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HOF models

About this topic


HOF models describe theoretical frameworks for the application of HOF. These can range from specific models of particular aspects of human performance, for example signal detection theory models of perception or decision making, to general models of the scope of human factors. The latter type of models are discussed here. General models of human factors are useful to describe the interaction of humans with other parts of a system. Such models can be used to raise awareness of the scope of human factors, and to support human factors analyses which aim to consider different aspects of a system.   

Relevance to rail 

The rail system is complex with multiple interacting elements coming together to deliver a safe and efficient rail service. Human factors models can help identify which of these elements are relevant to human performance in the railway. 

Approaches and models 


SHELL Model 








The SHELL model was developed by Hawkins in 1975, building on an earlier model, with a focus on the aviation system. It describes the human (referred to as ‘liveware’ in the model) as being at the centre of a system made up of four components: 

  • Software – software here refers to all non-physical intangible system components, including computer software but also procedures, rules and instructions, norms and conventions, etc. 
  • Hardware – hardware refers to all the physical elements of a system such as the controls and displays, tools and equipment, buildings, components, etc. 
  • Environment – environment refers to the physical environment (lighting, noise, weather, etc.) as well as the organisational and cultural environment. 
  • Liveware – liveware occurs twice in the model; first at the centre representing the person being considered, and second representing all the other people that person interacts with at different levels of the organisation, including co-workers and managers.  

In applying the SHELL model, all the interfaces between the liveware (person) at the centre of the model and the other elements of the system should be considered.  


UK HSE Model 

The UK Health and Safety Executive uses a simpler model which describes HOF as considering three interrelated aspects: 

  • The job – this includes aspects such as the tasks that must be conducted, the workload imposed on workers, the working environment, and the design and use of equipment 
  • The individual – this covers aspects such as the competence and skill of an individual and their personality and attitude.  
  • The organisation – this includes aspects such as the work patterns, culture, leadership and organisational resources. 

As with SHELL, the interactions between these three elements should be considered as part of a human factors analysis. 


Swiss Cheese Model 







The Swiss Cheese Model was developed by Reason to describe how accidents are a result of deficiencies in different layers of defences. The controls against accidents are represented as slices of Swiss Cheese, each with their own weaknesses which are represented as holes in the slices of cheese. Reason argued that accidents occur when a situation arises which exploits the weaknesses in all the individual defences. While primarily a safety management model, the Swiss Cheese model can also be applied as a human factors model with defences including organisational factors such as training, task and environment conditions, and individual or team actions.    


5×5 model 

The European Union Agency for Rail (ERA) has also developed a more complex 5×5 model to describe HOF. 




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