39
What Makes a Task Safety Critical?
FIGURE 3.2 The distinction between “ barriers” and “r obust solutions” (P SA, 2017).
such as how criteria for operational envelopes are defined, e.g. in terms of which
weather and ocean conditions are allowed under.
Barriers refer to functions which can identify triggering events and prevent them
from developing into an undesirable incident or which can mitigate possible losses
in case such incidents should occur. Safety critical tasks characterized as operational
barrier elements arguably first come into play as part of functions for monitoring
hazardous conditions and detecting failures with potential for escalation. Arguably
they are not to be considered a part of ensuring as “ robust solution”. This implies that
operational barrier elements are partly “p re-selected” as safety critical task through
how they are defined as being part of a barrier function implemented for MAHs.
The most noticeable challenges when identifying operational barrier elements is
to decide on where to draw the line between safety critical tasks being a part of
the robust solution and safety critical tasks being a part of barrier functions ( i.e.
operational barrier elements). As an aid in making this distinction, the categorization of safety critical tasks into Type A, B and C actions can be useful ( Øie et al.,
2014). As shown in Table 3.3, operational barrier elements are either categorized as
Type C and, in some cases, Type B actions (p lease note that the terms “ failures” and
“ incidents” here refer to those related to MAHs and not to occupational accidents).
Type A actions falls outside the definition of what is considered an operational
barrier element because it does not involve continuous or on demand monitoring and
control of barrier functions. For Type B actions, it may not always be clear cut whether
the safety critical task represents an operational barrier element or not. Examples
can be performing a crane lifting operation with the potential of dropped objects
onto critical structures or maintaining containment during maintenance on equipment
containing pressurized hydrocarbons. In such cases, precautionary steps necessary to
prevent a MAH incident from being triggered (T ype A) often coincides with actions
taken to observe and deal with initiating events (T ype C). While the former could be
What Makes a Task Safety Critical?
FIGURE 3.2 The distinction between “ barriers” and “r obust solutions” (P SA, 2017).
such as how criteria for operational envelopes are defined, e.g. in terms of which
weather and ocean conditions are allowed under.
Barriers refer to functions which can identify triggering events and prevent them
from developing into an undesirable incident or which can mitigate possible losses
in case such incidents should occur. Safety critical tasks characterized as operational
barrier elements arguably first come into play as part of functions for monitoring
hazardous conditions and detecting failures with potential for escalation. Arguably
they are not to be considered a part of ensuring as “ robust solution”. This implies that
operational barrier elements are partly “p re-selected” as safety critical task through
how they are defined as being part of a barrier function implemented for MAHs.
The most noticeable challenges when identifying operational barrier elements is
to decide on where to draw the line between safety critical tasks being a part of
the robust solution and safety critical tasks being a part of barrier functions ( i.e.
operational barrier elements). As an aid in making this distinction, the categorization of safety critical tasks into Type A, B and C actions can be useful ( Øie et al.,
2014). As shown in Table 3.3, operational barrier elements are either categorized as
Type C and, in some cases, Type B actions (p lease note that the terms “ failures” and
“ incidents” here refer to those related to MAHs and not to occupational accidents).
Type A actions falls outside the definition of what is considered an operational
barrier element because it does not involve continuous or on demand monitoring and
control of barrier functions. For Type B actions, it may not always be clear cut whether
the safety critical task represents an operational barrier element or not. Examples
can be performing a crane lifting operation with the potential of dropped objects
onto critical structures or maintaining containment during maintenance on equipment
containing pressurized hydrocarbons. In such cases, precautionary steps necessary to
prevent a MAH incident from being triggered (T ype A) often coincides with actions
taken to observe and deal with initiating events (T ype C). While the former could be