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Mechanical Hazards

Mechanical hazards arise from relative movements between parts of the human body and objects such as work equipment or work objects, which lead to their contact. The result of this contact can be accidents that lead to injuries.

According to the accident statistics of the German Social Accident Insurance (DGUV), about three quarters of all occupational accidents are caused by mechanical hazards (Fig. 1-1).

Accidents caused by contact with parts moving in controlled or uncontrolled manner and with dangerous surfaces, as well as accidents caused by falling, slipping, tripping and twisting, each account for the highest proportion of all occupational accidents, at around 25 %. Accidents related to transport tasks and mobile work equipment account for 20% of all occupational accidents. Accidents caused by fall from heights, which are often serious or fatal, account for about 6 % of occupational accidents.

Fig. 1-1 Share of accidents due to mechanical hazards in the total number of occupational accidents in 2018 [1]. Fig. 1-1 Share of accidents due to mechanical hazards in the total number of occupational accidents in 2018 [1].

The severity of possible injuries depends on the geometric and physical properties of the moving objects. An important criterion is the kinetic energy with which a moving part, e.g. work equipment, parts of work equipment or a work object, hits the body part or, conversely, the moving body part hits the stationary object. The kinetic energy depends, for example, on the speed and mass of the moving objects. Other influencing factors are the geometry and the material properties, in particular the hardness and elasticity of the colliding surfaces. The injury severity will be lower if the moving part has an obtuse rather than a pointed geometry or a soft rather than a hard surface. The same applies to the body parts involved when soft elastic (arm) instead of hard, bony (finger) regions meet.

Due to the diversity of mechanical hazards (see Fig. 1-2), a differentiated consideration of risk reduction measures is required. Some basic design rules are as follows:
The first design rule for risk reduction of mechanical hazards is to reduce the acting energy to a non-hazardous level. However, so far, there have only been known limit values for individual cases [2]. An example of this are limit values for the design of powered doors on vehicles and for machine safety doors. A new quantity of values has recently been obtained, e.g. through research into safeguarding human-robot collaboration. As a result, biomechanical limit values for an assessment of mechanical risk are now available for further areas of the human body [3].

The second design rule for risk reduction of mechanical hazards is to ensure local or temporal separation between humans and moving parts. For this purpose, guards are used for local separation or protective devices, e.g. light curtains or laser scanners for temporal separation.

If such a separation is not possible, the third design rule is to provide personal protective equipment, e.g. in the case of mechanical hazards due to tripping, slipping and falling accidents, the provision of safety shoes with appropriate slip resistance. If such measures are not possible, the means of choice is the specification of key behaviours.
Mechanical hazards occur in particular in connection with the use of work equipment, when handling work objects, e.g. during transport work or due to design deficiencies in the workplace.

Mechanical hazards can be subdivided into

  • Hazards due to unprotected parts moving in a controlled manner,
  • Hazards due to parts with dangerous surfaces such as corners, edges, tips, blades, surfaces with high surface roughness,
  • Hazards associated with the transport and use of mobile work equipment,
  • Hazards due to parts moving in an uncontrolled manner,
  • Risks of falling due to slipping, tripping, twisting an ankle, and
  • Hazards due to persons falling from height onto a lower surface or an object.

The following overview shows typical danger zones or sources of danger that can be used to identify the subgroups of mechanical hazards mentioned (Fig. 1-2).

Fig. 1-2 Subgroups of mechanical hazards with typical danger zones or sources of danger Fig. 1-2 Subgroups of mechanical hazards with typical danger zones or sources of danger

Literature

[1] Special evaluation by the Statistics Department of the German Social Accident Insurance (DGUV), 25.10.2019
[2] Kommission Arbeitsschutz und Normung (KAN): Quetschstellen – Arbeitsgrundlagen für die Normung, 1996 [Commission for Occupational Health, Safety and Standardization (KAN): KAN study Crushing points - Working principles for standardization, 1996] (in German language only)
[3] FB HM-080: DGUV Information Collaborating robot systems - Design of systems with "Power and force limitating" function Issue 08/2017

Authors and contact persons

  • Thomas Mössner
  • Marlies Kittelmann

For further detailed information please refer to our German Website.

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