Cause Consequence Risk Analysis

The Cause Consequence methodology originates from the nuclear industry and is employed for modelling risks arising from products and processes. The methodology used has not changed significantly since the early 70’s and uses linear estimation of probabilities in order to generate a quantified measure for the undesirable events predicted by a risk model.

The Advanced Cause Consequence Analysis (ACCA ) tool is a method by which the user can produce a risk model using various building blocks (known as Symbols) which can be drawn onto one or more Worksheets to represent the Hazard . The Critical Event identifies the starting point of the scenario and usually pertains to a Hazardous situation being analysed. Several Hazards can be linked together, each with a single Critical Event, as an Undertaking .

Once the risk scenario has been drawn it is validated and an Excel compatible Algorithm File (ALF ) can be generated for subsequent simulation .

ISAE provides the necessary environment to allow the existing ACCA tool to run over and update its data elements.

ISAE Explorer Screen Access

The Explorer screen allows access to the following items from within the Engineering information folder:

Þ System Parameters

Þ Parametric Sets

Þ Consequences

In addition, Hazards added to ISAE under the Engineering Information folder on the explorer screen are duplicated on the Explorer screen underneath the Engineering Information folder as shown:

This is to provide quick and easy access to ACCA functions without having to navigate any further through ISAE .

ACCA Functions accessible from here and how to access them are as follows:

Project Specific ACCA Functions

ACCA Function	How to select the function	Result
Report Function	· Select a project · Right mouse click · Select ‘Reports’	The Report Screen is displayed allowing the user to select the type of Report required
Generate an integrated ALF for a project	· Select a project · Right mouse click · Select ‘Generate Integrated ALF ’	The system opens an Excel spreadsheet and generates the algorithm file.
View Project Log	· Expand the contents of a Hazard · Double-click on ‘Project Activity Log’	The Log screen for the project is shown.
Export an existing project	· Select a project · Right mouse click · Select ‘Export’	The system will take the user to the ‘Apportionment’ screen.
Create Apportionment Tables	· Select Project · Right mouse click · Select ‘Create Apportionment Tables’	The system will take the user to the ‘System Parameter List’ screen.
Delete this Project	· Select Project · Right mouse click · Select ‘Delete’	The system will request confirmation of the delete request. The user can either cancel or confirm the delete.

Hazard Specific ACCA Functions

All these functions are available for Hazards shown on the Explorer underneath the Engineering Information folder.

Function	How to select the function	Result
View/Maintain the Hazard Definition	· Expand the contents of a Hazard · Double-click on ‘Hazard Properties’	The system will take you to the ‘Hazard Definition’ screen.
View Hazard Activity Log	· Expand the contents of a Hazard · Double-click on ‘Hazard Activity Log’	All the events in the life-cycle of the Hazard can be viewed on the right of the Screen by expanding it to the right
Add a new Causal or Consequence Worksheet to an existing Hazard	· Select either Causal or Consequence Analysis · Right mouse click · Select ‘Add Worksheet ’	The system will create a Worksheet with the name ‘Worksheet X’, where X is the next number in sequence. The Worksheet is opened ready for input.
Verify that an existing Hazard is complete	· Select an existing Hazard · Right mouse click · Select ‘Verify’	See ‘Verification and Integrity Check of the Hazard ’
Generate an ALF for an existing Hazard	· Select an existing Hazard · Right mouse click · Select ‘Generate ALF ’	The system opens an Excel spreadsheet and generates the algorithm file.
Delete this Hazard	· Select Hazard · Right mouse click · Select ‘Delete’	The system will request confirmation of the delete request. The user can either cancel or confirm the delete.

13.1.3 Worksheet Definition and Manipulation

The following functions are available for worksheets shown on the Explorer as part of Hazards shown underneath the Engineering Information folder.

Function	How to select the function	Result
Edit the worksheet diagram	· Select a Worksheet · Right mouse click · Select ‘Edit Diagram’	The system will take you to the ‘Worksheet Editor’ screen.
Edit the worksheet details	· Select a Worksheet · Right mouse click · Select ‘Edit Details’	The system will take you to the ‘Worksheet Details’ screen (see ACCA User Guide)
Delete the worksheet from the system.	· Select a Worksheet · Right mouse click · Select ‘Delete’	The user will be prompted to confirm deletion of the worksheet . Conformation will result in the worksheet and its details being removed from the system.

The Causal Worksheet Editor

Unlike earlier version ISAE7 no longer links to external causal tools but uses its own worksheets to illustrate the causal logic. The worksheets are now split into Causal Analysis and Consequence Analysis. Create and access the worksheets as before.

NB: Users using older causal data should note that the causal worksheet has a facility to import the external causal data, this data is then removed from the ISAE database so ensure you have a backup of the data, and stored in its internal format.

Because of the complexity of the causal diagrams automated processed have to be added to assist the layout of the causal diagram. Selecting an AND or OR gate and clicking on the RH mouse click the menu shows the following functions:

Organise Children
All nodes beneath this Symbols are reorganised. This can lead to some Symbols over laying others.
Select Children
Use this option to select all children Symbols beneath the selected Symbol . You can then move the structure to another part of the page.
Straighten Children
Moving the Symbol can misalign it, use this option to align the child (but not its children) in the horizontal plane only.

Base events now have classification codes.

The Consequence Worksheet Editor Screen

This Screen displays a Worksheet area in which the various Symbols can be drawn and linked together logically to produce the required Risk Scenario .

At the top of the Worksheet drawing area is the title area which contains information about the Worksheet, the original Author, the Issue/Draft, whether Authorised or not and Modifications. The application automatically maintains this title area on the Worksheet. If this information requires editing the user must return to the relevant screens as follows:-

Þ Model Detail Screen	to change the Study or Panel details
Þ Worksheet Details Screen	to change the Author or Issue/Draft details

The graphical work area is manipulated by using. the menus and buttons at the top of the screen and the options available when the user right-mouse clicks on an empty area of the work area. For information on drawing the worksheet model itself see section 13.1.5 .

The following menu functions are also available:-

File	This allows the user to Save, Print or Close the Worksheet .
Edit	This allows the user to manipulate the worksheet detail by changing the size, font and cutting and pasting items on the worksheet.
Format	This allows the user a variety of options to format the layout of the worksheet .
View	This allows the user to Zoom in, out or to fit the page, view the Worksheet grid or Snap to grid or manipulate the colours used on the worksheet .

Remaining Specific ACCA Functions

Remaining specific ACCA functions that are available from within a Hazard are accessed in the same way as described in the ACCA user guide.

Drawing the Worksheet Model

Once the Worksheet has been opened the user can begin drawing the Model in the Worksheet Editor Screen. In order to do this the relevant Symbols must be placed on the Worksheet and connected by Relation Lines until the Model is complete. The Model can extend over several Worksheets using In- and Out- Connectors . Once the Model is completed to the user’s satisfaction each Worksheet must be saved (File/Save) and can be printed.

For further detailed information on producing the Model see the topics below.

Drawing The Symbols

To place a Symbol onto the worksheet , move the cursor to a blank area of the worksheet and press right-mouse click. The following menu will appear:

Select the Symbol required from the menu. A detail screen specific to the type of Symbol selected will appear prompting for information about the Symbol. Fill in the required details on the screen and press the save button. The Symbol will appear on the worksheet .

The available Symbols are described on the following pages and the relations are shown on page 80.

Barriers

These pertain to a range of physical, procedural and human factors related systems, measures or actions which might prevent or mitigate against the further escalation of a Critical Event into an undesirable Consequence (accident ). The number and connectivity of the Barriers within each diagram constitutes the algorithm for the development of the Critical Event into a number of potential Consequences.

The inputs can originate from one or more of the following sources:-

· another Barrier output

· a Connector output

· an Auxiliary Symbol

· a Critical Event

The outputs are generically named Fail (red) and Success (green) and basically constitute the logical paths out

They can each link to one of the following Symbols :-

· another Barrier input

· a Connector input

· an Auxiliary Symbol

· a Consequence

Each time a new Barrier is created the Barrier Screen is displayed to allow the user to
enter the required details.

The following fields may be entered:-

Symbol Id	Mandatory 14 characters defining the Symbol as follows: · Characters 1-2 - set to PH(Physical), PR(Procedural) or CR(Circumstantial depending on the category selected) · Characters 3-8 - set by the Classification code selected · Characters 9-10 - set by the Company code selected · Characters 11-14 – 4 digits uniquely defining the Symbol NB If Symbol Rules off is selected, the Symbol ID can be any characters up to a length of 20.
Text label	Mandatory. A text label of up to 50 characters. This also appears on the Symbol in the Worksheet .
Description	Optional description of up to 230 characters.
Classification	Using the … button select the classification code which this Barrier most closely fits, the Category is automatically set accordingly.
Probability	The “Failure” and “Success” texts may be altered if required to something more appropriate of up to 10 characters in length. The Failure Probability is a figure greater than 0 but not greater than 1. The probability of Success is calculated automatically as 1 minus the probability of Failure.

See section Parametric Variables and Formulae for details on how to set up a Parametric formula for this Barrier

Critical Event

The Critical Event (CE) identifies the starting point of the Model and usually pertains to a Hazardous situation being analysed. There is only one CE per model, usually placed at the bottom or left hand side of the page.

A Critical Event has only one output link that can be connected to a Barrier or an Auxiliary Symbol .

Each time a new Critical Event is created the Critical Event Screen is displayed in order to enter further information.

The following fields may be entered:-

Symbol Id	Mandatory. From 5 to a maximum of 10 characters defining the Symbol . It appears on the Symbol in the Worksheet
Text label	Mandatory. A text label of up to 50 characters. This also appears on the Symbol in the Worksheet .
Description	Optional description of up to 250 characters.
Probability / Frequency	One of these must be selected. The Probability must be a decimal number greater than 0 and up to 1 (default value is 1. The Occurrence is an integer in the range 1 to 30,000.

Consequences

The CCA methodology employs Symbols (Critical Events , Barriers etc.) to capture the escalation scenario associated with a Hazardous condition. In this context, a Consequence represents the end of a line of reasoning, culminating in an event which may be desirable or undesirable.

A Consequence may have many inputs, but has no outputs.

The input connections can originate from one of the following sources:-

· Barrier output(s)

· Connector output(s)

· Auxiliary Symbol (s)

Each time a new Consequence is created the Consequence Screen is displayed in order to enter further information.

The following fields may be entered:-

Symbol Id	Mandatory. From 5 to a maximum of 10 characters defining the Symbol . It appears on the Symbol in the Worksheet .
Text label	Mandatory. A text label of up to 50 characters. This also appears on the Symbol in the Worksheet .
Description	Optional Description of up to 250 characters.
Scenario	Optional. An Accident Scenario can be selected from the list which is displayed by pressing the button to the right.
Impact Classification	One of the following classes must be selected: Environmental, Safety, Commercial or Broadly Safe.

Comments

When the Comment Symbol is selected a box is drawn in the Worksheet where the user can enter any text required. To edit the text double-click on the comment box. The comments can also be resized by selecting a corner and dragging it to the required specification.

Once created a Comment can be attached to another Symbol in the Worksheet via the blue relation line. This line is for documentation purposes only and has no logical significance for the Model. A Comment may not have any inputs.

AND Gates

An AND Gate is a logical Symbol which multiplies a number of inputs and generates one output. It is used to influence the Probability of a Barrier or Critical Event .

The inputs can originate from a number of Basic Event or other Gate outputs (default 2).

The output can link to a State , Barrier , Critical Event or Out-Connector only.

Each time a new AND Gate is created the AND Gate Screen is displayed in order to enter further information.

The following fields may be entered:-

Symbol Id	Mandatory. From 5 to a maximum of 10 characters defining the Symbol . It appears on the Symbol in the Worksheet .
Description	Mandatory. A description of up to 50 characters. This also appears on the Symbol in the Worksheet .
Memo	Optional further description.

OR Gates

An OR Gate is a logical Symbol which subtracts the product of its inputs from the sum of the inputs and generates one output. It is used to influence the Probability of a Barrier .

The inputs can originate from a number of Basic Event or other Gate outputs (default 2).

The output can link to a State , Barrier , Critical Event or Out-Connector only.

Each time a new OR Gate is created the OR Gate Screen is displayed in order to enter further information.

The following fields may be entered:-

Symbol Id	Mandatory. From 5 to a maximum of 10 characters defining the Symbol . It appears on the Symbol in the Worksheet .
Description	Mandatory. A description of up to 50 characters. This also appears on the Symbol in the Worksheet .
Memo	Optional further description.

States

This Symbol depicts the result of a logical combination arising from AND-Gates and/or OR-Gates.

The State will produce the probability for a Barrier . It is an alternative to inputting a probability in the Barrier dialog box. The probability is deduced from the State’s input instead.

A State has one input and one output only.

The inputs can originate from the logical output of AND and OR gates only.

The output can only link to a Barrier .

Each time a new State is created the State Screen is displayed in order to enter further information.

The following fields may be entered:-

Symbol Id	Mandatory. From 5 to a maximum of 10 characters defining the Symbol . It appears on the Symbol in the Worksheet .
Text label	Mandatory. A text label of up to 50 characters. This also appears on the Symbol in the Worksheet .
Description	Optional description of up to 250 characters.

Auxiliary Symbols

An Auxiliary Symbol constitutes a logic flow support structure. It can be either a Parallel Gate or a Splitter Gate. It is designed to distribute the probability according to certain criteria instead of simply Fail/Pass as in a Barrier .

An Auxiliary Symbol allows the manipulation of multiple direction probabilities by splitting the probabilities evenly (Parallel) or dividing them in a predetermined (weighted) fashion (Splitter).

A Parallel Gate takes one input and generates multiple equivalent outputs (to a maximum of 5), weighted to add up to the value of the input.

A Splitter Gate takes one input and splits it into a number of outputs (to a maximum of 5), which add up to the value of the input.

The input originates from a Barrier output or an In-Connector.

The output can link to a number of potential Symbols namely:-

· a single Barrier input

· a Connector input

· a Consequence

Each time a new Auxiliary Symbol is created the Auxiliary Symbol Screen is displayed in order to enter further information.

The following fields may be entered:-

Symbol Id	Mandatory from 5 to a maximum of 10 characters defining the Symbol . It appears on the Symbol in the Worksheet .
Text label	Mandatory. A text label of up to 50 characters. This also appears on the Symbol in the Worksheet .
Class	One of Procedural, Physical or Circumstantial must be selected
Type	Parallel/Splitter (see above)
No. of outputs	A figure between 2 and 5
Output Descriptions	A description of each output of up to 50 characters.
Weighting	For a Splitter Symbol a weighting must be entered for each output in the range 01 - 99. The sum of the weightings must be equal to 100. The input value will be distributed accordingly.

Basic Events

These are primary failures of equipment or human actions

The Basic Event output provides input for Gates only. It supports no inputs.

Each time a new Basic Event is created the Basic Event Screen is displayed in order to enter further information

The following fields may be entered:-

Symbol Id	Mandatory 16 characters defining the Symbol as follows: · Characters 1-2 - always set to BE · Characters 3-4 - set to PH(Physical), PR(Procedural) or CR(Circumstantial depending on the category selected) · Characters 5-10 - set by the Classification code selected · Characters 11-12 - set by the Company code selected · Characters 13-16 – 4 digits uniquely defining the Symbol NB If Symbol Rules off is selected, the Symbol ID can be any characters up to a length of 20.
Classification	Using the … button select the classification code which this Base Event most closely fits, the Category is automatically set accordingly.
Text label	Mandatory. A text label of up to 50 characters. This also appears on the Symbol in the Worksheet .
Description	Optional description of up to 250 characters.
Probability	A decimal number greater than 0 and up to 1 (default value is 1).
Frequency	A decimal number defining the Frequency .

In-Connectors

Connectors are essentially continuity pointers to the rest of a large Model which cannot be contained on a single Worksheet . An In-Connector must be linked from an Out-Connector on another Worksheet in the same Model.

An In-Connector can link to:-

· a Barrier input

· a Consequence

· an Auxiliary Symbol input

Each time a new In-Connector is created the Connector Screen is displayed in order to enter further information.

The following fields may be entered:-

Symbol Id	Mandatory. From 5 to a maximum of 10 characters defining the Symbol . It appears on the Symbol in the Worksheet .
Text label	Mandatory. A short description of the In-Connector. This also appears on the Symbol in the Worksheet .
Description	Optional description of up to 250 characters.

Out-Connectors

Connections can be made from Out-Connectors to In-Connectors in the same Model.

An Out-Connector originates from:--

· Barrier output(s)

· Auxiliary Symbol output(s)

Each time a new Out-Connector is created the Connector Screen is displayed in order to enter further information.

The following fields may be entered:-

Symbol Id	Mandatory from 5 to a maximum of 10 characters defining the Symbol . It appears on the Symbol in the Worksheet .
Text label	Mandatory. A short description of the Out-Connector. This also appears on the Symbol in the Worksheet .
Description	Optional description of up to 250 characters.
Link to	A list of the Symbol -Ids of the existing In-Connectors in the Model. The user must select the name of the In-Connector to be linked to this Out-Connector from the list.

Connecting Symbols on the Worksheet

To connect two Symbols, the user must carry out the following steps:

1. Click on the source Symbol . A dot will appear in the centre of the selected Symbol. Click on the centre dot and drag the connection to the target Symbol. A line will be drawn as the mouse is dragged to indicated the area covered by the new Relation. An arrow head determines the logic flow.
NB: If you want to draw a specific Barrier connection make sure you select the right mode using the toolbar buttons before making the connection:
Red - Relation is the Fail Connection
Green - Relation is the Success Connection

2. Release the left mouse button when over a target Symbol . These two Symbols are now connected. Repeat this procedure to add any number of Relation lines.

3. If the connection violates any of the predefined rules, then the Relation is not permitted and a relevant message is displayed on the lower status bar.

4. If the source Symbol is an Auxiliary Symbol then the user is prompted to define which of up to five outputs (ports) you are defining. Each output may only be used once. The Relation then has a label denoting the connection number.

Editing, Moving and Deleting Symbols and Relations

Editing Symbols

To select a Symbol click on it and a selection rectangle with handles in the corners and on the sides will appear.

To edit the Symbol details (Symbol Id, Text label etc.), double-click on the Symbol and the relevant Symbol detail screen will be displayed allowing the user to change the fields. Each type of Symbol has a different detail screen as described above.

To resize a Symbol select it and drag one of the handles using the left mouse button until the desired size is reached. Then release the mouse button and the Symbol will be redrawn at the new size.

Editing Relations

To select a Relation click on it and handles will be drawn at various points of the line. You can re-shape the line by clicking on one of the line handles, dragging it across the worksheet and release the mouse button.

Selecting a relation and pressing right mouse click will allow the following two options:

Add Link Text	A dialogue screen will appear to allow the user to key in free format text to describe the relation. This text will appear against the relation on the worksheet
Remove Link	This will delete the relation from the worksheet

Moving Symbols

To move a Symbol select it and keeping the left mouse button depressed, drag the mouse. A shadow image of the Symbol being moved will be displayed. When the Symbol has been re-positioned, release the mouse button and the Symbol is redrawn in the new position, moving all the connecting lines with it.

Copying Symbols

Symbols can be copied by selecting a Symbol or a group of Symbols and or pressing right mouse click and selecting Copy from the menu. The following prompt screen will appear:

Enter a name for the Symbol or group of Symbols that you are copying and press ‘OK’. The items you have copied will be placed in the Clipboard Library for future use.

To paste a group of copied Symbols into the worksheet you have to go to the Clipboard Library . Press the CLIP icon at the top of the screen. The Clipboard Library screen will be shown:

The clipboard library allows you to keep a permanent library of copies of Symbols or groups of Symbols as required. The following options are available:

Copy to Library
Delete	This will delete the entry from the library
Paste	This should only be available if you have selected an entry in the clipboard library. The contents of the clipboard entry will be pasted onto the worksheet .
Exit	This closes the form and returns to the worksheet

When copying a Symbol all the details entered for it will also be copied. The Symbol Detail screen will be displayed so that the user can change any details required (NB the Symbol Id must be changed).

N.B. Only Symbols can be copied, not the relation lines attached to them.

Deleting Symbols

To delete a Symbol select it and press the Delete key or select Edit/Delete from the Worksheet menu. When deleting a Symbol all the Relation lines connected to it will also be deleted.

Deleting Relation Lines

To delete a Relation Line select it and press the Delete key or select Edit/Delete from the Worksheet menu.

Printing the Worksheet

If the File/Print Worksheet option is selected the Worksheet can be printed. The following panel appears to assist the printing; the required printer must be selected.

Verification and Integrity Check of the Hazard

Although much of the validation process is carried out as the Hazard is being drawn there are some checks that cannot be completed until the whole Model is complete.

This function is carried out by selecting the relevant Hazard, clicking on the RH mouse button and selecting Validate Hazard.

The checks carried out include:-

· Ensuring that the Critical Event is specified.

· Ensuring that all the In- and Out- Connectors are correctly linked up.

· Ensuring that all Symbols have the correct number of inputs and outputs.

· Ensuring that In-connectors coming from a Logic tree can connect only with Base Events, Critical Events and Barriers, and that only one such connection is made.

If no errors are found the message Hazard validated – no Errors found appears at the bottom of the screen.

If one or more errors are found, the Hazard Validation Screen is displayed with the errors listed. A quick way of correcting these errors is to double-click on the relevant error in the list. This will display the Worksheet in question so that the correction can be made. The Worksheet should then be saved and exited.

The Refresh Error List button on the Hazard Validation Screen can then be pressed to check that all errors have been eliminated.

Links and Associations

Once all the individual Models have been built into the system, these can be amalgamated into one Integrated Model using the Model Association Worksheets. These allow the Models to be linked in various ways:-

1. A Real Consequence of one Model can determine the frequency of a Base Event of another Model.

2. A Critical Event of one Model can determine the frequency of a Base Event of another Model.

Virtual Consequences can be created by combining several differing Consequences from Individual Models . For example, the user may wish to create a “Broadly Safe” Integrated Consequence as the sum of lots of un-important individual Consequences such as Near Miss, Minor Delay etc. In this case the information passed from each Real Consequence is the calculated risk for each risk category.

As well as the above connections, links can be processed in the following ways:-

1. They can be split into 2 outputs with different weightings by means of Splitter symbols

2. They can be logically processed by means of AND and OR gates

3. Several links may be summed into a single link by means of Super Connector symbols.

4. The Model Association diagram can stretch over many Worksheets by means of In and Out connector symbols.

The Model Association Worksheet Editor

To create a new Model Association Worksheet RH mouse click on Links and Associations in the Explorer screen and select Add Worksheet. Enter the Worksheet name and a new Worksheet will appear in the list.

To edit this Worksheet double-click on it.

The new Model Association Worksheet Editor operates in a similar way to the Consequence and Causal Worksheet Editors.

Symbols are entered on the Screen by clicking the RH mouse button and selecting the required symbol from the list.

Connections are made between symbols by selecting the originator symbol and dragging the mouse from the centre of this source symbol to the centre of the target symbol, drawing a connecting line.

The available Model Association Symbols and the possible connections associated with each one are described on the following pages.

Model

A list of all available Models is displayed. This list can be scrolled until the required Model is found. On selecting a Model the symbol is placed on the Worksheet with the Model name beside it.

No editing can be performed on the Model symbol itself, however the following types of connections can be made from the Model:-

Model to Virtual Consequence (Risk link)
Model to Out Connector (Risk link)
Model to Risk Super Connector (Risk link)
Model to Frequency Super Connector (Frequency link)
Model to Risk Splitter (Risk link)
Model to Frequency Splitter (Frequency link)
Model to Model (Frequency link)
Model to AND/OR Gate (Frequency link)

In the case of a Frequency link the user will be asked whether the connection is from a Consequence. If the user selects Yes, a list of the available Consequences for this Model is displayed so that the required Consequence can be selected. Otherwise a list of the available Critical Events (normally only one) is displayed.

In the case of a Risk link a list of the available Consequences is displayed automatically.

Each Consequence or Critical Event can have only 1 output.

The selected Consequence is then drawn above the Model symbol on the Worksheet.

In the case of a Model to Model link the user is then presented with a list of the available Base Events in the target Model and must then select the required one. This Base Event is then also drawn below the target Model. A Base Event can have several inputs.

Virtual Consequences

Virtual Consequences are a conceptual summation point for several Consequences from different Hazards.

The user can either create a new Virtual Consequence or can select one previously created in ISAE.

If a new one is created the following screen is shown:

The following fields may be entered:-

Name	Mandatory. From 5 to a maximum of 10 characters defining the Symbol . It appears on the Symbol in the Worksheet and must be unique.
Description	Mandatory. A short description of the In-Connector. This also appears on the Symbol in the Worksheet .
Group	Optional. Can be se selected from the drop-down list.

The Virtual Consequence details can be edited by double-clicking on the symbol.

Virtual Consequences can have only 1 output.

A Virtual Consequence can only be connected to another Virtual Consequence or to an Out-Connector.

Super Connectors

Super Connectors allow several inputs to be summed into one output. All inputs to the Super Connector must be of the same type i.e. either Frequencies, Probabilities or Risks.

If inputs are Frequencies or Probabilities the output is the sum of all niputs.

If inputs are Risks, the output is the sum of the risks for each of the 13 Risk categories.

The user is asked whether the inputs to this Super Connector are Risks. If so a Risk Super Connector is created, otherwise a Frequency Super Connector is drawn.

Super Connectors can have only 1 output.

No editing can be performed on the Super Connector symbol itself, however the following types of connections can be made from the Super Connector:-

Risk Super Connector to Virtual Consequence (Risk link)
Risk Super Connector to Out Connector (Risk link)
Risk Super Connector to Risk Super Connector (Risk link)
Frequency Super Connector to Frequency Super Connector (Frequency link)
Risk Super Connector to Risk Splitter (Risk link)
Frequency Super Connector to Frequency Splitter (Frequency link)
Risk Super Connector to Out Connector (Risk link)
Frequency Super Connector to AND/OR Gate (Frequency link)

Splitters

Splitters allow several inputs to be split into 2 outputs according to the specified allocation percentage for each output. All inputs to the Splitter must be of the same type i.e. either Frequencies, Probabilities or Risks.

The following Screen is shown:

If the user selects the Outputs to be Frequencies or Probabilities the split percentage of the first Split must be entered as a value between 0 and 100. The second Split value will then be automatically calculated. The Description fields can also be entered.

Each output is the percentage allocation of the inputs – in this case Output 1 (Pedestrian ) will be allocated 90% of the input Frequencies/Probabilities and Output 2 (Road Vehicle) will be allocated 10%.

Similarly if the user selects the Outputs to be Total Risk, the 2 percentage values are calculated in the same way.

Each output is the percentage allocation of the inputs applied to all the Risk categories lumped together in this case Output 1 (Pedestrian ) will be allocated 90% of the input Risks values for all Risk Categories and Output 2 (Road Vehicle) will be allocated 10%.

However if the user selects Individual Risk the screen appears as follows

In this case the user can specify a different percentage allocation for each of the 13 Risk Categories.

For example Output 1 (Pedestrian ) will be allocated 10% of the input Risks for the Worker Loss of Life category and Output 2 (Road Vehicle) will be allocated 90% of the input Risks for the same category.

Splitters can have only 2 outputs.

The following types of connections can be made from the Splitter:-

Risk Splitter to Virtual Consequence (Risk link)
Risk Splitter to Out Connector (Risk link)
Risk Splitter to Risk Super Connector (Risk link)
Frequency/Probability Splitter to Frequency Super Connector (Frequency link)
Risk Splitter to Risk Splitter (Risk link)
Frequency/Probability Splitter to Frequency Splitter (Frequency link)
Risk Splitter to Out Connector (Risk link)
Frequency Splitter to AND/OR Gate (Frequency link)

AND and OR Gates

These symbols perform logical operations on the inputs to produce one output in each case. The algorithms are the same as those for the Gates in the Consequence and Causal domains.

Only Frequencies and/or Probabilities can be linked to the gate.

AND and OR Gates can have only 1 output.

The following types of connections can be made from the AND/OR Gate:-

AND/OR Gate to Base Event (Frequency link)
AND/OR Gate to Frequency Splitter (Frequency link)
AND/OR Gate to Frequency Super Connector (Frequency link)

IN and OUT Connectors

These symbols are used to connect Worksheets. These Connectors have the same functions as Virtual Consequences except that they can be linked across Worksheets. Only Risk links may be connected in this way.

When a Worksheet is full an Out-Connector must be created so that the diagram can be continued on another Worksheet. The user will be asked to give a unique name to this Out-Connector.

Out-Connectors can only be linked to In-Connectors.

An In-Connector must then be drawn on the succeeding Worksheet. A list of the available Out-Connectors will be displayed and the user must select the one to be connected to this In-Connector. If there are no Out-Connectors then an In-Connector cannot be created.

The following types of connections can be made from an In-Connector:-

In-Connector to Virtual Consequence (Risk link)
In-Connector to Risk Super Connector (Risk link)
In-Connector to Risk Splitter (Risk link)

Validating the Model Association Worksheets

Before a World IALF can be run, the Model Associations must be validated..

Although much of the validation process is carried out as the Model Associations are being drawn there are some checks that cannot be completed until the whole World Model is complete.

To do this RH mouse click on Links and Associations in the Explorer screen and select Validate Model Associations.

The checks carried out include:-

· Ensuring that each Splitter has 2 outputs.

· Ensuring that all the In- and Out- Connectors are correctly linked up.

· Ensuring that Symbols have the correct number of inputs and outputs.

If no errors are found the message Valdiation complete – no Errors found appears at the bottom of the Explorer screen.

If one or more errors are found, the Model Association Validation Screen is displayed with the errors listed. A quick way of correcting these errors is to double-click on the relevant error in the list. This will display the Worksheet in question so that the correction can be made. The Worksheet should then be saved and exited.

The Refresh Error List button on the Model Association Validation Screen can then be pressed to check that all errors have been eliminated.