KANBrief 3/13

Slip resistance of floors and footwear: test results and reality may differ widely

For those responsible for safety and health at work, reducing slipping accidents is a major concern. Selection of a suitable non-slip floor and shoe combination is of crucial importance in this context. The right combination can be found only when the test methods for determining the slip resistance reflect real-case conditions. Researchers at the University of Wuppertal have questioned the suitability of the existing test methods and developed purposeful proposals for improvements. The detailed results will be published shortly in a dissertation on the development of a slip-resistance matrix for the selection of floors and footwear for the reduction of slipping accidents.

Slipping during walking accounts for around 10% of all occupational accidents in Germany, and is therefore a blackspot in the accident statistics. In a research project conducted from 2009 to 2012 at the University of Wuppertal and sponsored by the German Social Accident Insurance (DGUV), a slip-resistance matrix was developed by which the risk of slipping can be predicted as a function of the slipresistance potential of floors and footwear, and presented by means of the "traffic-light" model (red/amber/green). This enables the user to simplify risk assessment considerably and to select slip-resistant floors and footwear according to logical criteria.

Correct selection relies upon the availability of valid results of standardized test methods. Users must be able to assume that products with better test results do in fact exhibit a higher level of protection when used in practice at the workplace. Studies had shown however that footwear and floors were in some cases evaluated incorrectly during type examination. The issue has therefore been addressed and the validity of standardized test methods examined. The results formed the basis for proposals for amendments.

Which shoe is appropriate for which floor?

Comprehensive empirical studies were conducted in which the coefficients of friction were measured of 90 floors in combination with 100 safety and outdoor shoes and with soapy water and engine oil serving as the lubricants. This assured that industrial conditions were modelled representatively. The average slip-resistance potential of floors and footwear was determined from the results for each lubricant, and realistic rankings produced which approximate the conditions actually present in industry.

Correlation analyses were used to compare the realistic rankings with "standard rankings" obtained by means of test methods described in standards. These included all European and German type examination procedures for floors and for safety, protective and occupational footwear.

Wet floors and shoes on oil are problem cases

Practical product evaluation of floors is currently possible only by means of the test method in accordance with the ASR A1.5/1,2 Technical Rules for Workplaces (Floors) or DIN 51130 (Testing of floor coverings – Determination of the anti-slip property – Workrooms and fields of activities with slip danger, walking method – Ramp test) (Ramp test) for floors in oily working areas. The evaluation of safety footwear by the test combination of ceramic tile and water to EN ISO 13287 "Personal protective equipment – Footwear – Test method for slip resistance" corresponds to the slip resistance of footwear under realistic conditions.

No other standardized test method used for type examination besides these two methods exhibits a sufficiently close correlation to the rankings determined in practice. This result shows clearly that for floors in wet working areas and for footwear in oily working areas, in particular, no suitable standardized test methods exist.

The incorrect evaluation can be attributed to the reference materials and test media employed. For valid testing of the slip-resistance properties of wet floors, the "StarLP" reference sole was determined in the course of the research project with water serving as the test lubricant. The "Standard floor covering II" reference floor in conjunction with engine oil as the test lubricant proved suitable for footwear in oily working areas.

Conclusions for standardization

The responsible standards committees in Europe (CEN/TC 339 for floors and CEN/TC 161 for footwear) and the regulatory bodies in Germany should take up the proposals for valid test methods, gather experience with the reference materials, particularly regarding the uncertainty of measurement and comparability between laboratories, and revise the test methods in the medium term. This would offer an opportunity to use a more differentiated product evaluation in order to facilitate selection of footwear and floors in consideration of actual conditions, and to reduce the large number of slipping accidents sustainably.

Dr Christoph Wetzel