KAN Report 4

	Crushing points - working basis for standardization, 06/1996, F. Sasse (9 MB)
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Summary

Review and assessment of the situation


1. Crushing points represent a high safety risk. Following an analysis of statistics it has been established that accidents in which parts of the body are crushed occur frequently. Hands and arms are exposed to by far the highest risk.
   
   
2. The report provides an overview of national regulations and national, European and international standards or draft standards in which statements are made on force restriction at crushing points. It becomes clear that the various sets of rules are based on different measuring and analysis methods. The fact that terms and definitions are not standardized makes it considerably more difficult to transfer limit values. An analysis of standardization projects has shown that as far as C standardization is concerned, measures for force limitation have already been established. However, a standardized method for determining load values has not been adopted. Force, pressure or energy units, for example, may be used to describe load. In some cases, details of measuring equipment and measuring conditions are not provided.
   
   
3. A variety of experiments carried out and the resulting limit values for the biomechanical load resistance of the body and individual parts of the body are described. Since most test series originate from other independent areas, such as the automobile industry, results cannot be referred to when establishing generally applicable limit values for making crushing points safe. This is also due to that fact that questions are formulated in different ways and peripheral conditions cannot be compared (e.g. tests on corpses or dummies).
   
   
4. In some application areas (printing and paper processing machines, bus doors, power-operated doors and gates), experiments have already been carried out to limit crushing power. The method selected involves the determination of what are known as comfort values (discomfort thresholds determined with the help of groups of test people). The study describes the permissible forces established and the measuring equipment and processes used.
   
   Determining the need for research
   
   
5. Research has revealed a substantial deficit with regard to the transferability of biomechanical load values from existing experiments in general to application at crushing points. It is therefore necessary to make separate experiments available for establishing load values for the relevant parts of the body at risk. The study recommends the pragmatic method of ascertaining comfort values, which have already proven successful in several cases, as a mean of fixing limits for safeguarding against crushing points. Ascertaining limits for the hand/arm region is stated as a priority.
   
   
6. The author recommends examining the influence of the design of closing edges on machines. Results should provide the basis for drawing up proposals for minimising the risk of injury.
   
   
   Assessing the measure to "limit active forces"
   
   
7. Possible measures aimed at making crushing points safe are given. Two arguments speak in favour of limiting force: in the case of certain machining processes, it is difficult or impossible to make the danger zone safe by keeping it separate. Limiting active forces can prove to be an economical and operator-friendly measure in such cases. In addition, it should be emphasised that this method complies with the "Safety of machinery; basic concepts, general principles for design" philosophy laid down in basic standard DIN EN 292, which stipulates that the risk should first be minimised with the help of constructive measures before other safety measures are taken.
   
   
8. It is important to note that in certain cases (e.g. paper-cutting machines), permissible forces can only be reduced to a certain extent if the machine's function is to be guaranteed.
   
   
   Determining limits
   
   
9. Most sets of rules specify a (static) force limit of 150 N as a common value. The study explains that, taken on its own, a static value is unsuitable for describing the danger adequately.
   
   
10. There is a variety of parameters which has to be taken into account when determining key values. It is therefore necessary to use standardized measuring equipment and to define measuring conditions. In particular, spring rigidity depending on the part of the body in question must be determined in order to be able to obtain and assess comparable values. As far as ascertaining permissible limits is concerned, dynamic forces and the duration of load must be recorded in addition to static forces.

 

 

KAN´s recommendations

The Commission for Occupational Health, Safety and Standardization (KAN) endorses the results of the study and has decided to publish it as a KAN Report.

 

Overall evaluation

The report provides a comprehensive overview of studies carried out in the field of force limitation at crushing points. The current status of technical regulations in this field is presented. The need for research to establish load values is described.

This project therefore represents a good working basis for standardization work.

 

General need for action


1. KAN recommends that a B standard be drawn up in accordance with machinery directives in order to inform the manufacturer of how crushing points can be made safe by restricting active forces. As well as specifying recommended values for individual parts of the body, measuring procedures should be standardized taking account of peripheral conditions similar to those experienced in practice.
   
   
2. KAN is to make the results of the study available to CEN/TC 122 via DIN in order to assist the work of WG 1, which has been awarded a corresponding standardization mandate. KAN underlines the need to combine physiological and technical aspects when drafting the standard and has asked the working group accompanying the project to make itself available for cooperation with WG 1.
   
   
3. KAN has drawn the attention of the AA 1 (terminology) of the Standards Committee on Ergonomics, the national reflecting committee responsible, to the fact that, with the continuation of C standardization and specification of crushing force limits, the later standardization work is commenced, the harder it will be to implement a B standard.
   
   
   Need for research
   
   
4. KAN has appealed to those responsible (e.g. research sponsors) to support research in the areas specified below. If possible, they should work towards implementing a research project (CEN N 1022 - Safeguarding crushing points on machines by means of a limitation of the active forces, pre-standardization research) already commissioned by the EU as part of the 4th framework programme.
   
   
5. Determining load values for individual parts of the body based on discomfort thresholds. Examinations of the hand/arm area take priority. These should be based on studies already conducted by the Institute for occupational safety of the Berufsgenossenschaften.
   
   
6. Determining the resilience of parts of the body with the aim of using results to derive standardized specifications for the use of measuring equipment with defined spring rigidity.
   
   
7. Drawing up proposals for the design of closing edges on machinery with the aim of reducing the risk of injury.
   
   
8. Establishing realistic peripheral conditions based on the analysis of accidents involving machinery. Static and dynamic forces as well as the duration of load should be taken into account.