When a floor is slip-tested, the result comes back as a Pendulum Test Value, or PTV. It's a single number — but people often misunderstand what it means, and that can lead to either false confidence or unnecessary panic. Here's what a "safe" PTV actually is, and the nuances the specialists want you to know.
The three slip-potential bands
The UK Slip Resistance Group (UKSRG) and the Health and Safety Executive (HSE) classify floors into three bands based on their PTV:
| Slip potential | Pendulum Test Value (PTV) |
|---|---|
| High | 0 – 24 |
| Moderate | 25 – 35 |
| Low | 36 and above |
So the short answer to "what's a safe floor?" is: one that achieves a PTV of 36 or above in the conditions in which it's actually used.
Where the "36" comes from
The threshold isn't arbitrary. It traces back to research carried out by the Building Research Station in the late 1950s, which measured the coefficient of friction that able-bodied people need to walk safely on the level. That work produced a scale of slip risk:
| Coefficient of friction | Risk of slipping |
|---|---|
| 0.19 | 1 in 2 |
| 0.24 | 1 in 20 |
| 0.29 | 1 in 10,000 |
| 0.34 | 1 in 100,000 |
| 0.36 | 1 in 1,000,000 |
Because a PTV is roughly 100 times the coefficient of friction, a coefficient of 0.36 — a one-in-a-million slip risk — corresponds to a PTV of 36. That is why 36 became the benchmark for "low slip potential."
Wet or dry — which figure matters?
This is where many people go wrong. A floor might score a comfortable PTV in the dry and a dangerous one in the wet. Since most slips happen on contaminated surfaces, the wet result is usually the critical figure for any area that can get wet — entrances in bad weather, kitchens, bathrooms, pool surrounds, and so on.
That said, UKSRG cautions against treating "wet PTV 36" as a rigid, universal minimum. Millions of people safely cross floors every day whose wet PTV is below 36 — because those floors stay dry in normal use and any spills are cleaned up quickly. The right standard depends on how the space is genuinely used.
PTV is not a simple pass/fail
The guidelines are explicit: a PTV should be interpreted as part of a risk assessment, not as a pass/fail line. Several factors matter alongside the number:
- The test itself has an inherent uncertainty of one to two units, so a PTV of 35 is not meaningfully more dangerous than a 36.
- Footwear, contamination and cleaning regimes all affect real-world risk.
- The floor manufacturer's guidance on suitable end-uses should be taken into account.
In other words, the PTV tells you a great deal — but it is evidence to be weighed, not a verdict on its own.
Barefoot areas are tested differently
For areas used barefoot — swimming pools, changing rooms, spa and bathroom floors — the test uses a softer Slider 55 (TRRL) rubber rather than the Slider 96 (4S) used for shod areas. A gym changing room used both ways may be tested with both.
Frequently asked questions
Is a higher PTV always better?
Generally yes for slip safety, but very high-grip surfaces can be harder to clean or uncomfortable underfoot, so the aim is a surface that is appropriately safe for its use, not simply the highest possible number.
My floor scored 35. Is it dangerous?
Not necessarily. A 35 sits at the top of the "moderate" band and, given test uncertainty, is close to the low-risk threshold. A specialist can advise whether treatment is warranted based on how the area is used.
Can an anti-slip treatment raise my PTV?
Yes — a properly applied treatment can lift an existing floor into the low-slip band, and a re-test documents the result.