The terms guard and shield are often used interchangeably when referring to safeguarding cutting and turning machines. However, there is a significant difference between the two words.
OSHA 29 CFR 1910.217 defines a guard as an enclosure that prevents anyone from reaching over, under, around, or through the guard even if they really tried. Guards are often used when a machine risk assessment shows a high level of exposure to recognized hazards.
Guards can be separated into two categories: point-of-operation and perimeter. Point-of-operation guards are designed to enclose only the area on a machine where the work is actually done to make a finished part. A perimeter guard can be used when a larger area requires protection. Perimeter guards can also be used to enclose a group of machines that may not otherwise be safeguarded.
ANSI B11 safety standards require that guard access doors be electrically interlocked using switches designed to be difficult to defeat. This is particularly important for doors that are frequently accessed.
Shields, on the other hand, are designed for lower levels of exposures (to hazards). Most shields are designed to knock down chips and coolant in cutting/turning operations, while still providing visibility into the point of operation.
Other shields are designed to prevent inadvertent contact with rotating parts. A common example is the use of a chuck shield on an engine lathe. Although not required, shields may also be interlocked. Using an interlocked shield is considered best safety practices and is highly recommended when feasible.
When the question arises as to which to apply, remember that guards must always provide a higher level of protection than shields.
Rockford Systems encourages all employees to exceed the minimum requirements and abide by best safety practices at all times.