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Safety and environmental standards for fuel storage sites
Final report
121
210 This is followed by a review of the key tasks to identify the potential errors within each task
that could lead to the hazardous event under consideration. Techniques for this include (among
others):
Tabular Task Analysis.
■
‘Human HAZOP’.
■
The output of this can be summarised in a critical task list (Table 14):
Table 14
Critical task list
Critical activity and/or task Nature of the error leading
to the hazardous event of
tank overflow
Performance shaping
factors relating to the task
that could influence the
probability of error
Opening manual routing valve
between the transfer pump
discharge and a designated
receiving tank
Opening the wrong valve and
thereby transfer the tank under
review
Poor labelling of valves
–
All communication by single
–
channel radio from the control
room
Significant proportion of new
–
process operators with little
on-site experience
Human error probability assessment
211 Figure 29 illustrates the process of assessing the human error probability (HEP) for the critical
task or key step within the task.
Figure 29
Process for assessing human error probability
212 The steps in the assessment process are as follows:
Select an appropriate ‘generic’ human error probability, based on the task type and/or the
■
nature of the error.
This human error probability could then be modified based on the performance shaping
■
factors or error producing conditions relating to the people carrying out the task and the
conditions under which they are working.
213 There are a number of standard methods such as APJ (Absolute Probability Judgment),
HEART, THERP etc to assess the potential error probability. However, these require a level of
training and specialist understanding to use and those new to the assessment of human error
probability should seek assistance.
Critical task list
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Select task or key step
Generic (random)
human error probability
Systematic factors
PSF or EPC
Task type
Assessment of
human error probability
(HEP) for task