Problems with walking surfaces cause over half of all slip and fall injuries. While it’s easy to spot some of these hazards — such as uneven surfaces, spills and debris — this is usually not the case with a particular problem: low traction. Not only is low traction generally invisible, it’s not immediately obvious how to quantify it and tell when to do something about it.
You can’t go by perceptions, because multiple factors are at play. If ten people walk across the same floor, each might have a different sense of whether the floor is safe or slippery. Reasons for these different perceptions include unique gaits, strides and footwear choices, including type of shoe, type of sole and each sole’s degree of wear. There are also unconscious or forgotten adjustments—people who walk the same areas daily come to know the slippery spots and often alter their approaches and walking patterns until those spots seem safe. A pedestrian’s experience is also influenced by factors such as an area’s lighting and the floor’s finish, so you simply cannot rely on personal assessments of a floor’s traction.
Fortunately, there is a scientific method to measure a surface’s coefficient of friction in an objective manner. This method will help identify problem areas and point out when you need to improve traction, and thta helps prevent slip and fall injuries.
Coefficient of Friction
A surface’s coefficient of friction (COF) relates to energy. The more energy required to drag something over a surface, the higher the COF and the less likely the surface is to contribute to a slip and fall incident.
Factors affecting COF include:
- Presence of liquid, grime or other residue
- Maintenance of the surface
- Age and deterioration of the surface
The Occupational Safety and Health Administration (OSHA) requires employers to keep floors clean and dry in 29 CFR 1910.22(a), but the regulation does not specify a minimum COF. In an interpretation letter written in 2003, OSHA references a regulatory preamble that recommends a COF of 0.5, but this document does not list a standard or procedure for testing. The Americans with Disabilities Act (ADA) recommends a COF of 0.6 on level surfaces but also does not list a standard or procedure for testing.
Tribometry, or the science of measuring friction, traces back to the 15th century and to none other than Leonardo da Vinci. This science uses instruments called tribometers to evaluate friction and traction. Tribometers measure one or both of the following:
- Static Coefficient of Friction (SCOF) — The amount of horizontal force it takes to initiate movement in a horizontal motion. (The potential for someone to slip.)
- Dynamic Coefficient of Friction (DCOF) — The horizontal force that is required to maintain horizontal motion. (The potential for someone to slide after they slip.)
Although tribometry is a science, learning to use a tribometer to measure COF doesn’t require a college degree. Tribometers are easy to use and come in many different types. Some are designed for dry surfaces, others for wet, and some will work on both.
It is important to note that there is no way to calculate the COF of a wet surface based on the COF of same surface when dry, and vice versa – so if you need the COF for wet as well as dry, be sure to choose a tribometer that is able to measure each way.
National consensus standards provide a basis for using tribometers correctly. Some are even specific to the type of tribometer and the type of finish on a floor. Standards exist for everything from polished floors to tires on a paved roadway. Some are for real-world conditions while others apply only in laboratory settings. Some examples are:
- ANSI/NFSI B101.1 Test Method for Measuring Wet SCOF of Common Hard-Surface Floor Materials
- ANSI/NFSI B101.2 Test Method for Measuring Wet DCOF of Common Hard-Surface Floor Materials
- ASTM F609-05 Standard Test Method for Using a Horizontal Pull Slip Meterx
Whether you use a simple slip meter or the most advanced tribometer available, the COF readings range from 0.1 to 1.0. Tribometers vary in accuracy and reliability, but always, the higher the reading, the higher the traction on a surface, and the lower the reading, the higher the chance of a slip and fall incident. Be aware, however, that a very high COF can cause people to stumble or trip on the surface. For optimum hazard control, most standards recommend a COF between 0.5 and 0.8.
Knowing the COF of each surface in your facility can help you prioritize cleaning, refinishing and resurfacing efforts. Measurements can also show if a surface is becoming more slippery or less slippery as the result of efforts to increase its COF. In many cases, changing cleaning procedures or floor finishes might be all that is needed to improve the COF and reduce slip and fall injuries.