no "exposed rotating parts that would lacerate human skin" in a DRONE document?

[Strydr]

Sorry for the newbie question but 107 operations all contain this statement "Does not contain any exposed rotating parts that would lacerate human skin upon impact with a human being." and I just cannot understand why that statement exists in an official document pertaining to drones. The last that I heard a propeller rotates, has blades that will lacerate human skin on impact and our drones have 4 of them.
So this statement makes absolutely no sense to me, could someone please explain why it is there?
Thank you!

 

[kenautelevo2pro]

I believe this can be accomplished by adding propeller guards or cages which fit around the propellers to protect them from coming into contact with objects. Obviously it would need to be more protective than these but this might be the idea:

 

[GFields]

You may be reading the requirements for flying over people

 

[redleger]

Part 107 subpart D discusses how to mitigate issues when flying over people. The rules make it virtually impossible and essentially, if interpreted as written, require a parachute, or some other device capable of slowing the fall in the event of a failure. If operating under the lowest standard for small drones, then you need propeller guards. If operating under the large drone class, it's basically impossible. Welcome to the FAA rules.