This article describes and includes illustrations of slippery tiled walking surfaces on stairs and walkways.

Page top photo: a combination of glass block, glazed ceramic tile, and concrete on these steps provide a walking surface whose slip and fall hazard is partly a matter of luck: which part of the step will receive the walker's foot?

We discuss COF - coefficient of frictio, SCOF - static coefficient of friction, and DCOF - Dynamic Coefficient of Friction and we cite recommended DCOF for tiled surfaces.

Tiled Walks & Stairs: Outdoor Slip & Fall Hazard

Various industry, ANSI, ASTM, OSHA, ADA standards recommend a static coefficient of friction (SCOF) of 0.5 or higher (ADA 0.6 or above) and define surfaces with SCOF of 0.4 or lower as "low traction", i.e. "slippery".

But just how slippery is a tiled walking surface? Well, as our friend Mark Cramer says, "... It depends" on both the surface conditions and on how you measure slipperiness.

Photo: this ceramic tile bathroom floor has a low spot that retains puddles of soapy shower watrer and thus adds to the slipperiness of the floor.

COF Coefficient of friction - tests giving a numeric value indicating the amount of friction or slip-resistance between two objects or surfaces

SCOF Static Coefficient of Friction - tests the friction of an object that moves from a standing or still position - its "break-away" point.

DCOF Dynamic Coefficient of Friction - (DCOF) tests the friction of an object that is already in motion - kinetic energy.

Model building codes attempt to address the effects of algae, ice, snow, and water on stairs and walkways.

But because building codes & standards cannot anticipate every possible physical cause of slipperiness on walking surfaces or stairways, codes generally do not attempt to address every possible slippery substance that might be present such as algae, ice, snow, water, even spilled oil or food or wet paint on steps.

Since building codes cannot anticipate every possible slip trip and fall hazard, instead codes and standards typically state something like the text shown below.

1009.5.2 Outdoor conditions. Outdoor stairways and outdoor approaches to stairways shall be designed so that water will not accumulate on walking surfaces.

In other than occupancies in Group R-3, and occupancies in Group U that are accessory to an occupancy in Group R-3, treads, platforms and landings that are part of exterior stairways in climates subject to snow or ice shall be protected to prevent the accumulation of same. - IBC (International Building Code) [43]

or

Slippery conditions on stairways must be corrected. - OSHA standard on temporary workplace stairways [42]

Most ceramic tile surfaces, unless specifically designed with a rough or anti-slip surface, are quite slippery to start with, and where installed outdoors, in our opinion, are a serious slip and fall hazard that is increased with even the slight moisture deposit of morning dew or fog.

Experts agree that when measuring "slipperiness" or the coefficient of friction (COF), the coefficient of dynamic friction (DCOF) is more relevant than the static coefficient of friction (SCOF) (De march 2019).

More recent developments described by the Tile Council of North America and given below as a PDF, note shortcomings of the classic SCOF, DCOF, and wet DCOF tests, now supplanted by DCOF A Cutest.

Excerpt: When tested using SLS solution as per the procedure in section 9.6.1, tiles with a wet DCOF of less than 0.42 (including by way of example, but not in limitation, polished tiles), shall only be installed when the surface will be kept dry when walked upon and proper safety procedures will be followed when cleaning the tiles.

Because glazed ceramic tile surfaces can be quite slippery even indoors, the tile industry and other experts have studied the coefficients of both static and dynamic friction on ceramic floor tiles.

However for the purpose of comparing the slipperiness of surfaces, experts often study first the static coefficient of friction or SCOF.

Current methods for measuring SCOF for ceramic tile give an SCOF ranging between about 0.60 and 0.85 for dry tile and 0.38 to 0.82 for wet ceramic tile. (De march 2019, BOT method).

The walkway shown here, installed at a home in northern Minnesota, is a particular falling hazard as it is in a climate where snow, ice, frost, and rain are common.

The sharp edge of the paver step insertion at the top of the tile section (these are concrete tiles with a rather smooth finish surface) just adds to the injury risk of a fall.

Above: glazed ceramic tile on this sloped walkway is a fall hazard even if the tile job itself survives the freeze-thaw cycle of northern Minnesota winters.

Just how slippery a tile surface will be depends on a combination of quite a few factors that include not just the static coefficient of friction (SCOF) of the tiled surface and include

• The walking surface coefficient of friction (COF)
  
  of the particular tile surface or glaze.
• The properties of the walker's shoe sole, or sock, or bare foot,
  
  contacting the walking surface, including surface roughness, flexibility, and contact area size
• The slope of the surface
  
  (significant in the photo above). Some slope is needed to assure that a tiled walking surface drains and does not hold standing water, but excessive slope adds to the slip fall hazard.
• The velocity and weight
  
  of the person walking or running over the surface (think about those FEDEX and UPS delivery drivers who run up your front walk and steps to deliver a package)
• Weather conditions
  
  such as the presence of water, snow, or ice on the surface
• Surface contaminants
  
  e.g. oil, or contaminants in water on the tiled surface, such as soap or soap film

Research on the DCOF, SCOF & COF of ceramic tile

• ADA Recommendation for Tiled Walking Surfaces: surface must be “firm, stable and slip resistant.
  
  In 2003 the ADA retracted its guideline of .60 on horizontal surfaces and .80 on ramps. because the tile industry lacked a standard testing method.
  
• American National Standards Institute, A137.1:2022 - Standard Specification for Ceramic Tile, American National Standard Specifications for Ceramic Tile, Clemson, 2012
  
  Excerpt: ANSI A137.1:2022 describes the normally available sizes and shapes of ceramic tile.
  
  This American National Standard covers a breadth of information, including the basis for acceptance and testing methods prior to installation, marking and certification of ceramic tile, definitions of relevant terms, and physical properties of Standard Grade Ceramic Tile, Second Grade Ceramic Tile, Decorative Tile, and Specialty tile.
  
  It also indicates the proper way to assess the ability for the tiles to resist water after they are properly glazed.
  
  The standard defines a tile as “A ceramic surfacing unit, usually relatively thin in relation to facial area, having either a glazed or unglazed face and fired above red heat in the course of manufacture to a temperature sufficiently high to produce specific physical properties and characteristics.”
  
  The standard provides information related to understanding ceramic tile for manufacturers, retailers, and even consumers.
• ANSI A137.1 Standards for Ceramic Tile (2012):
  
  This publication presents voluntary standard specifications for ceramic tile. It lists and defines various types, sizes, physical properties, and grading procedures for ceramic tile, including mosaic tile, quarry tile, pressed floor tile, glazed wall tile, porcelain tile, trim units, and specialty tile.
  
  This standard provides quality criteria for buyers, specifiers, installers, manufacturers, and the public in general. It is intended for reference or inclusion in the ceramic tile section of project specifications and contracts.
  
  ... tiles suitable for level interior spaces expected to be walked upon when wet shall have a wet DCOF of 0.42 or greater when tested with the BOT-3000 per the procedure in the standard (i.e., per the DCOF A Cutest.).
  
  ... DCOF alone should not be the only factor in determining the appropriateness of a tile for a particular application. ...
  
  To specify a surface as slip resistant follow ANSI A137.1-2012 Section 6.2.2.1.10)..
• ANSI/ASSE TR-A1264.3-2007 Technical Report: Using Variable Angle Tribometers (VAT) for Measurement of the Slip Resistance of Walkway Sur faces
• ASTM C1028-07e1 Standard Test Method For Determining The Static Coefficient Of Friction Of Ceramic Tile And Other Like Surfaces By The Horizontal Dynamometer Pull-Meter Method - used to measure SCOF - obsolete, withdrawn
• BOT-3000 (Binary Output Tribometer) -a small machine runs approximately 8” across a surface, measures the DCOF of tile to give a digital reading.
  
• Chang, Wen-Ruey. "The effect of surface roughness on the measurement of slip resistance." International Journal of Industrial Ergonomics 24, no. 3 (1999): 299-313.
• Demarch, Aline, Elcio Angioletto, Angela W. Vieira, Andreza Dal Molin, Oscar Rubem K. Montedo, and Elidio Angioletto. COEFFICIENTS OF STATIC AND DYNAMIC FRICTION OF CERAMIC FLOOR TILES: PROPOSAL OF NEW METHOD OF SURFACE ROUGHNESS DETERMINATION [PDF]  International Journal of Metrology and Quality Engineering 10 (2019): 4.
  
  Excerpt from Conclusions:
  
  There are many methods to determine the characteristics of ceramic tiles in order to determine the quality and applicability of ceramic tiles.
  
  Some of them is related to security and reliability, such as the determination of surface roughness in order to allow the correct specification.
  
  Such method brings some uncertainty and new alternatives play an important role in this industrial sector.
  
  This work presents a proposal of new method of surface roughness determination for ceramic tiles. The roughness test yielded parameters that correlate well with the empirical evaluation.
  
  The comparative study shows that the roughness method gives a greater guarantee to the ceramic floor in a specific place of use.
• Grieser, Brian C., Timothy P. Rhoades, and Raina J. Shah. "Slip resistance." Prof Saf 47, no. 6 (2002): 43-48.
• Kim, In-Ju, and Richard Smith. "Observation of the floor surface topography changes in pedestrian slip resistance measurements." International Journal of Industrial Ergonomics 26, no. 6 (2000): 581-601.
• NFSI B101.1-2020 Test Method for Measuring the Wet SCOF of Hard-Surface Walkways
• OSHA Recommendation for tiled walking surfaces: 0.5 SCOF
  
  OSHA does not have mandate a particular COF for walking/working surfaces.
  Non-mandatory Appendix A to Subpart D section A 4.5 in the Notice of Proposed Rulemaking for Walking Working Surfaces for general industry states
  
  "The Occupational Safety and Health Administration recommends that walking surfaces have a static coefficient of friction of 0.5 SCOF. "
  
• Simpson, Katelyn, COEFFICIENT of FRICTION, NEW METHOD, NEW REQUIREMENTS, DCOF AcuTest™ [PDF] Tile Council of North America, 100 Clemson Research Blvd., Anderson, SC 29625 USA, Tel: 864-646-8453, Author's Email: ksimpson@tileusa.com - retrieved 2023/05/20, original source https://tcnatile.com/wp-content/uploads/2023/01/Tile-Initiative_CoefficientOfFriction.pdf
  
  Excerpt:s
  
  A major change is underway regarding the coefficient of friction for tile, the frequently cited and specified measurement of a tile’s frictional resistance and the parameter most closely related to traction and slipperiness.
  
  The commonly specified and often misunderstood value of 0.60 static coefficient of friction (SCOF), determined by the ASTM C1028 test method, has been superseded by a new method, new test conditions, and a new threshold value, all of which can be found in the 2012 edition of ANSI A137.1, the American National Standard Specifications for Ceramic Tile.
  
  The previously mandated method determined a tile’s SCOF using a 50 lb. weight, a Neolite sensor and a strain gauge.
  
  The new method, titled the DCOF AcuTestSM, determines dynamic coefficient of friction (DCOF) with a sophisticated instrument called the BOT-3000, a type of tribometer1 specific for flooring applications.
  ...
  ... note that the results from the old SCOF method cannot be directly compared to the new DCOF method.
  
  First, the frictional resistance between two objects at rest (for example a shoe sole and a tile surface) is different and higher than that measured when motion is already taking place.
  
  Second, the new test method uses 0.05% SLS solution, which is more slippery than the deionized water used in ASTM C1028.
  
  Third, the new method applies less force to the test sensor than the force applied in ASTM C1028. These differences and others make it impossible to compare directly between the two methods.
  ...
  
  For this reason and others, the C1028 method cautions that the SCOF value should never be used to predict slip resistance.
  
  Similarly, ANSI A137.1 cautions that DCOF alone should not be the only factor in determining the appropriateness of a tile for a particular application.
• Strautins, Carl J. SUSTAINABLE SLIP RESISTANCE: AN OPPORTUNITY FOR INNOVATION [PDF] Proceedings of Qualicer (2008).
  Abstract:
  
  Ceramic tiles along with most flooring surfaces can become less slip resistant with use. This can occur rapidly such that some relatively new products can become hazardous within a short period of time.
  
  Currently there are no recognised methods to identify such problematic products.
  
  This introductory paper highlights the benefit of using accelerated wear test methods in combination with portable tribometers to evaluate long term slip resistance.
  
  These methods provide manufacturers an opportunity for innovation by identifying and satisfying consumers’ expectations for sustainable slip resistant tiles.
  
  Product development occurs effectively through a systematic process of continual improvement. Manufacturers that develop suitable products will create a superior position in this growing niche market.
  
  Excerpt:
  
  Although not detected using Rz as a surface roughness parameter, it is postulated that the inherent slip resistance is affected primarily due to the micro-texture of the ceramic tile surface being polished as the asperities are worn down.
  
  For profiled tiles, the upper surface will preferentially wear as this is where foot contact predominantly occurs. Thus the wear resistant characteristics of the tile are most important.
  
  The wear of the tile surface is even more critical where there is no significant interlocking effect between the shoe tread and the surface profile.
  
  Mechanically aggressive cleaning systems are known to have caused near-instantaneous slip resistant losses in some surfaces.
  
  Thus the cleaning and maintenance regime should be considered when assessing the potential long term slip resistance of a flooring system.
  
• Terjék, Anita, and Annamária Dudás. "Ceramic Floor Slipperiness Classification–A new approach for assessing slip resistance of ceramic tiles." Construction and Building Materials 164 (2018): 809-819.
• Terjék, Anita, and Zsuzsanna Józsa. "Analysis of surface properties determining slip resistance of ceramic tiles." Periodica Polytechnica Civil Engineering 59, no. 3 (2015): 393-404.
• Terjek, Anita. "Slipping properties of ceramic tiles/Quantification of slip resistance." In IOP Conference Series: Materials Science and Engineering, vol. 47, no. 1, p. 012017. IOP Publishing, 2013.
  
• UNE-ENV 12633:2003: Method of determination of unpolished and polished slip/skid resistance value, 2003

...

Continue reading SLIPPERY STAIRS, WALKS, ROOFS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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