Including Systems Factors in Accident Models

Large-scale engineered systems are more than just a collection of technological artifacts They are a reflection of the structure, management, procedures, and culture of the engineering organization that created them. They are usually also a reflection 

Effectively preventing accidents in complex systems requires using accident models that include that social system as well as the technology and its underlying science. Without understanding the purpose, goals, and decision criteria used to construct and operate systems, it is not possible to completely understand and most effectively prevent accidents. 

Awareness of the importance of social and organizational aspects of safety goes back to the early days of System Safety In 1968, Jerome Lederer, then the director of the NASA Manned Flight Safety Program for Apollo, wrote  

Too often, however, these non-technical aspects are ignored. 

At least three types of factors need to be considered in accident causation. The first is the proximate event chain, which for the Herald of Free Enterprise includes the assistant boatswain s not closing the doors and the return of the first officer to the wheelhouse prematurely. Note that there was a redundant design here, with the first officer checking the work of the assistant boatswain, but it did not prevent the accident, as is often the case with redundancy [115,155]. 

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