TSA Insight Magazine Issue 6 - Magazine - Page 33
Ian Travers, Director, Ian Travers Limited
www.iantravers.co.uk
www.iantravers.co.uk
Deciding on the Most Important Tasks
From the initial list of category 3 and 4 tasks the next stage is to select those which make the greatest
contribution to controlling the risk of a major incident. This is done by applying the matrix shown in Figure
2. Each task should be ranked by its relative importance to preventing a major incident. For example, in the
prevention of overfilling a tank during loading, checking the ullage space in the tank before adding product
could be considered as more important then say monitoring the rate of filling. This is not to say both are not
important, but this sifting stage is aimed at ranking all the tasks first identified. The guide words ‘helpful’,
‘important’ and ‘vital’ help with these judgements. The next issue to consider is the potential consequence
of an error made for each task. So if an error would either immediately, or at some time later, result in a
major incident then it should be ranked as ‘Serious’, alternatively, if the consequence could only be minor,
even performed incorrectly, it should be classed as ‘minor’. For example, routing product into the wrong
tank, if the products were incompatible and could cause an adverse reaction would be considered serious
whereas routing the product to the wrong tank where the result has only quality but no safety implications,
could be considered as ‘Minor’ in consequence.
Figure 2: Deciding on the most critical safety related tasks
The first tranche of safety critical tasks subject to reliability analysis should be those rated as high criticality.
Probability of Error
A short summary of HSE’s job-related performance influencing factors, PIF’s, are used to decide what the
risk of error is for each task selected from the criticality analysis stage. These factors are shown in Figure
3. A simple scoring system is used to rate each PIF. Each factor is scored using 6 points if the factor is not
met, zero if it is fully satisfied and for any uncertainty or only partial compliance – 3. The example shown in
Figure 3 rates the chance of error as ‘high’ because there is no written procedure or clear indications on the
plant / equipment to guide people to the correct actions.
Opportunity for Recovery
Some errors may be discovered in time to prevent a major incident. Figure 4 shows the factors to consider
when making these judgements. In this case there is a ‘moderate’ chance of recovery of an error in this task.
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