Floor slip resistance is an important safety measure that all architects must be aware of when specifying flooring materials. In general, architects are concerned about slip resistance where floors can become wet from water (such as on ceramic tile in bathrooms) or from grease and oils (such as in commercial kitchens or garages).
The coefficient of friction (COF) is the measurement of a surface's frictional resistance. Essentially, this number tells you how slippery a surface is. A COF of 0 (zero) means that there is no friction between the two surfaces. Therefore, for slip resistance purposes, a higher number means the surface is less slippery when tested. Most architectural surfaces will have a COF that is less than 1, but it is possible to have materials with a COF higher than 1.
Ceramic tile is a primary material where architects want to know about the slip resistance for the flooring material. The methods used to test the COF were changed in 2012 so we should understand the test methods and current standards.
SCOF - The Old Measurement System
Prior to 2012, the coefficient of friction (slip resistance) for ceramic tile was tested using the method specified in ASTM C1028, which provided the Static Coefficient of Friction (SCOF). In this test, water was placed on the floor and a weighted plate with a sensor was placed over the water. The sensor measured the force required to set the weighted plate in motion. However, this test is not appropriate for measuring the slipperiness of floors since people are generally already in motion and are trying to STOP slipping instead of trying to start slipping. In addition, the testing method was susceptible to variations in running the test including human error. ASTM C1028 was deemed to be ineffective at measuring the slipperiness of floors.
DCOF - The New Standard Measurement
In 2012, the American National Standards Institute updated their ANSI 137.1 standard to change the measurement system for tile slip resistance to DCOF, or Dynamic Coefficient of Friction. The new test measured the amount of force required to keep an object in motion as it slides over a tile. This new test better reflected real life situations where a person slips on wet tile. The new test is called the DCOF Acutest.
ANSI 137.1 was updated again in 2017. The new update incorporates ANSI 326.3, which is the American National Standard Test Method for Measuring Dynamic Coefficient of Friction of Hard Surface Flooring Materials. This standard provides a test method, but also includes discussion about how the wet DCOF value of 0.42 is acceptable as a minimum value for surfaces that are expected to be walked on when wet with water. The standard can be downloaded from the Tile Council of North America.
Tribometer Measuring Device
The device used to measure the new DCOF is called a tribometer and the most common device used is the BOT-3000. It is a fully automatic device that drags itself across the floor and measures the slip resistance of a rubber pad that is attached to the bottom of the device. Human interaction is not required, except for the press of a button to start the test, so the results are more reliable than the old SCOF tests.
Slip Resistance for Level Interior Floors
The new measurements in ANSI 137.1-2017 and ANSI A326.3 require that tiles wet with water have a minimum slip resistance of 0.42 DCOF. Keep in mind that this is a minimum level of slip resistance for level interior floors that are wet with water. Other situations, such as standing water, oil, grease, or other slippery substances, may require higher DCOF numbers.
It is also important to point out that a DCOF of 0.42 doesn't necessarily equate to a safe floor; nor does a DCOF below 0.42 indicate a dangerous floor. For instance, A326.3 points out that hard surfaces with a DCOF of less than 0.42 are often used in shopping malls and hotel lobbies, but the materials are kept dry and safe cleaning procedures are used. The specifier of hard flooring materials must make a floor selection based on many factors that can affect occupant safety.
Slip Resistance for Other Areas
Unfortunately, there are no prescribed DCOF values for areas other than level interior floors since there are an infinite number of other conditions possible. For instance, wet ramps or auto mechanic floors where there is a lot of oil will require a higher level of slip resistance. Another similar area is a commercial kitchen where salad dressing or other cooking oils may be spilled on the floor.
Selecting the Right Tile for Slip Resistance and Safety
Since there aren't specific guidelines for slip resistance in areas other than level interior surfaces, architects and interior designers must work closely with their tile manufacturer to determine the proper flooring selection in special areas. Some tiles, such as quarry tile, are inherently more slip resistance with DCOF values that can be as high as 0.60 DCOF. In addition, tiles can be finished with an abrasive coating material that will provide more resistance to slips. In some instances, other materials (like rubber or linoleum) may be required to provide a safe floor for building occupants.
Other Standards and Tests
There are other standards for architects to be aware of. These standards apply to other types of flooring such as polished floors and other types of coated or hard floors.
ASTM D2047 provides a test method to determine the SCOF for polish-coated floors using the James Machine.
ANSI B101.1 provides a test method for determining the wet DCOF for common hard surfaces using the BOT-3000 tribometer.
ANSI B101.2 provides a test method for determining the wet DCOF for floors treated with chemical or physical surface treatments.
ANSI B101.4 provides a test method for determining the slip resistance for wet barefoot conditions.
ANSI B101.6 is a guide for reducing slips, trips, and falls when using commercial entrance matting.
For more information on the B101 series of standards, visit the National Floor Safety Institute.
If you would like to read more about the change to DCOF and the AcuTest, the Tile Council of North America has a technical bulletin titled Coefficient of Friction and the DCOF AcuTest. The National Floor Safety Institute also has a lot of great information on their website.