Measuring the slip resistance of floorings and footwear

Introduction

Testing and assessment of anti-slip characteristics is of major importance for the prevention of slipping accidents. Numerous different methods and devices have been developed over the years to measure the slip resistance of floorings and footwear. Different European countries have adopted various test methods and rating systems. Because these test methods are based on different principles and are used under different conditions there is no correlation between them. No single test currently in use is perfect. All have their advantages, but also their own particular flaws and disadvantages.

Floorings

The most common test methods for floorings are ramp tests, tribometer tests and pendulum tests.

Ramp test

A widely used test is the ramp test according to the German norm DIN 51130. This test requires an operator who is protected by a fall restraint harness. The operator, wearing standard footwear, walks backwards and forwards over a sample of a flooring material that has been evenly coated with oil. Beginning with the ramp in a horizontal position, he gradually increases the angle of inclination until the limit of safe walking is reached and the test person slips. The acceptance angle obtained is used to express the degree of slip resistance.

The ramp test is also carried out barefoot with the use of soapy water as a contaminant (DIN 51097)^[3]. The angle at which slipping occurs is used to establish an A, B or C rating for the barefoot test (Table 2)^[2]. Barefoot ramp tests are useful in wet areas, such as swimming pools and saunas.

The ramp test allows testing of all types of floorings, such as ceramics, granite, natural stone, timber, steel gratings and flexible materials. The ramp test can also be used to determine the slip resistance of profiled surfaces. To a certain degree this test method takes into account the human walk. However, ramp test work requires well-trained operators in order for reliable and reproducible results to be obtained. This test is not suitable for on-site tests. The ramp test is the preferred test method for instance in Germany, France and the Benelux countries.

Tribometer test

This test method is based upon a friction force measurement. A body equipped with sliders is pulled at a constant speed over the flooring surface. The force required to pull the body is determined over the length of the measuring distance.

The coefficients of dynamic friction measured with the GMG 200 or with its predecessor, the GMG 100, are evaluated as follows. At coefficients lower than 0.30, the floor is classified as being insufficiently slip resistant. An acute risk of slipping exists. The slip resistance of the floor must be improved. If necessary, a new floor must be installed. If coefficients of friction of between 0.30 and 0.45 are measured, the floor may be classified as slip resistant, but risk-oriented measures such as those described in the section on the prevention of slip accidents must be taken, in consideration of operational requirements. Where the coefficient of friction exceeds 0.45, the floor is deemed to be serviceable without qualification. It exhibits an adequate slip resistance potential, and the risk of slipping is low even under unfavourable conditions, such as moisture.

Other tribometers are the FSC 2000 and BCRA Tortus. These devices are not covered by a standard at present. In Italy, Ministerial decree 236/89 requires slip resistant floorings to have a friction coefficient greater than 0.4 in the dry and wet state, as measured with the BCRA Tortus. Some such devices are considered to give over-optimistic slip resistance readings on wet, polished or glazed surfaces.

Pendulum test

SlipSTD PAS

Co-financed by the European Commission, the SlipSTD project had the objective to define common 'European' minimum slip resistance requirements for ceramic tiles based on defined and measurable surface properties in preference to traditional slip resistance testing. It was conceived as a joint approach to overcome the objections to and shortcomings of the various approaches outlined above. The SlipSTD PAS (Publically Available Standard) is the outcome from that^[6]. It suggests a new approach for testing the surface of a hard floor covering, to determine an acceptable slip resistance performance levels appropriate to the floor covering’s installed usage and foreseeable contamination. It envisages three classes for hard floor coverings:

• Class 1: Hard floor coverings for internal pedestrian areas that are foreseeably clean and dry and are routinely maintained as such.  
• Class 2A: Hard floor coverings for internal pedestrian areas foreseeably contaminated with water and/or dry contaminants. 
• Class 2B: Hard floor coverings for internal pedestrian areas foreseeably contaminated with other liquid contaminants with viscosity higher than water, such as oil and grease. 

Coverings are classified through the measurement of surface characteristics of the material (primary surface parameters) measured using optical topography techniques.

Footwear

Glycerine or sodium lauryl sulphate solution acts as contaminant on the surface. The frictional force is measured and the dynamic coefficient of friction is calculated. Depending on the test conditions, the friction coefficients must fulfil certain requirements given in EN 20345 (Table 4)^[8].