Kevan Brassington, NBS Technical Author and SlipSTD member, guides specifiers away from the slippery slope of floor covering design.

If you have ever specified a floor covering that requires slip resistance properties, then you are probably aware of the difficulties in determining its slip resistance performance. If your research included the guidance in NBS Building work sections M40 (ceramic tiles and other hard floor coverings) and M50 (resilient floor coverings), you will know of the slip resistance recommendations provided by such organizations as the UK Slip Resistance Group (UKSRG) and Stone Federation Great Britain. They recognize the Transport Research Laboratory pendulum test as the preferred method of determining a Slip Resistance Value, or as it is now known a Pendulum Test Value (PTV).

The Pendulum Test

This simulates the action of a shod foot slipping by swinging an imitation heel clad with standard soling rubber over the test surface. BS 7976 Pendulum testers defines the apparatus and test method, while other standards, e.g. BS EN 14231 Natural stone tiles, refine the test method for particular floor coverings. PTVs can be obtained for dry surfaces and surfaces contaminated with water. Research has proved the pendulum test to be accurate and reliable and it has been adopted by the Health and Safety Executive (HSE) as the standard test for the assessment of floor slipperiness in dry and contaminated conditions. It also has the advantage of being portable and therefore capable of producing in situ values. The HSE emphasizes that pendulum operators need to be fully trained to obtain consistent results. Table 1 from the UKSRG Guidelines 2005 compares the relative risk of slipping with PTVs.

Table 1

Slip potential PTV
High 0–24
Moderate 25–35
Low 36+

So, having established what minimum dry and/or wet PTV is required for your particular application, you start searching manufacturers' literature for products that meet the required value. If you are lucky you will find performance figures that have been produced using the pendulum test. However, for some floor coverings, particularly those products originating in mainland Europe, you may find slip resistance performance indicated in other formats, e.g. R9 to DIN 51130 or BCRA Tortus wet μ >0.4 to Decree DM 14.06.

DIN 51130 and DIN 51097

These are German test methods that require an operator with standard footwear (DIN 51130) or barefoot (DIN 51097) to walk on the test surface. Known also as the ramp test, the inclination angle of the test surface, can be varied under the control of the operator, the test surface can be sprayed with liquid contaminant at a prescribed rate, motor oil (DIN 51130) or a soap solution (DIN 51097). The operator, wearing a fall restraint harness gradually increases the inclination of the ramp until he or she feels insecure or slips when walking up and down the slope. The angle at which slipping occurs is used to establish a classification 'R' value for the shod test (Table 2) and an A, B or C rating for the barefoot test (Table 3).

Table 2: DIN 51130

Classification Slip angle (°)
R9 6–10
R10 10–19
R11 19–27
R12 27–35
R13 >35

 Table 3: DIN 51097

Classification Slip angle (°)
A 12–17
B 18–23
C >24

The contaminants used in these tests give cause for concern as they are not representative of contaminants generally found in the workplace. The Health and Safety Laboratory has developed a refined version of the test using water as a contaminant and has determined that consistent results can be obtained when the test is undertaken by trained operatives.

A common failing of specifiers is to assume that the 'R' scale starts with R1 offering the lowest slip resistance and terminates with the highest value at R13, thereby producing the misconception that R9 products offer a high degree of slip resistance. Floor coverings rated at R9 and in some instances R10 subjected to some contaminants can prove to be unacceptably slippery. The obvious problem with the ramp test is the inability to use the test equipment on site.

BCRA Tortus

The less well known test is used in Italy, but is not favoured in the UK despite originating here. The test is defined by the HSE as a sled test, being a self-propelled trolley that moves across the test surface measuring the coefficient of friction. The HSE has found that sled tests can be unreliable as tests values for surfaces, when contaminated with water, may indicate the surface to be less slippery than the same surfaces tested in dry conditions.

The UK specifier wanting to use products such as resilient floor coverings from Germany or ceramic tiles from Italy is faced with considering R or Tortus values knowing that the test methods are not favoured by the HSE, UKSRG and other UK organizations. European countries other than the UK, Germany and Italy are beginning to favour either the pendulum or ramp test. Spain has passed legislation requiring the use of the pendulum test, while France is planning to adopt a modified version of the ramp. In this way European countries are becoming entrenched as either pendulum or ramp users. Some manufacturers are recognizing the problem and are beginning to supply PTVs and R values for their products. Recognizing this impediment to trade, a CEN committee has been charged with establishing a single acceptable test method. The latest information emanating from the committee suggests this is not going to prove possible. Work continues, progress is being made, but it would seem the test method problem is not going to be quickly resolved, or is it?

The SlipSTD project

This is co-financed by the European Commission (Note 1) and has a project 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.' The project is nearing completion and has succeeded in proposing a simple three value classification system that takes into account the anticipated type of contaminant, the existence of any slip reducing control measures and cleaning regime. A set of standard surfaces with different slip resistance characteristics has also been established that will provide a reproducible validation tool for slip resistance measurement.

Designers will be able to specify hard floor coverings by SlipSTD classification in the knowledge that slip resistance requirements will be met. Manufacturers will be able to test their products using their preferred test methods calibrated against the standard surfaces, mark their products with the appropriate SlipSTD class and market their products with a common slip resistance classification in all EC countries. The SlipSTD Consortium believes the classification system need not be restricted to hard surfaces, and can be extended to other floor coverings.

The SlipSTD project is coordinated by CERAM Research Ltd, and includes as UK members The Tile Association, the HSE and the RIBA (represented by NBS). A publically available specification (PAS) will be published in the summer of 2009 detailing the classification system, an indication of the supporting research work and recommendations for the cleaning and maintenance of ceramic and natural stone floor coverings.

Note 1: Through the Sixth Framework Programme (FP6) Horizontal Research Activities Involving Small and Medium Enterprises.