BS EN 16165 Annex D — The Tribometer Test

How the tribometer test works

The tribometer is a self-contained portable instrument with a rubber slider mounted on a spring-loaded arm. The instrument is placed on the surface, levelled, and triggered. A small motor drags the slider at a defined velocity (typically a few centimetres per second) while a load cell records the horizontal force needed to maintain motion.

The output is the dynamic coefficient of friction — a dimensionless number, typically expressed to two decimal places, with practical values for floor surfaces in the range 0.05 to 0.80.

Common tribometer instruments

• GMG-200 — German-manufactured, widely used in European tribometer testing
• BOT-3000 — North American, used predominantly under ANSI standards
• Tortus — Earlier-generation portable friction tester, less common today

Each instrument has its own calibration regime, slider compound and sweep velocity, so cross-comparison between tribometer types is not straightforward.

Where tribometers add value

Tribometer data is most useful as a supplement to pendulum data in specific contexts:

• Forensic analysis of incidents where the pendulum result is borderline
• Research and product-development testing where continuous friction measurement is needed
• Cross-referencing UK pendulum data to international (often North American) friction data using comparable methodology
• Testing surfaces too small or oddly shaped for pendulum slider sweeps

Why the pendulum remains the UK primary method

The UK National Foreword to BS EN 16165:2021 explicitly states that the pendulum (Annex C) is considered the only one of the four methods that should be relied on to correctly assess pedestrian slip risk in wet conditions. The reasons are well established:

• Four decades of UK forensic and HSE experience are with the pendulum
• The pendulum's heel-strike geometry better simulates the slip moment in walking
• UK PTV bands (HSE 0–24, 25–35, 36+) are pendulum-derived; tribometer COF values do not translate one-to-one
• Court and insurance practice in the UK references pendulum results, not tribometer COF

Tribometer data therefore complements but does not replace pendulum data in UK practice.

Tribometer to PTV — the comparability question

There is no robust general formula for converting tribometer COF to pendulum PTV. The relationship is surface-dependent and contamination-dependent. For specific surface types and contamination conditions, empirical correlations have been published, but applying these correlations outside their tested range is unreliable.

If a tribometer result needs to be expressed as PTV — for example, to compare to a UK specification — the safest approach is to take both measurements on the same surface and report each on its own scale, with the correlation noted only as approximate.

ANSI A326.3 and the North American context

The North American standard ANSI A326.3 specifies tribometer testing using the BOT-3000 or comparable instruments, producing the Dynamic Coefficient of Friction (DCOF) value. This is the dominant friction metric in North American practice, with thresholds typically set at DCOF 0.42 wet for satisfactory performance. UK readers encountering ANSI DCOF data should not assume it translates directly to UK PTV expectations — the methods, sliders and reporting conventions differ.