International Journal of Environmental Research and Public Health

Article A Bibliometric and Visualized Overview for the Evolution of Process Safety and Environmental Protection

Jie Xue 1,2,3,* , Genserik Reniers 1,4,5, Jie Li 6,7,*, Ming Yang 1, Chaozhong Wu 2,3 and P.H.A.J.M. van Gelder 1

1 Safety and Security Science Group (S3G), Faculty of Technology, Policy and Management, Delft University of Technology, 2628BX Delft, The Netherlands; [email protected] (G.R.); [email protected] (M.Y.); [email protected] (P.H.A.J.M.v.G.) 2 Intelligent Transportation Systems Center (ITSC), Wuhan University of Technology, Wuhan 430063, China; [email protected] 3 National Engineering Research Center for Water Transport Safety (WTSC), Wuhan University of Technology, Wuhan 430063, China 4 Antwerp Research Group on Safety and Security (ARGoSS), Faculty of Applied Economics, University Antwerp, 2000 Antwerp, Belgium 5 CEDON (Center for Economics and Corporate Sustainability), KU Leuven, Campus Brussels, 1000 Brussels, Belgium 6 College of Safety Science and Engineering, Liaoning Technical University, Huludao 125105, China 7 State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081, China


* Correspondence: [email protected] (J.X.); [email protected] (J.L.)


Citation: Xue, J.; Reniers, G.; Li, J.; Abstract: This paper presents a bibliometric overview of the publications in the principal international Yang, M.; Wu, C.; van Gelder, journal Process Safety and Environmental Protection (PSEP) from 1990 to 2020 retrieved in the P.H.A.J.M. A Bibliometric and Web of Science (WoS) database to explore the evolution in safety and environmental engineering Visualized Overview for the design and practice, as well as experimental or theoretical innovative research. Therefore, based Evolution of Process Safety and on the WoS database and the visualization of similarities (VOS) viewer software, the bibliometric Environmental Protection. Int. J. analysis and scientometric mapping of the literature have been performed from the perspectives of Environ. Res. Public Health 2021, 18, document types, publication and citation distribution over time, leading authors, countries (regions), 5985. https://doi.org/10.3390/ institutions, the corresponding collaboration networks, most cited publications and references, ijerph18115985 focused research fields and topics, research trend evolution over time, etc. The paper provides a

Academic Editors: Gianpaolo Di comprehensive and quantitative overview and significant picture representation for the journal’s Bona, Antonio Forcina and Filippo De leading and evolutionary trends by employing specific aforementioned bibliometric analysis factors. Carlo In addition, by reviewing the evolutionary trends of the journal and the proposed investigated factors, such as the influential works, main research topics, and the research frontiers, this paper reveals the Received: 12 May 2021 scientific literature production’s main research objectives and directions that could be addressed and Accepted: 31 May 2021 explored in future studies. Published: 2 June 2021 Keywords: bibliometrics; environmental protection; scientometric mapping; VOSviewer; Web of Publisher’s Note: MDPI stays neutral Science; evolutionary trends with regard to jurisdictional claims in published maps and institutional affil- iations. 1. Introduction Bibliometrics originated from library and information science [1]. A bibliographic analysis is mainly applied to characterize the structure and research trends of a specific field Copyright: © 2021 by the authors. or journal by utilizing a quantitative methodology [2–4]. Additionally, it is a comprehensive Licensee MDPI, Basel, Switzerland. visual analysis method augmented with network topology that could detect the influential This article is an open access article authors, institutions, and countries in a specific research domain [5] and demonstrate a distributed under the terms and journal’s influence and productivity [1]. conditions of the Creative Commons Moreover, scientific literature mapping by utilizing bibliometric methods is an effec- Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ tive complement to the traditional structured literature review, as it is able to provide a 4.0/).

Int. J. Environ. Res. Public Health 2021, 18, 5985. https://doi.org/10.3390/ijerph18115985 https://www.mdpi.com/journal/ijerph Int. J. Environ. Res. Public Health 2021, 18, 5985 2 of 29

broader spectrum of research analysis [6,7]. Compared with a structured review, a bibli- ographic analysis provides a more wide angle on the analysis coverage breadth and the literature review depth [2]. In addition, bibliographic analysis has already been widely conducted in previous studies for analyzing various journals in different research subjects to explore and understand the specific research domain and research trends in the last few years. The typical bibliometrics analysis researches objects and topics, including journals, countries, authors, institutions, keywords, etc. Furthermore, the quantitative analysis is the fundament of bibliometric analysis, and the quantitative and qualitative are always combined during the practical analysis process. For instance, quantitative analysis is uti- lized with respect to the number of publications, while a qualitative analysis needs to be conducted when analyzing and summarizing a specific cluster’s theme. The quantitative analysis for the total number of citations of a particular publication could also reflect the quality and impact of the publication. Many scholars who conducted the related research used bibliometric mapping meth- ods. For instance, Li et al. [8] provided a bibliometric mapping review of the hotspots of lifecycle assessment for bioenergy. Zhi and Ji [9] explored the bibliometric mapping approach to give a review of quantitatively evaluated global scientific constructed wetlands research. Mao et al. [10] employed the bibliometric mapping to quantitatively analyze industrial wastewater treatment literature publications. Li et al. [11] did a preliminary overview of bibliometric mapping for the safety science community. Merigó, Miranda, Modak, Boustras, and de la Sotta [1] used bibliometric mapping to analyze forty years of safety science in terms of publications trends, leading producers (author, institutions, countries/regions), and highly cited papers and references also analyzed in the research. Additionally, as the knowledge carrier, scientific journals have published almost any research for a particular knowledge domain. The analysis of a specific journal helps un- derstand the research of the area in some aspects. Several papers have conducted the research for journal analysis, e.g., Journal of Infection and Public Health [12], Group Decision and Negotiation [13], Mechanism and Machine Theory [14], European Journal of Operational Research [15], Resources, Conservation and Recycling [16], Transportation Research Part A: Policy and Practice [17], Computers & Industrial Engineering [18], Knowledge-Based Systems [19], International Journal of Fuzzy Systems [20], Industrial Management & Data Systems [21], etc. Process Safety and Environmental Protection (PSEP) is the principal international journal covering the branches of engineering related to the research fields of safety of industrial processes and the protection of the environment. To explore the evolution in safety or environmental engineering design and practice, as well as experimental or theoretical innovative research, we strive to review the journal’s publication records and most significant trends through a general bibliometric analysis. Therefore, in the present study, the overview of the journal’s basic information and extraordinary contributions are recognized and analyzed in detail by the combination of qualitative and quantitative analysis, the related analyses involving the publication distribution and citation structure; leading authors, institutions, and countries (regions); influential publications; and focused research fields, as well as the research trend evolutionary process. Additionally, based on the information retrieved in the Web of Science Core (WoS) Collection database, the tool of the visualization of similarities (VOS) viewer, i.e., VOSviewer, which was developed by van Eck and Waltman [22], has been employed to perform a bibliometric analysis and scientometric mapping of publications from a visualization view. The purpose of the present study is to (1) help related journal editors develop suitable strategies by examining more influential research types to achieve their development goals, (2) provide inspiration for academia and help them understand the most popular research fields and trends with the most publication potential, thus identifying and choosing the targeted research themes, and (3) concerning the benefits to readers, they can more intu- itively and easily obtain more specific and accurate information that they are interested in from a large number of bibliometric data. Int. J. Environ. Res. Public Health 2021, 18, x 3 of 31 Int. J. Environ. Res. Public Health 2021, 18, 5985 3 of 29

The remainder of this paper is organized as follows: first, Section 2 presents the ma- terialsThe and remainder bibliometric of analysis this paper methods is organized utilized asin the follows: paper. first, Second, Section the 2statistical presents anal- the ysismaterials and graphical and bibliometric analysis results analysis are methods detailed, utilized including in the the paper. publication Second, trends the statisticaland cita- tionanalysis distribution; and graphical leading analysis authors, results institutions, are detailed, and countries/regions; including the publication influential trends works and in PSEP;citation and distribution; identified leadingresearch authors, fields and institutions, research andevolutionary countries/regions; trends in influential the perspective works ofin keyword PSEP; and co-occurrence. identified research Additionally, fields and the research accompanying evolutionary discussions trends inare the conducted perspective in Sectionof keyword 3. Finally, co-occurrence. Section 4 Additionally,concludes the themain accompanying findings of the discussions paper and are delivers conducted the recommendationsin Section3. Finally, for Section the readers.4 concludes the main findings of the paper and delivers the recommendations for the readers. 2. Materials and Methods 2. Materials and Methods 2.1.2.1. Bibliographic Bibliographic Data Data InIn this this paper, paper, a a typical typical journal journal PSEP PSEP with with a a high high reputation reputation in in the the research research fields fields of of safetysafety of industrialindustrial processesprocesses and and protection protection of theof the environment environment and and with with a relatively a relatively rapid rapidincrease increase of impact of impact factor, factor, quick reviewquick review speed, andspeed, online and article online publication article publication time, etc., time, was etc.,selected was asselected the candidate as the candidate journal to journal be analyzed. to be analyzed. TheThe data data were were retrieved retrieved on on 9 9 January January 2021 2021 from from the the WoS WoS Core Collection, which is is ownedowned by by Clarivate Clarivate Analytics. Analytics. The The advanced advanced search search module module was was employed, employed, and and the the strat- strat- egyegy for for obtaining obtaining data data was, was, “Publication “Publication Name: Name: SO SO = = (Process (Process Safety Safety and and Environmental Environmental Protection),Protection), Indexes == SCI-EXPANDED,SCI-EXPANDED, Timespan Timespan = 1990–2020”.= 1990–2020”. In In total, total, 3152 3152 publications publica- tionswere were obtained obtained from from the Web the ofWeb Science, of Science, and the and PSEP the PSEP publications publications had 13 had different 13 different types types(some (some of the of papers the papers were were classified classified into more into more than onethan category). one category). The proportionThe proportion of each of eachdocument document type type is shown is shown in Figurein Figure1. Note1. Note that that articles articles and and reviews reviews are are more more essentialessential documentdocument types in scientificscientific outputs,outputs, andand these these two two types types have have nearly nearly 90.09% 90.09% (2965 (2965 articles arti- clesand and reviews) reviews) in PSEP. in PSEP. The The total total number number of citations of citations was was 44,879, 44,879, and theand average the average number num- of bercitations of citations per publication per publication was 14.24. was 14.24.

FigureFigure 1. 1. DocumentDocument types types of of PSEP PSEP from from 1990 1990 to to 2020. 2020. 2.2. Bibliometric Methods and Analysis Tool 2.2. Bibliometric Methods and Analysis Tool In the present paper, bibliometric methods were applied, and the bibliometric mapping toolIn VOSviewer the present was paper, used bibliometric to analyze the method journals paperswere applied, in a visual, and user-friendlythe bibliometric way. map- The pingbibliometric tool VOSviewer analysis was originated used to from analyze information the journal and papers library in science, a visual, which user-friendly was first way.proposed The bibliometric by Otlet [23 ].analysis In the originated data science from age, information bibliometric and methods library werescience, combined which waswith first network proposed analysis by Otlet and [23]. data In visualization the data science techniques, age, bibliometric and then methods a new area were named com- binedbibliometric with network mapping analysis was produced. and data The visualization bibliometric techniques, mapping wasand about then quantitativea new area namedmethods bibliometric (mathematics mapping and statistics) was produced. for visually The representing bibliometric scientificmapping literature was about based quan- on titativebibliographic methods data. (mathematics and statistics) for visually representing scientific literature basedAdditionally, on bibliographic in bibliometrics, data. a threshold is used to select the minimum frequency of occurrence of the knowledge unit included in the network node. In the analysis of different knowledge units, the set of the specific threshold will have individual differences. Its pri- Int. J. Environ. Res. Public Health 2021, 18, 5985 4 of 29

mary purpose is to extract the core knowledge network formed by the analyzed knowledge units. It should be noted that the related results would be different by employing different thresholds in bibliometric analysis for different research topics and analytical problems, and there is generally no clear standard. In general, scholars set the threshold and conduct the related analysis directly under the premise that the problem explained is clear and the network constructed is easy to analyze and reasonable. The threshold usually is set to 3, 5, 10, 15, 20, 30, etc. [20,24–26], and the smaller the threshold setting, the larger and more complex the extracted knowledge network is. Recently, bibliometric mapping analysis became popular not only inside the scientific communities of information and library science, but also in other scientific communi- ties. More than 30 free tools have already been developed for bibliometric mapping, and VOSviewer is a famous tool among these tools [27,28]. VOSviewer is short for Visual- ization of Similarity, developed by van Eck and Waltman from Leiden University, the Netherlands, in 2010. The tool has several functions for bibliometric mapping, including collaboration analysis (e.g., authors, institutions, and countries/regions), topics analysis (e.g., keyword or terms), and citation-based analysis (e.g., bibliographic coupling and co-citations). Several papers have already applied VOSviewer to do bibliometric mapping analysis in environmental protection and safety-related topics, such as climate change [29], heavy metal removal [30], carbon emissions [31], contamination of water bodies [32], carbon capture and storage [33], soil remediation [34], safety culture [25], construction safety [35,36], process safety [37], domino effect [38], laboratory safety in universities [39], road safety research [40], etc.

3. Results and Discussion 3.1. Publication Trend and Citation Distribution The publication trend (including the number of papers) is the mirror and indicator for reflecting and measuring the scientific activities and attention to a specific domain. Figure2 and Table1 show the annual increase trend of PSEP publications. The increase of the annual outputs shows the increased attention to the topic scope of the PSEP from scientific communities. PSEP, as one of the leading journals in industrial process safety and environmental protection, has released a total of 16 publications in 1990, according to its earliest record in WoS. Moreover, the number of publications has increased slowly before 2013, and the average value for the number of publications per year before 2013 was around 48. After 2013, the publication trend increased rapidly, and the outputs reached more than 100 papers per year, with the number of papers in 2019 being 432 (exceeding 400 the first time). Additionally, the cumulative percentage of the number of publications showed that nearly 50% of cumulative publications from PSEP were published after 2016, which means that the most recent five years (2016–2020) have contributed roughly half of all of the papers that have been published in PSEP from 1990 to 2020. Int. J. Environ. Res.Int. Public J. Environ. Health Res.2021 Public, 18, x Health 2021 18 5 of 31 , , 5985 5 of 29

FigureFigure 2. 2. TheThe number number of of publications publications in in each each year year of of PSEP PSEP from from 1990 1990 to to 2020 2020 in in Web Web of of Science. Science.

Table 1. Annual publications and citations of PSEP. Table 1. Annual publications and citations of PSEP.

Years NPYears % of NP3152 % CNP of 3152 % of CNP CNP % TC of CNP CPP TC CPP 1990 16 0.51% 16 0.51% 14 0.88 1990 161991 0.51%31 0.98%16 0.51% 47 1.49%14 0.88186 6.00 1991 311992 0.98%34 1.08%47 1.49% 81 186 2.57% 6.00204 6.00 1992 341993 1.08%38 1.21%81 2.57% 119 204 3.78% 6.00275 7.24 1993 381994 1.21%37 119 1.17% 3.78% 156 275 4.95% 7.24249 6.73 1995 57 1.81% 213 6.76% 219 3.84 1994 371996 1.17%37 156 1.17% 4.95% 250 249 7.93% 6.73276 7.46 1995 571997 1.81%36 213 1.14% 6.76% 286 219 9.07% 3.84560 15.56 1996 371998 1.17%41 250 1.30% 7.93% 327 10.37%276 7.463266 79.66 1997 361999 1.14%49 286 1.55% 9.07% 376 11.93%560 15.56519 10.59 2000 57 1.81% 433 13.74% 1028 18.04 1998 41 1.30% 327 10.37% 3266 79.66 2001 42 1.33% 475 15.07% 656 15.62 1999 492002 1.55%44 376 1.40% 11.93% 519 16.47%519 10.59353 8.02 2000 572003 1.81%52 433 1.65% 13.74% 571 1028 18.12% 18.04957 18.40 2001 422004 1.33%56 475 1.78% 15.07% 627 19.89%656 15.62785 14.02 2002 442005 1.40%64 519 2.03% 16.47% 691 21.92%353 8.021033 16.14 2006 58 1.84% 749 23.76% 1194 20.59 2003 522007 1.65%71 571 2.25% 18.12% 820 26.02%957 18.401660 23.38 2004 562008 1.78%49 627 1.55% 19.89% 869 27.57%785 14.021516 30.94 2005 642009 2.03%56 691 1.78% 21.92% 925 1033 29.35% 16.141026 18.32 2006 582010 1.84%53 749 1.68% 23.76% 978 1194 31.03% 20.591360 25.66 2011 57 1.81% 1035 32.84% 1720 30.18 2007 712012 2.25%58 820 1.84% 26.02% 1093 1660 34.68% 23.381527 26.33 2008 492013 1.55%56 869 1.78% 27.57% 1149 1516 36.45% 30.941297 23.16 2009 562014 1.78%102 925 3.24% 29.35% 1251 1026 39.69% 18.322005 19.66 2010 532015 1.68%183 978 5.81% 31.03% 1434 1360 45.49% 25.663863 21.11 2016 247 7.84% 1681 53.33% 4508 18.25 2011 57 1.81% 1035 32.84% 1720 30.18 2017 309 9.80% 1990 63.13% 5062 16.38 2012 58 1.84% 1093 34.68% 1527 26.33 2013 56 1.78% 1149 36.45% 1297 23.16 2014 102 3.24% 1251 39.69% 2005 19.66 2015 183 5.81% 1434 45.49% 3863 21.11 2016 247 7.84% 1681 53.33% 4508 18.25 Int. J. Environ. Res. Public Health 2021, 18, x 19 of 31

3.4. Research Fields Identification and Research Trends Evolution Keywords are one of the essential elements supplied by the authors of the paper to show the paper’s core content. Author keywords are imperative, since they are used as the topics/concepts/methods that are presented to deliver and communicate to the scien- tific community by the authors. The author keyword co-occurrences network demon- strates another perspective of themes in PSEP, and it can be observed that it illustrates the main author keywords that frequently occur together in PSEP. Considering the fact that many keywords only appeared a few times, they obviously have not had significant influences on the main themes of PSEP. Therefore, in the present study, to focus on the main themes, only the keywords occurring at least five times were selected to construct the co-occurrence analysis map and indicate the research topics. Thus, 407 keywords were extracted based on the threshold of the keyword’s frequencies. The keyword co-occurrence network for the clusters (groups) of PSEP is shown in Figure 8. Note that the larger the nodes and character fonts, the more often the keywords are used.

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Int. J. Environ. Res. Public Health 2021, 18, x 6 of 31

Table 1. Cont.

Years2017 309 NP %9.80% of 3152 1990 CNP 63.13% % of CNP 5062 TC 16.38 CPP 2018 344344 10.91% 10.91% 2334 2334 74.05% 74.05% 42754275 12.4312.43 2019 432432 13.71% 13.71% 2766 2766 87.75% 87.75% 27422742 6.356.35 2020 386 12.25% 3152 100.00% 544 1.41 2020 386 12.25% 3152 100.00% 544 1.41 Note: NP = number of publications, CNP = cumulative number of publications, TC = total citations, CPP = citationsNote: NP per = papernumber = TC/NP.of publications, The colors CNP range = cumulative from green tonumber red in theof publications, related column TC indicate = total thecitations, smaller the numberCPP = citations and the closerper paper the color = TC/NP. is to green The colors in that range column. from green to red in the related column indicate the smaller the number and the closer the color is to green in that column.

3.2. Leading Authors, Institutions,Figure and Countries/Regions8. Keyword co-occurrence cluster of PSEP papers. 3.2.1.3.2. Leading Leading Authors, Authors Institutions, and Collaborations and Countries/Regions 3.2.1. Leading Authors and CollaborationsObviously, the keyword “adsorption” is the most used author’s keyword with 122 Authors are the knowledgeoccurrences, producers followed of PSEP, by “kinetics” and an (80), author’s “response production surface methodology” and (74), “risk as- Authors are the knowledge producers of PSEP, and an author’s production and col- collaboration analysis can easilysessment” show (73), the “optimization” leading researchers (67), “heavy and metals” the (56), author’s “safety” social (56), etc. There were six connectednesslaboration analysis in PSEP. can Theeasily whole showclusters author’s the of leading keywords, collaboration researchers separated network by and different the is author’scolors illustrated and socialrepresenting in Figurecon- the3 following, themes: andnectedness the author in PSEP. who The had whole a minimum author’sThe number bluecollaboration group of ( publications ) was network mainly isconcentrated of illustrated 10 was on regarded in waste Figure and as 3,pollutants the remediation. This cluster included keywords such as “adsorption” (122), “kinetics” (80), “heavy met- leadingand the authorauthor inwho PSEP. had Tablea minimum2 lists the number leading of authorspublications of PSEP, of 10 and was indicates regarded thatas the there als” (56), “wastewater” (43), “activated carbon” (40), “isotherm” (34), “biosorption” (23), areleading 69.70% author (23/33) in PSEP. of them Table within 2 lists thethe giantleading connected authors of component PSEP, and indicates (GCC) of that the there authors’ are 69.70% (23/33) of them within“composting” the giant connected (22), “thermodynamic” component (22), (GCC) “volatile of organicthe authors’ compound” (22), etc. collaboration network (cluster 1, theThe red red group group ( ) mainly in Figure focused3). Consideringon environmental the protection sparsely methodologies and collaboration network (cluster 1, the red group ( ) in Figure 3). Considering the sparsely connected network structure oftechnologies. other groups, This onlycluster the contained GCCof keywords the authors’ such ascollaboration “response surface methodology” connected network structure of other groups, only the GCC of the authors’ collaboration network was selected to analyze(74), the “optimization” author’s social (67), connection “wastewater intreatment” PSEP.Note (44), “photocatalysis” that authors (43), “biodiesel” network was selected to analyze the(34), author’s “advanced social oxidation connection process” (32),in PSEP. “electrocoagulation” Note that authors (31), “biodegradation” (30), with only the publication type of editorial material are not included in Table2. The node with only the publication type of“artificial editorial neural material network” are not(24), included “water treatment” in Table (24), 2. Theetc. node size is proportionate to the number of publications of an author; the node color represents size is proportionate to the number ofThe publications purple group of ( an ) wasauthor; mainly the about node waste color management represents and sustainable devel- the clusters of authors in the sameopment. group. This Additionally, cluster was represented the links by between keywords authors such as “anaerobic present digestion” (31), the clusters of authors in the same group. Additionally, the links between authors present the collaboration relations between“pyrolysis” authors, (28), and “recycling” the wideness (27), “lifecycle of the link assessment” shows the(24), authors’ “biomass” (21), “environ- the collaboration relations betweenment” authors, (20), “biogas” and the (19), wideness “mathematical of the modeling” link shows (18), “combustion” the au- (17), “mass trans- collaboration strength. thors’ collaboration strength. fer” (15), “energy” (14), “sustainable development” (12), “emissions” (12), etc.

FigureFigure 3.3. The whole authors’ collaboration collaboration network network of of PSEP PSEP from from 1990 1990 to to 2020 2020 (the (the minimum minimum num- number ber of publications = 3). of publications = 3). Int. J. Environ. Res. Public Health 2021, 18, 5985 7 of 29

Table 2. Leading authors in PSEP based on the number of publications (minimum number of publications = 10).

Rank Author EBMs C/R Institution NP TC APY CPP 1 Khan, Faisal Y Canada Mem. Univ. Newfoundland 62 1938 2014.50 31.26 2 Amyotte, Paul N Canada Dalhousie Univ. 28 1101 2011.96 39.32 3 Thomas, P. J. Y UK Univ. Bristol 27 251 2012.48 9.30 4 Forster, CF N UK Univ. Birmingham 24 243 1996.17 10.13 5 Mannan, M. Sam N USA Texas A&M Univ. 24 346 2012.13 14.42 6 Shu, Chi-Min N Taiwan Natl. Yunlin Univ. Sci. & Technol. 23 172 2015.26 7.48 7 Tan, Raymond R. N Philippines De La Salle Univ. 17 417 2014.12 24.53 8 Reniers, Genserik N Belgium Univ. Antwerp/Delft Univ. Technol. 16 137 2018.25 8.56 9 Richardson, SM N UK Imperial Coll. London 16 97 1996.00 6.06 10 Hassim, Mimi H. Y Malaysia Univ. Teknol. Malaysia 15 197 2015.00 13.13 11 Mckay, Gordon N Qatar Hamad Bin Khalifa Univ. 15 2897 2003.00 193.13 12 Streat, M N UK Univ. Loughborough 15 443 2001.47 29.53 13 Yang, Ming N Netherlands Delft Univ. Technol. 15 250 2016.07 16.67 14 Edwards, DW Y UK Univ. Loughborough 14 307 2000.71 21.93 15 Jiang, Juncheng N China Changzhou Univ. 14 51 2018.79 3.64 16 Wang, Deming N China China Univ. Min. & Technol. 14 240 2017.93 17.14 17 Abbassi, Rouzbeh Y Australia Macquarie Univ. 13 106 2017.69 8.15 18 Jones, JC N UK Univ. Aberdeen 13 19 2005.85 1.46 19 Pasman, Hans J. N USA Texas A&M Univ. 13 249 2012.15 19.15 20 Stephenson, T N UK Cranfield Univ. 13 189 1999.77 14.54 21 Swithenbank, J N UK Univ. Sheffield 13 163 2001.62 12.54 22 Wang, Kai N China China Univ. Min. & Technol. 13 76 2019.00 5.85 23 Cozzani, Valerio N Italy Univ. Bologna 12 139 2016.42 11.58 24 Khakzad, Nima N Canada Ryerson Univ. 12 376 2017.58 31.33 25 Chen, Guoming N China China Univ. Petr. 11 152 2017.82 13.82 26 Jones, R. D. N UK City Univ. London 11 106 2009.73 9.64 27 Shu, Li N Australia RMIT Univ. 11 111 2017.18 10.09 28 Fabiano, Bruno Y Italy Univ. Genoa 10 271 2013.80 27.10 29 Foo, Dominic C. Y. Y Malaysia Univ. Nottingham 10 136 2015.10 13.60 30 Halder, Gopinath N India Natl. Inst. Technol. Durgapur 10 76 2018.50 7.60 31 Shon, Ho Kyong Y Australia Univ. Technol. Sydney 10 60 2017.80 6.00 32 Yang, Shengqiang N China China Univ. Min. & Technol. 10 67 2018.90 6.70 33 Zhang, Laibin N China China Univ. Petr. 10 128 2016.60 12.80

As shown in Table2, Faisal Khan (Mem. Univ. Newfoundland, Canada) is the most productive author in PSEP with 62 publications. He is also the only author with more than 50 papers in PSEP, followed by Paul Amyotte (Dalhousie University, Canada), P.J. Thomas (University of Bristol, UK), C.F. Forster (University of Birmingham, UK), M. Sam Mannan (Texas A&M University, USA), and Chi-Min Shu (National Yunlin University of Science and Technology, Taiwan), with more than 20 papers published in PSEP, ranked in the top 2–6 positions, respectively. Furthermore, Kai Wang (China University of Mining & Technology, China) holds the largest average publication year (APY) of 2019.00, and Gordon Mckay (Hamad Bin Khalifa University, Qatar) is the author who has the most citations (2897) and the highest average number of citations (193.13). The productivity distribution of the (leading) authors was not balanced; there were just a few authors who have published a large number of papers, resulting in the uneven distribution of the total number of citations of leading authors. In addition, the highly productive editorial board members of PSEP are also highlighted in Table2. Among the leading authors, 24.24% (8/33) are editorial board members, which indicates that the editorial board members play a relatively important role among the leading authors, as well as within the process safety and environmental protection research domain. Additionally, as shown in Table2, 27.27% (9/33) of the leading authors originate from the United Kingdom.

3.2.2. Leading Countries/Regions and Collaboration The countries/regions cooperation relation in the explored field was also visualized and analyzed by utilizing collaboration networks analysis to investigate affiliated countries Int. J. Environ. Res. Public Health 2021, 18, x 8 of 31

Int. J. Environ. Res. Public Health 2021, 18, 5985 8 of 29 3.2.2. Leading Countries/Regions and Collaboration The countries/regions cooperation relation in the explored field was also visualized and analyzed by utilizing collaboration networks analysis to investigate affiliated coun- andtries institutesand institutes through through the VOSviewerthe VOSviewer software. software. As As shown shown in in Figure Figure4, 4, the the minimum minimum numbernumber ofof publicationspublications was 10, and 44 44 countries/regions countries/regions were were included included in in the the network. network. It Itshould should be be noted noted that that a node a node was was apportioned apportioned to toeach each co-author co-author of a of publication a publication in the in thenetworks. networks. The node’s The node’s color colorpresents presents the averag the averagee time for time the forpublications the publications of each ofcountry each country[41]. The [ 41node’s]. The size node’s denotes size denotesthe related the publication related publication number, number, and the thickness and the thickness of the links of theindicates links indicates the international the international collaboration collaboration degree [38,42], degree i.e., [38 the,42], larger i.e., the the larger node theis, the node more is, thecritical more the critical country/region the country/region is, and the is, andthicker the thickerthe line the is, line the is,closer the closer the cooperation the cooperation rela- relationshiptionship between between countries/regions. countries/regions.

FigureFigure 4.4. Countries/regionsCountries/regions collaboration network in PSEP publications.

FigureFigure4 4 indicates indicates thatthat China (with 678 678 pub publicationslications and and 9615 9615 total total citations) citations) and and the theUnited United Kingdom Kingdom (with (with 476 publications 476 publications and 7517 and total 7517 citations) total citations) have been have at the been forefront at the forefrontand play andthe predominant play the predominant roles in PSEP. roles inMean PSEP.while, Meanwhile, China mainly China collaborates mainly collaborates with the withUSA, the Australia, USA, Australia, Taiwan (region), Taiwan (region), United Ki Unitedngdom, Kingdom, South Korea, South Japan, Korea, Canada, Japan, Canada, Nether- Netherlands,lands, etc. Similarly, etc. Similarly, the close the collaboration close collaboration countries/regions countries/regions with the United with the Kingdom United Kingdomare Canada, are China, Canada, Australia, China, Australia, Iran, Germany, Iran, Germany, India, Italy, India, Netherlands, Italy, Netherlands, France, France, etc. Addi- etc. Additionally,tionally, among among the close the close collaboration collaboration countries/regions, countries/regions, China China and andthe theUSA USA have have the themost most immediate immediate cooperation cooperation and and research research rela relationshiptionship in in PSEP. PSEP. Moreover, Moreover, as shownshown inin TableTable3 ,3, in in terms terms of of the the publication publication time, time, Thailand Thailand (with (with the the largest largest average average publication publication yearyear (APY)(APY) ofof 2018.14),2018.14), QatarQatar (2017.62),(2017.62), andand TunisiaTunisia (2017.43)(2017.43) areare thethe toptop threethree relativelyrelatively activeactive researchresearch countriescountries recently,recently, andand havehave thethe latestlatest outputoutput inin PSEPPSEP accordingaccording toto thethe investigatedinvestigated resultsresults fromfrom thethe corecore databasedatabase ofof thethe WoS.WoS. Furthermore,Furthermore, the the PhilippinesPhilippines (with (with anan averageaverage citationcitation ofof 28.59),28.59), FinlandFinland (27.13),(27.13), andand SaudiSaudi ArabiaArabia (25.36)(25.36) areare thethe onlyonly threethree countriescountries whosewhose average average citations citations exceeded exceeded 25. 25 Generally,. Generally, more more international international collaboration collabora- needstion needs to be to promoted be promoted andenhanced and enhanced to share to share knowledge knowledge globally globally in the in future. the future.

Int. J. Environ. Res. Public Health 2021, 18, 5985 9 of 29

Table 3. Leading countries/regions in PSEP based on the number of publications (minimum number of publications = 20).

Rank C/R Continent NP TC APY CPP 1 China Asia 678 9615 2017.27 14.18 2 UK Europe 476 7517 2006.32 15.79 3 India Asia 240 4251 2015.92 17.71 4 Iran Asia 228 3514 2017.00 15.41 5 USA North America 160 2357 2013.86 14.73 6 Australia Oceania 152 1739 2013.55 11.44 7 Canada North America 147 2957 2013.82 20.12 8 Malaysia Asia 136 3181 2016.00 23.39 9 Italy Europe 113 1431 2014.58 12.66 10 Spain Europe 102 1227 2015.61 12.03 11 France Europe 91 1285 2012.60 14.12 12 Brazil South America 82 784 2016.99 9.56 13 Taiwan Asia 82 865 2015.09 10.55 14 South Korea Asia 77 658 2017.18 8.55 15 Turkey Asia and Europe 62 1189 2013.89 19.18 16 Netherlands Europe 59 705 2013.00 11.95 17 Japan Asia 48 548 2014.17 11.42 18 Germany Europe 47 710 2011.11 15.11 19 Saudi Arabia Asia 45 1141 2016.96 25.36 20 Romania Europe 35 527 2016.71 15.06 21 Egypt Africa and Asia 33 457 2015.97 13.85 22 Belgium Europe 31 339 2016.42 10.94 23 Pakistan Asia 26 299 2017.38 11.50 24 Tunisia Africa 26 343 2017.58 13.19 25 Norway Europe 25 292 2015.80 11.68 26 Greece Europe 24 302 2012.17 12.58 27 Finland Europe 23 624 2013.43 27.13 28 Poland Europe 23 392 2015.57 17.04 29 Philippines Asia 22 629 2014.95 28.59 30 Thailand Asia 22 173 2018.14 7.86 31 Mexico North America 21 241 2017.43 11.48 32 Qatar Asia 21 252 2017.62 12.00 33 South Africa Africa 20 239 2017.10 11.95 Note: C/R = country/region, NP = number of publications, TC = total citations, APY = average publication year, CPP = citations per paper (average citations) = TC/NP.

3.2.3. Leading Institutions and Collaborations Figure5 illustrates the institution collaboration network for PSEP during the entire explored timespan. The node’s size presents the number of publications (the bigger the note is, the more publications the institution has), and the links between two nodes indicate the collaboration relationship between two institutions (the thicker the link is, the closer the cooperation they have). In addition, each institution in the network has a minimum of 10 publications in PSEP, and 77 institutions meet the threshold. As shown in Table4, China University of Mining & Technology (China) has the highest number of publications at 73; Nanjing Tech University (China) has the largest APY at 2018.87. In Canada, the Memorial University of Newfoundland gets the highest number of total citations of 1854 among the leading institutions of PSEP, and Dalhousie University holds the highest average citations of 37.24 (the only institution whose average numbers of citations exceeded 30). With a total number of citations of 1229, Dalhousie University is also the institution whose total number of citations exceeded 1000, except Memorial University of Newfoundland. Additionally, 29.63% (8/27) of the leading institutions are from the United Kingdom. Int. J. Environ. Res. Public Health 2021, 18, x 10 of 31

ceeded 30). With a total number of citations of 1229, Dalhousie University is also the in- Int. J. Environ. Res. Public Health 2021, stitution18, 5985 whose total number of citations exceeded 1000, except Memorial University10 of 29of Newfoundland. Additionally, 29.63% (8/27) of the leading institutions are from the United Kingdom.

FigureFigure 5.5. InstitutionInstitution collaborationcollaboration networknetwork ofof PSEPPSEP publicationspublications fromfrom 19901990 toto 2020.2020.

Table 4. Leading institutionsTable in PSEP4. Leading based institutions on the number in PSEP of publications based on the (minimum number numberof publications of publications (minimum = 20). number of publications = 20). Rank Institutions C/R NP TC APY CPP Rank Institutions C/R NP TC APY CPP 1 China Univ. Min. & Technol. China 73 772 2018.53 10.58 1 China Univ. Min. & Technol. China 73 772 2018.53 10.58 2 Mem. Univ. Newfoundland Canada 63 1854 2014.63 29.43 3 Texas A&M Univ.2 Mem. Univ. USA Newfoundland 44 625 Canada 2013.5263 1854 2014.63 14.20 29.43 4 Univ. Loughborough3 Texas UK A&M Univ. 44 958 USA 2002.89 44 625 2013.52 21.77 14.20 5 Delft Univ. Technol.4 Univ. Netherlands Loughborough 41 397UK 2015.1744 958 2002.89 9.68 21.77 6 Chinese Acad.5 Sci.Delft China Univ. Technol. 35 Netherlands 295 2017.9741 397 2015.17 8.43 9.68 7 Dalhousie Univ. Canada 33 1229 2012.30 37.24 8 China Univ. Petr.6 Chinese China Acad. Sci. 30 271 China 2017.2735 295 2017.97 9.03 8.43 9 Hlth & Safety7 Lab. Dalhousie UK Univ. 30 399 Canada 2009.0033 1229 2012.30 13.30 37.24 10 Univ. Leeds8 China UK Univ. Petr. 30 533 China 2004.87 30 271 2017.27 17.77 9.03 11 Univ. Teknol. Malaysia9 Hlth Malaysia & Safety Lab. 30 446 UK 2015.07 30 399 2009.00 14.87 13.30 Shandong Univ. Sci. & 12 China 29 730 2018.69 25.17 Technol.10 Univ. Leeds UK 30 533 2004.87 17.77 13 Cranfield Univ.11 Univ. Teknol. UK Malaysia 28 Malaysia512 2005.57 30 446 2015.07 18.29 14.87 Natl. Yunlin Univ.12 Sci. & Shandong Univ. Sci. & Technol. China 29 730 2018.69 25.17 14 Taiwan 27 249 2015.67 9.22 Technol.13 Cranfield Univ. UK 28 512 2005.57 18.29 15 Islamic Azad Uni.v Iran 26 544 2017.00 20.92 14 Natl. Yunlin Univ. Sci. & Technol. Taiwan 27 249 2015.67 9.22 16 Indian Inst. Technol. India 25 374 2013.36 14.96 17 Nanjing Tech.15 Univ. Islamic China Azad Uni.v 23 74 Iran 2018.8726 544 2017.00 3.22 20.92 18 Univ. Tehran16 Indian Iran Inst. Technol. 23 509 India 2016.87 25 374 2013.36 22.13 14.96 19 Tsinghua Univ.17 Nanjing China Tech. Univ. 22 327 China 2016.23 23 74 2018.87 14.86 3.22 20 China Univ. Petr. East18 ChinaUniv. China Tehran 21 194 Iran 2017.8623 509 2016.87 9.24 22.13 21 Curtin Univ. Australia 21 302 2016.48 14.38 22 Univ. Birmingham19 Tsinghua UK Univ. 21 238China 1997.8122 327 2016.23 11.33 14.86 23 Univ. Malaya20 China Univ. Malaysia Petr. East China 21 599 China 2016.38 21 194 2017.86 28.52 9.24 24 Univ. Nottingham21 Curtin UK Univ. 21 Australia616 2014.0021 302 2016.48 29.33 14.38 25 Univ. Sci. & Technol.22 ChinaUniv. China Birmingham 21 127 UK 2017.7121 238 1997.81 6.05 11.33 26 Hlth & Safety Execut. UK 20 111 2008.50 5.55 27 Univ. Sheffield23 Univ. UK Malaya 20 Malaysia257 2005.0521 599 2016.38 12.85 28.52 Note: C/R = country/Region, NP = number of publications, TC = total citations, APY = average publication year, CPP = citations per paper (average citations) = TC/NP. Int. J. Environ. Res. Public Health 2021, 18, 5985 11 of 29

3.3. Influential Works 3.3.1. Influential Works Published by PSEP Publications with a large number of citations often indicate the influence of the publication in a specific research domain, i.e., the number of publications exceeding a certain citation threshold allows the identification of the number of publications that have a certain level of influence [43,44]. In this paper, the publications with more than 100 citations are identified as influential works in PSEP. Therefore, 25 publications are listed in Table5 . The paper by Ho and McKay [45] held the highest number of citations of 1530 and the biggest average number of citations per year of 66.52. Moreover, there were seven publications with a total number of citations of more than 200. Additionally, there were two papers among the first five most cited papers (2/5 = 40.00%), and 24.00% (6/25) of the top 25 most cited papers were review papers, while, as shown in Figure1, only 2.89% of all publications were the review papers. The statistical fact that a relatively small number of publications accomplished with a relatively high total number of citations indicated that the document type of review paper was more likely to get more citations.

Table 5. Top 25 most cited papers published in PSEP during 1990–2020 (papers were ranked with the total number of citations).

Rank Title Authors Type PY TC ACPY A comparison of chemisorption kinetic models applied 1 Ho, Y.S; McKay, G. Article 1998 1530 66.52 to pollutant removal on various sorbents Kinetic models for the sorption of dye from aqueous 2 Ho, Y.S; McKay, G. Article 1998 1026 44.61 solution by wood A review on application of flocculants in wastewater 3 Lee, C.S.; Robinson, J.; Chong, M.F. Review 2014 362 51.71 treatment A review of hazards associated with primary lithium 4 Lisbona, D.; Snee, T. Article 2011 264 26.40 and lithium-ion batteries Treatment technologies for petroleum refinery effluents: Diya’uddeen, B.H.; Daud, W.M.A.W.; Aziz, 5 Review 2011 241 24.10 a review A.R.A. Indicators of sustainable development for industry: a 6 Azapagic, A.; Perdan, S. Article 2000 240 11.43 general framework Dynamic safety analysis of process systems by 7 Khakzad, N.; Khan, F.; Amyotte, P. Article 2013 225 28.13 mapping bowtie into Bayesian network Anaerobic co-digestion of fat, oil, and grease (FOG): a Long, J.H.; Aziz, T.N.; de los Reyes, F.L.; 8 Article 2012 178 19.78 review of gas production and process limitations Ducoste, J.J. Adsorptive removal of basic dyes from aqueous solutions by surfactant modified bentonite clay 9 Anirudhan, T.S.; Ramachandran, M. Article 2015 168 28.00 (organoclay): kinetic and competitive adsorption isotherm Electrochemical oxidation remediation of real 10 Garcia-Segura, S.; Ocon, J.D.; Chong, M.N. Review 2018 167 55.67 wastewater effluents—a review Miandad, R.; Barakat, M.A.; Aburiazaiza, 11 Catalytic pyrolysis of plastic waste: a review Review 2016 162 32.40 A.S.; Rehan, M.; Nizami, A.S. Effect of pH, temperature, and air flow rate on the 12 continuous ammonia stripping of the anaerobic Gustin, S.; Marinsek-Logar, R. Article 2011 152 15.20 digestion effluent Assessing the inherent safety of chemical process 13 routes—is there a relation between plant costs and Edwards, D.W.; Lawrence, D. Article 1993 148 5.29 inherent safety Efficient removal of coomassie brilliant blue R-250 dye Sharma, G.; Naushad, M.; Kumar, A.; Rana, 14 using starch/poly (alginic acid-cl-acrylamide) S.; Sharma, S.; Bhatnagar, A.; Stadler, F.J.; Article 2017 145 36.25 nanohydrogel Ghfar, A.A.; Khan, M.R. Biodiesel production from waste oil feedstocks by solid Peng, B.X.; Shu, Q.; Wang, J.F.; Wang, G.R.; 15 Article 2008 141 10.85 acid catalysis Wang, D.Z.; Han, M.H. Systems approach to corporate sustainability—a 16 Azapagic, A. Article 2003 134 7.44 general management framework Int. J. Environ. Res. Public Health 2021, 18, x 11 of 31

Int. J. Environ. Res. Public Health 2021, 18, 5985 12 of 29

24 Univ. Nottingham UK 21 616 2014.00 29.33 25 Univ. Sci. & Technol. China China 21 127 2017.71 6.05 Table 5. Cont. 26 Hlth & Safety Execut. UK 20 111 2008.50 5.55 Rank27 TitleUniv. Sheffield Authors UK 20 257 2005.05 Type 12.85 PY TC ACPY SustainableNote: Industry C/R = country/Region, 4.0 framework: a systematic NP = number of publications, TC = total citations, APY = average pub- Kamble, S.S.; Gunasekaran, A.; Gawankar, 17 literature review identifying the current trends and Review 2018 128 42.67 lication year, CPP = citations per paper (average citations) = S.A.TC/NP. future perspectives Use of membrane technology for oil field and refinery 18 3.3. Influential Works Munirasu, S.; Abu Haija, M.; Banat, F. Review 2016 128 25.60 produced water treatment—a review 3.3.1. Influential Works Published by PSEP The diffusion behavior law of respirable dust at fully Zhou, G.; Zhang, Q.; Bai, R.N.; Fan, T.; 19 mechanized cavingPublications face in coal with mine: a CFD large numerical number of citations often indicate the influenceArticle of the2017 pub- 121 30.25 Wang, G.; simulationlication and in a engineering specific research application domain, i.e., the number of publications exceeding a certain Methods and models in process safety and risk 20 citation threshold allows the identificationKhan, of the F.; Rathnayaka, number of S.; publications Ahmed, S. thatArticle have 2015a cer- 120 20.00 management:tain level of past, influence present, and [43,44]. future In this paper, the publications with more than 100 citations Characterization of products from the pyrolysis of 21 are identified as influential works in PSEP.Buah, W.K.;Therefore, Cunliffe, 25 A.M.; publications Williams, P.T. are listedArticle in 2007Table 117 8.36 municipal solid waste 5. The paper by Ho and McKay [45] held the highest number of citations of 1530 and the 22 Design of water-using systems involving regeneration Kuo, W.C.J.; Smith, R. Article 1998 114 4.96 biggest average number of citations per year of 66.52. Moreover, there were seven publi- An experimental study for characterization the process cations with a total number of citations Kong,of more B.; Li, than Z.H.; 200. Wang, Additionally, E.Y.; Lu, W.; there were two 23 of coal oxidation and spontaneous combustion by Article 2018 109 36.33 Chen, L.; Qi, G.S. electromagneticpapers among radiation the first technique five most cited papers (2/5 = 40.00%), and 24.00% (6/25) of the top Bi-level25 fuzzy most optimization cited papers approach were for review water papers,Aviso, while, K.B.; Tan, as R.R.;shown Culaba, in Figure A.B.; Cruz, 1, only 2.89% of all 24 Article 2010 106 9.64 publicationsexchange in eco-industrial were the review parks papers. The statistical factJ.B. that a relatively small number of 25 Harnessingpublications methane emissions accomplished from coal with mining a relatively high Warmuzinski, total number K. of citations Articleindicated2008 that 106 8.15 the document type of review paper was more likely to get more citations. Total citations Note: PY = publication year, TC = total citations, ACPY = average citations per year, ACPY = Current year−Publication year+1 Furthermore, Figure 6 demonstrates the citation distribution of PSEP publications from 1990 to 2020.Furthermore, Overall, according Figure 6to demonstrates the increasing the of citation the number distribution of citations, of PSEP the publications number of publicationsfrom 1990 togradually 2020. Overall, decreased. according In addition, to the there increasing were 1924 of the publications, number of citations, the the highest numbernumber of of publications publications among gradually various decreased. intervals, In that addition, had no there more were than 1924 ten publications, citations. Notethe that, highest among number the publications of publications cited amongno more various than ten intervals, times, there that were had no 447 more than ten publications withcitations. no citations. Note that, Considering among the that publications a paper’s publication cited no more requires than a ten certain times, there were period, the citations447 publications cannot be with counted no citations. in time. ConsideringHowever, except that a for paper’s the 183 publication publications requires a certain of 2020, 59.06%period, (264/447) the citations of the publications cannot be counted had zero in time.citations. However, Note exceptthat, since for the most 183 of publications of the influential2020, works’ 59.06% research (264/447) topics of were the publicationscross-fused with had zerothe research citations. hotspots Note that, in Sec- since most of the tion 3.4, the relatedinfluential literature works’ productions research topics are not were discussed cross-fused and with analyzed the research in detail hotspots in this in Section 3.4, section. the related literature productions are not discussed and analyzed in detail in this section.

Figure 6. Citation distributionFigure 6. ofCitation PSEP publications. distribution of PSEP publications. Int. J. Environ. Res.Int. Public J. Environ. Health 2021 Res., Public18, x Health 2021, 18, 5985 14 of 31 13 of 29

3.3.2. Influential Works Int.Cited J. Environ. by Res.PSEP Public Health 2021, 18, x 19 of 31 3.3.2. Influential Works Cited by PSEP Highly cited worksHighly cited cited by worksPSEP papers cited by in PSEP our local papers dataset in our can local be datasetconsidered can bethe considered the intellectual basesintellectual of PSEP. bases The co-citation of PSEP.Int. J. Environ. The netw co-citation Res. orkPublic ofHealth highly network 2021, 18 , citedx of highly references cited (the references mini- (the minimum 19 of 31 3.4. Research Fields Identification and Research Trends Evolution mum number numberof citations of citations of a paper of a was paper 15) was was 15) constr was constructed.ucted. In total, In total,43 highly 43 highly cited cited references Keywords are one of the essential elements supplied by the authors of the paper to references werewere identified identified andand obtained obtained from from theshow the89,287 the 89,287 paper’s references references core content. of PSEP. of Author PSEP. The keyw The co-cita-ords co-citation are imperative, network since they are used as 3.4. Research Fields Identification and Research Trends Evolution tion network amongamong these these 43 43 papers papers is is displayed displayedthe in intopics/concepts/methods Figure Figure 77.. The nodenode standsthatstands are presenteforfor aa highlyhighlyd to deliver cited and reference, communicate to the scien- cited reference,and and the the size size is is proportional proportional to to the thetific number numbercommunity of citesof by cites fromtheKeywords fromauthors. the the PSEPare The onePSEP author papers. of thepapers. keywordessential The label elementsco-occurrences here supplied just network by the demon- authors of the paper to show the paper’s core content. Author keywords are imperative, since they are used as The label here showsjust shows the firstthe first author author or first or twofirststrates authorstwo another authors and perspective the and publication the of publication themes year in PSEP, ofyear aand paper. of it can be In observed addition, that it illustrates the main author keywordsthe topics/concepts/methods that frequently occur togetherthat are presentein PSEP.d to deliver and communicate to the scien- links between each node present the co-citation relations of highly cited references. Link a paper. In addition, links between each node presentConsidering the co-citationtific the communityfact that relations many by keywordsthe authors.of highly only The appeared author akeyword few times, co-occurrences they obviously network demon- cited references.wideness Link wideness indicates indicates the co-citation the haveco-citation strength not had between significantstrengthstrates another theseinfluences between perspective references. on thesethe main of refer-Thethemes themes color in of PSEP, PSEP. shows and Therefore, theit can be inobserved the present that it illustrates the ences. The colordifferent shows the groups different of these groups references, of thesestudy,which references, to focus was onmain theclustered which authormain wasthemes, keywords based clustered only on that the the freq keywordsbased co-citationuently occuroccurring strengthtogether at least in PSEP. five times were Considering the fact that many keywords only appeared a few times, they obviously on the co-citationof thesestrength references of these byreferences using the by bibliometricselected using theto construct bibliometric data analysisthe co-occurrence data based analysis on analys the basedis clustering map and indicate method the research topics. have not had significant influences on the main themes of PSEP. Therefore, in the present included in the widely used VOSviewerThus, 407 keywords software, were as extracted introduced based in on Section the threshold 2.2. Noteof the keyword’s that frequencies. on the clustering method included in the widelyThe used keyword VOSviewer co-occurrencestudy, tosoftware, focus network on theas main introducedfor thethemes, clusters only (groups) the keywords of PSEP occurring is shown at least in five times were in Section 2.2. Notethe investigated that the investigated references references can onlyFigure be 8.can Note included only thatselected bethe in includedlarger oneto construct the cluster, nodes in onethe and co-occurrence cluster, character their position fonts, analys the inismore map the often and the indicate keywords the research topics. and their positionoverall in the network overall and network the connections and theare used. connections to the referencesThus, to 407 the keywords in references other were clusters inextracted other show based how on the closely threshold of the keyword’s frequencies. related it is, both within its own cluster and withThe otherkeyword clusters. co-occurrence network for the clusters (groups) of PSEP is shown in clusters show how closely related it is, both within its own clusterFigure and8. Note with that other the larger clusters. the nodes and character fonts, the more often the keywords are used.

Figure 8. Keyword co-occurrence cluster of PSEP papers.

Obviously, the keyword “adsorption” is the most used author’s keyword with 122 occurrences, followedFigure by8. Keyword “kinetics” co-occurrence (80), “response cluster surface of PSEP methodology” papers. (74), “risk as- FigureFigure 7. Co-citation 7. Co-citation network network of highly of highly cited cited refere referencencesessment” groups groups (73), based based“optimization” on co-citation on co-citation (67), strength. “heavy strength. metals” (56), “safety” (56), etc. There were six clusters of keywords, Obviously,separated by the different keyword colors “adsorption” and representing is the most the following used author’s themes: keyword with 122 Furthermore, TableFurthermore, 6 lists the Table highly6 lists cited the re highlyferencesThe blue cited of group occurrences,PSEP references ( )publications was followedmainly of PSEP concentrated by ranked publications“kinetics” by on (80), waste ranked“response and pollutants by surface remediation.methodology” (74), “risk as- This cluster includedsessment” keywords (73), “optimization” such as “adsorption” (67), “heavy (122), metals” “kinetics” (56), (80), “safety” “heavy (56), met- etc. There were six the number of citations.the number Most of citations.of the influent Mostial of works the influential cited by worksPSEP were cited journal by PSEP articles, were journal articles, als” (56), “wastewater”clusters (43),of keywords, “activated separated carbon” by(40), different “isotherm” colors (34), and “biosorption” representing the (23), following themes: accounting for accounting81.40% (35/43). for 81.40% Additionally, (35/43). the Additionally,“composting” blue group (22), the( “thermodynamic”The ) bluewas blue groupthe group biggest ( (22),) was was “volatilecluster mainly the biggestorganic concentrated compound” cluster on waste (22), and etc. pollutants remediation. with the most citationswith the (277), most citationsand the red (277), group and ( the )The was red red groupthe group Thisbiggest ( cluster ) mainly was cluster included the focused biggestwith keywords on the environmental cluster most such withas “adsorption” protection the most methodologies (122), “kinetics” and (80), “heavy met- publications (12).publications As shown (12). in Figure As shown 7, ther ine technologies.Figurewere six7, thereclusters Thisals” werecluster (56), (groups) “wastewater”sixcontained clusters for keywords the (43), (groups) highly “activated such foras “responsecarbon” the highly (40), surface “isotherm” methodology” (34), “biosorption” (23), “composting” (22), “thermodynamic” (22), “volatile organic compound” (22), etc. cited references:cited references: (74), “optimization” (67), “wastewater treatment” (44), “photocatalysis” (43), “biodiesel” (34), “advanced oxidationThe red process” group (32), ( ) mainly“electrocoagulation” focused on environmental (31), “biodegradation” protection (30), methodologies and The blue groupThe ( ) bluewas primarily group ( ) concentrated was primarily“artificial on concentrated neuralenvironmentaltechnologies. network” on (24), environmentalprotection This “water cluster treatment” theoriescontained protection (24), keywords etc. theories such as “response surface methodology” and techniquesand (especially techniques adsorption (especially theory adsorption and application).The theory purple and(74),group The application).“optimization” ( most ) was influential mainly (67), The about “wastewater most works waste influential management treatment” works and(44), sustainable “photocatalysis” devel- (43), “biodiesel” in this group werein this the group theory were for the adsorption theory for in adsorptionopment. solution This [46–48] incluster(34), solution “advanced wasand represented [46adsorption– 48oxidation] and by adsorption ofprocess”keyw gasesords (32), such of “electrocoagulation” gasesas “anaerobic [49], digestion” (31), “biodegradation” (31), (30), “artificial neural network” (24), “water treatment” (24), etc. [49], modeling modelingfor the sorption for the processes sorption processes [50], and“pyrolysis” [isotherms50], and (28), isotherms “recycling”systems systems[51]. (27), “lifecycleMoreover, [51]. assessment” Moreover, the (24), the review“biomass” (21), “environ- ment” (20), “biogas” (19),The purple“mathematical group ( modeling” ) was mainly (18), about “combustion” waste management (17), “mass and trans- sustainable devel- on methodologies and techniques for removing heavy metal ions from wastewaters by Fu review on methodologies and techniques fer”for (15),removing “energy”opment. (14),heavy “sustainable This metalcluster development” wasions represented from (12), by “emissions” keywords (12),such etc.as “anaerobic digestion” (31), wastewaters byand Fu Wangand Wang [52] and[52] theand fundamental the fundamental theory theory for“pyrolysis” the for constitution the (28), constitution “recycling” and (27), properties and “lifecycle of assessment” solids (24), “biomass” (21), “environ- properties of solidsand liquids and liquids by Langmuir by Langmuir [53], etc., [53], are etc., also are impactful ment”also impactful(20), works “biogas” inworks (19), this “mathematical group. in this modeling” (18), “combustion” (17), “mass trans- fer” (15), “energy” (14), “sustainable development” (12), “emissions” (12), etc. group. The red group ( ) mainly focused on the methodologies and models for process safety The red groupand risk ( management) mainly focused in chemical on the andmethodologies process industries. and models Dynamic for safetyprocess analysis and risk assessment theory and models, e.g., Bayesian theory [54,55], bow-tie approach [56], etc., safety and risk management in chemical and process industries. Dynamic safety analysis and risk assessmentare developed theory and and models, widely e.g., used, Bayesian and the aforementionedtheory [54,55], bow-tie research approach was recognized as the [56], etc., are developedinfluential and works. widely Additionally, used, and the the other aforementioned impactful original research research was wasrecog- the reviews of the nized as the influentialavailable works. techniques Additionally, and methodologies the other impactful for risk analysis original in research chemical was process the industries by

Int. J. Environ. Res. Public Health 2021, 18, x 19 of 31

3.4. Research Fields Identification and Research Trends Evolution Keywords are one of the essential elements supplied by the authors of the paper to show the paper’s core content. Author keywords are imperative, since they are used as the topics/concepts/methods that are presented to deliver and communicate to the scien- tific community by the authors. The author keyword co-occurrences network demon- strates another perspective of themes in PSEP, and it can be observed that it illustrates the Int. J. Environ. Res. Public Health 2021, 18, 5985main author keywords that frequently occur together in PSEP. 14 of 29 Considering the fact that many keywords only appeared a few times, they obviously

Int. J. Environ. Res. Public Health 2021, 18have, x not had significant influences on the main themes of PSEP. Therefore, in the present20 of 31 study, to focus on the main themes, only the keywords occurring at least five times were selected to construct the co-occurrence analysis map and indicate the research topics. Khan and Abbasi [57] and the methods and models in process safety and risk management Thus, 407 keywords were extracted based on the threshold of the keyword’s frequencies. by KhanTheThe etkeyword al.green [58 group],co-occurrence the ( research ) mainly network concentrated for fuzzy for the sets on clusters accident by Zadeh (groups) prediction [59 ],of the andPSEP predictivehazard is shown assess- accidentin model for systemmentFigure methods 8. hazard Note andthat identification, modelsthe larger (esp theecially nodes prediction, fire and and character explosion and preventionfonts, mitigation). the more by often This Rathnayaka the cluster keywords was et al. [60], and characterized by keywords such as “computational fluid dynamics” (49), “modeling” (46), the utilizationare used. of Bayesian network and fault tree approaches for the safety analysis in “explosion” (43), “numerical simulation” (37), “dust explosion” (34), “consequence anal- processysis” facilities(23), “gas explosion” [61] and dependable(19), “hydrogen” systems (19), etc. [62], etc. TheThe yellow yellow group group ( ) mainly focused focused on the on process the inherent safety and safety risk andassessment hazard in identification andchemical assessment and process in chemical industries. and This process cluster was industries. represented The by keywords group contained such as “risk the early influ- entialassessment” works by (73), Edwards “process andsafety” Lawrence (43), “Bayesian [63] network” on the exploration (34), “inherent for safety” the relation(34), between “risk analysis” (23), “human factors” (22), “risk management” (18), “hazard identifica- planttion” costs (17), and “process the inherent design” (17), safety etc. of chemical process routes, and the multivariate system hazard identificationThe azure group and( ) mainly ranking focused methods on safety for and fire risk and management explosion strategy and toxic and chemical re- leasecost–benefit hazards byanalysis. Khan This and cluster Abbasi was composed [64]. In addition,of keywords Gupta such as and“safety” Edwards (56), “risk” [65 ] proposed a graphical(40), “J-value” methodology (19), “health” for inherent (14), “reliability” safety measurement,(13), “flash point” Khan (11), “radiation” and Amyotte (11), [66] detailed “nuclear” (10), etc. the cost and system design model for integrated inherent safety index, Koller et al. [67] Additionally, to further understand and analyze the research topics, evolutionary presentedprocess, a and safety, research health, frontiers and for environmental PSEP, the chronological impact evolution assessment of research methodology keywords for selecting the mostbased on reliable the average data publication from a variety date for of the substance publications databases in which the or keywords estimation ap- method, and peared in PSEP is demonstrated in Figure 9. Note that the VOSviewer software automat- Int. J. Environ. Res. Public HealthKhan 2021, et18, x al. [68] developed a safety-weighted hazard index for chemical20 process of 31 industry hazardically identification settled the most and suitable risk time assessment. interval and The span research for 407 keywords mentioned based aboveon the pub- was widely cited lication time (i.e., average publication year) of each keyword. The main research topics in by thevarious publications periods could in be PSEP recognized and identified and summarized as influential based on the works occurrence as well. frequency ofThe the keywordsThe green green group ingroup each ( period.) mainly concentrated Table concentrated 7 summarizes on on loss accident the prevention top prediction20 keywords inand that process hazard appeared assess- industries. The influentialmostFigurement frequently 8.methods works Keyword in wereand co-occurrenceeach models primarilysub-period. (esp cluseciallyter focused of PSEP fire papers.and on majorexplosion accident mitigation). hazards, This cluster accident was causes, and consequencescharacterized analysis, by keywords and such some as “computational specific original fluid contributionsdynamics” (49), “modeling” on managing (46), the risk of “explosion”Obviously, (43), the “numerical keyword “adsorption”simulation” (37), is th “duste most explosion” used author’s (34), “consequencekeyword with anal- 122 the dominooccurrences,ysis” (23), effect “gas followed ofexplosion” chemical by “kinetics” (19), accidents. “hydrogen” (80), “response The (19), most etc. surface cited methodology” works in this (74), group “risk as- were the book on losssessment” preventionThe yellow (73), “optimization” ingroup the process( ) mainly (67), industry “heavyfocused metals” on by the Lees process(56), [69 “safety”], safety the (56), book and etc. risk on There assessment chemical were six in process safety by Crowlclusterschemical and of andkeywords, Louvar process [ separated70 industries.], the book by This different on cluster the colors guidelineswas andrepresented representing for by chemical keywords the following process such themes: as quantitative“risk risk analysisassessment” byThe CCPSblue (73),group [71 “process], ( and ) was thesafety” mainly book (43), concentrated on “Bayesian the identification, on network” waste and (34), pollutants assessment,“inherent remediation. safety” and (34), prevention of This“risk cluster analysis” included (23), “humankeywords factors” such as (22), “adsorption” “risk management” (122), “kinetics” (18), “hazard (80), “heavy identifica- met- hazards for dust explosion accidents, which presented the evaluation of prevalent activities, als”tion” (56), (17), “wastewater” “process design” (43), “activated(17), etc. carbon” (40), “isotherm” (34), “biosorption” (23), Int. J. Environ. Res. Public Healthtesting 2021, 18“composting”, x methods,The azure (22), and group “thermodynamic” design ( ) mainly measures focused (22), for “volatileon safesafety operationorganic and risk compound” management techniques (22), strategy etc. by 20 Eckhoffof 31and [72]. The

significantcost–benefitThe and red influentialanalysis.group ( This ) mainly articles cluster focused was included composed on environmental the of researchkeywords protection such for theas methodologies “safety” domino (56), effect “risk” and for chemical accidenttechnologies.(40), features, “J-value” This sequences(19), cluster “health” contained analysis, (14), “reliability” keywords and accidental such (13), as “flash “response event point”escalation surface (11), “radiation” methodology” threshold (11), assessment, (74), “optimization” (67), “wastewater treatment” (44), “photocatalysis” (43), “biodiesel” as well“nuclear”The as thegreen (10), research group etc. ( ) bymainly Khan concentrated and Abbasi on accident [73] onprediction the common and hazard causes assess- or errors and (34), “advancedAdditionally, oxidation to further process” understand (32), “electrocoagulation” and analyze the research (31), “biodegradation” topics, evolutionary (30), consequencesment methods of and major models accidents (especially in chemicalfire and explosion process mitigation). industries, This etc. cluster was characterized“artificialprocess, and neural by research keywords network” frontiers such (24), asfor “water “computational PSEP, treatment” the chronological fluid (24), dynamics” etc. evolution (49), of research“modeling” keywords (46), “explosion”ThebasedThe purple on purple the(43), groupaverage “numericalgroup (publication ) was wassimulation” mainly primarily date about (37),for the “dustwaste about publications explosion” management waste in treatment(34), which and “consequence sustainable the keywords (especially anal-devel- ap- wastewater treatment).ysis”opment.peared (23), The in“gasThis PSEP most explosion”cluster is demonstrated significant was (19), represented “hydrogen” originalin Figure by keyw(19),9. research Note etc.ords that such contributions the asVOSviewer “anaerobic insoftware digestion” this group automat- (31), concerned the work“pyrolysis”ically onThe the settled yellow examination (28), the group “recycling”most ( suitable ) ofmainly water(27), time focused“lifecycle interval and on wastewater andassessment” the span process for 407(24),safety standard keywords “biomass” and risk methods based assessment(21), on “environ- the by pub-in APHA [74–76], ment”lication (20), time “biogas” (i.e., average (19), “mathematical publication year) modeling” of each keyword.(18), “combustion” The main (17), research “mass topics trans- in andchemical the significant and process overview industries. or This review cluster articles was represented included by the keywords analyzing such andas “risk summarizing of assessment”fer”various (15), periods“energy” (73), “processcould (14), be “sustainable recognizedsafety” (43), development” and “Bayesian summarized network” (12), based “emissions” (34), on the“inherent occurrence (12), etc. safety” frequency (34), the recentFigure 9. developmentsThe evolution of PSEP for research the technologies keywords over time of based photocatalytic on the average publication water treatment year. [77] and “riskof the analysis” keywords (23), in “human each period. factors” Table (22), 7 su “riskmmarizes management” the top 20 (18), keywords “hazard that identifica- appeared landfilltion”most leachate (17), frequently “process treatment in design” each sub-period. (17), [78], etc. etc.

TheThe azure azure group group ( ) mainly focused focused on safety on coal and mine risk management safety; it primarily strategy and contained com- pendiacost–benefit works, analysis. for instance, This cluster Cheng was composed et al. [79 ]of designed keywords such an intelligent as “safety” (56), gel “risk” for fire prevention and(40), extinguishing “J-value” (19), to “health” control (14), coal “reliability” spontaneous (13), “flash combustion point” (11), (CSC), “radiation” Wang (11), et al. [80] estab- “nuclear” (10), etc. lished aAdditionally, model of airflow to further dust understand migration and an foralyze underground the research topics, mine evolutionary tunnels and achieved a betterprocess, air curtain and research dust frontiers suppression for PSEP, effect,the chronological and Karacan evolution et of al. research [81] delivered keywords an overview for thebased capture on the average and utilization publication ofdate coal for minethe publications methane in in which the perspectivethe keywords ofap- mining safety andpeared greenhouse in PSEP gasis demonstrated reduction, in etc. Figure The 9. Note aforementioned that the VOSviewer works software were automat- highly influential in ically settled the most suitable time interval and span for 407 keywords based on the pub- this group. lication time (i.e., average publication year) of each keyword. The main research topics in various periods could be recognized and summarized based on the occurrence frequency of the keywords in each period. Table 7 summarizes the top 20 keywords that appeared most frequently in each sub-period.

Figure 9. The evolution of PSEP research keywords over time based on the average publication year.

Figure 9. The evolution of PSEP research keywords over time based on the average publication year.

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Table 6. Highly cited references of PSEP publications ranked by the number of citations.

Rank References Source Title DT Cluster Citations 1 [46] The Journal of Physical Chemistry Over the adsorption in solution JA 3 52 2 [74] —— Standard methods for the examination of water and wastewater Book 5 48 3 [47] Royal Swedish Academy of Sciences About the theory of so-called adsorption of soluble substances JA 3 48 4 [49] Journal of the American Chemical society The adsorption of gases on plane surfaces of glass, mica, and platinum JA 3 45 5 [69] —— Loss prevention in the process industry Book 2 45 6 [50] Process biochemistry Pseudo-second order model for sorption processes JA 3 41 7 [48] Journal of the sanitary engineering division Kinetics of adsorption on carbon from solution JA 3 32 8 [55] Process Safety and Environmental Protection Dynamic safety analysis of process systems by mapping bowtie into Bayesian network JA 1 27 9 [53] Journal of the American chemical society The constitution and fundamental properties of solids and liquids. Part I. Solids JA 3 26 10 [71] —— Guidelines for chemical process quantitative risk analysis Book 2 25 11 [59] Information and Control Fuzzy sets JA 1 25 An intelligent gel designed to control the spontaneous combustion of coal: fire prevention and 12 [79] Fuel JA 6 24 extinguishing properties 13 [58] Process safety and environmental protection Methods and models in process safety and risk management: past, present, and future JA 1 24 14 [75] —— Standard methods for the examination of water and wastewater Book 5 23 15 [72] —— Dust explosions in the process industries Book 2 23 Assessing the inherent safety of chemical process routes: is there a relation between plant costs and 16 [63] Process Safety and Environmental Protection JA 4 22 inherent safety? 17 [82] —— Human error Book 1 21 18 [76] —— Standard methods for the examination of water and wastewater Book 5 20 19 [61] Reliability Engineering & System Safety Safety analysis in process facilities: comparison of fault tree and Bayesian network approaches JA 1 20 20 [67] Industrial & Engineering Chemistry Research Assessing safety, health, and environmental impact early during process development JA 4 18 21 [52] Journal of environmental management Removal of heavy metal ions from wastewaters: a review JA 3 18 22 [70] —— Chemical process safety: fundamentals with applications Book 2 17 23 [64] Process Safety Progress Multivariate hazard identification and ranking system JA 4 17 Safety weighted hazard index (SWeHI): a new, user-friendly tool for swift yet comprehensive hazard 24 [68] Process Safety and Environmental Protection JA 4 17 identification and safety evaluation in chemical process industries 25 [83] Safety science Risk management in a dynamic society: a modelling problem JA 1 17 26 [60] Process safety and environmental protection SHIPP methodology: Predictive accident modeling approach. Part I: Methodology and model description JA 1 17 27 [78] Journal of hazardous materials Landfill leachate treatment: review and opportunity JA 5 17 28 [84] Chemical Engineering Science Wastewater minimization JA 1 17 29 [62] Reliability Engineering & System Safety Improving the analysis of dependable systems by mapping fault trees into Bayesian networks JA 1 16 30 [77] Water research Recent developments in photocatalytic water treatment technology: a review JA 5 16 31 [85] Analytical chemistry Colorimetric method for determination of sugars and related substances JA 5 16 Effects of air volume ratio parameters on air curtain dust suppression in a rock tunnel’s fully mechanized 32 [80] Advanced Powder Technology JA 6 16 working face 33 [86] Journal of hazardous materials Escalation thresholds in the assessment of domino accidental events JA 2 15 34 [87] Journal of hazardous materials Domino effect in chemical accidents: main features and accident sequences JA 2 15 35 [51] Chemical engineering journal Insights into the modeling of adsorption isotherm systems JA 3 15 36 [65] Journal of Hazardous Materials A simple graphical method for measuring inherent safety JA 4 15 Int. J. Environ. Res. Public Health 2021, 18, 5985 16 of 29

Table 6. Cont.

Rank References Source Title DT Cluster Citations Coal mine methane: a review of capture and utilization practices with benefits to mining safety and to 37 [81] International journal of coal geology JA 6 15 greenhouse gas reduction 38 [56] Reliability Engineering & System Safety Dynamic risk analysis using bowtie approach JA 1 15 39 [57] Journal of loss Prevention in the Process Industries Techniques and methodologies for risk analysis in chemical process industries JA 1 15 40 [73] Journal of Loss Prevention in the process Industries Major accidents in process industries and an analysis of causes and consequences JA 2 15 41 [66] Journal of Loss Prevention in the Process Industries I2SI: a comprehensive quantitative tool for inherent safety and cost evaluation JA 4 15 42 [54] Chemical engineering science Plant-specific dynamic failure assessment using Bayesian theory JA 1 15 43 [88] Industrial & Engineering Chemistry Fundamentals A new two-constant equation of state JA 2 15 Note: Cluster matches the color for each cluster group in Figure7, DT = document type, JA = journal articles. Int. J. Environ. Res. Public Health 2021, 18, x 19 of 31

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3.4. Research Fields Identification and Research Trends Evolution Keywords3.4. are Researchone of the Fields essential Identification elements and supplied Research by Trends the Evolutionauthors of the paper to show the paper’s coreKeywords content. are Author one of keyw the essentialords are imperative, elements supplied since they by theare authorsused as of the paper to the topics/concepts/methodsshow the paper’s that core are content.presente Authord to deliver keywords and communicate are imperative, to sincethe scien- they are used as the tific communitytopics/concepts/methods by the authors. The author that arekeyword presented co-occurrences to deliver and network communicate demon- to the scientific Int. J. Environ. Res. Public Healthcommunity 2021, 18, x by the authors. The author keyword co-occurrences network19 of 31 demonstrates strates another perspective of themes in PSEP, and it can be observed that it illustrates the Int. J. Environ. Res. Public Health 2021, 18, x 19 of 31 main author keywordsanother perspectivethat frequently of themes occur together in PSEP, in and PSEP. it can be observed that it illustrates the main Int. J. Environ. Res. Public Health 2021, 18, x 19 of 31 Consideringauthor the fact keywords that many that keywords frequently only occur appeared together a infew PSEP. times, they obviously 3.4.Considering Research Fields the Identificatio fact thatn and many Research keywords Trends Evolution only appeared a few times, they obviously have not had significant3.4. Research influences Fields Identificatio on the mainn and Researchthemes Trends of PSEP. Evolution Therefore, in the present have notKeywords had significant are one of influences the essential on elements the main supplied themes by the of authors PSEP. of Therefore, the paper to in the present study, to focus on the3.4. main KeywordsResearch themes, Fields are oneIdentificatio only of the the essentialn andkeywords Research elements Trends occurring supplied Evolution atby leastthe authors five timesof the paper were to study,show to focusthe paper’s on thecore main content. themes, Author onlykeywords the are keywords imperative, occurring since they atare least used fiveas times were selected to constructshowthe thetopics/concepts/methods Keywordsthe co-occurrence paper’s are core one content. of analysthe that essentialAuthor areis presentemap keyw elements ordsandd to suppliedaredeliverindicate imperative, and by thethecommunicate sinceauthorsresearch they of toarethe topics. the usedpaper scien- as to Thus, 407 keywordsselectedthetificshow were topics/concepts/methods community to the constructextracted paper’s by core thethebased content. co-occurrenceauthors. thaton Author the areThe presentethreshold author keyw analysis dordskeyword to ofdeliver are mapthe imperative, co-occurrences andkeyword’s and communicate indicate since networkfrequencies. they the to are the research demon- used scien- as topics. Thus, The keyword 407co-occurrencetific keywordsstratesthe communitytopics/concepts/methods another werenetwork perspective by extractedthe authors.for of thatthemesthe basedThe are clusters inpresenteauthor PSEP, onthe keyword andd(groups) to threshold itdeliver can co-occurrences be and ofobserved of PSEPcommunicate the that keyword’s isnetwork itshown illustrates to thedemon- scien- frequencies.in the The strates another perspective of themes in PSEP, and it can be observed that it illustrates the Figure 8. Note thatkeyword themaintific larger communityauthor co-occurrence thekeywords nodesby the that networkauthors.and freq characteruently The for occurauthor the fonts, together clusterskeyword the in more PSEP. (groups)co-occurrences often of the PSEPnetwork keywords is demon- shown in Figure8. Notemainstrates that Consideringauthor theanother larger keywords perspective the the fact that nodes that freqof manythemesuently and keywords character inoccur PSEP, together onlyand fonts, itappeared canin PSEP. be the observed a more few times, oftenthat theyit illustrates the obviously keywords the are used. are used. havemainConsidering not author had keywordssignificant the fact that influencesthat freq manyuently onkeywords the occur main together only themes appeared in of PSEP. PSEP. a few Therefore, times, they in the obviously present havestudy, notConsidering to had focus significant on the factmain influences that themes, many on onlykeywords the themain keywords themesonly appeared of occurring PSEP. a fewTherefore, at times,least five theyin the times obviously present were study,selectedhave notto tofocus had construct significant on the mainthe influences co-occurrence themes, onlyon the theanalys main keywordsis themes map occurringand of PSEP. indicate Therefore,at least the fiveresearch in times the presenttopics. were selectedThus,study, 407 to to focuskeywords construct on the werethe main co-occurrence extracted themes, based only analys theon thekeywordsis thresholdmap and occurring ofindicate the keyword’s at theleast research five frequencies. times topics. were Thus,Theselected keyword 407 tokeywords construct co-occurrence were the extracted co-occurrence network based for analyson the the isclusters threshold map and(groups) of indicate the keyword’s of thePSEP research isfrequencies. shown topics. in TheFigureThus, keyword 4078. Note keywords co-occurrencethat the were larger extracted thenetwork nodes based forand onthe character the clusters threshold fonts, (groups) ofthe the more ofkeyword’s PSEPoften theis frequencies. shownkeywords in FigureareThe used. keyword 8. Note that co-occurrence the larger the network nodes andfor characterthe clusters fonts, (groups) the more of often PSEP the is keywords shown in areFigure used. 8. Note that the larger the nodes and character fonts, the more often the keywords are used.

Figure 8. Keyword co-occurrenceFigure 8. Keyword cluster co-occurrenceof PSEP papers. cluster of PSEP papers. Figure 8. Keyword co-occurrence cluster of PSEP papers. Obviously, theFigure Obviously,keyword 8. Keyword “adsorption” the co-occurrence keyword clus “adsorption”is terth eof mostPSEP papers. used is the author’s most used keyword author’s with keyword 122 with 122 oc- occurrences, followedcurrences,Figure byObviously, 8. followed“kinetics” Keyword the co-occurrence bykeyword (80), “kinetics” “response “adsorption” cluster (80), of PSEP surface “response is papers. the mostmethodology” surfaceused author’s methodology” (74),keyword “risk with as- (74), 122 “risk assess- Obviously, the keyword “adsorption” is the most used author’s keyword with 122 ment”occurrences, (73), “optimization” followed by “kinetics” (67), “heavy(80), “response metals” surface (56), methodology” “safety” (56),(74), “risk etc. as- There were six sessment” (73), “optimization”occurrences,sessment”Obviously, (73), followed (67), “optimization” the “heavykeyword by “kinetics” metals”“adsorption” (67), (80),“heavy (56),“response metals” is “safety”the most surface(56), used“safety” (56), methodology” author’s etc. (56), There etc.keyword There(74), were “risk werewith six as- 122six clusters of keywords,clusterssessment”clustersoccurrences, separated of keywords,of (73),keywords, followed “optimization”by different separated by “kinetics” colors(67), by bydifferent “heavy (80), differentand “response metals”colorsrepresenting colors and (56), surface representing “safety” and themethodology” representing following (56), the etc. following There (74), themes: the were “riskthemes: following six as- themes: The blue groupclustersThesessment” (The ) bluewas of blue keywords, (73), groupmainly group “optimization” (separated concentrated) was was mainly by mainly(67), different “heavy concentrated on concentrated colorswaste metals” and onand (56), representingwaste pollutants“safety” on and waste pollutants (56), the andfollowingremediation.etc. There pollutantsremediation. themes: were six remediation. This cluster includedThisThisclusters cluster keywordsThe cluster ofblue included keywords, included group such ( keywordsseparated )as was “adsorption” mainly bysuch different such concentrated as “adsorption” as (122),colors “adsorption” onand “kinetics” waste (122),representing and“kinetics” (122), pollutants(80), the “kinetics” “heavy(80),following remediation. “heavy met- themes: (80),met- “heavy met- This cluster included keywords such as “adsorption” (122), “kinetics” (80), “heavy met- als”als” (56), (56),The “wastewater” “wastewater”blue group ( (43), )(43), was “activated mainly “activated concentrated carbon” carbon” (40), on “isotherm” waste (40), “isotherm”and (34), pollutants “biosorption” (34),remediation. “biosorption” (23), (23), als” (56), “wastewater”als”“composting”This (56), cluster(43), “wastewater” “activated included (22), “thermodynamic” keywords (43), carbon” “activated such (40), (22),as carbon” “adsorption” “isotherm” “volatile (40), organic“isotherm” (122), (34), compound” “kinetics” “biosorption” (34), “biosorption” (80), (22), “heavy etc. (23), (23), met- “composting” (22),“composting” “composting”“thermodynamic”als” The(56), red “wastewater” (22), group (22), “thermodynamic”“thermodynamic” ( ) (22), mainly(43), “activated“volatile focused (22), oncarbon” organic (22), “volatileenvironmental “volatile (40), compound” organic “isotherm” protection organiccompound” (34), (22), compound”methodologies “biosorption” (22),etc. etc. (22),and(23), etc. The red group technologies.The“composting”( )The mainly red red group group This (22),focused cluster (“thermodynamic” ) mainly oncontained environmental focused focused keywords (22), on environmental “volatile on such environmental protection asorganic “response protection compound” methodologies surface protection methodologies (22), methodology” etc. methodologies and and and technologies. Thistechnologies. clustertechnologies.(74), “optimization”The contained red This Thisgroup cluster ((67), keywords ) mainly “wastewatercontained contained focused such keywords treatment” on keywords as environmental “response such (44), as such “response“photocatalysis” surfaceprotection as “response surface methodology” methodologies (43), methodology” surface“biodiesel” and methodology” (74),(74),(34), “optimization”technologies. “optimization”“advanced This oxidation cluster (67), “wastewater process” “wastewatercontained (32), keywords treatment” “electrocoagulation” treatment” such (44), as “photocatalysis” “response (44), (31), “photocatalysis” “biodegradation”surface (43), methodology” “biodiesel” (30), (43), “biodiesel” (74), “optimization”(34),“artificial(74), (67), “advanced “optimization” “wastewater neural oxidation network” (67), treatment” process”“wastewater (24), “water (32), (44), treatment”“electrocoagulation” “photocatalysis” (24),(44), etc.“photocatalysis” (31), “biodegradation”(43), “biodiesel”(43), “biodiesel” (30), (34), “advanced oxidation process” (32), “electrocoagulation” (31), “biodegradation” (30), (34), “advanced oxidation“artificial(34),The “advanced process” purpleneural network”groupoxidation (32), ( )“electrocoagulation” (24), process”was “watermainly (32), treatment” about “electrocoagulation” waste (24), management(31), etc. “biodegradation” (31), and “biodegradation” sustainable (30), devel- (30), “artificial neural“artificial network”opment.“artificialThe neural purple This(24), neural cluster network” “watergroup network” was ( treatment” ) representedwas (24), mainly “water “water aboutby(24), treatment” keyw treatment” etc.wasteords (24),management such etc. (24), as “anaerobic etc. and sustainable digestion” devel- (31), The purple groupopment.“pyrolysis”The (The purple )This purplewas (28), cluster groupmainly group“recycling” was ( aboutrepresented ) was was (27), mainlywaste mainly“lifecycle by about managementkeyw aboutassessment” wasteords waste suchmanagement (24),asand management “anaerobic “biomass” sustainable and sustainable digestion” (21), and devel-“environ- sustainabledevel- (31), devel- opment.“pyrolysis”ment”opment. This(20), This “biogas”(28), cluster cluster “recycling” (19), waswas “mathematical represented represented (27), “lifecycle by modeling” keyw byassessment” keywordsords (18), such “combustion”(24), as such “anaerobic“biomass” as “anaerobic(17), (21),digestion” “mass “environ- trans- (31), digestion” (31), opment. This clusterment” was (20), represented “biogas” (19), by“mathematical keywords modeling” such as (18), “anaerobic “combustion” digestion” (17), “mass (31), trans- “pyrolysis”fer”“pyrolysis” (15),(28), “energy” (28), “recycling” “recycling” (14), “sustainable (27), (27), “lifecycle“lifecycle development” assessment” assessment” (12), “emissions” (24), (24), “biomass” “biomass” (12), etc.(21), “environ- (21), “environment” “pyrolysis” (28), “recycling”fer”ment” (15), (20), “energy” “biogas”(27), (14),“lifecycle (19), “sustainable “mathematical assessment” development” modeling” (24), (12), (18), “biomass” “emissions” “combustion” (21),(12), (17), etc. “environ- “mass trans- ment” (20), “biogas”(20), “biogas”fer” (19), (15), “mathematical “energy” (19), “mathematical (14), “sustainable modeling” modeling” development” (18), “combustion” (18), (12), “combustion” “emissions” (17), (12), “mass (17),etc. trans- “mass transfer” (15), “energy” (14), “sustainable development” (12), “emissions” (12), etc. fer” (15), “energy” (14), “sustainable development” (12), “emissions” (12), etc.

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( )(19), mainly mainly on “hydrogen” Thisthe focused cluster focusedprocess (19),on was the onsafetyetc. represented process the and process safety byrisk keywords and safetyassessment risk assessment such and as risk in“risk in assessment in chemical and processchemicalassessment”chemical industries.The and yellowand process (73), process Thisgroup “process industries.industries.cluster ( ) safety”mainly was This (43),focused This represented cluster “Bayesian cluster on was the represented wasprocessnetwork” by representedkeywords safety (34), by keywordsand“inherent suchrisk by assessment keywords suchassafety” “risk as “risk(34), in such as “risk “risk analysis” (23), “human factors” (22), “risk management” (18), “hazard identifica- assessment” (73),assessment” “processchemicalassessment” safety”and (73), (73),process “process “process(43), industries. “Bayesian safety” safety” This (43), cluster (43),network” “Bayesian “Bayesianwas represented network”(34), “inherent network” (34), by keywords “inherent safety” (34), such safety” “inherent (34), as “risk (34), safety” (34), assessment”tion”“risk (17),analysis” “process (73), (23), “process design” “human safety” (17), factors” etc. (43), (22), “Bayesian “risk management” network” (34), (18), “inherent “hazard safety” identifica- (34), “risk analysis” “risk(23), analysis”“human factors” (23), “human (22), factors”“risk management” (22), “risk management” (18), “hazard (18), identifica- “hazard identification” “risktion”The analysis”(17), azure “process (23),group design” “human ( ) mainly (17), factors” etc. focused (22), on“risk safety management” and risk management (18), “hazard strategy identifica- and tion” (17), “process(17), design”tion”cost–benefit “process The(17), azure(17), “process design” analysis. etc.group design” This (17),( ) clustermainly (17), etc. etc. was focused composed on safety of keywords and risk such management as “safety” strategy (56), “risk” and The azure group(40),Thecost–benefit ( The“J-value” azure ) mainly azure analysis. group (19),group focused “health” This ( ) clustermainly mainly on (14), safety was focused“reliability” focused composed and on safety risk on(13), of keywords safety management“flashand risk point” and suchmanagement risk (11),as “safety”strategy management“radiation” strategy (56), and “risk” (11),and strategy and cost–benefit analysis.cost–benefitcost–benefit“nuclear”(40), This “J-value” cluster analysis.(10), analysis. etc.(19), was “health” ThisThis composed cluster cluster (14), was “reliability”of was composed keywords composed (13), of keywords such “flash of as keywords point” “safety”such as(11), “safety” such (56),“radiation” as(56),“risk” “safety” “risk” (11), (56), “risk” “nuclear”Additionally, (10), etc. to further understand and analyze the research topics, evolutionary (40), “J-value” (19),(40), (40),“health” “J-value” “J-value” (14), (19), (19), “reliability” “health”“health” (14), (14), (13),“reliability” “reliability” “flash (13), point” “flash (13), (11), point” “flash “radiation” (11), point” “radiation” (11), (11), “radiation”(11), (11), “nuclear”process,Additionally, and (10), research etc. to frontiersfurther understandfor PSEP, the and chronological analyze the evolution research of topics, research evolutionary keywords “nuclear” (10), “nuclear”etc. basedprocess,Additionally, (10),on and the etc.research average to further frontierspublication understand for PSEP,date forthe and thechronological an publicationsalyze the evolution research in which oftopics, researchthe keywords evolutionary keywords ap- Additionally, toprocess,pearedAdditionally,based further onin and PSEPthe understand research average is todemonstrated furtherfrontiers publication and for understand in anPSEP, dateFigurealyze thefor 9. chronological theNote and publicationsresearch that analyze the evolution VOSviewer topics,in thewhich of research evolutionaryresearch softwarethe keywords keywords topics,automat- ap- evolutionary process, and researchprocess,basedicallypeared frontiers and settledon in the researchPSEP forthe average is mostPSEP, demonstrated frontiers suitablepublication the chronological time forin date intervalFigure PSEP, for 9. andthe Note evolution publicationsspan chronological that for the 407 VOSviewer of keywordsin research which evolution softwarethebased keywords keywords on of automat-the research pub- ap- keywords licationically settled time (i.e.,the most average suitable publication time interval year) ofand each span keyword. for 407 keywordsThe main basedresearch on topicsthe pub- in based on the averagebasedpeared on publication the in PSEP average is demonstrateddate publication for the in publications dateFigure for 9. 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Note Table and thatyear) 7 su su mmarizes theofmmarized each VOSviewer keyword. the based top on20The software thekeywords main occurrence research automat-that frequencyappeared topics in ically settled thesettled mostvariousmostof suitablethe frequently keywords mostperiods time suitable couldin in eachinterval each be sub-period. timerecognizedperiod. and interval Table span and 7 andsuformmarizesmmarized 407 span keywords for thebased 407top on 20 keywords thebased keywords occurrence on basedthatthe frequency appearedpub- on the publication lication time (i.e.,time averageofmost (i.e., the frequently averagekeywords publication in publication eacheach year) sub-period.period. of year) eachTable of7keyword. su eachmmarizes keyword. 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Figure 9. The evolution of PSEP research keywords over time based on the average publication year. Figure 9. The evolution of PSEP research keywords over time based on the average publication year. Figure 9. The evolution of PSEP research keywords over time based on the average publication year.

Figure 9. TheThe evolution evolution of of PSEP PSEP research research keywords keywords over over time time based based on on the the average average publication publication year. year.

Int. J. Environ. Res. Public Health 2021, 18, 5985 19 of 29

Table 7. Top 10 keywords for PSEP in terms of various periods.

Before 2008 2008–2012 2013–2017 2018–2020 R Keyword F Keyword F Keyword F Keyword F 1 Risk 40 Risk assessment 73 Adsorption 122 Microbial community 14 2 LCA 24 Safety 56 Kinetics 80 CCD 13 3 Combustion 17 Modeling 46 RSM 74 CSC 12 4 HAZOP 15 Explosion 43 Optimization 67 Ionic liquid 12 5 Runaway reaction 15 Inherent safety 34 Heavy metals 56 Toxicity 11 6 Health 14 Anaerobic digestion 31 CFD 49 Forward osmosis 11 Sustainable Wastewater 7 12 Recycling 27 44 Sensitivity analysis 9 development treatment 8 Radiation 11 Biosorption 23 Photocatalysis 43 Industry 4.0 8 Consequence 9 Incineration 11 23 Wastewater 43 Air leakage 7 analysis 10 Pollution 9 Human factors 22 Process safety 43 Microwave 7 Spontaneous coal 11 Environmental impact 9 Regeneration 21 Activated carbon 40 7 combustion Numerical 12 Offshore 8 Biomass 21 37 Process optimization 7 simulation 13 Effluent 7 Sustainability 21 Bayesian network 34 Coal mine 7 14 Transportation 7 Activated sludge 20 Biodiesel 34 Catalytic ozonation 7 15 Atrazine 7 Environment 20 Isotherm 34 Coal and gas outburst 6 16 LPG 7 Gas explosion 19 Dust explosion 34 Synergistic effect 6 17 Phosphorus removal 7 J-value 19 AOP 32 Drinking water 6 Mathematical 18 Major hazards 7 18 Electrocoagulation 31 Moisture content 6 modeling 19 Decision making 7 Process design 17 Biodegradation 30 Mineralization 6 20 Waste incineration 7 Accident 17 Pyrolysis 28 Electro-oxidation 5 Note: R = rank; F = frequency of each keyword; LCA = lifecycle assessment; HAZOP = hazard and operability studies; LPG = liquefied petroleum gas; RSM = response surface methodology; CFD = computational fluid dynamics; AOP = advanced oxidation process; CCD = central composite design; CSC = coal spontaneous combustion.

Overall, the PSEP was mainly focused on the topics related to the fields of safety of industrial processes and protection of the environment. In the present study, to explore and extract the evolutionary process and trends of the main research topics in PSEP, the special topics of publications in the separated four periods are summarized and analyzed. Earlier publications (before 2008) were focused mainly on the topics concerned with waste incinerator design and combustion efficiency analysis [89–92], treatment and uti- lization of (municipal) solid waste [93–95], incineration residues and emissions manage- ment [96–98], economic and environmental impact assessments and sustainable develop- ment [99–102], reduction of flue gas emissions from fuel combustion [103], risk analysis for offshore platform-related problems [104,105], boiling liquid expanding vapor explo- sion (BLEVE) (especially related to liquefied petroleum gas (LPG)) [106,107], risk-based decision-making [108,109], human health risk analysis [110], thermal radiation safety assessment [111], runaway reaction inhibition system design and evaluation [112], loss prevention analysis in process industry [113], etc. The main analysis/process methods include incineration [114], biological phosphorus removal [115], catalytic combustion [116], lifecycle assessment (LCA) [117,118], hazard and operability (HAZOP) analysis [119,120], mathematical modeling [89], fuzzy logic theory [121,122], computer-aided fault tree analy- sis (FTA) [109], etc. Between 2008 and 2012, publications were devoted to the research topics about the application and optimization of anaerobic digestion (especially the anaerobic digestion of organic solid wastes and wastewater sludges) [123,124], resource recycling and waste regeneration reuse [125,126], activated sludge utilization and treatment [127–129], biomass- derived liquid biofuels [130], optimal process design (especially based on inherent safety or under uncertainty) [131–133], explosion overpressures analysis and prediction (especially Int. J. Environ. Res. Public Health 2021, 18, 5985 20 of 29

caused by a gas explosion) [134], explosion accident hazard assessments and prevention (es- pecially coal combustion/gas explosion) [135], inherent safety and cost evaluation [136,137], human factors in safety management [138], J-value safety analysis [139,140], etc. Addition- ally, anaerobic digestion [124,141], biosorption [142], biomass gasification [143], vacuum thermal recycling [144], computational fluid dynamics (CFD) [145], principal component analysis (PCA) [132], analytic hierarchy process (AHP) [146], Monte Carlo simulation (MCS) [147], etc., became the widely used techniques/methods among scholars during this period. Subsequently, during the period between 2013 and 2017, the research emphasis turned to topics such as pollution management framework [148], analysis of isotherms and ki- netics of adsorption [149], heavy metals risk assessment and removal [150], wastewater treatment (especially based on the advanced oxidation process (AOP) and electrocoagula- tion (EC)) [151], biodiesel processing and production [152], process safety framework and model [153], risk-based design [154], hazardous materials transportation safety [155,156], investigation and risk analysis of fire and explosion accidents (especially dust explo- sion) [154,157], etc. In terms of analysis/process methods, AOP [158], EC [159], photocatal- ysis degradation [160], activated carbon adsorption [161], biodegradation [162], catalytic pyrolysis [163], response surface methodology (RSM) [164], quantitative risk assessment (QRA) [165,166], multi-objective optimization [167], fuzzy FTA [168], numerical simula- tion [169,170], and Bayesian network (BN) [154], etc., were widely applied by scholars. In recent years (2018 and beyond), some of the focused research topics/methods were the continuation of the previously initiated research areas, e.g., BLEVE, HAZOP, AOP, EC, CFD, RSM, MCS, QRA, BN, PCA, etc. In addition, a few new research topics emerge in this period, such as catalytic degradation of organics (especially utilizing a microbial commu- nity) [171,172], application of ionic liquids [173], degradation and toxicity analysis [174,175], the application of microwave for waste treatment [176,177], safety of drinking water and its treatment [178], mineralization technology for pollutant emission control [179], In- dustry 4.0 [180–182], mine fires and CSC prevention [183,184], air leakage measurement and sealing techniques [185,186], risk analysis and prevention considering synergistic effects and domino effects [187,188], etc. It is obvious that scholars pay more attention to advanced techniques, as well as traditional methods, to conduct real-world industrial prob- lems, for instance, catalytic ozonation [189], forward osmosis [190], photocatalytic [191], electro-oxidation [191], biochar adsorption [192], artificial neural networks [193], genetic algorithm [194], (global) sensitivity analyses [195,196], process optimization method (e.g., RSM, CCD) [197,198], bowtie analysis [199], fuzzy AHP [200,201], dynamic BN [187,202], etc., for environment protection and process safety and risk analysis.

4. Conclusions This study presents a bibliometric journal analysis perspective to explore the evolution in safety or environmental engineering design and practice, as well as experimental or theoretical innovative research. Various bibliometric analyses, scientometric mapping, and statistical techniques are utilized to identify and unearth the evolution trends and detailed characteristics of the publications as indexed by the Web of Science. To validate the application of our purpose, the principal and influential international journal PSEP is taken as the case study journal to explore the influencing factors behind the rapid development of journals and reveal the main research trends of the safety of industrial processes and the protection of the environment. The main findings for our case study journal could be summarized as follows: (a) until the statistical time of this paper, PSEP has published 3152 literature productions and drawn 44,879 citations, and the corresponding number keeps increasing over time. (b) Faisal Khan is the most productive author and the only author with more than 50 papers in PSEP, followed by Paul Amyotte and P. J. Thomas. Additionally, Gordon Mckay is the most influential author (with 2897 citations and the highest average number of citations of 193.13). Moreover, the editorial board members play a relatively important role among Int. J. Environ. Res. Public Health 2021, 18, 5985 21 of 29

the leading authors and within the process safety and environmental protection research domain. (c) China is the leading country with the highest number of publications and citations, followed by the United Kingdom and India. Additionally, China and the USA have the closest cooperation and research relationship in PSEP. It is expected that more international collaboration could be promoted and enhanced to share knowledge globally in the future. (d) The leading institutions are China University of Mining & Technology (with the highest number of publications of 73), Nanjing University of Technology (with the largest average publication year of 2018.87), Memorial University of Newfoundland (with the highest number of total citations of 1854), and Dalhousie University (with the highest average citations of 37.24). Furthermore, 29.63% of the leading institutions are from the United Kingdom, and the most productive countries and institutions both regard China. (e) The most influential work published in PSEP held 1530 citations and the biggest average citations per year of 66.52. In addition, there are seven literature productions with the minimum citations of 200, and the document type of review paper is more likely to get more citations. However, 61.04% publications in PSEP have no more than ten citations, and there are still a certain number of publications that are not cited. Furthermore, there are 43 highly cited references (most of them are journal articles) that can be regarded as the core intellectual bases of PSEP. These works concern adsorption theory, process safety and risk management methods and models, inherent safety, loss prevention, domino effect, waste treatment, and coal mine safety. The related reviews for the highly cited references could deliver further detailed insights in the explored domain for scholars. (f) Several keywords/topics, such as “adsorption”, “kinetics”, “response surface methodology”, “risk assessment”, “optimization”, “heavy metals”, and “safety”, are the most popular hotspots of PSEP. Additionally, the popular keywords in various periods reveal the chronological evolutionary process and trends of the emerging or long-lasting research hotspots of PSEP during the last 30 years. The topics of the selected publications from the case study journal mainly concentrate on the research fields of protection of the environment and safety of industrial processes. For specific research areas, the mainstream research areas of our case study journal, includ- ing the waste and pollutants remediation, environmental protection methodologies and technologies, waste management and sustainable development, accident prediction and hazard assessment methods and models, process safety and risk assessment, and safety and risk management strategy and cost–benefit analysis, etc., are recognized. In addition, some new emerging topics in the research community could be highlighted and recommended for scholars and stakeholders. In respect to environmental protection, some emerging topics are recognized, such as catalytic pyrolysis of waste, sustainability of the production of fuels, analysis of kinetics and adsorption mechanisms, activated carbon adsorption, supercritical water processes, climate change mitigation technology (especially catalytic conversions of greenhouse gas), catalytic degradation of organics (especially utilizing mi- crobial community), application of microwave for waste treatment, safety of drinking water and its treatment, mineralization technology for pollutant emission control, etc. In view of industrial process safety, the mainly focused topics are failure of complex systems, mine fires and coal spontaneous combustion prevention, inherent safety and cost evaluation, risk analysis and prevention considering synergistic effects and domino effects, optimization for hazardous materials transportation, J-value analysis and assessment of accidents, safety culture and process safety education, human and organizational factors of safety, etc. As for Industry 4.0 (especially smart manufacturing and production, big data, Internet of Things), accompanied with artificial intelligence (e.g., the application of artificial intelligence for wastewater treatment and deep learning-based forecast modeling for safety/risk-related topics), are widely used as the hotspots for the research fields of PSEP. In terms of tech- niques/methods, heterogeneous catalysis, photocatalysis degradation, advanced oxidation process, biochar for adsorption, machine learning (especially deep learning), response surface methodology, numerical simulation, HAZOP, bowtie, dynamic Bayesian network, dynamic and computer-aided fault tree analysis, hybrid artificial neural network, genetic Int. J. Environ. Res. Public Health 2021, 18, 5985 22 of 29

algorithm approach, etc., are widely used and applied advanced emerging techniques, as well as traditional methods, among global scholars for solving the environment protection, safety, and risk analysis problems. The aforementioned new future trends contribute to offering safer and cleaner living and production environments for human beings, which will further promote the harmonious coexistence of man and nature and achieve social and economic development sustainability. This paper provides a comprehensive and quantitative overview and significant pic- ture representation for the journal’s leading and evolutionary trends by employing specific bibliometric key impact factors, such as the document types, publication distribution and citation structure, most cited works, the trends of research topics, and prominent con- tributing authors, countries (regions), and institutions, etc. Additionally, by reviewing the evolution trends of the journal and the proposed investigated factors, such as the influential works, main research topics, and the research frontiers, this paper delivers various research objectives and directions that could be addressed and explored in future studies for related scholars worldwide, as well as for related journal editors, to position their journal to align with the focus topic of the safety of industrial processes and the protection of the environ- ment. However, note that the results obtained from the present paper are dynamic, and may change over time along with the emergence of new research hotspots or mainstream subjects and some specific variables increasing/decreasing in the study. In the follow-up research, some other data sources, e.g., Scopus, Google Scholar, and EconLit, etc., and some other document types, e.g., books, proceedings books, PhD theses, etc., could be contained as a supplement for scholars applying our proposed methodology for exploring the evolutionary trends for a particular knowledge domain. Additionally, some comparative analysis and inductive research for different journals in a specific research area could be conducted in further study. Nevertheless, some expert knowledge should be considered when selecting the most relevant journals and articles, especially for a very wide study field that may lead to a huge workload of a subsequent analysis and an overloading and time-consuming phenomena for the analysis tools.

Author Contributions: Conceptualization, J.X.; methodology, J.X. and J.L.; software, J.X. and J.L.; validation, J.X. and M.Y.; resources, C.W. and J.X.; data curation, J.X. and G.R.; writing—original draft preparation, J.X.; writing—review and editing, J.X., M.Y., G.R., and P.H.A.J.M.v.G.; visualization, J.X. and J.L.; supervision, C.W. and P.H.A.J.M.v.G.; funding acquisition, J.X. and J.L. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the National Natural Science Foundation of China, grant numbers 51874042 and 51904185, and the China Scholarship Council, grant number 201706950088. The APC was funded by Technische Universiteit Delft. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Conflicts of Interest: The authors declare no conflict of interest.

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