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Three Layer Model + Floor Safety


3-Layer Model and Floor Safety


The three layer model is a simple but powerful tool for understanding and managing the overall risk of slipping. The three layers comprise: the human layer, the contamination layer (or barrier layer) and the floor layer. Most slips start with a heel strike. On a clean dry floor the shoe heel strikes the floor. On some floors, there will be some water or contamination and this can create a barrier. The contamination, especially water, oil or other viscous material can create a "hydrodynamic squeeze film", that lifts the shoe and you begin to slide. The effect can be like aqua-planing and your foot can then accelerate at up to 15 meters per second (faster than Usain Bolt) for up to 600mm before it takes off. You tend to land where the slip started.


3 layer model


3-Layer Model Wider Context


The three layer model mirrors the physics of s slip: 1) shoe heel + 2) the contamination between shoe and floor + 3) the floor. It can also be used to model the factors that you can control to minimise slip risk. In its wider sense, the HUMAN LAYER includes everything related to the pedestrian and his/her reasons for being on the floor... it would include such things as footfall (the number of people on the floor every day), the type of footwear being used and whether there is any control (e.g. in a swimming pool shower room most people will wear bear feet, while in a kitchen, many kitchen staff will be advised to wear safety shoes) causing you to fall and land where the slip started.


Human Layer: shoe heel, walking speed, gait, weight...
Contamination Layer: dirt, water etc between the shoe and floor
Floor Layer: material, hardness, porosity, surface finish...


Human Layer Controls

Can you control what shoes people wear, how fast they walk, bare foot access, wheelchair access etc?... e.g. kitchen staff may benefit from good slip resistant footwear.

3 layer model

Contamination Layer Controls

Can you control ingress of water or contamination, frequency of cleaning, method of cleaning, access to floor when wet? e.g. after cleaning, if the floor is high risk when wet, always ensure floor is fully dry before staff walk on it.

Floor Layer Controls

Is the floor suitable for the required use? Is the slip resistance of the floor durable, can the floor be kept clean? Will the surface finish (including coatings, paints etc) change?

Top Tip:

Consider the factors you can control to reduce the overall slip risk.

Measure the floor slip risk with and without contamination.


Human Layer: shoe heel, walking speed, gait, weight...
Contamination Layer: dirt, water etc between the shoe and floor
Floor Layer: material, hardness, porosity, surface finish...


  • The human layer determines the level of grip that is required

  • The level of contamination will limit the available grip

  • The clean dry floor will indicate the maximum grip available from the floor

SlipAlert makes it quick and easy to measure and monitor the floor slip risk in different conditions. You can measure available slip resistance of the floor in normal use, when clean and dry, and when wet or otherwise contaminated. This enables you to make informed decisions and manage the overall slip risk.


Slip Risk Numbers and 3 Layer Model


The floor may give a reading of 130 or less in the dry, making it a low risk when clean and dry. You should also consider the clean wet value and the likelihood the floor will be wet. A shopping Mall entrnce area will need better slip resistance (lower risk) than a quiet area of the Mall that is never wet.


SlipAlert Test Value (STV)

< 130

130 - 136

137 - 160

161 - 179

> 180

Wet Slip Risk

Low Risk

Low Risk



High Risk

Suitable for

Very Wet

Wet Areas

Transitional Areas - can occasionally become wet

Areas kept largely dry

Dry Areas








> 40

39- 36

35 -24

23 - 19



(Co-efficient of Friction)

> 0.40

0.39- 0.36

0.35 - 0.24

0.23 - 0.19



Once you understand the actual measure of risk for your floor, you can ensure that cleaning and maintenance enables you to maintain a safe enough level of risk. If the level of risk begins to rise, you should check the cleaning and maintenance regime.


Guide to Slip Prevention

The links below reflect the links on the pages of the Pocket Guide to Slip Prevention.

Slip Prevention Extra Detail

Order Your Pocket Guide

The printed version of the Pocket Guide to Slip Prevention is a free publication designed to help you to manage slip risk. Contact SlipAlert




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