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KANBrief 1/19

Quick couplers on construction machinery: a better standard for safety

Work involving construction machinery often requires different tools to be fitted to the boom. Quick couplers (also termed quick hitches) enable machine operators to switch tools without leaving the machine controls. Sadly, many serious or even fatal accidents occur when tools are not correctly interlocked with the quick coupler and consequently fall. KAN is involved in work on improving the relevant standards and making the design of quick couplers safer.

Hydraulic quick couplers are used above all on excavators. They are attached to the excavator boom and enable the tools required for the work, such as backhoe buckets, chisels or pipe tongs, to be fitted within just a few seconds. For this purpose, the tools are hooked into place on one side and locked on the other, generally by means of pins on the quick coupler that engage with holes or beneath a roller on the tool. If this procedure has been performed correctly, the tool is attached securely to the excavator and can be used.

Incorrect use is virtually inevitable

On the majority of quick coupler systems, the tool is locked in place on the side facing away from the operator. The operator is not therefore able to see whether the pins are correctly extended, i.e. whether or not they are in engagement with the holes. Some systems have a signalling pin on the operator's side to indicate that the engagement pins are extended, or employ sensors signalling at the machine controls that the coupler is properly engaged. It is not always immediately apparent that a tool is not properly locked in position. Should for example the engagement pins merely clamp the tool firmly but not engage properly with it, the tool can still be manipulated by the operator. When it is subjected to load however, it breaks loose and then generally drops.

In their user information, the manufacturers recommend a method for testing that the tool is locked in position. It is foreseeable however that in practice, this test will often not be performed. The accident statistics bear this out: according to information from the BG BAU, the German Social Accident Insurance Institution for the building trade, this was the cause of 8 fatal accidents and 45 serious accidents between 2010 and mid-2018. In the majority of these accidents, the cause was incorrect locking. This shows that including a factor dependent upon deliberate human action in the safety concept is not an effective solution. The EU Machinery Directive requires reasonably foreseeable misuse to be considered during the risk analysis. In this case, it has not been given adequate consideration.

Annex B of EN 474-1:2006+A5:2018, the current harmonized standard governing earth-moving machinery, sets out requirements for quick couplers. These requirements have been revised and will be replaced in the near future by a reference to the international ISO 13031 standard, Quick couplers. Although some requirements have been improved, the test by the operator still forms part of the safety concept.

Standardization must adapt

Occupational safety and health institutions and market surveillance authorities in several Euro­pean countries consider the state of the art now to be more advanced than that described in the standards. Quick couplers are available on the market that provide the operator with clear information on the locking state. Design solutions also exist that reduce the likelihood of the tool dropping should it not be locked correctly in position. These solutions enable the operator to detect the fault in time and take appropriate measures.

The European market surveillance authorities' Administrative Co-operation Working Group (ADCO) with responsibility for earth-moving machinery has therefore formulated key points for amendments that need to be made to the standard in order to make quick couplers safer and consistent with the Machinery Directive. In the interests of speedy implementation, direct incorporation into the European standard is favoured.

A group tasked with discussing the concerns has been set up in the CEN standards committee. Following initial meetings, the work was however placed on hold in anticipation of the results of discussions by the European Commission's "Machinery" group. Although this has resulted in work on this important topic being delayed, it is positive that the opinion of the EU Member States can have a direct influence in this way upon reformulation of the requirements in the standard. ADCO and the Machinery group are called upon to discuss the proposals made expeditiously and to forward them to CEN.

The entire market should also make efforts to improve legacy equipment. Yet another aspect of work on construction sites will thus become safer.

Dr Michael Thierbach
thierbach@kan.de