be improved/Must be improved/Not applicable

Yes, For more information, please read my journal

Are the conclusions supported by the results?

Yes/Can be improved/Must be improved/Not applicable

Yes, For more information, please read my journal

3. Point-by-point response to Comments and Suggestions for Authors

Comments 1:

The article is dedicated to an issue with a high practical relevance in modern construction, namely improving the fire safety of plastic pipe penetrations.

Response 1:

First of all, I would like to thank the review committee for reviewing and providing comments, which will make this article more complete.

Comments 2:

Lines 29–88

Therefore, it would be logical to consider modern fire protection measures for such engineering utility lines in the introduction—fire collars, cuffs, thermal insulation materials. This approach would allow the authors to emphasize the advantages of the proposed method of wrapping PVC pipes with galvanized steel sleeves.

Response2:

I have marked the modified parts with yellow and red fonts, such as on Lines 71–76.

Therefore, this study focuses on a simplified improvement technique for cases where PVC piping penetrates fire-rated compartments in existing structures. This method involves adding a metal sleeve over the PVC conduit to improve fire resistance and smoke-sealing performance. Compared to conventional methods outlined in current firestop test specifications—such as fire collars, cuffs, and thermal insulation materials—this proposed approach is simpler and more feasible to implement. By applying a metal sleeve to the exterior of existing piping, this method enhances penetration performance without being dependent on the quality of firestop installation and also significantly reduces retrofit costs. Furthermore, this study presents a detailed method for on-site testing of smoke leakage performance at pipe penetrations.

Comments 3:

The introduction should also state the aim of the research, so that the methods and conclusions presented in the article are clearer to the reader.

Response 3:

I used yellow to fill in the red font, such as on Lines 77–80.

By applying a metal sleeve to the exterior of existing piping, this method enhances penetration performance without being dependent on the quality of firestop installation and also significantly reduces retrofit costs. Furthermore, this study presents a detailed method for on-site testing of smoke leakage performance at pipe penetrations.

Comments 4:

Reference [1] should be replaced with a more recent publication that explains the general issues of fire protection for plastic pipe penetrations.

Response 4:

I used yellow to fill in the red font, such as on Lines 453–454.

Corrected reference [1] to Zhaoyu Ye, Charles M. Fleischmann, Anthony K. Abu and Dennis Pau, Estimation of effective thermophysical properties of firestopping sealants: Methodology and case study, Fire Safety Journal, Vol. 141: 103928, 2023.

Comments 5:

Verify the information regarding smoke exposure during fires from references [8] and [9].

Response 5:

I used yellow to fill in the red font, such as on Lines 462–463.

Upon further review, the information regarding the hazards of smoke in fire from references [8] and [9] is correct.

Comments 6 :

Check the relevance of reference [11] from 2006, which concerns fire proof doors, and make sure that there have been no changes in Taiwanese legislation over the past 19 years.

Response 6:

I used yellow to fill in the red font, such as: Lines 466。

The relevant regulations in Taiwan have not changed, and reference [11] has been revised to Taiwan Building Technical Regulations, Taiwan,  2025

Comments 7:

Lines 90–217

The experimental section is presented in a detailed and professional manner. The methods, equipment, and calculations used in the study raise no concerns.

Response 7:

Dear Sir/ Madam,

Thank you to the committee members for their review and affirmation. I have used the English editing provided by MDPI.

4. Response to Comments on the Quality of English Language

Point 1:

The English is fine and does not require any improvement.

Response 1:    (in red)

Dear Sir/ Madam,

Thank you to the committee members for their review and affirmation. I have used the English editing provided by MDPI.

5. Additional clarifications

My entire paper has been completely revised through the English editing service provided by MDPI.

Response to Reviewer 3 Comments

1. Summary

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files. [This is only a recommended summary. Please feel free to adjust it. We do suggest maintaining a neutral tone and thanking the reviewers for their contribution although the comments may be negative or off-target. If you disagree with the reviewer's comments please include any concerns you may have in the letter to the Academic Editor.]

2. Questions for General Evaluation

Reviewer’s Evaluation

Response and Revisions

Does the introduction provide sufficient background and include all relevant references?

Yes/Can be improved/Must be improved/Not applicable

[Please give your response if necessary. Or you can also give your corresponding response in the point-by-point response letter. The same as below]

Are all the cited references relevant to the research?

Yes/Can be improved/Must be improved/Not applicable

Yes, For more information, please read my journal

Is the research design appropriate?

Yes/Can be improved/Must be improved/Not applicable

Yes, For more information, please read my journal

Are the methods adequately described?

Yes/Can be improved/Must be improved/Not applicable

Yes, For more information, please read my journal

Are the results clearly presented?

Yes/Can be improved/Must be improved/Not applicable

Yes, For more information, please read my journal

Are the conclusions supported by the results?

Yes/Can be improved/Must be improved/Not applicable

Yes, For more information, please read my journal

3. Point-by-point response to Comments and Suggestions for Authors

Comments 1:

The novelty and main contributions of the manuscript need to be highlighted.

Response 1:

A：I have marked the modified parts with yellow and red fonts, such as on Lines 71–80.

1.Therefore, this study focuses on a simplified improvement technique for cases where PVC piping penetrates fire-rated compartments in existing structures. This method involves adding a metal sleeve over the PVC conduit to improve fire resistance and smoke-sealing performance. Compared to conventional methods outlined in current firestop test specifications—such as fire collars, cuffs, and thermal insulation materials—this proposed approach is simpler and more feasible to implement. By applying a metal sleeve to the exterior of existing piping, this method enhances penetration performance without being dependent on the quality of firestop installation and also significantly reduces retrofit costs. Furthermore, this study presents a detailed method for on-site testing of smoke leakage performance at pipe penetrations. By applying a metal sleeve to the exterior of existing piping, this method enhances penetration performance without being dependent on the quality of firestop installation and also significantly reduces retrofit costs. Furthermore, this study presents a detailed method for on-site testing of smoke leakage performance at pipe penetrations.

Comments 2:

Only two specimens (one with and one without a sleeve) were used. Please justify the sample size and discuss whether this limited number affects the statistical reliability of the results.

Response 2:

I used yellow to fill in the red font, such as on Lines 249-259.

2. Although only two specimens were tested in this study, the fire-resistance test duration was 60 minutes. If any issues existed in the specimens, abnormal phenomena would have manifested during this period. In both tests, the furnace temperature followed the standard time–temperature curve specified in CNS 15814-1 [2], confirming the validity of the testing environment. Additionally, the temperature rise of the specimens during the 60-minute test period was within reasonable expectations, indicating that the tests were successfully conducted. The results obtained are thus considered representative. Moreover, the method of installing metal sleeves is not a complex procedure—it simply involves attaching a sleeve over the PVC pipe, a task that can be performed by general plumbing technicians. Therefore, the test results from the two specimens are deemed reasonably representative, and extensive specimen testing is not deemed necessary.

Comments 3:

The fire resistance test was based on a 1-hour duration. It would be valuable to include whether tests were repeated or if results may vary due to pipe composition, sleeve dimensions, or other environmental factors.

Response 3:

I used yellow to fill in the red font, such as on Lines 370-385.

3.Although other tests were performed during the fire resistance testing in this study—such as the method where metal sleeves were installed on both the fire-exposed and non-fire-exposed sides of the specimen—it was eventually decided to present only the method where the metal sleeve is installed on the non-fire-exposed side. The reason is that if installing the metal sleeve only on the non-fire side can already pass the fire resistance test, then in actual buildings, if metal sleeves are installed on both sides of the wall, the result should at least meet the performance demonstrated in this study. This study focuses solely on PVC pipes, which are commonly used in Taiwan, and confirms the effectiveness of the proposed improvement. If other pipe materials or sizes are involved in the future, further relevant testing is recommended. The method proposed in this study should provide a certain level of improvement in fire resistance performance for PVC pipes, as PVC itself is not fire-resistant and tends to melt. Therefore, the addition of a metal sleeve can provide at least some level of enhancement. The thickness of the metal sleeve used in this study is 3.0 mm. Generally, galvanized steel of this thickness offers good durability and corrosion resistance, and can last for a long period of time. However, if corrosion issues are a concern in specific environments, it is recommended to use stainless steel sleeves instead.

Comments 4:

The thermocouple placement (T1 at 25 mm, T2 at 325 mm) was clearly stated. However, further explanation is needed on why these distances were selected and how sensitive the temperature changes are to positioning.

Response 4:

I used yellow to fill in the red font, such as on Lines 201-206.

4.According to CNS 15814-1 [2], a thermocouple must be installed at a position 25 mm from the wall. In addition, the standard requires that the extension length of the specimen on the unexposed side must be at least 300 mm. Therefore, thermocouples are installed both before and after the wall penetration. If the temperature readings at both positions meet the fire resistance rating criteria, the specimen can be deemed to have satisfied the required fire resistance performance.

Comments 5:

Equation (1) for corrected leakage rate includes multiple variables and correction factors. A step-by-step breakdown or sample calculation would aid reader comprehension and ensure reproducibility.

Response 5:

I used yellow to fill in the red font, such as on Lines 240-247.

5.Example Calculation:
Assume that during testing, the atmospheric pressure is 102,000 Pa, the ambient temperature is 27°C (300.15 K), the pressure increase is 10 Pa, the saturated water vapor pressure is 3,567 Pa, and the relative humidity is 50%. The leakage rate under standard conditions can then be calculated as follows:

  =Qa/(27+273.15) ×(2.89×10-3×(102000+10)-3.795×10-3×50%×3567)

  =0.96 Qa

Comments 6:

It is recommended to discuss Acoustic Emission-Based Pipeline Leak Detection and Size Identification Using a Customized One-Dimensional DenseNet in the introduction section of the manuscript.

Response 6:

I used yellow to fill in the red font, such as on Lines 97-104.

6.The principle of the smoke leakage performance test is based on a simplified one-dimensional flow assumption. It is assumed that a fire occurs on one side of the wall, generating pressure on the fire-exposed side. This pressure drives air through the gaps or openings in the wall, allowing it to reach the non-fire side. The airflow behavior can be derived from the law of conservation of energy using the Bernoulli equation. Therefore, by measuring the pressure difference across both sides of the specimen and the air density during the test, the leakage rate of the specimen can be calculated.

Comments 7:

The discussion suggests that a half-sleeve design could be more practical for existing installations. Including a schematic or prototype image of such a design would strengthen this recommendation.

Response 7:

I used yellow to fill in the red font, such as on Lines 400-401.

7. A schematic view of the galvanized sleeve cut in half is shown in Fig. 10

Figure 10. A schematic view of the galvanized sleeve cut in half

Comments 8:

The study lacks a dedicated section on limitations. Please consider discussing potential issues such as long-term durability of metal sleeves, corrosion risk, or performance under variable fire scenarios (e.g., flashover).

Response 8:

I used yellow to fill in the red font, such as on Lines 381-386.

8.Therefore, the addition of a metal sleeve can provide at least some level of enhancement. The thickness of the metal sleeve used in this study is 3.0 mm. Generally, galvanized steel of this thickness offers good durability and corrosion resistance, and can last for a long period of time. However, if corrosion issues are a concern in specific environments, it is recommended to use stainless steel sleeves instead.

Comments 9:

While results show improved performance, benchmarking against other common firestop materials or commercial products would help position this method within the broader context of fire safety solutions.

Response 9:

I used yellow to fill in the red font, such as on Lines 389-395.

9.This study focuses on improving the fire resistance performance of existing PVC pipes. Firestopping methods available in the market can achieve the same effect since they are all tested according to CNS 15814-1[2]. However, the method proposed in this study allows for immediate functionality, is easier to install, and reduces improvement costs. In comparison, market methods require thorough sealing to be effective, making the method presented in this study simpler.

Comments 10:

The quality of figures needs to be enhanced.

Response 10:

The modifications are as follows:

10. The figure has been annotated with text, such as on Lines 179-180, Lines 323-326, Lines 329-330, and Lines 400-401.

Comments 11:

The quality of English needs to be improved, and grammatical mistakes as well as the format of the journal need to be followed thoroughly.

Response 11:

The modifications are as follows:

11. The quality of the English and the article's formatting have been improved with translation and revision by the journal.

4. Response to Comments on the Quality of English Language

Point 1:

Overall, English writing should be improved and more coherent.

Response 1:    (in red)

The quality of the English and the article's formatting are assisted with translation and revision by the journal. At present, this entire paper has been completely grammatically corrected through the English editing service provided by MDPI.

5. Additional clarifications

I have sent this entire paper through the English editing service provided by MDPI for complete grammar correction.