Safety gear is one of the most important aspects of handling any power tool, especially angle grinders. Grinders are known for throwing out chunks of debris depending on the type of material you are cutting, which makes safety glasses mandatory. In addition, they are quite loud, so ear plugs are recommended. Plus, if you are cutting concrete or plastics, for example, the dust can be harmful to inhale, so a dust mask or respirator is required.
Angle grinders have handle attachments for a reason. While the type of material you are cutting can sometimes result in situations where one-handed use is acceptable, for proper safety you should always use the handle attachment so that both hands are continually on the machine; one hand holding the machine in place the other hand stabilizing the machine through the handle attachment. Only qualified professionals with years of experience should use the one-handed approach, and even then it is situational.
Attaching the blade is a vital part of angle grinder safety, as an improperly attached blade can wobble, causing incorrect cutting and chunks of the blade to fly off. In addition, a blade that is not properly fastened is dangerous as it can eventually work the nut holding it in place loose, causing the blade to fly off completely. Always ensure that the blade is tightened in place and fitted correctly, and check it periodically in between uses.
Different types of blades are meant to be used with specific types of materials. Using a metal blade to try and cut wood, for example, will cause the wood to burn rather than cut, and using a plastic blade to try and cut metal can result in the blade dulling excessively. Always use the proper blades with the corresponding material for best results, and to avoid potential injury from the blade warping, chunking, cracking or breaking.