The output of the Cause Consequence Analysis
is a Risk Model which requires quantification and simulation. The Algorithm
File is intended to capture the underlying logic, arising from the Symbols and
their interconnections in a Model, and facilitate further processing. The ALF
is a spreadsheet representation of the Model in Excel format.
ALFs can be generated on three levels:
To Generate a Hazard ALF select the required
Hazard in the Explorer tree. Press right
mouse click and select Generate ALF.
NB
Before an ALF can
be generated, the Hazard must have been validated using the Verify function.
A spreadsheet is
produced showing the Probabilities or Frequencies for each of the Symbols within
the selected Hazard. This Spreadsheet can be saved or printed using the relevant
buttons. A description of the formulae used to calculate the Probability or
Frequency for each Symbol in the Spreadsheet is given below.
Row 4 of the Spreadsheet
shows the Critical Event and its Frequency/Probability.
This can determined
in one of three ways:-
Columns L to O show
the Local and Global Sensitivity and Importance of the Critical Event.
The Local Importance is calculated as the Output
value for this Barrier divided by the Input value for the succeeding Symbol.
The Global Sensitivity is calculated as the
Local Sensitivity of this Barrier multiplied by the
Global Sensitivity of the succeeding Symbol.
The Global Importance is calculated as the
Local Importance of this Barrier multiplied by the Global Importance of the
succeeding Symbol.
The Local Sensitivity of an AND Gate is 1.
The Local Sensitivity of an OR gate feeding
another OR Gate is 1.
The Local Sensitivity of an OR gate feeding
an AND Gate is calculated as the Input value of the AND Gate divided by the
input value of this OR Gate.
The Local Importance of an AND Gate is calculated
as the Input value of the succeeding symbol divided by the input value of this
AND Gate.
The Local Sensitivity of an OR gate feeding
an AND Gate is 1.
The Local Sensitivity of an OR gate feeding
another OR Gate is calculated as the Input value of the succeeding OR Gate divided
by the input value of this OR Gate.
The Global Sensitivity is calculated as the
Local Sensitivity of this Gate multiplied by the
Global Sensitivity of the succeeding Symbol.
The Global Importance is calculated as the
Local Importance of this Gate multiplied by the
Global Importance of the succeeding Symbol.
The Local Sensitivity of a Frequency Base Event
is 1.
The Local Sensitivity of a Probability Base Event (BE2) is calculated
as (1- BE1) * (1-BE3) where BE1, BE2 and BE3 all feed the same Gate.
The Local Importance is calculated as the Input
value of the Base Event divided by the input value of the succeeding symbol.
The Global Sensitivity is calculated as the
Local Sensitivity of this Base Event multiplied by the
Global Sensitivity of the succeeding Symbol.
The Global Importance is calculated as the
Local Importance of this Base Event multiplied by the
Global Importance of the succeeding Symbol.
A Project ALF groups together all the Hazards
of a single Project into one Excel File.
To Generate an Integrated ALF select the required
Project in the Explorer tree. Press right mouse click and select Generate
Integrated ALF.
NB
Before an ALF can
be generated, each of the Hazards must have been validated using the Verify function.
Also, as the IALF
refers to data contained in the World ALF sheet, a World ALF must have been
previously generated (see next Section).
The user is asked
to select whether the ALF should be in Black and White – this is preferable
if the Spreadsheet is to be printed on a black and white printer.
The user must then
select a Loss Category. This will be the category selected for the Sensitivity
and Importance of each of the Consequences on the individual ALF sheets.
The completed Project
IALF consists of an initial Summary sheet, followed by the individual Hazard
ALF sheets, and ending with the IALF sheet.
The IALF file is saved under :
C:\PROGRAM FILE\ISAE\DATA\projectname\ALF-padname.xls
An additional Excel
sheet containing the GLEE data for each Accident is also produced.
The first sheet of the IALF shows the Project
ID and Name and lists all the Hazards included in the Project.
The second and subsequent Sheets of the IALF
(except the last) contain the ALF for each Hazard as described in the previous
section. Each of these sheets is named after the Sheet number and the Critical
Event ID.
The only difference from the Hazard ALF is
that for each Consequence listed the Global Sensitivity and Importance for the
selected category is shown in columns H and I. These values are taken from the
IALF sheet.
The final Sheet of the IALF contains a list
of all the Consequences in the Project together with the calculated Probabilities/Frequencies
and the Loss values for each of the Risk categories.
The Probability/Frequency in column G is taken
from the individual ALF sheet.
The values for each Loss Category (Worker Loss
of Life etc) are calculated as the Probability/Frequency multiplied by the GLEE
data for that Category as taken from the GLEE sheet, depending on the Accident
Number assigned to the consequence.
The Local and Global Sensitivity and Importance
for each Loss Category are also calculated and shown in the columns to the right
of each Loss Category.
The Local Sensitivity is the GLEE value for
that Category and Accident number.
The Local Importance is calculated as the Loss
value for this Consequence divided by the Loss value for the succeeding Symbol
on the World IALF sheet (usually an Integrated Consequence).
The Global Sensitivity is calculated as the
Local Sensitivity of this Consequence multiplied by the
Global Sensitivity of the succeeding Symbol.
The Global Importance is calculated as the
Local Importance of this Consequence multiplied by the
Global Importance of the succeeding Symbol.
The World IALF applies across all projects
defined in ISAE.
To Generate a World IALF double-click on the
World icon Hazard
Processing in
the Explorer tree. Then expand the Mathematical Model icon. Finally double-click
on Generate World IALF.
The World ALF can also be generated by clicking
on the relevant toolbar button at the top of the Explorer Screen.
As before, all Hazards must have been validated
before the World ALF will run. Also the Model Associations must have been previously
validated.
Before the World IALF generation starts a warning
message is displayed informing the user that this process takes some time and
that all World ALF files previously created must be closed.
The World IALF process creates an Excel file
for each Project in the System and also creates a World ALF book listing the
values for all Integrated Consequences.
All the World IALF files are saved under :
C:\PROGRAM FILE\ISAE\DATA\WORLD-padname\project.xls
These files are identical to the Project IALF
files described in the previous chapter.
The World IALF book is saved under :
C:\PROGRAM FILE\ISAE\DATA\WORLD-padname\ALF-WORLD.xls
The World IALF book consists of 2 Excel sheets.
Sheet 1 (WIALF) contains a list of all
the Integrated Consequences that have been defined in the Model Associations
worksheets in column B.
In cell M1 the user can enter the name of a
selected Integrated Consequence. This is taken into consideration when calculating
the Global Importance and Sensitivity.
Column G shows the total Frequency for each
Integrated Consequence, which is calculated by adding the Frequencies of all
Consequences and intermittent operators feeding the Integrated Consequence.
The individual risk values for each Loss Category
are shown in columns H to CN.
The values for each Loss Category (Worker Loss
of Life etc) are calculated by adding the relevant Loss Category values for
all Consequences and intermittent operators feeding this Integrated Consequence.
The Local and Global Sensitivity and Importance
for each Loss Category are also calculated and shown in the columns to the right
of each Loss Category.
The Local Sensitivity is always 1.
The Local Importance is calculated as the Loss
value for this Integrated Consequence divided by the Loss value for the succeeding
Symbol on the World IALF sheet (usually an Integrated Consequence).
If this consequence has been selected in cell
M1 then both the Global Sensitivity and Importance are set to 1; otherwise -:
Global Sensitivity of the succeeding Symbol.
The Global Importance is calculated as the
Local Importance of this Consequence multiplied by the
Global Importance of the succeeding Symbol.
Columns CU to DM list the Frequency and Loss
values for each of the Consequences contained in the Integrated Consequences.
These values are taken directly from the relevant IALF sheets and are listed
on this sheet solely to prevent the equations for each Integrated Consequence
from becoming too long (otherwise the complete directory and file name would
have to be included for each Consequence).
Sheet 2 (WIALF2) shows the values of
all intermittent operators used in the Model Associations worksheets.
The names of all Super Connectors are listed
in column A, the names of all Splitters are in column C and the names of all
IN/OUT Connectors are in column E.
For each Splitter listed in Column C, the percentage
values for each split are shown below the Splitter name.
Columns DA and DB list the Frequency and Loss
values for each Consequence and Critical Event referred to in the calculations
for the Integrated Consequences. These values are taken directly from the relevant
ALF sheets and are listed on this sheet solely to prevent the equations for
each Integrated Consequence from becoming too long.
Individual Risk Splitters are listed in columns DF to DW which specify the splits
defined for each of the individual risk categories.
As generating the World ALF is very time- and space- consuming it is possible that the system will not complete the World ALF in one run. Occasionally it is necessary to re-start the World ALF generation from the middle using the Restart WALF Calculations item.