what next said:
RPM is much lower than a conventional fan, so blade separation is certainly something to worry about, but not more than with turboprop aircraft.
Perhaps the open fan technology will no longer be subject to the blade-off containment regulations for low stage compressor fan blade failure?
They may be going to argue that with the planned slower rotating and shorter (and tapering) blades of the open fan that the blade off event will be less likely and with less energy than a propeller blade off event.
And the C-130 Hercules engines are approaching an open fan type engine by their multiple (propeller or fan) blades.
And there has never been protection in the regulations for trying to contain a propeller blade once it fractures (as far as I am aware).
It is very interesting to see the open fan technology arise from the ashes.