Human Factors

What is Hierarchical Task Analysis (HTA)?

Hierarchical Task Analysis (HTA) is a method for analysing tasks using a hierarchical structure. You start with a goal for what the task is trying to accomplish overall, break this down into top level sub-goals, and keep decomposing these sub-goals into more detail to create a tree-like structure. HTA is a fundamental technique for understanding tasks and processes in Human Factors. 

Human Factors

What is Hierarchical Task Analysis (HTA)?

Hierarchical Task Analysis (HTA) is a method for analysing tasks using a hierarchical structure. You start with a goal for what the task is trying to accomplish overall, break this down into top level sub-goals, and keep decomposing these sub-goals into more detail to create a tree-like structure. HTA is a fundamental technique for understanding tasks and processes in Human Factors. 

How do you conduct a HTA?

Generally, you would start with a top-level goal and break this down into further and further detail. This could be done on your own, or preferably with a team of people who have specialist knowledge of the task. You might need to first clarify the scope of the task, like where it should start and stop, and what conditions need to be in place before it commences. You could start with a blank piece of paper, which might be necessary in a design scenario, or for a lot of our work we will start with procedures and checklists to get an initial understanding of the task analysis.

How do you conduct a HTA?

Generally, you would start with a top-level goal and break this down into further and further detail. This could be done on your own, or preferably with a team of people who have specialist knowledge of the task. You might need to first clarify the scope of the task, like where it should start and stop, and what conditions need to be in place before it commences. You could start with a blank piece of paper, which might be necessary in a design scenario, or for a lot of our work we will start with procedures and checklists to get an initial understanding of the task analysis.

What are the key elements of a HTA?

The top goal describes the overall objective of the task. In many cases, this could be the same as the name of the procedures that are being analysed.

The top sub-goals are the first level of breakdown of the top goal, these can be thought of as the main chapter headings for the task.

The sub-goals are broken down further and further into steps, sub-steps and leaf nodes. As the hierarchical structure expands the representation might look something like an upside-down tree. To continue the metaphor: as the task structure branches out further the end boxes or steps are sometimes called leaf nodes. The analysis will step when the required level of information has been, this could be quite high up in the task structure or it could be expanded into layers of detail.

Plans form part of the HTA’s structure and allow the opportunity to understand the flow of the task. Plans are helpful for communicating contingencies and the sequence of steps, e.g. do steps 1-2, wait until temperature reaches 180dgrees then do steps 3-5. This is especially useful in processes with multiple variables and conditions.  

Preconditions are used to outline the task’s boundaries and the conditions necessary for the task to take place, e.g. windspeed should be below X, PPE should be available, the area should be secured, and personnel qualified to Level 3 should be available for the duration of the task.  

What tools do you need to conduct a HTA?

if you’re starting a HTA and want to jot down the main structure of a task. In a group or workshop setting, sticking Post It notes to a wall can be an engaging and effective way to develop a better understanding of a task, e.g. this might be for designing a new process or establishing what happened in an incident. 

Some people develop HTA’s using Word or Excel, by using a text-based hierarchy, however for complex tasks, this can hinder understanding and engagement. These tools limit our thinking because it’s harder to quickly understand the task hierarchy and breakdown when presented with a wall of words. Furthermore, it can be hard to edit and move boxes around.

 

What tools do you need to conduct a HTA?

if you’re starting a HTA and want to jot down the main structure of a task. In a group or workshop setting, sticking Post It notes to a wall can be an engaging and effective way to develop a better understanding of a task, e.g. this might be for designing a new process or establishing what happened in an incident. 

Some people develop HTA’s using Word or Excel, by using a text-based hierarchy, however for complex tasks, this can hinder understanding and engagement. These tools limit our thinking because it’s harder to quickly understand the task hierarchy and breakdown when presented with a wall of words. Furthermore, it can be hard to edit and move boxes around.

 

For more complex tasks we prefer task analysis software that has an intuitive graphical approach so it is easy to see how the task is broken down, so you can easily edit and adjust it, so it can be shared online and on an overhead projector so others can easily engage with it for feedback, and so it can link to other features that might be useful, e.g. like risk assessment and procedure development.

As this methodology presents information in a graphical manner, it provides users with the opportunity to have a more comprehensive understanding of the task.

What are the benefits and limitations of HTA?

One of the benefits of using HTAs is that it handle a lot of detail and complexity of a task. Complexity can be hidden, or we can expand the hierarchy to reveal more detail. This methodology allows users to have an overview of the task and see individual steps which require more focus during the analysis. 

HTA is useful in helping to bridge the gap between work-as-imagined and work-as-done. Often, procedures are used as the foundation of an HTA. However, documented procedures may be dated and have some missing steps that are necessary in order to complete the task.  Due to its graphical representation, HTAs allow users to highlight any discrepancies between what is documented and what is done in practice by capturing the feedback from workers and subject matter specialists. This reduces the chance of having misconceptions when carrying out a task and allows one to articulate tacit knowledge and find consensus around best practice.

HTA seems to be more suitable for simple and complicated tasks that have a clear goal, structure, a start and a finish, e.g. great for manufacturing and processes. It seems less suited to tasks that are open, volatile, uncertain, complex and ambiguous, e.g. responding to emergency trauma, creating a marketing strategy and managing a sales team. However, it should be noted that even within a complex context there will be patterned behaviour that could be mapped using HTA. 

Can I use HTA for design work?

HTA can be a used in the design process. It can be used to design different conceptions of how a task is carried out. These could be reviewed and discussed with a design team. Design requirements could be considered for each task step. Furthermore, the HTA itself can develop with the design, e.g. at the beginning of a design process the details of the task might not be fully known in which case the HTA can stop at a higher level, however as further detail is revealed and decided upon then this can be included in the HTA.

How is HTA used for risk analysis?

Once a detailed task analysis is completed using a HTA then this can provide an excellent vehicle for discussing and understanding the risks within the system. Each branch can be expanded into further detail and a review team can consider the likelihood and consequences of something going wrong at the different task steps. If using a specialist piece of software like SHERPA then a risk matrix can be used to score the risk, this will highlight where the major red risks are, where the medium amber risks are, and the greens which are low risk. Interventions can then be suggested to manage the risk. 

How is HTA used for risk analysis?

Once a detailed task analysis is completed using a HTA then this can provide an excellent vehicle for discussing and understanding the risks within the system. Each branch can be expanded into further detail and a review team can consider the likelihood and consequences of something going wrong at the different task steps. If using a specialist piece of software like SHERPA then a risk matrix can be used to score the risk, this will highlight where the major red risks are, where the medium amber risks are, and the greens which are low risk. Interventions can then be suggested to manage the risk. 

Can HTA be used for incident analysis?

Yes, a HTA can be used in two main ways: 1) the first would be to analyse the task that went wrong including all the failures that caused the event. Like a normal HTA this can start at a high level and breakdown the task and incident analysis in more detail where required; 2) the second would be to take the task that went wrong and analyse it as if it went ‘normally’, one could then assess that task for vulnerabilities and deviations, which should include but not be constrained by the actual incident sequence. The advantage of doing it this way is that you are likely to learn more than just the specifics of the incident sequence, and how normal work is performed.  

Can HTA be used for incident analysis?

Yes, a HTA can be used in two main ways: 1) the first would be to analyse the task that went wrong including all the failures that caused the event. Like a normal HTA this can start at a high level and breakdown the task and incident analysis in more detail where required; 2) the second would be to take the task that went wrong and analyse it as if it went ‘normally’, one could then assess that task for vulnerabilities and deviations, which should include but not be constrained by the actual incident sequence. The advantage of doing it this way is that you are likely to learn more than just the specifics of the incident sequence, and how normal work is performed.  

How is HTA used for Human Reliability Assessment?

Human Reliability Assessment refers to a general set of methods that examine what human failures could occur in a task, their likelihood and consequences. A detailed HTA is an excellent basis for a Human Reliability Assessment as each step can be considered in turn to anticipate what could go wrong and how. Within SHERPA that is a structured list of guidewords that can help the analyst consider all the different ways an error could occur. There is also a library of related to factors that could either increase or decrease the likelihood of these failures occurring. Once we know the errors and their consequences then we can make suggestions to manage the risk, and help prevent critical errors before they happen. 

Can HTA be used to develop procedures?

For industrial tasks procedures are often a good foundation for the task analysis. However, once these are reviewed by workers and subject matter experts they may change. This means that the procedures should be updated and the HTA provides a very good basis for doing this. SHERPA can greatly help here at all stages: it can import procedures, it has an intuitive graphical interface for reviewing the task, it can highlight where the main risks are, and it can output formatted procedures including warning, comments and pictures with the touch of a button. Furthermore, a HTA in SHERPA can be used as the basis for a digital procedure.  

How can HTA be used to develop training?

For the majority of tasks a generic approach to training is adequate, e.g. someone might go through the procedure a few times supervised by someone more experienced who offers advice and checks their work, until they are happy they can do it on their own. However, for critical tasks a more systematic approach may be needed. Using a HTA we can identify critical task steps. These steps can then form the basis of a training aid which specifies the knowledge and skill requirements for that task step. This establishes what needs to be known and done by the operator to perform the step correctly. SHERPA has templates for conducting this sort of analysis.

Some clients really like the detail of a HTA for training so they can elicit the tacit knowledge in an aging workforce so it does not leave when people retired; it can specify expert knowledge from an expert workforce so it can be incorporated when training new staff (e.g. if moving from R&D to manufacturing); it can specify the reason for training so it is not cut from diminishing budgets I.e. it can be directly linked to risk in the task. HTA can provide the basis for a detailed and systematic approach for training tasks. 

Can HTA be used for different sectors?

Yes, we use HTA in our work across many different sectors for different reasons, some of which are outlined above. This includes risk and human reliability assessments for oil, gas and chemical plants; design review for medical device designers; procedure and training development for pharmaceutical manufacturing and supporting human performance across other safety critical sectors. The different ways that HTA can be used as a basis for supporting task performance is most powerful when all of these elements are combined, e.g. there is a risk assessment, new design intervention, risk informed procedures and improved training.  

Advanced HTA Tools and Techniques

At HRA, we can help you master the ability to create HTAs for your analysis. Our SHERPA software will help you create HTAs with a click of a button. This intuitive all-in-one platform also provides the ability to develop further analysis on your HTAs, such as the Failure Mode and Performance Influencing Factors (PIFs) analysis, Swimlane analysis, and Link Analysis. 

If you are looking for a course to learn more about utilising HTAs to ensure safe working practices, our Safety Critical Task Analysis (SCTA) Course can help you develop the knowledge and skills in carrying out SCTA reviews. The course includes an introduction to Human Factors, the principles and practice of creating HTAs with feedback/coaching, and recommendations for establishing best practices through procedural and training documentation. If you would like to know more about the SCTA course, click the button below.

Advanced HTA Tools and Techniques

At HRA, we can help you master the ability to create HTAs for your analysis. Our SHERPA software will help you create HTAs with a click of a button. This intuitive all-in-one platform also provides the ability to develop further analysis on your HTAs, such as the Failure Mode and Performance Influencing Factors (PIFs) analysis, Swimlane analysis, and Link Analysis. 

If you are looking for a course to learn more about utilising HTAs to ensure safe working practices, our Safety Critical Task Analysis (SCTA) Course can help you develop the knowledge and skills in carrying out SCTA reviews. The course includes an introduction to Human Factors, the principles and practice of creating HTAs with feedback/coaching, and recommendations for establishing best practices through procedural and training documentation. If you would like to know more about the SCTA course, click the button below.