No guard will eliminate the possibility of injury. The best guard has zero parts, meaning that the need for a guard is eliminated by designing-out the hazard. When a guard is required, the following requirements shall be followed.
The Guard Cannot Create an Additional Hazard
Guards and other safety devices cannot themselves create an unsafe
condition. Examples of this are a guard that is so heavy as to injure someone if dropped, a guard that provides a shear point when adjacent to a moving part, a guard assembly that causes the assembly to be unstable, or a hinged guard assembly that can drop and pinch or shear a body part. Consider each guard as a potential hazard until proven otherwise.
Avoid structures that are stores of potential energy, either through gravity, or through springs or pneumatics. Stable bases to support free-standing guards. Sliding assemblies instead of lifted. Counterbalanced guards preferred over guards supported by springs or dampers. Measures
should be taken to reduce contact pressure between moving guard edges and fixed structures through increases in area and reductions in force.
The Hippocratic Oath of Safety: “First, do no harm.” A situation where a falling guard injures someone is indefensible.
Guard Life and Reliability
Guards must be durable and of materials suitable for the environment
intended.
a) Guards must be strong enough to last the life of the machine.
b) Integrate the guard as part of the required machine structure. Use materials of the same type as the machine, or materials that are impervious to the greatest range of potential chemical exposure. Replacement of a damaged guard must be considered in the design process.
Visibility
Clear plastics (or consider open mesh) that permit the operator to see the process or the hazard area. Forms of radiation must be considered in selection of guarding materials. If plastics are used in x-ray applications, the material must prevent x-ray transmission.
