A pendulum slip tester is a device designed to measure the friction of walking surfaces. It works by swinging a weighted arm fitted with a rubber slider across the surface. The amount of resistance encountered translates into a slip resistance value.
Originally developed by the UK Transport and Road Research Laboratory (TRL) in the 1950s for road testing, this equipment is now the gold standard in assessing pedestrian safety.
The BS 7976-2 Standard
BS 7976-2 is the British Standard that defines the method for measuring slip resistance using the pendulum tester. It specifies procedures for both wet and dry conditions, ensuring repeatable, reliable results.
This standard is recognized worldwide. In fact, equivalent standards exist in Australia (AS 4663), the U.S. (ASTM E303), and ISO. It’s widely used in construction, facility management, sports, and even forensic accident investigations.
Principle of Operation
Think of it like a child’s swing. The pendulum arm swings down, and if the surface is very slippery, the swing loses very little energy, continuing smoothly. If the surface has good grip, the slider drags, reducing the pendulum’s motion.
This energy loss is measured as the Pendulum Test Value (PTV). The higher the PTV, the safer the surface.
Key Components of the Equipment
The pendulum slip tester is carefully engineered. Its main components include:
- Pendulum Arm – the swinging part of the tester that carries the slider.
- Test Foot (Slider) – the replaceable rubber pad that makes contact with the floor.
- Spring Mechanism – ensures consistent force during each swing.
- Release Mechanism – allows precise, repeatable release of the pendulum.
- Base Unit & Leveling System – ensures stability and correct angle of swing.
- Scale & Pointer – displays the PTV reading.
- Calibration System – guarantees accuracy and compliance with BS 7976-2.
The Test Foot (Slider) in Detail
Sliders are critical. Typically, two main rubbers are used:
- 4S Rubber (Standard Shoe Sole) – simulates pedestrian footwear.
- TRL Rubber – used for more specialized applications like road surfaces.
Sliders must be conditioned (abraded and cleaned) before testing to ensure accuracy. A worn or contaminated slider can give misleading results.
Surface Preparation Before Testing
For reliable readings, surfaces must be free of dust, grease, or residues. In wet tests, controlled water application is used to mimic real conditions such as rain, spills, or cleaning.
Step-by-Step Testing Procedure
- Place and level the equipment.
- Fit the correct slider.
- Adjust height so the slider makes proper contact.
- Release the pendulum to swing across the surface.
- Read the PTV on the scale.
- Repeat several times for accuracy.
Interpreting Test Results
PTV values fall into clear categories:
- 0–24 PTV: High slip risk
- 25–35 PTV: Moderate slip risk
- 36+ PTV: Low slip risk (considered safe)
This classification applies particularly to wet conditions, as dry readings are usually higher.
Factors Affecting Accuracy
- Environment – temperature and humidity can affect rubber properties.
- Operator Technique – consistent handling is vital.
- Slider Condition – worn or dirty sliders give unreliable data.
Calibration and Verification
Like any precision instrument, pendulum testers need regular calibration. Typically, calibration is required annually, with interim verification checks before critical tests.
Advantages of Pendulum Slip Testing
- Portable and easy to use indoors or outdoors.
- Works on a wide variety of surfaces, from tiles to asphalt.
- Recognized by courts, insurers, and regulators.
