We’ve all become familiar with friction throughout our lives. Friction warms our hands when we rub them together quickly, and can even create enough heat to start a fire when two sticks are rubbed together. Friction is simple enough, right? So what is the coefficient of friction or COF?
A coefficient is a value, usually between 0 and 1, which is multiplied with a variable in an algebraic term. The formula for determining the COF allows us to specify the COF if we know two of the other values in the equation.
Now that we know the equation and we know the values we can calculate the Coefficient of Friction. It is important to understand that COF of an object in motion will not be the same as COF of an object at rest. These differences are noted as Static vs. Kinetic friction. Calculations using the frictional force of an object that is motionless relative to the floor will allow us to determine Coefficient of Static Friction. Calculations using the frictional force of an object that is already sliding on the floor will allow us to determine the Coefficient of Kinetic Friction.
In the application of floor safety it is the Coefficient of Static Friction that we are concerned about, because even while walking a shoe is (or should be) motionless relative to the floor surface. Slip and falls occur when the Coefficient of Static Friction is low enough to allow the friction force between the shoe and the floor to be overcome by common horizontal forces related to standing and/or walking.
You see, as we stand or walk, there are horizontal forces present between your shoe and the floor. These forces are caused by a variety of events, or factors in the environment. For example, if you are walking on a ramp there will be horizontal forces present that are not present when walking on a level surface. On level ground, the angle between the floor surface and your leg will determine the intensity of horizontal forces. 99% of the time these forces are not strong enough to overcome the friction force between your shoe and the floor, but when they do your shoe will begin to slide. This is the beginning of a slip and fall.
The Static Coefficient of Friction will vary for a variety of reasons. For example, when water is present between the two objects the friction force will be different, thus the COF is lowered. Also, different soles on different types of footwear means different friction force for each individual walking on a given surface. This ever-changing value represents the entire range of frictional force for each individual shoe on a given surface. Obviously we would not need to calculate COF for every shoe type and every environmental condition, but we can set a benchmark to describe safe conditions and unsafe conditions. Organizations such as OSHA and ADA have hinted at benchmarks for static COF , but because of the wide range of COF on any given floor due to different shoe type or environmental factors, no hard number has been put forth as a benchmark. OSHA recommends .5 on any level surface, and the ADA recommends .6, but it is left to the discretion of the decision maker at the facility to determine a safe condition. That being said, we are all still liable for the safety conditions at our workplace.
As a safety manager or maintenance engineer you can use the equation above to log slip resistance, improve areas that have questionable COFs, and thereby limit corporate liability in the event of a slip and fall. If you have the resources, purchase an ASM 825 slip meter so you can easily monitor the COF on floors throughout your facility, noting the value before treatment and after in your log book. If you cannot purchase a meter simply having documentation about the treatment process can be very beneficial when facing a slip and fall lawsuit.
When a person sues an organization over a slip and fall they usually attempt to show that the organization was negligent in addressing the slippery floor. Meaning, they knew about it, and didn’t do anything about it. With a log-book full of records you’ll be able to show that the organization recognized that there was an issue and treated the issue to within tolerable levels. This eliminates negligence as a case for slip and fall victims and negligence is the overarching reason plaintiffs are awarded millions of dollars in slip and fall lawsuits.
Take the time to investigate your facility for slip and fall hazards. Do you have slippery surfaces in entryways, stairwells, bathrooms, hallways, etc? You can greatly improve the COF with the right non-slip treatment product from Slip Resistant Solutions. Take a look and be the hero in your organization!