OSHA's regulations for machine guarding are fairly generic -- however, they are wide reaching. The two most widely relevant OSHA regulations which cover machinery, industrial machine, and automation equipment are:

OSHA 1910.212(a) One or more methods of machine guarding shall be provided to protect the operator and other employees in the machine area from hazards such as those created by point of operation, ingoing nip points, rotating parts, flying chips and sparks. Examples of guarding methods are-barrier guards, two-hand tripping devices, electronic safety devices, etc.

OSHA 1910.212 (a)(3) The point of operation of machines whose operation exposes an employee to injury, shall be guarded. The guarding device shall be in conformity with any appropriate standards therefore, or, in the absence of applicable specific standards, shall be so designed and constructed as to prevent the operator from having any part of his body in the danger zone during the operating cycle.

Note that this last regulation allows OSHA to enforce any appropriate standard, which allows OSHA to enforce all relevant ANSI standards.

For this reason, guarding should be designed such that a person cannot reach over, under, around, or through a guard into a hazard. Here are two ANSI standards that often apply to machines and machinery in a manufacturing facility:

ANSI B15.1 3.2.1 All motion hazard guards shall meet the following requirements.
(a) They shall prevent entry of hands, fingers, or other parts of the body into a point of hazard by reaching through, over, under, or around the guard.

ANSI B11.19 Performance Standard for Safeguarding 7.1.3 The design and construction of the barrier guard shall ensure that individuals cannot reach the hazard by reaching over, under, around, or through the barrier guard.