by George Sotter, PE, PhD, and John C. Sotter
Specifying flooring that will not be slippery even when it can get wet or otherwise lubricated in use is critical for safety purposes. The 2012 International Building Code (IBC) lays out slip resistance, but there are weaknesses with the requirements—not least of all in that it places a burden on flooring specifiers in particular. Design professionals must be able to justify using a specific flooring under various circumstances (e.g. lobby, restroom, swimming pool deck, and commercial kitchen), and understand how to use flooring that does not meet IBC’s wet slip resistance requirement.
For decades, it was widely believed the Americans with Disabilities Act (ADA) required a static coefficient of friction (dry or wet as applicable) of 0.60 or higher for level floors and 0.80 for ramps. In fact, this was never true, and the Access Board of the U.S. Department of Justice has disavowed any responsibility for this custom. (For more, see the letter by David Capozzi [United States Access Board] to J.G. Sotter, dated May 17, 2011). The previously used test method, ASTM C1028, Standard Test Method for Determining the Static Coefficient of Friction of Ceramic Tile and Other Like Surfaces by the Horizontal Dynamometer Pull-meter Method, was withdrawn in 2014 with no replacement. The worst part of ASTM C1028 was it sometimes gave very high slip resistance ratings for floors that were very slippery when wet. Consequently, the poor test method and its misleading results were likely the cause of many accidents and hundreds of millions of dollars expended on flooring inappropriate for its intended use.
The 2012 IBC (in effect in most states at this writing), Section “2103.6−Ceramic tile,” states:
Ceramic tile shall be as defined in, and shall conform to the requirements of, ANSI A137.1.
This is all it says about the subject. However, there is no indication other flooring—such as granite, vinyl, marble, or wood—should have any different slip resistance requirement from that of ceramic tile. Simply put, we do not change our shoes when we step from tile onto marble, so many in the industry assume the same test and safety standard applies to all types of indoor flooring.
Photos courtesy Sotter Engineering Corporation
ANSI A137.1
Coefficient of friction (COF) describes the ratio (F/W) between the force necessary to cause an object to slide across a surface and the weight of the object. When the object begins at rest, the ratio is the static coefficient of friction. When the object is already in motion, it is the dynamic COF (DCOF). Static friction applies to pedestrians who are standing still.
In 2014, American National Standards Institute (ANSI) A137.1, American National Standard Specifications for Ceramic Tile, was revised to read:
[DCOF] does not predict the likelihood a person will or will not slip on a tile surface … 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 using SLS [wetting agent] solution as per [BOT-3000E tribometer procedure].
Tiles with a DCOF of 0.42 or greater are not necessarily suitable for all projects. The specifier shall determine tiles appropriate for specific project conditions, considering by way of example, but not in limitation, type of use, traffic, expected contaminants, expected maintenance, expected wear, and manufacturers’ guidelines and recommendations [emphasis added].
The latter is normally nowhere to be found, as most manufacturers do not want a suggestion of liability. The IBC, by reference to ANSI A137.1, puts the burden of responsibility for slip safety on “the specifier.”
The Tile Council of North America (TCNA) made major contributions to ANSI A137.1. Among these, is the addition of the possibility a slip may also be affected by:
The material of the shoe sole and its degree of wear, the speed and length of stride at the time of a slip, the physical and mental condition of the individual at the time of a slip, whether the floor is flat or inclined, how the surface is used, how the tile is structured, and how drainage takes place if liquids are involved. (See Katelyn Simpson’s article for the Tile Council of North America [TCNA], “Coefficient of Friction: New Method, New Requirements—Introducing the DCOF AcuTest.”).
I have not been this confused about any subject in a long time. This article seems to be trying to describe a can of worms or possibly more applicable, a Medusa head of snakes, where the liability of all parties is in jeopardy due to the fact that a test was withdrawn with no replacement and we cannot trust the tile manufacturer’s COF numbers to be accurate. So, the specifier, or the firm for which the specifier works, is liable for any accident on the floor because there is no objective criteria to use to make a decision of what material or product to use. Then Figure 1 says the Architect is liable at the purchase order event, when the Architect didn’t write the purchase order. How does the Architect know that the slip resistance is not as advertised when a purchase order, that the Architect didn’t write, is created? This implies that the Architect needs to pay, out of their own pocket, for testing all the different types of tile on the project because there is no way to know that the slip resistance is not as advertised.
The same dynamic occurs when the Contractor has no idea whether the tile in the box that was delivered is not to spec. Then the Contractor needs to test all of the tile to protect themselves.
Then post-installation, according to Figure 1, the installer is liable? The poor installer didn’t pick the tile, the Architect did and barring a truly horrendous installation, it would be the tile that is slippery, not the installation. But, once the tile is installed, that is when the installed tile can be tested and if it does not pass, is it the tile manufacturer’s fault? After all, the Architect relied on the manufacturer’s (untrustworthy?) data to select the tile. And, there is no reason in the world why the architect should be required to pay to test a tile, that for all intents and purposes, does not yet exist, because there has only been a purchase order. What are they supposed to test? And, finally, the Owner is not going to accept liability for a tile installation. They will go back to the Contractor and Architect to get whole.
So we have a Hobson’s Choice, or a Catch-22. I have read my share of ridiculous standards over the years, but this one leads the pack further than Usain Bolt could ever dream.
This article is scholarly, detailed, well-researched and completely silly. Utterly ignores the reality of the construction process and the responsibility of the parties in the construction process.
The recommendations here are almost completely unfeasible as presented and are unlikely to be adopted in any North American construction project.
Also, the tile standards cited are not new, they were introduced in 2012 IBC, which is now being superseded by 2016 IBC. The article might be new.
The bio mentions that George Sotter is a member of ASTM, but there is a notable lack of mention of ongoing slip testing activities in Subcommittee F13.10 related to standardizing the slip testing industry. This group has already published F2508-16 Standard Practice for Validation, Calibration, and Certification of Walkway Tribometers Using Reference Surfaces and is working on additional standard WK47077 New Practice for Using Walkway Tribometry Data in Estimating Pedestrian Slip Resistance Thresholds and Comparative Traction.
There has been extensive research relatively recently at the University of Southern California that finally attempts to correlate slip test (tribometer) measurements to actually slipping tests on human subjects. The ASTM standards are born out of some of this research and may soon become THE standard for slip testing. Our firm rarely gets involved with slip testing. However, the industry generally seems to be fragmented, with various experts defending their own test equipment (which they often have a financial interest in promoting), and, therefore, standardization appears to be difficult to achieve.
The BOT 3000 device noted in this article did not correlate well with human slip tests in the USC study. However, there are two pendulum-type devices (also mentioned in this article) that did perform well. I think mentioning this research and the ongoing work at ASTM would be helpful and perhaps provide some clarity to readers of this article, at least about the direction of the industry.
My feet are like very good bourbon. (yes, really) To make really good Bourbon (25, 50 and 100 year blends) requires a specialized person with extraordinary taste buds. Their taste buds are so precise and sensitive, that they can detect even the most minute changes to the blend, allowing them to come up with an amazing final product. As a manufacturer of waterproofing products (including deck coatings) I’ve been asked many times over the years to show that my deck coatings will not be a slip hazard, especially when wet and/or raining. It’s easy to add slip resistant additives to sealers, but will they really work, especially when wet? I’ve come to trust my feet over any test out there.
1. Apply deck coating to large sample board (4’x4′)
2. Allow to fully cure.
3. Put on old dress shoes that the souls have worn out (so they have the least amount of rubber/traction)
3. Rub your feet over the floor surface. Most importantly is to put one foot way out front (almost at 45° to the floor surface) and rub your shoe back and forth. Most people slip when their foot is extended forward, and when they set it down on the floor it slips forward. If it feels too slippery, don’t use it.
4. Pour water on the sample So there is a lot of standing water on it) and repeat step 3. The wet test is the most crucial one. After you do this a few times, one quickly develops a good sense and feel as to what is acceptable and what is not.
The conflict: In principal, the rougher the surface, the better the traction. BUT…, it’s much harder to clean. All too often, the demand for easy cleaning influences the decision leading to materials that simply don’t have sufficient slip resistance.
I am all in favor of standardized (measureable) tests that will give dry and wet friction results. If you ask me, build a device mimicking a human foot at 45° angle to the floor, and mount a dress show that the grooves on the souls have been ground smooth. Now push this device down and forward on the floor (both wet and dry) and you should have a pretty good idea where you stand. Maybe additional tests will need to be added to resemble other conditions, but this should give you a pretty good idea on where a product really stands.
I have seen slip resistant test results all over the place, which in many cases did not reflect how that product will behave in the “real world”. I then performed my own dry and wet tests while wearing dress shoes and could pretty much convince any specifier on the spot as to whether a product was acceptable or not. Don’t believe me? I’ve been manufacturing/selling deck coatings (and many other waterproofing systems) for over 30 years. Sqft of installed product: Millions! Lawsuits: ZERO!
This really isn’t that complicated.
Amir: I love the simplicity and the approach. Thanks.
With all due respect, perhaps you should stick to your professional expertise in manufacturing and selling deck coatings and waterproof systems. Please contact me for further consultation and National standard compliance. I am on linkedin and will send you any factual information, codes, standards or videos to either refute, backup or help explain where you may be confused or ill advised.
Scott: I would be interested in speaking with you. so, kindly call 301-775 -3602 when convenient for you……..thanks.
Hi Scott, I am adjuster investigating a slip and fall claim in FL. I am tasked with reviewing a photo/video of a slip and fall on exterior ceramic tiles and they are asking if the tiles meet FL code. Would you kindly be of assistance? Are there any codes in FL speaking to the surface texture of exterior ceramic tiles in a commercial setting?
David,
I hope you got an answer before this time. Yes there is a commercial code requirement ANSI A137.1 and the method of testing A326.3.
Minimum DCOF values for level surfaces from the new ANSI A326.3 (with specific project conditions):
Interior, Dry (ID) 0.42 (p.2 of the standard)
Interior, Wet (IW) wet with water 0.42 (p.2)
Interior, Wet Plus (IW+) wet plus (as declared by manufacturer; including barefoot areas) 0.50 (p.5)
Exterior, Wet (EW) wet 0.55 (p.5)
Oils/Greases (O/G) 0.55 (p.6)