The microroughness of a surface has a significant impact on its slip resistance. This is due to a phenomenon known as hydraulic uplift created by the hydrodynamic squeeze film. When a slip event occurs in wet or contaminated conditions, the heel will slide across the surface. This will compress the fluid or contaminant.

If the surface is sufficiently rough the fluid disperses into the valleys, and the peaks ensure a good sole/floor contact.
If the surface is insufficiently rough the sole is unable to make contact with the floor due to the fluid film, and friction is significantly reduced.

In addition to obtaining a Pendulum Test Value (PTV), supplementary information from a surface roughness meter, which can measure the Rz parameter, is recommended by

• Ireland’s Health & Safety Authority (HSA)
• UK Health & Safety Executive (HSE)
• UK Slip Resistance Group (UKSRG)

The table below gives an indication of expected slip potential in water-wet conditions.

Surface microroughness (Rz) can be a good indication of the effects of wear. Over time the peaks of the floor microroughness can be worn down, thus reducing Rz and slip resistance. A significant change in surface roughness can often be an indication of a poor cleaning regime. Valleys in the floor micro-surface can often become clogged with dirt over time, thus reducing the measured Rz distance.

Quin Friction Laboratories measures floor surface microroughness (Rz), in accordance with BS 1134-1, as part of our system of operation when performing slip resistance testing.

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