Comparison of methods to measure the coefficient of friction of floor coverings

Aims
Same level falls represent about one quarter of all work accidents involving stoppage. In part, the origin of the accident is the loss of equilibrium due to slipping. INRS has been developing and using two test methods, (LabINRS and PFT - Portable Friction Tester), for many years to, assess the coefficient of friction of floor coverings. An experimental standard drawn up by the European Committee for Standardization (CEN) proposes two other methods (Inclined plane and Pendulum SRT - Skid Resistance Tester). The aim of this study, conducted in partnership with the French Scientific and Technical Centre for Building (CSTB), was to compare the four methods with a view to assessing their relevance.

Methodology
To carry out this comparative study, INRS developed a psychophysical method to assess the “feeling” of slipping on floor coverings. It established a reference classification for a group of 15 coverings ranging from least slippery to most slippery, assessed in the presence of oil or a water solution. This group was then measured with the four methods studied in the presence of the two pollutants. The four methods were assessed from the metrological point of view by comparing them to the reference method and from the point of view of practicality in use.

Results
Metrologically, this study showed that the Inclined plane method gives very good results. In addition, the classification of floor coverings using this method is widely used by professionals.
However, its application has major drawbacks including the need to use test subjects and the impossibility of taking on-site measurements.
LabINRS also gives very good metrological results. It is simple to apply, but also has the drawback of not allowing on-site measurements.
In contrast, the Pendulum SRT, on account of its very simple operating principle, is suited to on-site measurements. It is widely used by professionals. However, the correlation with the psychophysical method is low, raising questions about its ability to classify floor coverings according to their slipperiness. Moreover, it does not allow qualification of every type of floor covering, e.g. those with macro-unevenness.
As for the PFT, the metrological results turned out to be very satisfactory. It allows both laboratory and on-site measurements on every type of floor covering. INRS has previous experiment of its use, in particular to qualify floor coverings intended for the food-processing industry.

Conclusions
At the present time, the two methods proposed by the standard do not classify floors in the same way, which is “troublesome” in standardisation. Furthermore, floor covering manufacturers, floor layers and prevention specialists need a means to measure the coefficient of friction both in the laboratory and on-site.
As the PFT is satisfactory in both metrological and practical terms, it will be proposed to the CEN. It has the advantage of being as satisfactory as the Inclined plane method, metrologically speaking, and also of being as practical in use as the Pendulum SRT.