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.
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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.
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
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Citations & References
In addition to any citations in the article above, a full list is available on request.
Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
Decks and Porches, the JLC Guide to, Best Practices for Outdoor Spaces, Steve Bliss (Editor), The Journal of Light Construction, Williston VT, 2010 ISBN 10: 1-928580-42-4, ISBN 13: 978-1-928580-42-3, available from Amazon.com
Paul Galow [Website galowconsulting.com ] - technical consultant on networking, LAN design, applications support. Galow Consulting Services [Website galowconsulting.com ] , 914-204-1749, email: paulgalow@galowconsulting.com
Eric Galow, Galow Homes, Lagrangeville, NY. Mr. Galow can be reached by email: ericgalow@gmail.com or by telephone: 914-474-6613. Mr. Galow specializes in residential construction including both new homes and repairs, renovations, and additions.
[4] "Are Functional Handrails Within Our Grasp" Jake Pauls, Building Standards, January-February 1991
[5] Access Ramp building codes:
UBC 1003.3.4.3
BOCA 1016.3
ADA 4.8.2
IBC 1010.2
[6] Access Ramp Standards:
ADA (Americans with Disabilities Act), Public Law 101-336. 7/26/90 is very often cited by other sources for good design of stairs and ramps etc. even where disabled individuals are not the design target.
ANSI A117.4 Accessible and Usable buildings and Facilities (earlier version was incorporated into the ADA)
ASTM F 1637, Standard Practice for Safe Walking Surfaces, (Similar to the above standard
[7] The Circular Staircase, Mary Roberts Rinehart
[8] Construction Drawings and Details, Rosemary Kilmer
[9] Falls and Related Injuries: Slips, Trips, Missteps, and Their Consequences, Lawyers & Judges Publishing, (June 2002), ISBN-10: 0913875430 ISBN-13: 978-0913875438 "Falls in the home and public places are the second leading cause of unintentional injury deaths in the United States, but are overlooked in most literature. This book is unique in that it is entirely devoted to falls. Of use to primary care physicians, nurses, insurance adjusters, architects, writers of building codes, attorneys, or anyone who cares for the elderly, this book will tell you how, why, and when people will likely fall, what most likely will be injured, and how such injuries come about. "
[11] The National Institute of Standards and Technology, NIST (nee National Bureau of Standards NBS) is a US government agency - see www.nist.gov
"A Parametric Study of Wall Moisture Contents Using a Revised Variable Indoor Relative Humidity Version of the "Moist" Transient Heat and Moisture Transfer Model [copy on file as/interiors/MOIST_Model_NIST_b95074.pdf ] - ", George Tsongas, Doug Burch, Carolyn Roos, Malcom Cunningham; this paper describes software and the prediction of wall moisture contents. - PDF Document from NIS
[12] Slips, Trips, Missteps and Their Consequences, Second Edition, Gary M. Bakken, H. Harvey Cohen,A. S. Hyde, Jon R. Abele, ISBN-13: 978-1-933264-01-1 or
ISBN 10: 1-933264-01-2,
available from the publisher, Lawyers ^ Judges Publishing Company,Inc., www.lawyersandjudges.com sales@lawyersandjudges.com
[13] Slips, Trips, Missteps and Their Consequences, Gary M. Bakken, H. Harvey Cohen, Jon R. Abele, Alvin S. Hyde, Cindy A. LaRue, Lawyers and Judges Publishing; ISBN-10: 1933264012 ISBN-13: 978-1933264011
[14] The Stairway Manufacturers' Association, (877) 500-5759, provides a pictorial guide to the stair and railing portion of the International Residential Code. [copy on file as http://www.stairways.org/pdf/2006%20Stair%20IRC%20SCREEN.pdf ] -
[27] "The Dimensions of Stairs", J. M. Fitch et al., Scientific American, October 1974.
[28] Stair & Walkway Standards for Slipperiness or Coefficient of Friction (COF) or Static Coefficient of Friction (SCOF)
ANSI A1264.2
ANSI B101
ASTM D-21, and ASTM D2047
UL-410 (similar to ASTM D-21)
NSFI 101-B (National Floor Safety Institute)
NSFI Walkway Auditing Guideline (WAG) Ref. 101-A& 101-B (may appear as ANSI B101.0) sets rules for measuring walkway slip resist
OSHA - (Dept of Labor CFR 1910.22 does not specify COF and pertains to workplaces) but recognizes the need for a "qualified person" to evaluate walkway slipperiness
ADA (relies on the ANSI and ASTM standards)
[29] A. Sacher, International Symposium on Slip Resistance: The Interface of Man, Footwear, and Walking Surfaces, Journal of Testing and Evaluation (JTE), ISSN: 1945-7553, January 1997 [more focused on slipperiness of polished surfaces
[30] Algae is widely recognized as a slippery surface - a Google web search for "how slippery is algae on steps" produced more than 15,000 results on 8/29/12)
[31] Slipperiness of algae on walking surfaces, warning, Royal Horticultural Society, retrieved 8/29/2012, original source: http://apps.rhs.org.uk/advicesearch/profile.aspx?pid=418
[32] Slipperiness of algae: "Watch your step, wet rocks and algae are slippery" Oregon State University warning 1977 retrieved 8/29/2012, original source: http://www.worldcat.org/title/watch-your-step-wet-rocks-and-algae-are-slippery/oclc/663683915
[33] Coefficient of friction of algae on surfaces [like stair treads]: Delphine Gourdon, Qi Lin, Emin Oroudjev, Helen Hansma, Yuval Golan, Shoshana Arad, and Jacob Israelachvili, "Adhesion and Stable Low Friction Provided by a Subnanometer-Thick Monolayer of a Natural Polysaccharide", Langmuir, 2008 pp 1534-1540, American Chemical Society,
retrieved 8/29/2012, Abstract: Using a surface forces apparatus, we have investigated the adhesive and lubrication forces of mica surfaces separated by a molecularly thin, subnanometer film of a high-molecular-weight (2.3 MDa) anionic polysaccharide from the algae Porphyridium sp. adsorbed from aqueous solution. The adhesion and friction forces of the confined biopolymer were monitored as a function of time, shearing distance, and driving velocity under a large range of compressive loads (pressures). Although the thickness of the dilute polysaccharide was < 1 nm, the friction was low (coefficient of friction = 0.015), and no wear was ever observed even at a pressure of 110 atm over 3 decades of velocity, so long as the shearing distances were less than twice the contact diameter. Atomic force microscopy in solution shows that the biopolymer is able to adsorb to the mica surface but remains mobile and easily dragged upon shearing. The adhesion (adsorption) of this polysaccharide even to negatively charged surfaces, its stable low friction, its robustness (high-load carrying capacity and good wear protection), and the weak (logarithmic) dependence of the friction force on the sliding velocity make this class of polyelectrolytes excellent candidates for use in water-based lubricant fluids and as potential additives to synovial fluid in joints and other biolubricating fluids. The physical reasons for the remarkable tribological properties of the ultrathin polysaccharide monolayer are discussed and appear to be quite different from those of other polyelectrolytes and proteins that act as thick “polymer brush” layers.
[35] Jason R. Stokes, Lubica Macakova, Agnieszka Chojnicka-Paszun, Cornelis G. de Kruif, and Harmen H. J. de Jongh, "Lubrication, Adsorption, and Rheology of Aqueous Polysaccharide Solutions, Langmuir 2011 27 (7), 3474-3484
[36] "Coefficients of Friction for Ice", The Physics Factbook™, Glenn Elert, Ed., retrieved 8/29/12, original source: http://hypertextbook.com/facts/2004/GennaAbleman.shtml
[37] "Coefficients of Friction for Ice", The University of the State of New York Reference Tables for Physical Setting/Physics. New York: The State Education Department, 2002. Op. Cit.
[38] Serway Physics for Scientists and Engineers 4th edition (p. 126.)
[39] "How Slippery Is It", retrieved 8/29/12, original source http://www.icebike.org/Articles/howslippery.htm
[40] John E. Hunter, "Friction Values", The Source, Society of Accident Reconstructionists, Winter 1998. Study of frictional values of car tires involved in collisions on snow or ice covered roadways.
[41] Frictional Coefficients of some Common Materials and Materials Combinations, The Engineering Toolbox, retrieved 8/29/2012, original source: http://www.engineeringtoolbox.com/friction-coefficients-d_778.html [copy on file as Friction and Coefficients of Friction.pdf ]
[42] Stairways and Ladders, A Guide to OSHA Rules, OSHA, U.S. Department of Labor, 3124-12R 2003 - Web Search 05/28/2010 original source: http://www.osha.gov/Publications/osha3124.pdf. OSHA regulations govern standards in the construction industry and in the workforce Quoting from OSHA whose focus is on workplace safety and so excludes discussion of falls and stair-falls in private homes:
OSHA estimates that there are 24,882 injuries and as many as 36 fatalities per year due to falls from stairways and ladders used in construction. Nearly half of these injuries are serious enough to require time off the job--11,570 lost workday injuries and 13,312 non-lost workday injuries occur annually due to falls from stairways and ladders used in construction. These data demonstrate that work on and around ladders and stairways is hazardous. More importantly, they show that compliance with OSHA's requirements for the safe use of ladders and stairways could have prevented many of these injuries. -osha.gov/doc/outreachtraining/htmlfiles/stairlad.html
[43] International Building Code, Stairway Provisions, Section 1009: Stairways and Handrails, retrieved 8/29/12, original source: http://www.amezz.com/ibc-stairs-code.htm [copy on file as IBC Stairs Code.pdf]
[44] Model Building Code, Chapter 10, Means of Egress, retrieved 8/29/12, original source: http://www2.iccsafe.org/states/newjersey/NJ_Building/PDFs/NJ_Bldg_Chapter10.pdf, [copy on file as NJ_Bldg_Chapter10.pdf] adopted, for example by New Jersey. International Code Council, 500 New Jersey Avenue, NW, 6th Floor, Washington, DC 20001, Tel: 800-786-4452
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