Inherently Safe Design acc. to ISO 13854
Standards define limits as follows:
An actuator designed to not exceed any of these values does not pose a crushing hazard.
Another alternative is to keep minimum distances between actuators and stationary machine frame. Harmonized Standard DIN EN ISO 13854 (refer to essential standards for machine safety) defines minimum distance per body part.
|Body Part||Minimum Distance|
|Whole body||≥500 mm|
|Foot, arm||≥120 mm|
|Hand, fist||≥100 mm|
Typically, machine movement has the most significant risk of all hazards for injury, crushing and entanglement among them.
Crushing may all together be avoided in restricting force and pressure, or distance of movement, to safe values.
Some 50 years ago, a lone warning sign may have been reguarded as an adequate protection strategy in industry. At least since the first edition of European Machinery Directive in 1989, an industrial machine must not cause injury by its moving parts. Some of these hazards can be avoided by inherently safe design.
Most machines do however need fixed and moveable guards. Highly capable fast paced production equipment must be fitted with additional locking devices. Often there is not enough space to establish minimum distance behind light curtains, two-hand devices or such. Well designed machines permit adjustment and maintenance from outside of hazardous areas.
I have been involved in safe machine design since 1995. Drawing from my experience and knowledge I shall suggest practical solutions. Do not hesitate to contact chartered engineer Wolfgang Grassberger.
European Machinery Directive 2006/42/EG – MD mandates protection from dangerous moving parts of a machine. These must either be safe on their own, or else be guarded, or fitted with protective devices. There is just one execption for parts involved in the process, parts that cannot be made completely inaccessible as operator intervention is absolutely unavoidable. Harmonized Standards define a minimum distance to avoid crushing, or maximum force, energy and pressure to prevent such injury. Steps must also be taken by OEM to avoid blockage of moving parts, or else provide a safe way to unblock them.
A variety of hazards arise from moving parts of an industrial machine. Slow movement may be easy to avoid, but can ultimately be just as devastating as high speed. Crushing hazard is one of the major concerns. Entaglement of fingers or sleeves by pulleys, sprokets, shafts and rolls typically causes severe injury and permanent invalidity. Some processes require sharp edges that can inflict lacerations or stab wounds. Fast movement is capable to cause major injury even by blunt impact. Blocked parts, or pending loads may easily be mistaken for safely stopped, but can suddenly come loose.
In limiting crushing force to 75 N, injury can be avoided. Kinetic energy must at the same time be limited to 4 J, and pressure to 25 N/cm². Another possibility is to keep a minimum distance between moving and stationary parts. Harmonized Standard DIN EN ISO 13854 contains relevant details.