Comparison of measurement methods of the friction coefficient of floor coverings

According to the statistics of France's National Health Insurance Fund for Salaried Employees, falls on the same level represent about one quarter of occupational accidents resulting in sick leave. Loss of balance due to slipping is one of the causes of such falls. For some twenty years now, INRS ( France's National Research and Safety Institute for the Prevention of Occupational Accidents and Diseases) has been using two testing methods namely the LabINRS and PFT (Portable Friction tester), for evaluating the coefficients of friction of floor coverings.An experimental standard drawn up by the Eurpopean Committee for Standardization (CEN) proposes two other methods (Ramp test and Pendulum SRT -Skid Resistance Tester). The aims of this study, conducted in partnership between INRS and CSTB (France's Scientific and Technical Centre for the Building), were thus to compare the four methods, to assess the practical aspects od each of them, and to define the limits of them. To be relevant, the 4 measurement methods need to be sufficiently representative of the slip perceived during walking, and to be sufficiently discrimatory with respect to slips. INRS developed a psychophysical rating method, the aim of which was to make it possible to establish reference rankings bases on "perceived slipperiness". Those rankings were to be compared with the rankings obtained using the metrological methods.This study shows that, from a purely metrological point of view, the ramp test and the psychophysical method give the highest correlation coeffficients. The second advantage of the ramp tests is its renown among trade professionals who have been using it for categorising floor coverings for several decades now, regardless of the types of flooring and of their fields of use. However, implementing it suffers from major drawbacks, such as the need to use test subjects and the impossibility of taking measurements on site. The labINRS method gives correlation coefficients with the psychophysical method that are very good and that are almost equivalent to those obtained with the ramp test. In addition , it is very simple to implement; however, it suffers from the drawback of not making it possible for measurements to be taken in situ. Conversely, due to its very simple operating principle and to it being easy implement, the pendulum SRT is the best suited to taking measurements in situ. Its renown is high as it has been in use for many years for qualifying road surfaces and pedestrian surfaces. However, the correlation coefficients with the psychophysical method are low, raising questions as to its capacity to rank floor covering as a function of slipperiness.In addition, it does not make it possible to qualify correctly all types of floor covering, e.g. coverings with macro-relief. As for PFT, the correlation coefficients with the psychophysical method are very satisfactory. Even though it was originally designed to qualify road surfaces, INRS has considerable experience in using it for qualifying pedrestrian surfaces, in particular such surfaces that are designed for use in the food insdustry. it makes it possible to take measurements in the laboratory and in situ, on any type of floor covering.27p., ill. bibliogr