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Wet Pendulum Slip Resistance Test

The wet pendulum friction tester is a device that was first developed to measure the skid resistance of road surfaces to assess the condition in a road traffic accident. Since then the pendulum tester has been used to assess the slip resistance of pedestrian flooring surfaces and the risk of slipping.

The equipment was specified in the first Australian Standard for slip resistance; AS/NZS 3661.1:1993 Slip resistance of pedestrian surfaces – Requirements. The wet pendulum slip test essentially comprises a metal boot with a spring loaded rubber slider on the bottom that swings down and slides across the surface. The boot swings back up, in which the height it swings back up tells us how slippery the floor is. The more slippery; the higher the pendulum swings back up.

How is the Pendulum Slip Test Conducted ?

The test is conducted in a wet condition by spraying the surface with water. The pendulum is swung across the surface five times as a minimum and the average of the last three readings are used to calculate the average after testing five products or locations.  

The machine is simplistic, however operators require formal training under a NATA accredited program to ensure quality and reliability of the wet pendulum slip ratings obtained. We have observed a number of people conducting the test incorrectly which may affect the final slip rating significantly.

To ensure the accuracy of results, it is always recommended to ensure that any test reports provided by a testing company are accredited by the National Association of Testing Authorities (NATA). This means that they are technically competent having been auditing by a semi-government organisation and that they have a quality management system in place.

Changes in the Pendulum Slip Testing Method

There have been some changes over the years in the testing methodology since the first Australian Standard AS/NZS 3661.1. The latest Australian Standards include the wet pendulum slip test for both new and existing surfaces, being AS 4586:2013 Slip resistance classification of new pedestrian surface materials and AS 4663:2013 Slip resistance measurement of existing pedestrian surfaces. The differences in the new slip resistance testing standard basically includes the use of a lapping film to condition the rubber slider materials. This effectively discriminates, or spreads the results of smoother surfaces.

The wet pendulum slip resistance test may be conducted using one of two types of sliders. Slider 96 which was formerly known as Four S or Slider 55, formerly known as TRRL or TRL rubber. Slider 96, which is named from the hardness of the slider in IRHD or Shore A, is generally used for all surfaces and Slider 55 is used for more barefoot situations as it is a softer material, being more similar to the resilient nature of wet feet. Slider 55 has also been used to undertake independent slip resistance testing of pavers and stone used particularly for external paths and road surfaces.

The individual measurements of wet pendulum testing are provided as a British Pendulum Number (BPN), being of a unit less measurement. The average of the five measurements or BPN is known as a Slip Resistance Value (SRV). This may get confusing, particularly when there are other aspects relating to sloping surfaces and ramps which include Slope Design Values (SDV) and Slope Correction Values (SCVs). More of these intricacies of slip resistance testings and ratings will be discussed further through these pages and the blog.

One of the advantages of the pendulum slip testing equipment is that the machine is portable and can be taken onsite to verify the slip resistance of the surface, unlike the inclining barefoot ramp and oil-wet ramp tests. Contaminants other than water can also be used, such as measuring the effect of oil or soapy liquid to assess how this may affect the slipperiness of the surface.

Assessing Pendulum Slip Test Ratings

To this day, there is still great debate in Australia as to assessing the risk of slipping when comparing the measurements obtained from the pendulum friction tester. Originally AS 3661.1 required that a wet surface obtain a Coefficient of Friction (CoF) of at least 0.40 (BPN of 39) for a level walking surface. This threshold limit was then rejected partially in 1999 and completely in 2002 when the first version of AS 4586 and AS 4663 were released. These new documents outlined a risk management system in assessing the notational contribution of the risk of slipping when wet.

This risk management assessment is in limbo at the release of AS 4663-2013 where the risk assessment has been removed until an updated version of HB 197 An introductory guide to the slip resistance of pedestrian surface materials.



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