Liveware (central component)
The most valuable and flexible component in the system is the human element, the liveware, placed at the centre of the model. Each person brings his or her own capabilities and limitations, be they physical, physiological, psychological, or psychosocial. This component can be applied to any person involved with the operation or in support of the operation. The person under consideration interacts directly with each one of the four other elements. Each person and each interaction, or interface, constitute potential areas of human performance investigation.
Liveware (peripheral)
The peripheral liveware refers to the system's human-human interactions, including such factors as management, supervision, crew interactions and communications.
Hardware
Hardware refers to the equipment part of a transportation system. It includes the design of work stations, displays, controls, seats, etc.
Software
Software is the non-physical part of the system including organizational policies, procedures, manuals, checklist layout, charts, maps, advisories and, increasingly, computer programs.
Environment
Environment includes the internal and external climate, temperature, visibility, vibration, noise and other factors which constitute the conditions within which people are working. Sometimes the broad political and economic constraints under which the system operates are included in this element. The regulatory climate is a part of the environment inasmuch as it affects communications, decision-making, control, and co-ordination.
Step 2-Determine occurrence sequence
As the investigator moves to addressing questions of "how and why", there is a need to link the data identified in the first step of the process. Reason's (1990) model of accident causation, utilizing a production framework, can be used by an investigator as a guide to developing an occurrence sequence. Reason's model facilitates further organization of the work system data collected using the SHEL model, and an improved understanding of the influence of that data on human performance. The occurrence sequence is developed by arranging the information regarding occurrence events and circumstances around one of five production elements, i.e., decision makers, line management, preconditions, productive activities, and defence.
The production elements themselves are basically aligned in a temporal context. This temporal aspect is an important organizing factor since the events and circumstances that can lead to an accident or incident are not necessarily proximate in time, nor in location, to the site of occurrence. By establishing a sequential ordering of the data, Reason's (1990) concept of active versus latent factors is introduced.
