Im an ex roofer and we used them heaps with no dramas, except swarf in the eyes. A year ago I was using a mates 9" grinder cutting my boat. His gaurd had a problem comming lose which I didnt know, cutting down the guard had slipped out of the way and my hand went straight onto the disc. Funny thing as soon as I felt it I thought this wont be pretty. Not much pain, no blood just a nice neat slit from top to bottom, luckily just touching the bone, not cut but burnt.
I use a 4.5" one near enough everyday with the real thin blades on them with no probs.