The Occupational Safety and Health Administration (OSHA) is very specific about bench grinder safety. OSHA refers to bench grinders as "Abrasive Wheel Equipment Grinders." The safety rules for this machinery are in 29 Code of Federal Regulations (CFR) 1910. OSHA has a very detailed checklist for the bench grinder on its website.
OSHA Regulation 29 CFR 1910.215(a)(2)-(b)(9)
There are four basic safety elements to the bench grinder that serve as are guards or shields. The flange and spindle guard protect the worker from the spinning wheel. The eye shield is an optional protector for the worker who should be wearing eye protection. The adjustable tongue guard helps suppress flying debris and sparks. It should be no more than 1/4-inch from the wheel. The work rest is the point of operation. The worker should position the work piece on the rest so it touches the wheel from the front or edge. The rest should be 1/8-inch from the wheel.
OSHA Regulation 29 CFR 1910.215(d)(1)
Inspect the abrasive wheel before mounting it to the equipment. Check the wheel for any visual damage. If damaged, do not use it. Inspect the wheel for internal integrity; this is the "ring test." Tap the wheel "gently with a nonmetallic implement." You can use the handle of a screwdriver or a wooden or plastic mallet for thicker wheels. You should hear a ring. If the sound is more of a thud or dead sound, you likely have a faulty, unusable wheel. Further inspect to make sure the wheel's RPM rating matches the RPM of the bench grinder.
Regulation 29 CFR 1910.22(a) & .212(b)
Make sure the grinder is free from dirt and the area around it is free from clutter and debris. Workers need to ensure they have enough space for free movement during work. Securely mount the grinder to the work surface before starting grinding operations.
OSHA Regulation 29 CFR 1910.94(b)(2)
If the grinder has dust collectors or a powered exhaust, it must be in good working order. Check these before grinding operations begin. Ensure they are clear of clogs and debris that may hinder safe operation.
Regulation 29 CFR 1910.304(f)(4) - .305(j)(4)(i)(F)
Check electrical and grounding connections on the grinder before turning it on. Check to see that the cords or connections are in good condition; free from splits, cuts, or other damage. Check to see if the grinder has an individual on/off switch. If there has been any bypassing of electrical components or safeguards, do not use the equipment until making repairs.
Some Additional Good Rules
Make sure the abrasive wheel reaches its full RPM before engaging in abrasive work. Do not crowd the wheel to the point that it slows. Do not grind on the side of the wheel. Do all work on the face or edge near the rest. Make sure all eye equipment has no smudges or scratches blocking your view of the work. Do not wear loose clothing or other articles the wheel could catch, i.e., name badges, shirttails or sleeves, or jewellery. Make sure the area where you stand is dry. Consider using ear protection in addition to other personal protective equipment.