Guys,
This is incident was a freak accident, it has never happened before. Each windmill is equipped with a computer which controls the direction of the mill and the pitch of the blades. The computer in this particular windmill malfunctioned, and instead of pointing the tower indirectly into the wind and alter the pitch of the blades, to slow down the prop, it remained stuck in one position pointing directly into the wind with the blades optimized for low wind speeds. This meant that as the wind picked up the windmill just kept going faster and faster, the blades creating too much lift. Furthermore the braking system had broke in storm a few days earlier, so there was no way to stop it.
All the guys on the ground could do was wait for the inevitable. The windmill had already been spinning out of control for hours before any camera crew got there, and it apparently took another two hours before the windmill failed, as the wind speed kept increasing.
Pretty amazing that the prop managed to go that fast before breaking though.