Dec. 10, 2017, 7:44 p.m. PST
ok - found it
I will reproduce the relevant section here so we can look at it
The intent of this competition is to develop technologies that can be rated for people to safely fly in the future. Consequently, the competition requires that all device architectures are, at the fundamental concept level, "human-ratable." The organizers define "human-ratable" as follows:
A device that has no systems or components, except for primary structure, in which a single point failure results in loss of an operator's life or limb.
Systems or components which, in the event of their failure, permit safe landing of the operator, may be of single string design.
Structure and component suitability
The primary structure may be a single point of failure if:
adequate proof testing is performed, or
it is designed to loads significantly higher than expected loads (safety factor ≥ 1.5) and its structural integrity is regularly inspected.
Adequate quality, performance, and service life of all components must meet appropriate requirements for the intended application.