What exactly does the shield protect you from?

I just played a few rounds to confirm:

The shield prevents death from all solid objects, including the rotating spike cylinder, and fire. It also prevents you from tripping on the tile piles that occassionally block either side of the path, and from tripping during mistimed jumps where you fall short and hit the incoming ledge. All of these objects, once hit, deactivate the shield.

When in the mining tunnel, the shield DOES NOT prevent you from tilting your mine cart into the tunnels blocked with boulders (the boost does).

The shield does not save you from falls, water hazards, or broken mine track.

The first Temple Run also included a power-up with the same properties but was called Invisibilty.

Follow-up for Invisibility

It has the same properties as Invisibility from the last game (Temple Run). It saves you from:
1. All solid objects.
2. Fire.

After one hit, it deactivates.
It also deactivates if not used for a period of time.