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Vishwadeep Khatri
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Bowtie Analysis is a risk assessment and mitigation tool that is primarily used to identify control gaps. It gives us a bow like diagram where the risk is at the knot of the bow while pathways from causes of the event to its consequences become the sides of the bow. It is an effective visualization tool to differentiate between reactive and proactive risk management.

 

An application-oriented question on the topic along with responses can be seen below. The best answer was provided by Mohamed Asif on 1st Nov 2022.

 

Applause for all the respondents - Himanshu Sharma, Ambikesh Tiwari, Dimple Tiwari, M V Ramana, Godwin Thomas, Mohamed Asif, Gulshan Kumar, Rakesh Chandra.

Question

Q 517. What is Bowtie Analysis? How does it compare against FMEA? Provide relevant examples.

 

Note for website visitors - Two questions are asked every week on this platform. One on Tuesday and the other on Friday.

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Bowtie Analysis is used for risk assessment, risk management and risk communication.

By using bowtie diagram we can visualise risk. It shows the causes and consequences of an event. More over the control measures to mitigate the risk is also shown on the diagram. 

 

Having potential causes and control barriers on one side and having potential outcomes and defense causes the other side of the hazardous event gives this analysis the shape of "Bow Tie". It simply combines Fault Tree (FT) and Event Tree (ET).  

2105265580_Screenshot2022-11-01at2_04_54PM.thumb.png.81c40fab4516377b171396c5e5fdb029.png

Bow-tie Shape reference

 

1720681902_Screenshot2022-11-01at1_41_19PM.thumb.png.074fb118425dd61d15c173e0ca21f5db.png

Bow-tie Modelling 

Examples:

722857090_Screenshot2022-11-01at2_06_45PM.thumb.png.32768e92cc638da0ca7f9a12c983ecbe.png

Factory Fire Bow-tie Example

 

2024022170_Screenshot2022-11-01at2_08_06PM.thumb.png.eaedee538a94fb80d812d7ae71f2b1d8.png

Financial Product Bow-tie Example

 

1440426255_Screenshot2022-11-01at2_09_08PM.thumb.png.46f172c4649b199e2d6560dc0fb58e1d.png

Car Crash Bow-tie Example

 

Bow-tie use cases:

Risk Analysis

Reliability Engineering 

Safety Assessment 

Mining 

 

FMEA use Cases:

Chemical

Aerospace 

Military

Automobile

Electrical

Mechanical

Large scale industries 

 

Difference between FMEA and Bowtie:

FMEA is Bottom-up and Bowtie can be constructed using both bottom-up and top-down approach 

FMEA is quantitative whereas Bowtie is qualitative 

 

In general, risk analysis helps an organization to identify risks and potential threats to its internal operational processes and provides severity and likelihood of those occurrences. Below is the list of risk analysis methods and techniques.

 

Qualitative:

Bowtie Analysis

Delphi Technique

SWIFT Analysis

Fly Analysis

Risk Register

Probability-Impact Matrix

Risk Categorisation

Expert Judgement

 

Quantitative:

Monte Carlo simulation

Decision Tree Analysis

Sensitivity Analysis

Three-Point Estimation

FMEA

Scenario Analysis

Latin Hyper Cube Simulation

 

Conclusion: 

Even though there are many risk assessment methods like Bowtie, FTA, FMEA, etc., they focus with single threats and most of the time struggle to represent multiple simultaneous failures.

FMEA systematically identifies the effects/consequence of Failure mode and used to remove/reduce the possibilities of failure and Bowtie, predominantly gives hazard insights and its management and helps to represent the influence of safety system on the shop floor accident scenario.   

Integrating them, both Bowtie and FMEA can be used together for hazard analysis and risk assessment. Detection rating and RPN calculation based on FMEA along with corrective measures to improvement RPN and subsequently using bowtie to identify safety critical barriers and associates actions can improve the effectiveness drastically. 

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What is Bowtie Analysis

The Bowtie analysis has been attributed back to Royal Dutch Shell in the 70’s / 80’s. Since then, oil and gas, mining and pharma  companies amongst others have used the Bowtie technique to identify and mitigate risk. More recently, financial institutions have warmed to the idea, seeing the benefit of this simple, yet comprehensive method to understand and communicate risk. The Bowtie technique is a logical way to explore and communicate risk. Its principles are simple, but the execution and presentation need care. Bowtie analysis is to asses high level of risk. It is a hazard identification and risk mitigation tool. It looks like a Bow tie , centre or knot of tie is the main event/ hazard and left hand side sources for main event and right hand side consequences as shown in picture:
 
Bowtie
 
There are 7 steps for Bowtie analysis as below:

1-Identify hazard

2-Identify Top Event

3-Identify Threats

4-Identify Consequences

5-Identify prevention barrier

6-Identify Mitigation barrier

7-Identify Escalation barrier

 

Below is the Example:

 

image.thumb.png.f4b6b7ce06b8f04dea7b56061d87c3ab.png

 

 

Compare to FMEA, Bowtie analysis simple and visual tool. FMEA is team oriented ,more systematic method to identify and mitigate technical risk .FMEA one of the core tool asper IATF -16949 requirement for automotive industry.
As per latest FMEA AIAG VDA1st eddition -  June 2019,  it categorise Action Pririoty to mitigate risk into High , Medium and Low category based on Severity, occurrence and detection ratings. There are 7 steps for FMEA as per AIAG VDA standard:
1.Planning and Preparation
2.Structure Analysis
3.Function Analysis
4.Failure Analysis
5.Risk Analysis
6.Risk Optimization
7. Result Documentation

Step 1 :- Planning & Preparation covers the scope definition project team make-up and project planning aspects of the study. A clear definition of the scope, set by the management team, minimize the probability of “Scope creep.” Project Planning is done following “Five T’s” and should be covered in the FMEA kickoff meeting. The information from this step is the basis for Step 2.

Step 2 :- Structure Analysis is used to identify and breakdown the system (Design or Process) into the system, subsystems and component element so that a comprehensive risk assessment can be conducted. This information is the basis for the next step.

Step :- 3 Function Analysis analyzes each system element identified in Step 2 in terms of its intended function(s) and corresponding requirements. The Function Analysis leads to a comprehensive and relevant Failure Analysis in Step 4.

Step :- 4  Failure Analysis marks the beginning of the next phase of the FMEA, Failure Analysis and Risk Mitigation. The purpose of the Failure Analysis Step is to identify failure modes, failure effects and failure causes to establish the basis for the risk assessment.

 

Step :- 5 Risk Analysis is where the level of risk for each failure mode is evaluated in terms of Severity, Occurrence and Detection (S-O-D).Items are then assigned an Action Priority Level of High, Medium or Low.

Step :- 6  Risk Optimization is the step where plans are developed that reduce risk and increase customer satisfaction by improving the design or process.

Step 7 :- Results Documentation is the final step where the results of the FMEA study and fully documented in a report.

 

Only Failure analysis steps seams similar to Bowtie analysis which shows relationship in failure chain. In FMEA Focus element is failure mode. If you question why failure mode occur then you will get answer of failure cause and what happen when failure mode comes than answer is failure effect.  Similarly in Bowtie if focus on main event and question Why ? Than answer is Sources and if question what happens than answer is consequences. As shown in picture below:
image.thumb.png.35b575739320d328a462dc2e42b2b86f.png
image.thumb.png.a910ae39599515663a2e5f72ef71c0e3.png
 
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Bowtie is a methodology and used as a risk assessment, A major accident is often the results of multiple barrier failures. It can often be difficult to understand which combination of barrier failures could lead to incident this is where bowtie diagram come in  a well constructed bow  tie dram helps everyone to visualized the risk by focusing on the barriers that prevent incidents from occurring or those that prevent one from getting worse. It is a visual assessment that can be understood. By peoples at all levels in an organization and can be far easier to communicate that risk assessment in tabular form.

 

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At the center of the diagram is the hazard which is something that has the potential to cause harm. Below the hazard sits the top event which describes the point at which control of the hazard is lost  and left-hand side we list the threads which are all the potential reasons that we could lose control of the hazard, on right-hand side are the consequences which is harm or damage, Which  that could result from top event. Any threat may trigger the top event which may trigger result in any of consequences.

 

Example : flammable liquid

image.png.03b57c1a4e1dfe4baf409bea9656b5fe.png

 

We can insert barriers. These are the measures we take prevent of mitigate unwanted threats and consequences. Barriers to the left of tope event are preventive barriers, they prevent the top event from occurring. The barriers to the right are mitigative barriers. They mitigates, or reduce, the consequences of the top event. Barriers should be described such as independent of one another, which means that each barrier alone can block the top event.  Barriers are not 100% reliable they can fail. History show they do fail. Bowtie can be used to analyze barrier failure by examine degradation factors. These don’t cause an event to happen directly but they can lead failure of barrier. By helping to communicate key process safety information a more process safety information, a more positive safety culture promoted. Bowtie diagrams are also fantastic training tool, contributing to an increase an process safety competence.

 

Below drawn Bowtie filter Dryer

 

image.png.83b47d73e7d4fcaff1d11107484c5c3e.png

Here all barriers are not reliable enough, In Bowtie analysis we can  use the color coding for prioritize action based on the impact.

 

Bowtie approach is proactive and reactive and work though the hazard and its management. FMEA is a systematic method for identifying effect or impact of failure mode. Bowtie focus entirely on safety and hazard whereas FMEA focus on performance, quality and readability.

FMEA talk about occurrence but Bowtie wont talk about occurrence factor.

 

Compare Bowtie and FMEA .

Bowtie approach is proactive and reactive and work though the hazard and its management. FMEA is a systematic method for identifying effect or impact of failure mode. Bowtie focus entirely on safety and hazard whereas FMEA focus on performance, quality and reliability.

Bowtie analysis most used for the risks that have high level of risk, particularly those  with high level consequences. 

FMEA talk about occurrence but Bowtie wont talk about occurrence factor .

Bowtie highlight risk between controls and management,

Bowtie analysis enhance the existing technique like FMEA by helping those involved in original identification or analysis studies to confirm their discussion and those not involved in the studies (but still responsible to manage the risk) to understand address the relevant issue.

“Bowtie analysis offers a simple but effective method to visualize risk and show that hazards are under control”

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Bow tie analysis

Preface

Bow tie analysis is a simple process for relating where new or enhanced controls may be worthwhile. It's a core part of threat treatment planning, particularly where there's a high position of threat or where control effectiveness is assessed as low.

Background

A bow tie is a graphical definition of pathways from the causes of an event or threat to its consequences in a simple qualitative cause- consequence illustration. It's a simplified combination of a fault tree that analyses the cause of an event or threat, the left- hand side of the illustration, and an event tree that analyses the consequences, the right- hand side. It's represented as a bow tie (Pic 1), where the knot of the bow tie is of the point where the fault tree paths meet, and the event tree spans out. While bow tie plates can be constructed from fault and event trees, they're more frequently drawn directly from a brainstorming session, furnishing a fruitful base for a group disquisition of controls.
image.png
 

The focus of bow tie analysis is on the walls or controls depicted to the left- hand side of the knot that can change the liability of the event or circumstance, or on those on the right- hand side that can change its consequences. It's used when assessing the absoluteness of controls, to check that each pathway from cause to event and event to consequence has effective controls, and that factors that could beget controls to fail (including operation systems failures) are honored.

A primary use of bow tie analysis is to identify control gaps, where fresh controls may be warranted. Examining causes, consequences and the being controls that address them helps to identify gaps in the current controls (as shown in Pic 1).

·        The most effective controls generally address causes, generally to stop them arising or leading to the threat (preventative controls). They should match the causes, in extent and nature. This requires that the causes and their counteraccusations for business objects be easily understood, frequently in some detail. For illustration, conservation systems are preventative controls for pitfalls associated with asset integrity.

·        On the right of the bow tie, controls should give applicable responses to consequences being felt or produce walls to the consequences developing. They might either impact the consequences on business objects directly (corrective or reactive controls), or descry changes snappily and give triggers for contingency plans(operative controls). For illustration, a bund around a storehouse vessel may not help a release of product, but it limits the spread of the release and hence the adverse consequences; a bank alarm is a operative control that allows fast response to a fire.

Bow tie analysis is an important contributor to the threat treatment stage of threat operation (Pic 2); threat treatment is the stage that enables us to decide benefit from the analysis carried out before in the process. Without threat treatment, we do no further than describe the situation in which we're operating.

image.png
 

A bow tie can also be used for recording information about a threat that doesn't fit the simple direct representation of a threat register. It can be used proactively to consider implicit events and scripts (pitfalls) and retrospectively to model events that have formerly passed.

The logical inflow of a bow tie illustration also provides a veritably effective means of illustrating the factors at work in relation to a major threat. This makes it useful for communicating with people outside the immediate group carrying out the analysis.

 

Simple Bowtie analysis

Simple Bowtie analysis can be conducted using straightforward templates like the one in Pic 3.

 

1.      Identify the threat to be examined in the bow tie analysis. Bow tie analysis is of utmost use for pitfalls that have high situations of threat, and particularly those with high consequences.

2.      Describe the threat, in the form (commodity happens) and leads to (a consequence for our objects) and note the main threat analysis issues from the threat register.

3.      List the causes of the threat on the left and the consequences of the threat on the right, drawing on material from the threat register and expanding where possible.

4.      List the being controls on the causes (preventative controls) below the causes on the left wing, and the controls on the consequences (corrective controls) below the consequences on the right. However, also show it doubly, on each side of the template, if a control acts on both causes and consequences.

5.      Assess the effectiveness of each control, by asking ‘ Is it designed well( could it work)? ’ and ‘ Is it enforced well( does it work)?

6.      Identify options for enhancing being controls, to ameliorate their effectiveness or to fill gaps. This may include enhanced monitoring and further frequent review, for illustration using control tone- assessment.

7.      Look for gaps, where there are causes and consequences for which there are no matching controls.

8.      Identify options for creating new controls to fill the gaps.

9.      estimate the advantages and disadvantages of each option, agree options to be pursued, and develop perpetration plans.

Pic 3 Bow tie analysis template
image.png
 

In utmost circumstances, conduct to produce new or revised controls will be enforced only if they induce a net benefit for the organization, where the advantages and benefits overweigh the disadvantages and costs when considered as a whole. still, controls should conform to applicable norms or nonsupervisory conditions, similar as those assessed by plant health and safety policy or legislation. In circumstances like this the net benefit criterion may not apply, and perpetration must do, irrespective of net benefit, to satisfy compliance scores. Benefits and costs should be interpreted more astronomically than simple fiscal measures.

Bow tie analysis is of utmost use in the following situations

        A simple illustration is needed to communicate the range of causes and consequences and the associated controls

        further detail about the causes and consequences of a threat is demanded than is contained in a threat register

        Where a graphical representation may be important clearer than textbook

        There are clear pathways from causes to the threat, and from the threat to the consequences

        The overall position of control effectiveness is believed to be low

        The focus is on relating controls, control effectiveness and control gaps and icing that each pathway has a control (a hedge)

        The situation is more complex than a single cause- event- consequence pathway, but not so complex that a full fault tree analysis and event tree analysis is warranted.

Bow tie analysis can be used for desirable influences as well as those we seek to avoid. In this case the controls aren't walls, but rather factors that support or enhance the pathways.

Bow tie analysis isn't useful when

        There are multiple causes that are linked in complex ways, for illustration when there might be AND and OR gates in a fault tree depicting the left- hand side of the bow tie

        Where detailed quantification is demanded.

Bowtie plates have several advantages

        the full range of initiating events (AKA pitfalls) are shown

        the intermediating safeguards (AKA walls) are easily shown

        the factual way in which these combine and escalate is easily shown

        the consequences side shows walls in an original manner

        the numerous possible consequence issues are defined

        the relation of the walls to the safety operation system can be made unequivocal

Bowtie illustration limitations disadvantages

        can bear in depth knowledge from subject matter experts for thickness on delineations and development methodology

        may take significant time to develop a meaningful bowtie illustration

        walls linked aren't independent of each other leading to a false sense of security

        confusing pitfalls with escalations factors

        limited norms on the development and use of bowtie plates

        can come relatively large and complicated

        does not give a quantitative assessment of threat

How does it compare against FMEA? Provide relevant examples.

 

FMEA is a systematic tool for identifying the effects or consequences of FM and is used to eliminate or reduce the chance of failure. Bowtie is considered as an approach that has both proactive and reactive elements and that systematically works through the hazard and its management.

Case Study

 

The FMEA and bow- tie methodology are applied to a particular type of accident in the anhydrous Sodium Sulphate plant, The critical outfit in plant consists of (Melter, boiler, crystallizer, thickener, evaporators, packing machines, centrifugal pump, plate heat exchanger and screw pumps). This outfit was named grounded on analysis of literal data of the plant and interviews with crucial labor force involved in the safety, conservation and operation.

 

 

 

 

RESULTS AND DISCUSSIONS

 

Risk Analysis Through the FMEA

There are nine subsystems linked, at which implicit failure mode ( FM) can do, as shown in Table 2. In this table, FMEA punctuation form is presented. It shows the form of FMEA for S, O and D. The advised RPN values and criticality for the failure modes are presented. There are several FM with high values of RPN. It can be observed that the values of RPN for quilting and sewing machines are 500, 490 independently. Packing machines are the loftiest criticality values of failure modes.

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Risk Analysis through the Bow-Tie Diagram

 

The main pitfalls on the left hand- side and demonstrates in a “Bow- tie illustration” shape how walls help the escalation of the original pitfalls to one of several final issues are introduced. As can be seen from these numbers, safety critical walls are linked and each of these is as- inked to artificial process with an individual responsible. Some shell spots use a point called matrix of permitted operations which defines in matrix format what conditioning may or may not be done if the applicable hedge isn't functional. This is a form of threat grounded operations, but it focuses on interdicted operations and it's understood the approach has not set up favor in ope- standing spots as it's too restrictive on operations.
image.png

 

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Bow tie analysis

To explore and communicate risk the Bow Tie technique is used, in 70’s and 80’s the Bow Tie principle to analyse and document risk has been attributed back to Royal Dutch

A bow tie in a simple qualitative cause-consequence diagram is a graphical depiction of pathways from the causes of an event or risk to its consequences. The left hand side of the diagram is a simplified combination of a fault tree that analyses the cause of an event or risk and in the right hand side, an event tree that analyses the consequences. Shown as a bow tie (Figure 1
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To identify control gaps, where additional controls may be warranted are the primary usage of bow tie analysis. Figure 1 helps to identify gaps in the current controls and examine causes, consequences and the existing controls that address them.In figure 2, the risk treatment stage of risk management shows Bow tie analysis has an important contributor; the analysis carried out earlier in the risk process treatment is the stage that enables to derive benefit. Without risk treatment, we do know the situation that describe in which we are operating.
image.png
For a very effective means of illustrating the factors at work in relation to a major risk the bow tie provides a logical flow thus making useful communication with people outside and the immediate group carrying out the analysis. Bow tie analysis can be conducted using straightforward in a simple way which is represented in Figure 3.
image.png
Complex bow ties: The mechanisms that cause a risk, and the mechanisms that lead to consequences can be drawn by bow tie diagrams showcased in Figure 4. Barriers on the pathways causes to the risk can be shown as controls.
image.png
 

Specific controls that support Management functions can also be shown and linked to the associated controls. Wherever necessary Bow ties can be linked, so that consequences from one bow tie become the causes in another.

Bow tie analysis usage:

To communicate the range of causes and consequences and the associated controls a simple diagram is required

Instead of text, a graphical representation is much clearer

From causes to the risk, and from the risk to the consequences there are clear pathways

Where the overall level of control effectiveness is low

A single cause-event-consequence pathway is more complex than the situation.

Bow tie analysis is not useful when:

In a complex ways there are multiple causes that are linked and where the detailed quantification is needed.

Example: In a fault tree depicting the left-hand side of the bow tie there might be AND and OR gates

Software for bow tie analysis

As indicated in the figure 3 a simple bow tie analysis can be conducted using templates that are straightforward tables in Microsoft Word.

Specific software may be useful when more complex bow ties represented in Figure 4
A six steps process involved in control design and implementation.
image.png

 

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What is a bowtie? It’s a risk assessment methodology that uses a pictorial representation of the pathways of the causes of an event to its consequences. The left side of the diagram are the causes that would trigger the event, the middle/knot of the bowtie is where the causes converge to trigger the event and the right side are the possible consequences of the event. The diagram provides a simple scheme to easily visualize all possible proactive and reactive risk management to avert an event.   

 

How to construct bowtie?

MS applications such as word/PowerPoint can be used in case of simple bowtie. In the below example, I used the idea map available in Minitab workspace to recreate. It doesn’t look like a bowtie, but it conveys the intent :)  

The first step in bow-tie analysis is to figure out the hazard. Anything in an organization that has the potential to cause damage if control over it is lost is considered a hazard. Typical hazards seen in industries include a process / product that does not comply with local government rules / regulations leading to product withdrawal from market or a total ban on the company to sell, improper design of a valve that could lead to an explosion resulting in loss of material and life, poor quality resulting in market erosion, etc. A hazard identification brainstorming event with subject matter experts from various disciplines is formulated by companies to identify all possible hazards and the ones that could cause maximum impact are typically selected for further detailed qualitative analysis using bowtie.

 

Top event: Once the hazard is finalized, then the next step is to find the top event. It is defined as the moment when the control is lost.        

 

Hazard

Flying an aircraft

Top event

Engine power loss

 

Now, list the causes that could lead to the event on the left and the consequence of the event to the right. Historical data can be used to figure out all possible causes/consequences that has occurred and proactive risk management tools/techniques can be used to figure out all possible causes/consequences that could occur.

 

image.thumb.jpeg.96edf2421ae56d550ca3ae98b2f3be6c.jpeg

 

Introduce barriers for each identified cause/consequence as highlighted in blue. As the name suggests, barriers are the controls that needs to be placed in the system so that the threats/causes do not occur or even if they do, they don’t lead to the top event (in this case, engine loss). The barriers on the consequence side should ensure that, in case the top event occurs, it does not further escalate and result in the impact/consequence. Typically, the barriers should be properly mistake proofed to ensure errors due to human behaviors are nullified. Once the bowtie analysis is completed, the subject matter experts along with management can analyze to take decision on the sufficiency of each barrier in lieu of the risk it averts. In cases where the probability of a particular barrier failure is high, escalation factors are used to analyze this failure and take preventive measures.

 

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Uses of bowtie:

a) Provides a structured systematic method to analyze a hazard/risk

b) Provides a quick view of the controls that are available and its sufficiency to effectively control

c) The scheme is simple and easy to understand, thus promoting communication to gain better ownership to manage risk, helps management to take decisions on the controls to improve/sustain by deploying additional resources

 

 

A comparison with FMEA:

Per ISO14971, “FMEA is a technique by which the consequences of an individual fault mode are systematically identified and evaluated. It is an inductive technique using the question “What happens if..?” Components are analyzed one at a time, thus generally looking at a single-fault condition. This is done in a “bottom-up” mode, ie., following the procedure to the next higher functional system level.

Failure Mode Effect Analysis (FMEA) is another risk analysis tool where the impact of every potential defect on the whole system is evaluated using a risk score. The risk score or the risk prioritization number is obtained using the formula: RPN = Probability x Severity x Detection wherein probability is the probability of the defect to occur, severity is the severity that that defect could cause when it occurs and detection is the probability of detecting the defect or the failure each determined using the current as-is state of the process. Once all potential failure modes are analyzed and a RPN number is calculated, usually either the top 10 is taken for improvement or a threshold value of RPN is set, above which all identified risks are to be improved. Effective control/preventive strategies are then designed to counter the three parameters (ie)., probability, severity and detection that would effect a change on the RPN.

Although at the outset, FMEA and bowtie are used for analyzing risk and their consequences, they are different in the way they are constructed, evaluated, presented, but the end objective remaining the same. In fact, based on the complexity, resource/expert availability, depth of analysis required, each tools shall be evaluated based on its features and the output of one can become the input to another one. For example, the FMEA report with all the potential failure modes can be the input to the bowtie to construct the cause and consequence for the top failures for further analysis.

 

 

 

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The Bowtie Principle was developed initially by Royal Dutch Shell in the 80’s. Since then various industries like Oil & Gas, Mining, Pharmaceuticals etc. have used the Bowtie Technique to analyze and mitigate risk .Bowtie Analysis also known as Papion Analysis is a Qualitative Risk Assessment Methodology that provides a way to effectively communicate risk scenarios in easy to understand graphical format and also shows the relationship between the cause of unwanted events and its potential loss and damage
image.png
CREATING A BOWTIE ANALYSIS
Step 1:-

Creating the Bow tie starts in the middle with the hazard and the Event that is being analysed. 

Step 2:- 

Left side will have all the the potential causes or threats that would lead to the event happening

Step 3:-
On the right-hand side list all the consequences that had a probability of happening if the event corresponding to the hazard occurred.
On the right-hand side list all the consequences that had a probability of happening if the event corresponding to the hazard occurred.

Step 4:-

Logical flow of the chart is created with potential threat happens linked to the hazard . Introduce countermeasures or Controls & Mitigation steps .

Step 5:- 

From right, for each Potential cause what control measures could be put in place that would prevent that possible cause from happening. Each control is ranked High, Medium, or Low in terms of its effectiveness in being able to stop the potential cause from occurring.

Step 6 :-
Repeat the process for the right-hand side, this time with the mitigation steps  that would limit or stop the potential outcome or consequences from impacting. 

Step 7 :- 
For each of the controls and mitigation steps it is wise to add the safety critical activities that need to happen to support them. 

In the final step of the process review the chart to do a safety risk assessment.
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ADVANTAGES OF BOWTIE ANALYSIS 
 

·        It is useful  beyond usual risk assessment and highlights the link between risk controls and management system.

·        Helps to ensure that risks are managed not just analysed.

·        Comprehensive and structured approach in risk assessment and risk mitigation .

·        Excellent for communicating risk related matter to non risk-domain employees.

·        Involves employees using practical approach

·        Assigns responsibility for hazard controls

Identifies where resources should be focused for risk reduction, i.e. prevention or mitigation
LIMITATIONS OF BOWTIE ANALYSIS

·        Qualitative .

·        Does not replace techniques such as HAZOP or FMECA .

·        Depends on experience of personnel and participation level of employees concerned .

·        Controls in bowtie are not  truly independent

·        Important controls are not obvious

·        Involves long duration to develop a meaningful bowtie diagram.

·        Barriers identified are not independent of each other leading to a false sense of security.

 

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Bowtie Analysis

A bowtie is a graphical representation of the pathways from the causes of any event or risk to its consequences. The diagram is shaped like a bowtie, creating a clear differentiation between reactive risk management and proactive.

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Benefits of bowtie analysis

The benefits of the Bowtie analysis include but not limited to:

  • It provides a structure to analyze a hazard systematically.
  • It helps make a decision to check the current level of control is sufficient or for those who are familiar with the concept, whether risks are As Low as Reasonably Practicable.
  • It helps to identify where and how investing resources would have the greatest impact.
  • Also increases risk communication and awareness.

We have eight basic steps in building of a bowtie diagram:

  1. Identify hazard:  This is the first step and the first step in managing risks is to identify what their sources are there.
  2. Identify top event: When we know that what is/are potentially hazardous then we need to know how we could lose control over it/them.
  3. Identify threats:  The next we need to consider the scenarios or events which could directly cause the occurrence of the top event.
  4. Evaluate consequences: Then after the top event occurs, the subsequent scenarios or events are now possible and  these consequences may have lead to losses and damage.
  5. Identify preventive barriers: The next step is to identify the barriers which should prevent the threats from reaching or causing the top event(s). These are the preventative barriers.
  6. Identify recovery barriers: Barrier(s) on the right side try to recover from the occurrence(s) of the top event(s) and this/these barrier(s) should prevent or alleviate the consequences and/or the resulting losses and destruction.
  7. Identify escalation factors:  The next step is now to identify the specific situations or conditions under which the barriers are less or not effective.
  8. Identify escalation factor barriers: The next and last step is to look at what barriers you have to prevent or manage these escalation factors.

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Comparison between Bowtie analysis and FMEA

Bowtie Analysis

FMEA

It is considered as an approach that has both proactive and reactive elements and that systematically works through the hazard its management.

It is  a model used to prioritize potential defects based on their severity, expected frequency and likelihood of detection

FMEA is a step by step approach to identify the possible failures in design, manufacturing or assembly process or product or service. FMEA is two types of 1. DFMEA 2. PFMEA

It is a systematic tool for identifying the effects or consequences of failure mode and is used to eliminate or reduce the chance of failure.

 

 

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Excellent answers from all respondents. If was a tough one to choose from. However, given the examples, structure of the answer and a clear comparison between bowtie and FMEA - Mohamed Asif's answer has been selected as the winner. 

 

All answers are a must read to get a good understanding of the tool!

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