As soon has i have started an engine, I run BEHIND the plane, I have seen4 strokes engines throw the prop 3 times and this can be very dangerous as previously mentioned.
My experience (but this is only my opinion) is that propeler separation risk can be reduced by performing a long breaking in in flight in the rich side and also having the valves perfectly adjusted.

We don't have many castrate members in the club (I didn't really investigate closely but I supose). A member stupidly lost 3 fingers last season.
The man was a HIGHLY experimented modeler, he started his saito 180, went behind the plane, a other guy was holding the plane, he puted full throttle for needle valve adjustement, he was performing all that in a very safe way when his sunglasses fall from his nose, he had the reflex to try to catch them........ and his hand went directly in the prop.