Understanding Coefficient of Friction (COF)

When discussing the coefficient of friction (COF) and/or slip resistance it is important to understand that a pedestrian (walking) surface does not have a COF or slip resistance in and of itself. The COF is a function of the interaction between TWO surfaces, one moving (pedestrian foot or footwear) across the other pedestrian surface. The composition and interaction of both surfaces determine the COF.

From a simple physics perspective, the coefficient of friction, COF, is a measure of the amount of friction existing between two surfaces. A low value of coefficient of friction indicates that the force required for sliding to occur is less than the force required when the coefficient of friction is high. The value of the coefficient of friction is given by:

COF = Frictional Force(F) / Normal force (N)

The direction of the forces given in this equation are as shown in Figure. The coefficient of friction is the ratio of a force to a force, and hence has no units. Typical values for the coefficient of friction when sliding is occurring, i.e. the dynamic coefficient of friction are:

  • for polished oiled metal surfaces, less than 0.1
  • for glass on glass, 0.4
  • for rubber on tarmac, close to 1.0

Four primary physical factors affect traction between a person’s footwear and the pedestrian surface they are walking on:

  • Flooring material (pedestrian surface) – controllable
  • Footwear sole material and condition – generally uncontrollable, except in some workplaces
  • Environmental contaminants – controllable
  • Gait dynamics (how an individual walks) – uncontrollable

Building owners, managers – what you should to know

As a building owner and/or manager you have a responsibility to ensure all pedestrian surfaces in your building are safe to walk on. That is, all flooring surfaces have adequate slip resistance appropriate to the location and/or intended use of each area of your building. This risk of slipping depends upon location and use of area, amongst other factors discussed below.

The Australian Standards Handbook HB197:1999 An Introductory Guide to the Slip Resistance of Pedestrian Surface Materials acknowledges the pedestrian contribution to the risk of slipping and also the nature of the anticipated activity and the probability of a range of contamination conditions. It intrinsically recognises that there is a significant difference between the type of flooring that would be safe, for example, in a large commercial kitchen and that in a domestic kitchen. 

The Handbook provides recommendations for pedestrian surface materials in many common generic locations/areas. The basic premise used to assess ‘contribution of the floor to the risk of slipping’ is the likelihood of the floor becoming wet or contaminated with a foreign substance and to some extent the type and amount of contaminant. Obviously and external pavement open to the weather should have a higher slip resistance than an office or retail floor inside a shopping centre. Likewise, a shopping centre food court should have a higher slip resistance that a retail floor area and public bathroom (potentially used by hundreds of people each day) should have a higher slip resistance than a hotel bathroom (potentially used by 1-2 people each day). Similarly, a sloping surface such as a disabled ramp should have a higher slip resistance than a level surface.

Other design considerations include:

  • The amount and type of expected traffic (vehicles, trolleys, people hurrying, elderly, disabled people with or without walking aids, and children)
  • Flooring characteristics (wear resistance and cleanability) and the consequences of exposure to the types of contaminants that might be anticipated
  • Environmental design factors (visibility issues and contamination minimization); management policy and maintenance practices (type of cleaning equipment, frequency and effectiveness of cleaning)
  • Environmental conditions (lighting and sloping surfaces) along with the footwear to be worn.
  • Compliance with occupational, health and safety requirements; special provisions for slip hazards (guards and handrails)
  • Visual aids (warning signage and contrasting stair nosing’s)

National Construction Code (NCC) Slip Resistance Requirements

The National Construction Code (NCC) includes safety performance requirements for safe design which requires most commercial buildings to provide slip resistive surfaces for safe movement, specifically emergency access and egress. The slip resistance requirements of the NCC state that “non-slip” and “non-skid” surfaces must be installed for pedestrian ramps, stair treads and landings. Further, parts of buildings may need to comply with disability access requirements.

Disability Access Slip Resistance Requirements

Where disability access is required, finishes must comply with Clause 7.1 of AS1428.1 Design for access and mobility Part 1 general requirements for access- Buildings. This states that all continuous accessible paths of travel shall have a slip-resistant surface.

Occupational Health & Safety Slip Resistance Requirements

The various state based Workplace Health and Safety (WHS) legislation regulate general duties for employers and controller of premises to identify, assess and control risks to employees and others at a place of work. This includes the provision to identify any foreseeable hazard arising from the premises that has the potential to harm the health or safety of any person accessing, using or egressing from the premises such as people slipping tripping or falling. Additionally, there are duties for safety in design, which extends to those who design, specify or supply floor surfaces intended for places of work.