What is the Pendulum Test? PTV explained

What the pendulum test is

The pendulum test is the method UK floor-safety professionals rely on to measure how slip-resistant a surface is. It is the test the Health and Safety Executive (HSE) points to when assessing slip risk, and it underpins the guidance published by the UK Slip Resistance Group (UKSRG). Because the instrument is portable, it can be used both in a laboratory and in place on a floor that is already installed and in use.

It works by imitating the thing that causes most slips: a heel striking the floor and sliding forward. A weighted arm fitted with a rubber slider swings down and sweeps across the surface, and the grip of the floor is read from how much it slows that swing. The pendulum was chosen by the UKSRG and HSE because it reproduces the thin film of water that forms under a foot on a wet floor, and because its readings have correlated well with real slip accidents since the 1950s.

How the test works

An operator levels the instrument on the surface, sets the slider contact length with a footprint ruler, then releases the arm from horizontal. As the slider drags across the floor, a trailing pointer is carried up the 0–150 scale and marks the result. In a standard test, eight swings are taken and the Pendulum Test Value (PTV) reported is the median of the last five. Readings are taken in three directions — the main line of travel, across it, and at 45° — and in both the dry and the wet state, because a floor is rarely equally grippy whichever way you cross it. When judging risk, it is the lowest PTV that matters most, not the average — that is the worst case a pedestrian could meet.

What a PTV score means

The link between grip and the chance of slipping comes from research originally carried out by the Building Research Station. A PTV is roughly 100 times the coefficient of friction, which gives the following picture for someone walking in a straight line on the level:

For everyday use these are grouped into three bands of slip potential:

What counts as a “safe” PTV

It is tempting to treat 36 as a magic pass mark. The UKSRG is careful to warn against exactly that. The test itself carries an uncertainty of a point or two, so there is no meaningful difference between a PTV of 35 and 36, and a single number should never be read as a hard pass/fail line.

What the guidance actually says is that a floor should achieve 36 or above in its normal operating condition. For a floor that stays clean and dry in use, that means 36+ when dry. For a floor that gets wet or contaminated, it means 36+ when wet — because that is the condition in which people slip. Plenty of floors with a wet PTV below 36 are walked on safely every day, because they are kept dry and spillages are dealt with quickly. The right target for your floor comes from a risk assessment of the whole picture — the surface, the likely contamination, the footwear, the task and the cleaning regime — not a number in isolation. Our guide to what PTV your floor needs works through this.

Wet versus dry testing

Almost any floor grips well when bone dry. Slips happen when water, grease or other contamination gets between shoe and surface and cuts the friction. That is why, for the great majority of spaces that ever get wet, the meaningful number is the wet PTV. A floor that scores well dry but poorly wet is exactly the kind that catches people out.

Sliders: shod and barefoot

Two standardised rubber sliders are used, depending on how the floor is walked on. Slider 96 (historically called 4S) represents a shod foot and is used for general areas. Slider 55 represents a wet bare foot and is used for showers, changing rooms and pool surrounds. BS EN 16165 refers to this softer rubber as Slider 57, but the UK’s long-standing preference is Slider 55. Where an area is used both shod and barefoot — a gym changing room, say — both sliders are used.

The standards behind it

In the UK the pendulum method sits under BS EN 16165:2021, which replaced the older BS 7976-2 and folded in the German DIN ramp standards. The UKSRG Guidelines, currently Issue 6, set out the recommended best-practice method and align with BS EN 16165. For results to be valid, the instrument must be calibrated at least once a year, and verified against reference surfaces before each day’s use — an uncalibrated or unverified pendulum produces numbers you can’t rely on.