Grinding disk are not dangerous if used correctly. Safety glasses and face shield, leather gloves, long sleeved heavy shirt. Pay attention to where you are shooting your sparks. They can ricochet off something and come back behind your face shield and saftey glasses, guard on machine, wheel matches machines rpm, don't bind wheel in slots, don't drop the wheel it may crack. Keep the guard between you and the wheel. Also, many people grind with the face of the wheel instead of the edge of the wheel. Grinding with the face can cause a couple serious conditions, one is it thins the wheel, which is not that serious, but as it thins the wheel it ca also wear through the fiberglass web that gives the wheel much of its integrity and make it much more apt to come apart. If you grind with the wheel semi flat its better, but, then the edge will start to thin and smaller pieces can fly off the edges and although not as dangerous as chunks still painful. This can be avoided by paying attention to the condition of your disk and when the edge starts thinning, grind something with the wheel totally perpendicular and wear the thin part of the edge away until it is at least 1/2 its normal thickness. Learn where the reinforcement is in the disk. The thin edge also becomes a whirling knife edge and will cut flesh in a heart beat.
Flappers wheels are fine in their place. When, the edge is thin they will toss off little pieces that are harmless if you are wearing good safety equipment. But, they do wear out faster than disks and being softer they conform more to the work piece. If you have a high spot a flapper wheel will not get it flat as quick as a disk because the flaps will go up and over the high spot a little bit and still remove a little of the low areas. The leave things a little bit rounded. Kind of like a slack belt grinder. The edges of flapper wheels can also become extremely thing and turn into a whirling knife edge and will cut flesh in a heart beat.
In conclusion, having used disk grinders from 4 1/2" to 9" for years in the metal trades I personally feel they are not much more dangerous than a belt grinder when used properly. If you have ever had a heavy grit belt start coming apart on a 2x72 while it is going at a high speed you would know it also has the potential for some serious injury. That is the nature of power tools, the Innocent looking drill press can turn into a flesh eating monster in a second of carelessness. Power saws of all types and sizes have maimed and killed. Lathes and milling machines the same.
YOU HAVE TO, inspect your equipment regularly for flaws, know now to use your tools their limitations hazards and analyze what you are attempting to do and look for potential traps everytime you use them. It doesn't have to be a long process, but it better be there and you had better pay attention to the tool and not be thinking about Susy's assets. Time and time again you see examples posted here of people who failed in these steps. I wish we wouldn't do this stuff, but, I applaud them for sharing this stuff as a learning tool for some and a reminder for the rest.
PAY ATTENTION PAY ATTENTION PAY ATTENTION PAY ATTENTION PAY ATTENTION
