key: cord-0778342-nhb54chn
authors: Brown, Kayleigh Rayner; VanBerkel, Peter; Khan, Faisal I.; Amyotte, Paul R.
title: Application of Bow Tie Analysis and Inherently Safer Design to the Novel Coronavirus Hazard
date: 2021-07-01
journal: Process Saf Environ Prot
DOI: 10.1016/j.psep.2021.06.046
sha: 6aab0e75cabc647ee53e76599f13b892411881c9
doc_id: 778342
cord_uid: nhb54chn

This work involves the application of process safety concepts to other fields, specifically bow tie analysis and inherently safer design (ISD) to COVID-19. An analysis framework was designed for stakeholders to develop COVID-19 risk management plans for specific scenarios and receptor groups. This tool is based on the incorporation of the hierarchy of controls (HOC) within bow tie analysis to identify priority barriers. The analysis framework incorporates inherently safer design (ISD) principles allowing stakeholders to assess the adequacy of controls along with the consideration of degradation factors and controls. A checklist has also been developed to help stakeholders identify opportunities to apply the ISD principles of minimization, substitution, moderation, and simplification. This work also considers barrier effectiveness with respect to human and organization factors (HOF) in degradation factors and controls. This paper includes a collection of bow tie elements to develop bow tie diagrams for specific receptor groups and scenarios in Nova Scotia, Canada. The pandemic stage (At-Peak or Post-Peak) and its influence on different scenarios or settings is also considered in this work. Bow tie diagrams were developed for numerous receptor groups; bow tie diagrams modelling a generally healthy individual, a paramedic and a hair salon patron contracting COVID-19 are presented in this work.

SARS-CoV-2, the novel coronavirus discovered in 2019, is the hazard of global concern with respect to the current pandemic. The risk of acquiring COVID-19 caused by the virus is driving unprecedented measures worldwide to prevent contact with the virus and to protect against the potentially severe consequences of infection. The risk posed by this hazard must be thoroughly identified and analyzed in order to design an effective risk reduction approach. This approach includes both prevention measures to limit the likelihood of coming in contact with the hazard as well as mitigation measures to reduce the severity of the consequences. Measures, or barriers, that have been well-socialized throughout the course of the pandemic response, include social J o u r n a l P r e -p r o o f distancing, working remotely, wearing face coverings and performing good hand hygiene. They have been critical for curbing the spread of COVID-19. However, these barriers are not 100% effective; for example, the barrier of social distancing can be degraded if individuals inadvertently come within 6 feet (2 meters) of each other. Identifying how barriers may fail or be degraded is a critical component of an effective risk reduction approach. Additionally, because not all prevention and mitigation techniques are equally effective, the preferred order of implementation should be considered. Lastly, communication of public health measures is a critical component of the pandemic response. Decision-makers and public health experts must educate and inform the public so they can understand their role in risk reduction and the significance of barriers. This highlights the need for effective risk assessment and communication. The complex nature of communicating risk is highlighted by the recent publication by the World Health Organization (WHO), which highlights the need for effective risk communication and community engagement (RCCE) in order to improve the public's willingness to follow COVID-19 public health measures. Identified challenges with communicating with different groups include complacency, lowered risk perceptions and reduced trust in government responses caused by growing pandemic fatigue and socio-economic and psychological stress caused by uncertainty. the crisis and restrictions (WHO, 2021) . To address this, WHO recommends four pillars for an RCCE strategy: be community-led, be data-driven, reinforce capacity and local solutions and be collaborative.

These concepts of risk assessment and communication are not isolated to the COVID-19

pandemic, but rather are fundamentals of process safety. A foundational pillar of the CSA (2017) process safety management standard is Understanding hazards and risks, which includes the Process risk assessment and risk reduction element. "Stakeholder participation/risk J o u r n a l P r e -p r o o f As mentioned above, not all prevention and mitigation controls are of equal effectiveness for a given situation. Therefore, prioritization of interventions is advisable. The hierarchy of controls (HOC) is the order of preferred consideration of risk reduction measures (Kletz and Amyotte, 2010) . The HOCin order of increasing preference -is administrative, active engineered, passive engineered and inherently safer design (ISD). Each of these types of controls should be considered when designing a risk reduction approach.

The scope of this work includes modeling the risk of individuals acquiring COVID-19 and the associated consequences. This work is motivated by the need for a comprehensive hazard analysis of the novel coronavirus, and the need for an effective means of communicating hazard and risk reduction measures. The objective of this research is to use bow tie analysis and the HOC to assess which barriers are the most effective at preventing the spread of COVID-19 and how to effectively communicate prevention and mitigation measures. This also included the consideration of degradation factors and degradation controls, specific pandemic stages and different receptor groups. An outcome of this work is an analysis framework, suitable for broad audiences and stakeholders that can be used to create specific bow tie diagrams for COVID-19 risk for their applications. This work was completed in Nova Scotia and includes bow tie adaptation requirements for Nova Scotia-scenarios and stakeholders. The next section describes how this work expands on the bow tie analysis described in EI/CCPS (2020).

J o u r n a l P r e -p r o o f

A review of the EI/CCPS (2020) bow ties was completed, and the following sub section describes and delineates how this research expands on this seminal document. Specifically, this project expands on EI/CCPS (2020) with respect to the following components:

-bow tie elements extending to include other examples of top events, threats, consequences, barriers, degradation factors and degradation controls, -human and organizational factors (HOF), -pandemic stage, and -hierarchy of controls (HOC).

The hazard and the top event terminology used in this paper are aligned with the accepted distinction between coronavirus, COVID-19 and SARS-CoV-2 (as described in Time (2020) and

Health ). Specifically, COVID-19 is the disease caused by SARS-CoV-2, the virus also known has novel coronavirus discovered in 2019. The bow tie hazard is therefore "Novel coronavirus in human population" with the top event specific to each receptor group, i.e., "COVID-19 [within a receptor group]." Receptor groups modelled in this work are: -Immunocompromised individual -Long term care facility resident -Primary care giver -Nurse J o u r n a l P r e -p r o o f -Paramedic -Grocery store employee -Elementary school student -Fitness studio patron -Hair salon patron Table 1 outlines the additional analysis of the bow tie elements to expand on the EI/CCPS (2020) bow ties. 

Use convention of novel coronavirus in human population or SARS-CoV-2

The top event is expanded to include different receptor groups. The receptor groups of interest include generally healthy individuals and extends to high-risk individuals and front-line personnel (i.e. hospital personnel).

The threats and consequences are expanded to include more potential scenarios in which individuals can contract the virus. The increased detail and comprehensiveness is more representative of routine and regular activities in order to understand the risk and the barriers that are in place to prevent COVID-19.

The prevention and mitigation barriers are updated to include best-practices that have been implemented over the course of the pandemic. These are based on recommendations and measures described by public health authorities (Government of Canada, Province of Nova Scotia).

Degradation factors and controls are also expanded based on public health recommendations and learnings J o u r n a l P r e -p r o o f as the pandemic has evolved. Sources include public health authorities and grey literature.

Many barriers rely on human behaviour, and hence, this project identifies the importance of HOF when developing and implementing risk reduction plans. Gurses et al. (2020) and PS Net (2020) discuss the influence of HOF on managing COVID-19 (e.g. staff fatigue and burnout, workflow adaptation and redesign, training, team restructuring, etc.). CCPS/EI (2018) also discusses addressing HOF in bow ties. In this project, HOF is considered and incorporated by identifying common HOF degradation factors, categorizing these degradation factors with respect to HOF degradation type (according to CCPS/EI (2018)) and identifying common respective degradation controls.

The WHO developed pandemic phases to assist with planning and response. WHO (2010) describes the six pandemic stages, as well as post-peak and post-pandemic stages, based on influenza (it is assumed this framework is also applied to the current COVID-19 pandemic). Phases 1-3 consist of primarily animal infections and few human infections. Phase 4 is characterized by sustained human-to-human transmission. In Phases 5 and 6, a pandemic is underway. Phase 5

consists of widespread human infection in a few countries in one geographical region. In Phase 6, there is community-level spread in more than one geographical region. The post-peak phase is a J o u r n a l P r e -p r o o f decrease in disease activity below peak levels; however, the possibility of waves (increased cases) is still present. Lastly, the post-pandemic stage is a decrease in disease activity to normal levels.

The pandemic life cycle stage are considered because the protocols, practices, government regulations and directives vary with respect to the stage. Within this research, Phase 6 (At Peak)

and Post-Peak are the stages of interest and are considered within this project scope.

In the context of COVID-19, the HOC has been referred to in a number of resources (CBC, 2020a;

Dalhousie, 2020; Johns Hopkins University, 2020; WorkSafeBC, 2020). The HOC is incorporated within this research, including inherently safer design (ISD). This paper describes an analysis framework for incorporating the HOC in bow tie analysis for COVID-19 risk reduction. This analysis framework expands on the protocol presented by Rayner Brown et al. (2020) .

The literature review is organized into the following three areas:

-Bow tie analysis in healthcare applications, -Bow tie analysis in pandemic scenarios and, -Lessons learned from previous pandemic scenarios.

The purpose of this literature review was to understand how bow tie analysis has been used previously in healthcare applications, to understand if bow tie analysis has been used previously in pandemic scenarios, and to understand lessons learned from other pandemics. The scope of the literature review included general internet searches, as well as archival journal articles in Science Direct.

Literature discussing the application of bow ties in healthcare as a proactive risk management Units (ICU). The hazards of focus in the study were different factors that could negatively impact patient safety, including drug incidents, pneumonia, and infections. The bow ties were proactive tools for identifying deficiencies in barriers and developing controls to address them. The diagrams helped stakeholders understand and convey hazard prevention measures. Wierenga et al. (2009) also describes similar findings with respect to managing medication risk. The authors identified that when a large number of risks are identified, it is important to prioritize the risks and the drawing of bow tie diagrams. When the scope of the study is more clearly defined and realistic, the bow tie methodology was easier to understand and more beneficial to those involved in the analysis.

J o u r n a l P r e -p r o o f Kerckhoffs et al. (2013) describes the use of bow tie diagrams to manage the safety of patients in the ICU. This work focussed on the identification of missing barriers to manage risk associated with intra-hospital transportation, extubation, and communication. The practicality and feasibility of implementing new barriers was emphasized in this work. The authors also reported that bow tie analysis was fairly easy to complete, which helped to improve adoption by ICU staff. 

The use of bow ties for previous pandemics or seasonal influenza was not found in literature. With respect to COVID-19, Lindhout and Reniers (2020) describes the use of bow tie analysis to develop an integrated pandemics control model that emphasizes the prevention of pandemics altogether;

this is aligned with the concept of ISD.

Other efforts have been undertaken to apply bow tie analysis to help address the current COVID-19 pandemic. ASSP (2020) provides a tool with aspects of bow tie analysis and layers of protection analysis (LOPA) to help assess and manage COVID-19 risk. Various webinars and workshops have also been offered to help different stakeholders use bow tie analysis in their specific application or workplace to help reduce risk (CGE, 2020a; CGE, 2020b; Protecht, 2020).

There have been two other specific coronaviruses that have spread from animals to humans and (2020) and Nova Scotia College of Physiotherapists (2020). Checklists are also recommended as a tool with respect to HOF in PS Net (2020) to help ensure safety protocols and steps are followed.

This section describes how ISD principles can be used for COVID-19 risk reduction. The following sub section describes how the ISD principles are observed in other controls in the hierarchy.

Other types of controls in the hierarchy, like procedural safety measures, may be improved through incorporating ISD principles and concepts with an ISD mindset. For example, in the field of dust explosions, the ISD principle of minimization is applied in cleaning and good housekeeping to remove dust and minimize the inventory of dust that poses a hazard. This minimization is achieved through the procedural safeguard of housekeeping programs (Amyotte et al., 2018) . With respect to COVID-19 controls, social distancing in the form of stay at home orders contains elements of the ISD principle of minimization. Minimization is applied to eliminate contact at workplace or public spaceswhile it is achieved through procedural means, it has aspects of minimization.

Clearly, this barrier can be easily degraded or defeated by individuals leaving their homes, whether it is for necessity or recreation.

Social distancing in the form of maintaining a 6 foot/2 meter space when outside of the home has characteristics of the ISD principle of moderation in the form of limitation of effects. The hazard still exists since the individual is outside of the home, but the likelihood of transmitting the virus to someone else or coming into contact with the virus from an infected individual is reduced. This barrier is also implemented using administrative means and this safe distance can be easily defeated in public, shared spaces if individuals are not compliant.

The ISD principle of substitution is observed with respect to the use of recommended cleaning products and disinfectants. It is recommended to substitute "natural" or "green" cleaners with bleach or alcohol-based solutions that are known to be effective at destroying the virus. While this may also be thought of using the appropriate product for the application, considering the ISD principle of substitution may lend itself to identifying more effective tools and barriers.

The ISD principle of simplification is observed in the guidance that long term care facility (LTCF) staff from outbreak facilities must not work in non-outbreak facilities. This guidance helps reduce hazards by reducing the complexity of the staffing process.

With all of the barriers mentioned above, degradation factors exist. For example, the barrier "LTCF (long term care facility) staff from outbreak facilities must not work in non-outbreak facilities" may be defeated in the case of staff shortage. These degradation factors need to be identified, along J o u r n a l P r e -p r o o f with corresponding degradation controls. After implementation, follow-up should be completed and barriers audited for effectiveness and compliance.

The following sub section describes how ISD guidewords, checklist questions and example-based guidance can be used to apply the principles of ISD to COVID-19 risk reduction.

To incorporate the principles of ISD, the use of checklist questions and example-based guidance is recommended. ISD checklist questions are a demonstrated tool to incorporate the principles of ISD (CCPS, 2009; Kletz and Amyotte, 2010) . Table 2 lists ISD checklist questions that have been developed for using ISD principles to reduce risk associated with COVID-19. The checklist questions in Table 2 were developed using the guidewords minimize, substitute, moderate and simplify. These guidewords are the general principles of ISD. Guidewords can be used as mindtriggers in the formulation of recommendations (Goraya et al., 2004) .

Example-based guidance allows users to find specific applications of ISD that may be applicable to their scenario or use as the basis for mind triggers to help them identify opportunities (Rayner Brown et al., 2020) . In this paper, the best-practices recommended by public health and sectorspecific guidance have been collected and can be referred to for implementation or be used to develop measures for their specific applications.

J o u r n a l P r e -p r o o f Are there alternative processes available for eliminating the exposure to the hazard?

Can alternate, more effective cleaning products or safety equipment be used? Moderate

Can personnel be segregated from the hazard (e.g. through social distancing) to reduce the risk to other personnel and minimize disruption to business operations in the event of an infection? Can processes and workflows in organizations be designed to limit the magnitude or severity of disruption due to an infection? Simplify

Have human factors been considered in the design of the workplace? Can equipment be designed such that it is difficult or impossible to create a potential hazardous situation due to an error? Can workflows and schedules be planned and optimized to facilitate simple turnover and minimize cross-over between individuals? Are there any other alternatives for simplifying operations? Is there additional equipment or resources that can be provided that would make working remotely easier?

A literature review was completed to collect Nova Scotia (NS) specific bow tie elements and receptor groups. This included a review and summary of the controls, and barriers, used by public health to prevent infection and transmission of the COVID-19 virus, as well as sector-specific best-

practices. This information about barriers forms the basis of example-based guidance; different J o u r n a l P r e -p r o o f stakeholders and organizations can use example-based guidance to identify barriers and reduce risk within their specific applications. A Glossary of Terms is presented in Table 3 to provide definitions of terminology for clarity and consistency, primarily with respect to the terms "social distancing", "isolation" and "quarantine."  you have been told by the public health authority that you may have been exposed and need to quarantine.  Other name: Self-isolate Example-based guidance Best practices recommended by public health and sector-specific guidance that can be implemented by others or be used to develop measures for their specific applications.

Rayner Brown et al. (2020) Hierarchy of controls (HOC)

The preferred order of consideration of riskreduction measures (from most to least effective): inherently safer design (ISD), passive engineered, active engineered and administrative (Kletz and Amyotte, 2010; NIOSH, 2020) Inherently safer design (ISD)

Avoiding hazards or reducing their likelihood or severity by changing the inseparable characteristics of the process, rather than through the use of add-on safety equipment and human action. Based on four principles: minimization, substitution, moderation and simplification. (Kletz and Amyotte, 2010) Passive engineering control Add-on safety device that does not require event detection and actuation of moving parts (e.g., plastic partition/barrier) (Kletz and Amyotte, 2010) Active engineering control Add-on safety device that requires event detection and actuation of moving parts (e.g., alarm). Note that vaccination has not been included as a barrier/control in this paper because during the timeframe of the project it had not yet been developed and was not an available barrier. Discussion on incorporating vaccination within the bow tie diagrams is included in Section 11. Consult with an HVAC professional to ensure the system is optimized.

Limit or avoid situations where there is an increased production of aerosols and droplets, including from singing, speaking loudly or yelling, and heavy breathing from exercising.

Ensure occupancy is reduced to minimum levels and when rooms are in use, maintain maximum ventilation rates. 

Identifying degradation factors associated with barriers is an important component of bow tie analysis. Table 5 provides a listing of degradation factors and controls for common barriers. Consult with an HVAC professional to ensure the system is optimized.

Limit or avoid situations where there is an increased production of aerosols and droplets, including from singing, speaking loudly or J o u r n a l P r e -p r o o f yelling, and heavy breathing from exercising.

Ensure occupancy is reduced to minimum levels and when rooms are in use, maintain maximum ventilation rates.

With respect to bow tie analysis, operational discipline can be thought of as a degradation factor control. Work in this area is currently underway at Dalhousie University. Murphy (2020) describes how performing and complying with the primary safeguards (practicing social distancing, wearing PPE and enhanced personal hygiene) are analogous to operational discipline in process safety. (2018) 

As discussed in Section 6, many degradation factors relate to human behaviour and HOF. Common HOF degradation factors categories are (CCPS/EI, 2018):

-slips and lapses, -mistakes, -unintended violation, -situational violation, -organizational optimizing, -personal optimizing -and reckless.

Categorizing these degradation factors with respect to the HOF degradation categories helps identify effective, common degradation controls (shown below in Table 6 ).

J o u r n a l P r e -p r o o f 

An analysis framework has been developed and is discussed within this section. As outlined by NHS (2009) , it is challenging to describe detailed infection control guidance for every occupation or workplace, or every scenario/situation where receptor groups may be at risk of exposure to the virus. This analysis framework is a tool for developing application-specific risk reduction plans based on the HOC to reduce the risk of COVID-19 transmission and contraction. The analysis framework shown in Figure 2 , which has been developed for incorporating the HOC in bow tie analysis, is an adaption of the protocol described by Rayner Brown et al. 2020. J o u r n a l P r e -p r o o f Stage 8: Use example-based guidance to identify administrative controls that reduce the probability or severity of threats or consequences. Add these barriers to the bow tie diagram.

Stage 3: Identify the top event of the bow tie (e.g. receptor-specific COVID-19) Stage 9: Use example-based guidance to identify opportunities for PPE to reduce the probability or severity of threats or consequences. Add these barriers to the bow tie diagram.

Stage 5: Use example-based guidance and ISD checklist questions to identify opportunities for ISD controls that eliminate threats or consequences. Add these barriers to the bow tie diagram.

Stage 7: Use example-based guidance to identify engineering controls that reduce the probability or severity of threats or consequences. Add these barriers to the bow tie diagram.

Stage 10: Identify degradation factors for barriers and identify corresponding degradation controls. Add these to the bow tie diagram.

Stage 11: Implement and follow up on barrier recommendations Stage 6: Use example-based guidance and ISD checklist questions to identify opportunities for ISD controls that reduce the probability or severity of threats or consequences. Add these barriers to the bow tie diagram. 

This section describes the application of the analysis framework to develop a bow tie based on the HOC. The bow tie elements captured in this example are drawn from publicly available literature and focuses on activities and scenarios highlighted as having more associated risk; additional bow elements (i.e., threats, barriers, degradation factors and controls) may be identifiable by subject matter experts in a collaborative bow tie workshop approach, as described by CCPS/EI (2018).

The bow tie diagrams are drawn using the BowTieXP software program. Note the "+" and "-" symbols on the bow tie elements appear as a function of the software for collapsing different features for space considerations and viewing. Red boxes have also been added to the bow tie diagrams to highlight the barriers identified and added during each stage of the protocol.

The following bow tie is completed assuming the pandemic is "At Peak" with respect to the number of cases within the jurisdiction (e.g. province) of interest.

J o u r n a l P r e -p r o o f

As previously stated in Section 2, the terminology for the hazard that is used in this research is "Novel coronavirus in human population" (shown in Figure 3 ).

As previously stated in Section 2, the terminology for the top event that is used in this research is with the top event "COVID-19 [within a receptor group]." When users are applying the analysis framework to their specific application/scenario of interest, the identification of the receptor within J o u r n a l P r e -p r o o f the top event helps define the scope of the bow tie analysis (e.g. what is the person or receptor group of concern for reducing the risk of .

For the purposes of this example, the receptor group being modelled is a "generally healthy person"

(shown in Figure 4 ).

Next consider how the top event could occur,i.e., how the generally healthy person could contract COVID-19. Consider the activities and settings where risk of coming into contact with the virus exists (shown in Figure 5 ). COVID-19 spreads via respiratory particles, so transmission modes for COVID-19 include breathing, talking, shouting, coughing and sneezing (Government of Canada, 2021f) ; the threats identified involve this aerosol transmission. This represents more J o u r n a l P r e -p r o o f risk in enclosed spaces and indoor settings. Additionally, the time of exposure also a relevant factor in threats and risk of contracting the virus. The threats that are identified include situations where the receptor group may be exposed for longer times.

Next identify the consequences; consider the effects or what could happen if the receptor group contracted COVID-19 (shown along with threats in Figure 6 ). In Figure 6 , the abbreviation "EMA" in the consequence "Extended EMA/lockdown" refers to the Emergency Management Act, which is the legislation in Nova Scotia that is "An Act to provide for a prompt and co-ordinated response to a state of emergency"

J o u r n a l P r e -p r o o f The listing of common degradation factors and controls are provided in Table 5 .

The last stage of the analysis framework includes the implementation of barriers and follow up. This includes audits to determine barrier effectiveness and health of barriers; barriers, as well as degradation controls, must be auditable (CCPS/EI, 2018).

The intent of the bow ties in this section are to show activity-based threats for coming in contact with the virus, the potential consequences of an infection, barriers/controls that may be in place or used and the respective degradation factors and controls. The bow ties may not be completely accurate or reflective of practices, and as with the EI/CCPS (2020) bow ties, feedback and input from subject matter experts and authoritative stakeholders should be solicited. Work in this area is currently underway at Dalhousie University.

These diagrams are shown in Figure 14 to Figure 17 (some diagrams are shown as left and right sides due to space limitations).

For the "At Peak" pandemic stage, bow tie diagrams have been completed to model the scenario associated with COVID-19 in the following specific receptor groups:

immunocompromised individual, resident in a long-term care facility (LTCF), primary care giver, grocery store employee, paramedic and, nurse. elementary school student, hair salon patron based on guidance made public by the Cosmetology Association of Nova Scotia (CANS, 2020) and, fitness studio patron (Government of Nova Scotia, 2020b) .

The example with the top event "Hair salon patron contracts COVID-19" is presented here. This 

Additional guidance has been developed for communicating features of bow tie analysis with non-CPI stakeholders. For example, for the bow tie diagram involving a paramedic contracting COVID-19 in Figure 14 and Figure 15 , plain language for describing the objective of bow tie analysis has been developed as follows:

Objective: Use Bow Tie Analysis to:

-Show how paramedic could contract COVID-19 -Show how to prevent paramedic contracting COVID-19 -Show what would be the consequences -Show how to mitigate the consequences -Show how prevention and mitigation barriers degrade and fail It has been found that adding labels for the hazard, top event, threats, and consequences, as well as the addition of legends for the bow tie elements, is beneficial when introducing bow tie diagrams to new audiences. The graphical nature of the bow tie improves the communication of hazardous scenarios to broad audiences through visualization, in comparison to other tabular-based approaches like a HAZOP (Hatch et al. (2019) .This paper has demonstrated how bow tie analysis is an effective tool for qualitatively communicating risk management. Quantitative analysis was out-of-scope of the current work, but it is recognized that bow tie analysis can be used for quantitative analysis and can be leveraged in cost-benefit analysis and decision-making. The use of quantitative data (e.g., probability of failure on demand, threat frequency, probability of consequences, demonstration of ALARP (As Low As Reasonably Practicable)) could be leveraged by decision-makers to weigh the cost-benefit of different risk management aspects. Work in this area is underway at Dalhousie University and Memorial University of Newfoundland.

Further work is being completed with engagement of local healthcare partners in Nova Scotia under an NSERC Alliance partnership grant. This collaboration with subject matter experts in infection prevention and control and completing bow tie analysis in a workshop setting allows for a thorough consideration of bow tie elements, including initiating events and barrier degradation factors. The work completed to date, as well as proposed work, has been well-received by a number of groups. There has been great enthusiasm for addressing challenges associated with communication of risk reduction plans and systematically assessing barrier effectiveness.

Healthcare partners have also identified potential uses of bow tie analysis for applications beyond COVID-19, which is consistent with literature review and is demonstrative of the value of this tool in applications beyond process safety. Corresponding degradation factors of the vaccine barrier include the vaccine effectiveness rate less than 100% (CDC, 2020) and vaccine hesitancy or refusal (The Guardian, 2020 ). An example of a degradation control includes education. Further work incorporating this new information is currently underway at Dalhousie University. Additionally, while barriers should ideally be independent and there should not be a common mode failure, this is unfortunately practically impossible (CCPS/EI, 2018). The consideration of degradation factors and controls helps to identify the vulnerability of different barriers to common mode failure. Additional identification of degradation factors and controls is being completed in ongoing work with partners, as outlined above.

J o u r n a l P r e -p r o o f

In closing, this project demonstrated how the process safety concepts of bow tie analysis and inherently safer design can be used in COVID-19 risk reduction. This work included the development of an analysis framework that incorporates the hierarchy of controls within bow tie analysis and encourages the consideration of ISD principles. This analysis framework can be used by a broad range of stakeholders to develop additional bow tie diagrams for their own specific applications and receptor groups of interest. This paper presented several bow tie diagrams that convey COVID-19 risk reduction measures for receptor groups including a generally healthy person, a paramedic and a hair salon patron. This project also emphasized the importance of identifying degradation factors and controls to ensure barrier reliability and effectiveness. Human and organizational factors (HOF) were also identified to play a significant role in barrier performance.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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COVID-19 Global Risk Communication and Community Engagement Strategy -interim guidance

Identifying airborne transmission as the dominant route for the spread of COVID-19

The authors gratefully acknowledge the Nova Scotia COVID-19 Health Research Coalition for funding the project. Thank you as well to Yajie Bu for providing assistance with literature review.J o u r n a l P r e -p r o o f