.2 it promotes the consideration of the interrelationships between these work system elements; and
.3 it focuses on the factors which influence human performance by relating all peripheral elements to the central liveware element.
The process initially attempts to answer the more simplistic questions of "what, who, and when" and then moves to the more complicated questions of "how and why". The resulting data becomes, for the most part, a collection of events and circumstances comprised of acts and conditions. Some of these will be of interest as unsafe acts and unsafe conditions.
There are four components to the SHEL model:
Liveware-L
Hardware-H
Software-S
Environment-E.
The SHEL Model is commonly depicted graphically to display not only the four components but also the relationships, or interfaces, between the liveware and all the other components. Figure 1 attempts to portray the fact that the match or mismatch of the interfaces is just as important as the characteristics of the blocks themselves. A mismatch can be a source of human error and identification of a mismatch may be the identification of a safety deficiency in the system. Figure 2 also depicts how this model can be applied to a complex system where multiple liveware, hardware, software and environmental elements exist.
