Do you find Dynamic Coefficient of Friction (DCOF) confusing? If so, you’re not alone. DCOF raises questions about the methods for measuring it, what DCOF measurements mean, how to compare DCOF values, and the requirements. Because DCOF is now the primary product performance measure used by the North American tile industry, ceramic (and that includes porcelain) tile specifiers must understand it.

FLOOR SLIPPERINESS & FRICTION

When selecting flooring materials, slip resistance is a key safety measure that tile specifiers have to consider. The dynamic coefficient of friction relates to traction and slipperiness on floors when a person walks on them. The ANSI A137 standard for measuring DCOF only applies to interior, level wet surfaces (per ANSI A326.3). It does not provide guidance for other areas such as exterior applications, sloped surfaces, or areas where oil and grease are present. (A recent update to the ANSI A326.3 standard for DCOF has added five reference categories that manufacturers can use to further designate product use applications.)

Friction is the innate force that resists the sliding motion of one surface against another, such as the motion of a foot against a tile floor. DCOF testing, therefore, helps provide information about a tile surface’s contribution to the many dynamics involved in why someone might slip or fall. When it comes to choosing the right tile for an area, DCOF is an important consideration, especially when selecting ceramic/porcelain tiles for floors that may get wet.

A SHORT HISTORY OF SLIP RESISTANCE MEASUREMENTS & TESTING

Prior to 2012, testing slip resistance for ceramic tile used a method that provided the Static Coefficient of Friction (SCOF). But a new and better way of determining COF emerged, allowing project specifiers to choose the right tile for the job more easily. The new measurement adopted by the North American tile industry is called Dynamic Coefficient of Friction or DCOF. In 2012, the American National Standards Institute updated the ANSI 137.1 standard to change the measurement system for flooring slip resistance to DCOF.

HOW DO SCOF AND DCOF TEST METHODS DIFFER?

Whereas the old test method determined the static coefficient of friction the new testing standard defines the dynamic coefficient of friction. In the context of people walking on ceramic floors, static friction is the frictional resistance one pushes against when starting in motion. However, the test for SCOF 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. The SCOF testing method was also susceptible to variations, including human error.

Conversely, dynamic friction is the frictional resistance one pushes against when already in motion (as opposed to just starting in motion). With both types of friction, a slip can occur when you push with more force than the surface can resist. The DCOF test better relates to real-life situations in which a walking person slips on wet ceramic tile. DCOF tests are performed with a slightly soapy liquid (water with .05% Sodium Lauryl Sulfate, or SLS) applied to a tile’s surface. This solution is more slippery than the de-ionized water used with the old SCOF test.

IS THERE A REQUIRED MINIMUM DCOF VALUE?

In 2017, ANSI 137 was again updated to incorporate ANSI A326.3, the American National Standard Test Method for Measuring Dynamic Coefficient of Friction of Hard Surface Flooring Materials. This standard requires tile flooring products to have a DCOF of 0.42 or greater when recommended for level, interior floors intended for walking upon when wet with water.

IS THE MINIMUM DCOF VALUE SUITABLE FOR ALL PROJECTS WITH TILE FLOORS?

Not all ceramic or porcelain tiles with a wet DCOF of 0.42 or greater are necessarily suitable for all projects. For example, a ceramic or porcelain floor with standing water, oil, or grease might require a higher DCOF. Specifiers must also consider the type of use, traffic, expected contaminants, expected maintenance, expected wear, and manufacturer’s guidelines.

IS A FLOOR WITH A MINIMUM DCOF OF 0.42 CONSIDERED SAFE?

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 (outside the food court), hotel lobbies, and office buildings where a glossy appearance and ease of cleaning are highly desirable, but with measures in place to keep the floor dry. Architects and designers must make ceramic flooring specifications based on many factors affecting occupant safety.

IS THERE A DCOF VALUE FOR OTHER TILE FLOORING APPLICATIONS?

The A326.3 standard originally did not provide a minimum DCOF for exterior tile applications, interior ramps and inclines, pool decks, shower floors, or flooring contaminated with material other than water or where minimal or no footwear is worn. For such applications, the flooring’s suitability relies on several other factors, such as drainage of the assembly, intended use, degree of incline, the variety of contaminants present, etc. A recent update to ANSI A326.3 does add 5 reference categories that can be used for further guidance in certain areas.

Architects and designers must determine the appropriate tile for special areas. For example, some manufacturers can apply an abrasive coating material that will provide more slip resistance. Our Cross-Colors Mingles with Cross-Tread is one such solution, a suitable choice for wet and greasy floor areas, as well as for exterior walking surfaces, and a great porcelain alternative to quarry tile (which is naturally more slip resistant). We also produce mosaic tiles with the Cross-Sheen finish, which have a Wet Dynamic COF of  ≥ 0.42. Their small sizes ensure frequent grout joints, which provide traction and drainage. (You can learn about all of our special finishes and coatings here.)

All Crossville flooring products have been tested using the A326.3 method. You can view our porcelain tile DCOF ratings here and our porcelain panel DCOF ratings here.