43
What Makes a Task Safety Critical?
factors in addition to “ consequence”, namely, task complexity and task frequency.
This, however, is not accompanied by any definitions of the various levels, and criticality is primarily indicated in terms of how strict the use of procedures should be
during operations. As such, this matrix did not prove to be a viable solution.
Running out of options, the final solution was to develop a method specifically
suitable for operational barrier elements. As shown in T able 3.2, the purpose of the
criticality ranking was to support decisions about whether to perform detailed or
coarse analysis of the operational barrier element ( Steps 3 and 4) and whether to
implement the operational barrier element as part of the system for barrier management ( Step 5). Experiences made from attempting to apply the methods published by
Health and Safety Executive UK and EI suggest that the criticality ranking should
include certain properties. It should be
• as accurate as possible to determine scalable ( high, medium and low) task
criticality, but without having to perform much, or if any, analysis and
• generic in the sense that it allowed ranking of operational barrier elements
associated with a wide variety of systems and operations ( marine, production, drilling, etc.).
Although neither of the available guidelines included a directly applicable method
for assessing criticality, together they offer valuable insights about what makes a
task safety critical. These insights were combined with the context provided by the
framework and definitions of barrier management to suggest a set of characteristics
of what determines task criticality.
Major accident hazard severity. The first question to be asked is if the operational
barrier element is associated with a barrier function implemented to manage risks
associated with MAHs. Establishing this link was also suggested by the EI guideline
( 2011) as part of the safety critical task identification, but it was not made part of the
tools recommended for rating criticality. What constitutes a major accident may vary
from company to company and/ or from regulator to regulator. Most companies do,
however, have this defined as part of their risk management philosophy, e.g. as risk
acceptance criteria operationalized by use of risk matrices.
A MAH with potential high level of severity could be one which immediately
results in multiple fatalities ( e.g. 5) if triggered, such as process fires. A MAH of
medium severity could be one which is limited to cause injuries or a lower number of
fatalities and only results in major accident losses in case of escalation. An example
could be an electrical fire in the utility area of an installation which does not have an
immediate effect on any main safety functions and which requires significant escalation to cause losses defined as a major accident. A MAH of low severity only has
the potential to cause losses defined as occupational accidents ( e.g. injuries or single
fatalities) or minor environmental impacts.
Definitions of the “ major accident hazard ( MAH) severity” levels are described
in Table 3.5.
Consequence ( from task failure). The next characteristic of a safety critical task is
to what degree the consequences from a failure have the potential to contribute to the
causation or realization of a major accident. This was also covered by both the EI and
What Makes a Task Safety Critical?
factors in addition to “ consequence”, namely, task complexity and task frequency.
This, however, is not accompanied by any definitions of the various levels, and criticality is primarily indicated in terms of how strict the use of procedures should be
during operations. As such, this matrix did not prove to be a viable solution.
Running out of options, the final solution was to develop a method specifically
suitable for operational barrier elements. As shown in T able 3.2, the purpose of the
criticality ranking was to support decisions about whether to perform detailed or
coarse analysis of the operational barrier element ( Steps 3 and 4) and whether to
implement the operational barrier element as part of the system for barrier management ( Step 5). Experiences made from attempting to apply the methods published by
Health and Safety Executive UK and EI suggest that the criticality ranking should
include certain properties. It should be
• as accurate as possible to determine scalable ( high, medium and low) task
criticality, but without having to perform much, or if any, analysis and
• generic in the sense that it allowed ranking of operational barrier elements
associated with a wide variety of systems and operations ( marine, production, drilling, etc.).
Although neither of the available guidelines included a directly applicable method
for assessing criticality, together they offer valuable insights about what makes a
task safety critical. These insights were combined with the context provided by the
framework and definitions of barrier management to suggest a set of characteristics
of what determines task criticality.
Major accident hazard severity. The first question to be asked is if the operational
barrier element is associated with a barrier function implemented to manage risks
associated with MAHs. Establishing this link was also suggested by the EI guideline
( 2011) as part of the safety critical task identification, but it was not made part of the
tools recommended for rating criticality. What constitutes a major accident may vary
from company to company and/ or from regulator to regulator. Most companies do,
however, have this defined as part of their risk management philosophy, e.g. as risk
acceptance criteria operationalized by use of risk matrices.
A MAH with potential high level of severity could be one which immediately
results in multiple fatalities ( e.g. 5) if triggered, such as process fires. A MAH of
medium severity could be one which is limited to cause injuries or a lower number of
fatalities and only results in major accident losses in case of escalation. An example
could be an electrical fire in the utility area of an installation which does not have an
immediate effect on any main safety functions and which requires significant escalation to cause losses defined as a major accident. A MAH of low severity only has
the potential to cause losses defined as occupational accidents ( e.g. injuries or single
fatalities) or minor environmental impacts.
Definitions of the “ major accident hazard ( MAH) severity” levels are described
in Table 3.5.
Consequence ( from task failure). The next characteristic of a safety critical task is
to what degree the consequences from a failure have the potential to contribute to the
causation or realization of a major accident. This was also covered by both the EI and