INTRODUCTION

Where control measures or barriers involving hardware have a relatively well-known path for managing long-term effectiveness, the approach to managing human tasks which prevent or mitigate major accidents can sometimes be less clear. The successful completion of these tasks can have a major impact on the management of hazards, so it is vital that such tasks are identified and managed in a logical, measurable and coherent manner.

There are various techniques available to support this aim, with ‘SCT’ and ‘SCTA’ often being discussed and considered as key terms and methods for identifying and managing such tasks.

TASKS

The International Association of Drilling Contractors (IADC) defines a HSE Critical Activity/Task as an “activity or task which provides or maintains barriers” (Ref. 1) which is a definition often used for bowtie analysis. Another definition, this time from the Energy Institute and with a Human Factors (HF) perspective, defines a Safety Critical Task as “a task where human factors could cause or contribute to a major accident.” (Ref. 2).

These definitions are essentially saying the same thing – critical tasks have a role to play in the management of Major Accident Hazards (MAHs), and as such require detailed consideration and analysis, with the SCTA and bowtie methods both potentially having a key role to play.

BOWTIE SCTS

The bowtie technique is commonly applied to hazards which have been identified as presenting the highest risk level at the company or site, the MAHs (Figure 1). For each MAH at the site, there is a corresponding bowtie diagram which identifies the barriers in place to prevent control of the hazard being lost, or to mitigate the consequences if control is lost. These barriers will be hardware (Safety Critical Elements), tasks/activities which people perform (SCTs), or a combination of the two.

Where an SCT is identified within the bowtie, supporting information is also recorded, including:

  • The person responsible for completing the task
  • The procedure associated with completion of the task, so the individual knows how and when to do the task
  • The means of verification of completion of the task

The bowtie method gives a robust means for identifying the tasks and the role they play in protecting against specific threats or mitigating the consequences of major accidents.

Generally, however, the bowtie will not investigate the individual steps or actions taken when performing the SCT itself, and this is where SCTA is of benefit.

Bowtie diagram

SCTA

Human psychology and physiology are not flawless, and therefore the fact that human error that can often be a potential contributor to major accidents, is an inherent part of every workplace.

Managing human failure and optimising performance are key to accident prevention, and this is best achieved by designing systems that work for people (i.e. are inherently safe), rather than relying on individuals to prevent accidents.

SCTA is a workshop-based method which identifies and analyses SCTs by assessing the task in detail, identifying types of potential human failures involved in the task, and recognising Performance Influencing Factors (PIFs) which make failures more or less likely. This analysis then assesses the measures in place to control and mitigate human error, as well as recommending additional measures where appropriate.

PREPARING FOR SCTA

In preparation for conducting SCTA, a screening exercise is undertaken to determine which on-site activities can be deemed ‘safety-critical’ and therefore require further assessment.

Often the list of procedures from the asset is a starting input for the screening exercise, however this is not a guaranteed way to catch all activities performed. There may be some not covered by procedures, so individuals are encouraged to consider all activities they perform.

UTILISING BOWTIES

So, knowing that there is a list of SCTs and their associated procedures from the bowtie analysis begs the question, how can we use this information in SCTA?

The answer is that to use it, we must also acknowledge the limitations. Where a bowtie’s strength is in identifying SCTs which have a role to play in the management of MAHs, it is not necessarily capable of catching all SCTs which can directly cause a MAH. The bowtie analysis may also not have considered scenarios outside of normal operations, for example start-up or shut-down (see Figure 2).

SCT vs SCTA

The bowtie-identified SCTs do however provide additional insight into which tasks and procedures have a role to play in MAHs. The detailed bowtie workshop has assessed every MAH, with consideration of human involvement on a threat-by-threat, consequence-by-consequence basis.

Due to this direct linkage to MAHs, the bowtie-generated SCT and procedure list therefore provides more detail regarding activities which require SCTAs than just a general list of company or asset procedures without context.

Utilisation of the information from the bowties at the SCTA screening stage, as well as input from individuals, procedure listings and other studies, can therefore ensure that all SCTs and associated procedures are captured from the outset of the SCTA process.

CONCLUSION

Where a task has been deemed as ‘safety critical’ this implies that if the task is completed incorrectly, or not done at all, there could be a serious safety implication.

These tasks can be identified and analysed in different ways, and it is important to consider that the SCT listing and supporting information from a bowtie assessment can form a useful input into the SCTA process, particularly when considered as part of the screening process.

Utilising the bowtie assessment can help to ensure that no SCTs and procedures have been missed in the SCTA, and can provide extra clarity and the ability to sanity check the output of the SCTA process

References

  1. International Association of Drilling Contractors Appendix 1 to Health, Safety and Environment Case Guidelines for Offshore Drilling Contractors, Issue 3.6, January 2015

2. Energy Institute. Guidance on Human Factors Safety Critical Task Analysis ISBN 978 1 78725 165 6, 2nd Edition, January 2020