D E PA R TM E NT S • H S E&T CO RN ER
Safety-critical task analysis is
not a silver bullet, but it can help
improve procedural integrity
Undertaking systematic process to identify
human factors issues can lead organizations
to focus on major accident hazards
BY VARUN SARPANGAL, MAREX
The term “human factors” has been in use
for over four decades in the drilling indus-
try. However, even today, there can be lim-
ited understanding in the field about what
the term actually covers. Often, there is a
misconception that it is just about human
behavior. While that is certainly part of the remit,
human factors is mainly about engineer-
ing (or re-engineering) the tasks, work
equipment and work environment in order
to get the best out of the people who are
carrying out the tasks.
The overall aim is to minimize the like-
lihood of accidents and improve safety in
the workplace.
The drilling industry has seen some
turbulent times of late. While companies
continue to look to optimize their opera-
tional costs, the costs associated with
human factors integration might appear
to be a deterrent for companies. While
it can be difficult to quantify the long-
term financial benefits of human factors
integration, the true benefit lies in what
it can offer in terms of major accident
prevention. It is arguable that with all the cost-
cutting measures the industry has seen
over the past few years, the risk of human
failure causing major accidents is now
considerably higher. Organizations should
remind themselves that the cost of car-
rying out these assessments and imple-
menting improvement measures would be
substantially lower than the cost of major
accidents. 52
Safety critical
When “human factors” is used in the
context of major accident hazards, it
concerns the severe consequences that
human failures can bring about in safety-
critical industries, such as drilling. It is
a statistically validated fact that a vast
majority of major accidents have some
level of “human error” as part of their root
cause. “Lack of situational awareness” is one
example of human failure that appears
in incident investigation reports. For
instance, the driller not gleaning crucial
information about certain changes in the
well at the right time could result in a
blowout that has catastrophic outcomes.
However, digging a bit deeper, it can be
seen that there are underlying human per-
formance influencing factors (PIFs) that
lead to such human failures.
Examples of PIFs that might affect the
driller’s situational awareness are fatigue,
distractions or a high cognitive workload
due to a poorly designed human-machine
interface. The best way to prevent human factors
issues from leading to costly accidents is
to proactively and pre-emptively carry out
a systematic study to identify and under-
stand the PIFs, and make sure they are
brought to their optimal states and main-
tained during ongoing operations.
Safety-critical task analysis
Safety-critical task analysis (SCTA), a
process that encompasses human reli-
ability analysis (HRA), can help achieve
this objective. The process consists of four
key steps:
1. Identification of safety-critical
tasks Safety-critical tasks are defined as those
tasks where human factors could cause,
contribute to, or fail to reduce the effect of
a major accident.
The first step of an SCTA involves iden-
tifying all safety-critical tasks. One of the
primary sources of data that could be used
for this step is the bowtie major hazard
analyses for the drilling installation. Its
output can be qualitatively analyzed to
identify all the associated tasks that are
required to make sure major accident haz-
ard control and mitigation barriers remain
in place and are effective. The resulting
information will be a list of safety-critical
tasks for further assessment and screen-
ing. 2. Prioritization ranking
of safety-critical tasks
As task characteristics and the sever-
ity of consequence of human failure in
carrying out the task correctly vary, some
safety-critical tasks can be more critical
than others. These need a more in-depth
assessment. A process for allocating a
priority ranking to each task has to be
established. There is guidance from the UK Health
and Safety Executive (HSE) on assessment
of safety-critical tasks and the Energy
Institute’s guidance on SCTA, which could
be used for the prioritization exercise. This
guidance would have to be appropriately
modified and tailored to suit the opera-
tions of the drilling installation.
Providing scores for the two aspects of
task characteristics and the severity of
consequence for each safety-critical tasks
allows the tasks to be ordered by overall
priority score. This can then be used to
group the tasks into high, medium and
low. The organization can then start by ana-
lyzing the high criticality tasks, before
moving on to the lower priority ones. The
scoring and prioritization of safety-critical
tasks should ideally be completed in a
workshop setting with members of the
workforce who have a detailed operational
understanding of the tasks.
NOVEMBER/DECEMBER 2022 • DRILLING CONTRACTOR
H S E&T CO RN ER • D E PA R TM E NT S
3. Development of hierarchical
task analysis diagrams
In order to assess the levels of human
interaction with systems and equipment,
a suitable assessment tool that uses a
systematic approach is needed to identify
potential for human failures within tasks.
Task analysis methods are used to
understand what is being carried out,
where hazards may be present and where
errors may occur.
Hierarchical task analysis (HTA), as the
name suggests, places a hierarchy on the
order of the tasks to be analyzed. It breaks
down a given human-performed activity
into goals, tasks and task steps.
The goal (the main task) is represented
at the top level, and the sub goals (task
steps) are represented at the next subordi-
nate level. The task steps, in turn, may be
broken into more detailed actions that per-
sonnel could take (sub-steps) represented
as nested boxes below each task step.
The method produces a tree structure,
along with an additional output being a
list of tasks outlining their sequencing in
order to meet the overall task goal. This
allows work procedures to be analyzed,
and various human errors and their sub-
sequent consequences can be identified.
Alongside the official company proce-
dures and work instructions for the safety-
critical tasks, other information gathered
from the worksite by the crew, such as
completed walk-through talk-through
(WTTT) templates, can be used as sources
of input toward building the task steps.
The WTTT process consists of an expe-
rienced person demonstrating how the
task is carried out onsite. It helps to under-
stand task steps, identify likely error traps
and aids discussion of how the operator
might typically deal with them. It also
helps in capturing and recording any devi-
ations from or gaps between how the offi-
cial procedures have been written (work
as imagined) and how work is actually
done on the ground (work as done).
4. Human reliability analysis
HRA is a process that uses a set of “guide
words” similar to those used in a hardware
HAZOP. The review team (similar to the
one formed for the safety-critical task
prioritization exercise) applies the guide
words to the lowest level of the developed
Driller Driller
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Driller Driller
Senior Toolpusher
Driller Driller
Driller Figure 1: An example of a hierarchical task analysis diagram.
hierarchical task analysis in order to iden-
tify the possible errors that could arise.
The guide words and questions should
be developed in line with established
methods, such as predictive human error
analysis and the systematic human error
reduction and prediction approach.
This exercise ensures that any devia-
DRILLING CONTRACTOR • NOVEMBER/DECEMBER 2022
53