  A cyber physical human complex system failure prevents the accomplishment of
the systems intended function. The failure of a complex system could be a
breakdown of any system hardware, human related factors, application software,
or the interaction between these components. Having knowledge about all these
three components would allow us to better understand the behavior,
interactions, and the associated failure mechanisms of the cyber physical human
systems as a whole. In this study, degradation mechanisms in these three
components are classified and discussed. The main categories are hardware
related degradation mechanisms including mechanical, thermal, chemical,
electronic and radiation effects degradation mechanisms. In addition to
hardware related degradation mechanisms, human failure modes, software errors,
and the failures due to cyber physical human interactions are presented and
discussed. This paper covers the main types of failure mechanisms in complex
systems and is beneficial for developing conceptual risk and reliability models
for complex systems.
