The Mathematical Modeling and Simulation of a New Mitigation System Including a Remote Impoundment

Round 1

Reviewer 1 Report

Several points are not clear or do not represent an interesting contribution. Here they are:

Eqs. (1) and (2) and Fig. 1: according to the authors  P1 is  “the pressure at the top”, i.e. the pressure at the liquid surface level.  In this case, when leakage progresses the value of P1 should not change, as it is the pressure originated by the vapor above the liquid or, if no vaporization is considered, by the inert gas (nitrogen) introduced there. Why do the authors assume that P1 changes significantly as the liquid level in the tank changes? (Instead, it is clear that P2 changes as liquid is released).

If the liquid contained in the tank is flammable, there is the possibility of formation of a flammable cloud followed by ignition and by a pool fire in the dike. Could in this situation be the liquid sent to the remote impoundment?

The two examples are based on rather small tanks, and this implies the existence of a small “reserve vessel” and rather short duration times for the emergency emptying of the affected tank. What about the case of the large tanks often existing in, for example, a refinery, with volumes of the order of 5,000 m3 ?

The analysis depends strongly on the hole diameter. The authors have assumed 6 inches in the case of HF, and 4 inches for the case of benzene. Why did they assume these values? How should the hole diameter be established?

How should the mitigation system (pumps capacities, remote impoundment volume) be designed? For the worst case? And which would be this worst case?

The results associated to the two cases considered are essentially fluid mechanics calculations… not much useful from the point of view of safety or risk analysis.

Concerning the consequences analysis (Section 4). The authors analyze the maximum distances reached by the ERPG 1, 2 and 3, which result to be essentially the same for both cases (with and without mitigation). However, they do not consider the different times during which the toxic cloud would exist for the two cases and its sure unfluence on the resulting dose and the consequent risk for the population downwind.

Author Response

Please see the attachment. Thanks.

Author Response File: Author Response.pdf

Reviewer 2 Report

Manuscript ID: processes-1057373
Title: The Development of a Mitigation System based on a Remote Impoundment

The authors put forward an improvement plan for the safety of hydrogen fluoride storage tanks by mitigation measures by using the simulation consequence analysis method, which provides an excellent arrangement and prospect for the storage and safety measures of hazardous substances. This research is very suitable for the journal and can attract more readers. I strongly recommend that it be released after minor modifications. Here are some comments:

1. It is recommended to organize the symbol and corresponding unit into a table or nomenclature.
2. On page 3, lines 93 and 94: “If leakage occurs, the chemical material in the storage vessel is automatically transferred to the reserve tank by a pump (Pump 1).” How to detect the leak which is suggested to add in the article.
3. On page 3, lines 94 and 95: “Also, the material that leaks to the outside is trapped in a dike.” The size of the dike is recommended to be described.
4. The physical property parameters of hydrogen fluoride that need to be input into the software, such as boiling point, are suggested to add description
5. In the mitigation measures, it is necessary to use a pump to recover the leaked hydrogen fluoride liquid pool. The pump itself and the additional transportation pipeline itself may also have the possibility of failure. How to confirm the reliability of the mitigation measures?
6. The pressure parameter of the storage tank is recommended to be supplemented
7. If the readers want to apply the relevant knowledge of this article, it needs to have a certain understanding of ALOHA. It is suggested that some relevant literature on ALOHA operation can be added so that readers can easily master the content of this study and the operation process.

 

Overall, this paper meets the standards of the Processes and should be published after addressing the comments above. I look forward to seeing this paper published online.

Author Response

Please see the attachment. Thanks.

Author Response File: Author Response.pdf

Reviewer 3 Report

Ref: processes-1057373

Journal: Processes, MDPI

 

Title: The Development of a Mitigation System based on a Remote Impoundment

 

 

A. General comments

·         This study is interesting and aims to design a mitigation system to handle a leakage accident of a storage tank and determine its design specifications through the use of modeling. The basic concept is that when leakage occurs, leakage material in a dike is drained to a remote impoundment installed under the ground, while the material in the storage vessel is transferred to a reserve tank by a pump at the same time.

·         Nevertheless, this is not to say that it is without blemish. I have several comments regarding the scientific part of the manuscript and I expect the authors to proceed in a resubmission after a major reformation of their article.

·         In the current version of the manuscript, the authors did not explain clearly what the novelty and key points of this study are.

·         A nomenclature would be useful. 

·         The manuscript’s similarity-index (by using the TURNITIN checker) is low, i.e. it is equal to 24%.

 

B. Specific comments

Title:

·         The paper’s title could be reformed in order to be more accurate as far as the paper’s aim is concerned.

 

Abstract:

·         The abstract could be reformed in order to present in a clearer way, the deductions of the work.

·         Lines 18-19: “To evaluate 18 the efficacy of this system. hydrogen fluoride and benzene storage vessels are tested.”

There is a grammatical error.

 

1. Introduction:

·         Lines 29-33: “The Fixborough disaster in England in 1974, [2] and a toxic gas release in 29 Seveso, Italy in 1978 [3] are representative examples of a material release from vessels.In the case of 30 South Korea, the leakage accident of HF (hydrogen fluoride) in Gumi in 2012 caused a lot of damage 31 around a residential area and this has become a major turning point in the field of chemical process 32 safety in South Korea”

The authors have to mention, as examples, more recent disasters.

·         The introduction motivates the study, quite all right, but if possible please make it clearer to the reader, i.e. what is the new scientific contribution of your work.

 

3. Case Studies

·         Lines 133-135: Figure 3 shows the level of the HF in the remote impoundment when the 133 capacity of Pump 2 is 50 m3/hr which is the optimal and smallest capacity to prevent the overflow of 134 the remote impoundment.

The authors have to explain analytically why a capacity of 50 m3/hr for the Pump-2 is the optimal one to prevent the overflow of the remote impoundment.

 

·         Lines 147-150: Figure 6 shows the level of benzene in the remote impoundment in the case when the capacity of Pump 2 is 238 m3/hr. With this capacity, it is certain that a fluid can be transported as quickly as possible while preventing the overflow of the remote impoundment. Figure 7 indicates that this system does not suffer from the switching on and off of Pump 2.

The authors have to explain analytically why a capacity of 238 m3/hr for the Pump-2 is the optimal one to prevent the overflow of the remote impoundment.

 

 

4.Consequence Analysis

 

·         Lines 170-179:The detailed descriptions for the ERPGs are as follows;

• ERPG-1 : This is the maximum concentration below of which nearly all individuals can be exposed to for up to 1 hour without experiencing effects other than mild transient adverse health effects or perceiving a clearly defined, objectionable odor [12]. 

• ERPG-2 : This is the maximum concentration below of which nearly all individuals can be exposed to for up to 1 hour without experiencing or developing irreversible or other serious health effects or symptoms that could impair an individual’s ability to take protective action [12]. 176

• ERPG-3 : This is the maximum concentration below of which nearly all individuals can be exposed to for up to 1 hour without experiencing or developing life-threatening health effects [12].

The text in lines 170-179, as you can see below with the violet color:

 

is identical (see the violet-colored phrases) with the following, coming from the literature, i.e.

“Warren W. Jederberg. "Issues with the Integration of TechnicaL Information in Planning for and RespondinG to NonTraditional Disasters", Journal of Toxicology and Environmental Health, Part A, 2005”

and must be revised.

 

·         Lines 186-189:Figure 8 shows the results of 186 ERPG-2 with and without a proposed mitigation system when the leak in the HF vessel occurs. The 187 simulation conditions for ALOHA are listed in Table 2. On the basis of the maximum distance for ERPG-2, the reduction effect of a proposed mitigation system is 0.6%, shown in Figure 8.

The correct figure is Figure 9 and not Figure 8.

 

·         Lines 182-183: Figure 9. The range of ERPGs when the HF leak occurs.: (a) In the case of no mitigation system; (b) In 182 the case a mitigation system is operated. The difference in ERPG-2 is only 4 m (638 m and 634 m).

The reader can’t understand easily the difference between the graphs “a” and “b”. These graphs seem to be exactly the same. In addition, an appropriate zoom-in illustration of the graphs is essential for their comprehension. Moreover, the additional depiction of a title on the axis of x and y is necessary. 

 

·         Lines 188-194: On the basis of the maximum distance for 188 ERPG-2, the reduction effect of a proposed mitigation system is 0.6%, shown in Figure 8. This 189 reduction effect is insignificant even though a proposed mitigation system can reduce the amount of 190 material leaked outside by 19.6%. The main reason for this is that the dispersion of liquids is mainly 191 determined by the cross sectional area of a dike. Even if there is no significant change in ERPG-2, the 192 proposed mitigation system can contribute to reducing a large amount of material leaked to the 193 outside. To obtain accurate results for the dispersion, more precise models should be employed.

The reader can’t understand easily this passage. So an analytical explanation of the results of this passage is necessary. 

 

 

5. Conclusions

·         Lines 196-205: Although a few worksites have installed this type of mitigation system, there has been no 196 scientific method to evaluate the mitigation impact. To understand the impact of a mitigation system, 197 the proposed mitigation system based on the remote impoundment is designed and evaluated based 198 on mathematical modeling and consequence analysis. When a leak occurs, the material in a storage 199 vessel is transported by a pump and the material in the dike flows into a remote impoundment 200 installed under the ground. Through case studies, it is confirmed that the proposed mitigation system 201 can handle materials safely and has a large impact on the reducing the impact of an initial accident. 202 When designing this type of mitigation system for a vessel, this study can also provide scientific 203 approaches and guidelines to determine the proper design specifications and help to reduce cost, 204 efforts, and time for performing the set of experiments.

·         In the current version of this manuscript, the authors did not present clearly what the novelty and key points and also the general conclusion of this study are.

·         This chapter is too short. The authors have to expand it, in order to present clearly the aims of this paper, and the produced scientific results as well.

 

References

·         The literature list includes 12 items, wherein 9 references came from the same journal. Updating the references list with more recent papers, would be necessary. So, the authors must enrich the “references” with more scientific papers.

Moreover, please see the attached document. 

Comments for author File: Comments.pdf

Author Response

Please see the attachment. Thanks.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

--- A "Nomenclature" section would help the reader.

--- Eqs. (1) and (2) and Fig. 1: the authors should explain what is exactly P2; the say it is “the leak at the bottom of the vessel”. So, it should be P1 plus the static pressure due to the liquid column. However, they assume that it is the atmospheric pressure, i.e. the pressure of the liquid flowing “after” the hole (already in the dike). It is not clear for the reader.

--- Fig. 6 and P1: according to this figure, the pressure at the liquid surface (P1) (inert gas) decreases to values as low as approximate 15,000 Pa, due to the fact that the volume of the inert gas increases as the liquid height decreases. However, in practice this would not occur as, due to the danger of tank collapse originated by vacuum, air or inert gas would enter to keep a constant pressure. The authors should clarify this/take it into account.

--- Section 4. Consequences analysis: the two situations showed in Fig. 10 imply essentially the same values of ERPGs for the system with and without mitigation arrangement. So, looking at these data, no differences seem to exist between both situations. Therefore, to emphasize and make clear the advantage of the proposed mitigation, the consequences on the population associated to the different exposure time corresponding to these two situations to the toxic/flammable cloud should be estimated by using the corresponding vulnerability (probit) expressions. 

Author Response

I appreciate for your review. We have followed as close as possible your reviews.

 

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Ref: processes-1057373

Journal: Processes, MDPI

New title: The Mathematical Modeling and Simulation of a New Mitigation

System including a Remote Impoundment

 

1. General comments

• A nomenclature would be useful.

 

1. Specific comments

Title:

• The paper’s title could be reformed in order to be more accurate as far as the paper’s aim is concerned.

Ok! The authors revised the title (comparatively with the previous submission). The title has been changed as the following: “The mathematical modeling and simulation of a new mitigation system including a remote impoundment”.

 

Abstract:

• The abstract could be reformed in order to present in a clearer way, the deductions of the work.

Ok! The authors revised the abstract (comparatively with the previous submission).

 

1. Introduction:

• Lines 29-33: “The Fixborough disaster in England in 1974, [2] and a toxic gas release in 29 Seveso, Italy in 1978 [3] are representative examples of a material release from vessels.In the case of 30 South Korea, the leakage accident of HF (hydrogen fluoride) in Gumi in 2012 caused a lot of damage 31 around a residential area and this has become a major turning point in the field of chemical process 32 safety in South Korea”

The authors have to mention, as examples, more recent disasters.

• The introduction motivates the study, quite all right, but if possible please make it clearer to the reader, i.e. what is the new scientific contribution of your work.

Ok! The authors revised the manuscript (comparatively with the previous submission), taking into account the following:

More specifically, the recent chemical accident is reported in this article as the following; Also, the huge explosion of ammonium nitrate in Beirut’s port (August in 2020) killed at least 181 people [4].

- Actually, our study is performed by the simulations based on the first principle equations. To clarify the aim of this study, a next sentence is added;

This study aims to provide guidelines how to determine design specifications of the proposed mitigation system based on the mathematical modeling.

 

3. Case Studies

 

• Lines 133-135: Figure 3 shows the level of the HF in the remote impoundment when the 133 capacity of Pump 2 is 50 m3/hr which is the optimal and smallest capacity to prevent the overflow of 134 the remote impoundment.

The authors have to explain analytically why a capacity of 50 m3/hr for the Pump-2 is the optimal one to prevent the overflow of the remote impoundment.

• Lines 147-150: Figure 6 shows the level of benzene in the remote impoundment in the case when the capacity of Pump 2 is 238 m3/hr. With this capacity, it is certain that a fluid can be transported as quickly as possible while preventing the overflow of the remote impoundment. Figure 7 indicates that this system does not suffer from the switching on and off of Pump 2.

The authors have to explain analytically why a capacity of 238 m3/hr for the Pump-2 is the optimal one to prevent the overflow of the remote impoundment.

Ok! The authors gave the necessary clarifications:

We commented that 50 and 238 m3/hr for each case study are the smallest to prevent the overflow. The smallest one means that the purchasing and design costs can be saved as much as possible. This value is found throughout the simulation under various capacities instead of analytical studies.  

 

4.Consequence Analysis

 

• Lines 170-179:The detailed descriptions for the ERPGs are as follows;
• ERPG-1 : This is the maximum concentration below of which nearly all individuals can be exposed to for up to 1 hour without experiencing effects other than mild transient adverse health effects or perceiving a clearly defined, objectionable odor [12].
• ERPG-2 : This is the maximum concentration below of which nearly all individuals can be exposed to for up to 1 hour without experiencing or developing irreversible or other serious health effects or symptoms that could impair an individual’s ability to take protective action [12]. 176
• ERPG-3 : This is the maximum concentration below of which nearly all individuals can be exposed to for up to 1 hour without experiencing or developing life-threatening health effects [12].

The text in lines 170-179, as you can see below with the violet color:

is identical (see the violet-colored phrases) with the following, coming from the literature, i.e.

“Warren W. Jederberg. "Issues with the Integration of TechnicaL Information in Planning for and RespondinG to NonTraditional Disasters", Journal of Toxicology and Environmental Health, Part A, 2005”

and must be revised.

• Lines 186-189: Figure 8 shows the results of 186 ERPG-2 with and without a proposed mitigation system when the leak in the HF vessel occurs. The 187 simulation conditions for ALOHA are listed in Table 2. On the basis of the maximum distance for ERPG-2, the reduction effect of a proposed mitigation system is 0.6%, shown in Figure 8.

The correct figure is Figure 9 and not Figure 8.

Ok! The authors gave the necessary clarifications.

 

• Lines 182-183: Figure 9. The range of ERPGs when the HF leak occurs.: (a) In the case of no mitigation system; (b) In 182 the case a mitigation system is operated. The difference in ERPG-2 is only 4 m (638 m and 634 m).

The reader can’t understand easily the difference between the graphs “a” and “b”. These graphs seem to be exactly the same. In addition, an appropriate zoom-in illustration of the graphs is essential for their comprehension. Moreover, the additional depiction of a title on the axis of x and y is necessary. 

Ok! The authors gave the necessary clarifications.

 

• Lines 188-194: On the basis of the maximum distance for 188 ERPG-2, the reduction effect of a proposed mitigation system is 0.6%, shown in Figure 8. This 189 reduction effect is insignificant even though a proposed mitigation system can reduce the amount of 190 material leaked outside by 19.6%. The main reason for this is that the dispersion of liquids is mainly 191 determined by the cross sectional area of a dike. Even if there is no significant change in ERPG-2, the 192 proposed mitigation system can contribute to reducing a large amount of material leaked to the 193 outside. To obtain accurate results for the dispersion, more precise models should be employed.

The reader can’t understand easily this passage. So an analytical explanation of the results of this passage is necessary. 

Ok! The authors gave the necessary clarifications.

 

 

5. Conclusions

• Lines 196-205: Although a few worksites have installed this type of mitigation system, there has been no 196 scientific method to evaluate the mitigation impact. To understand the impact of a mitigation system, 197 the proposed mitigation system based on the remote impoundment is designed and evaluated based 198 on mathematical modeling and consequence analysis. When a leak occurs, the material in a storage 199 vessel is transported by a pump and the material in the dike flows into a remote impoundment 200 installed under the ground. Through case studies, it is confirmed that the proposed mitigation system 201 can handle materials safely and has a large impact on the reducing the impact of an initial accident. 202 When designing this type of mitigation system for a vessel, this study can also provide scientific 203 approaches and guidelines to determine the proper design specifications and help to reduce cost, 204 efforts, and time for performing the set of experiments.
• In the current version of this manuscript, the authors did not present clearly what the novelty and key points and also the general conclusion of this study are.
• This chapter is too short. The authors have to expand it, in order to present clearly the aims of this paper, and the produced scientific results as well.

Ok! The authors revised the manuscript (comparatively with the previous submission).

 

References

• The literature list includes 12 items, wherein 9 references came from the same journal. Updating the references list with more recent papers, would be necessary. So, the authors must enrich the “references” with more scientific papers.

Ok! The authors gave the necessary clarifications.

 

Decision: My opinion is the manuscript could be published in the current version. 

Moreover, please see the attached document.

Comments for author File: Comments.pdf

Author Response

Thanks for your comment. Your reviews provide us a good opportunity to improve our article.

Please see and refer the attachment for the answers.

Author Response File: Author Response.pdf