by Katie Daniel | July 8, 2016 10:58 am
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Coefficient of Friction of Ceramic Tile and Other Like Surfaces by the Horizontal Dynamometer Pull-meter Method, was withdrawn in 2014 with no replacement.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.
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.”).
However, neither ANSI nor TCNA give any method of evaluating any or all of these variables. So what is a specifier to do? Slip and fall awards can at times far exceed $1 million in cases where, for instance, someone incurs brain damage and must be supported for life. For this and other general reasons of good practice and respect for safety, it behooves the specifier not to be negligent in setting slip resistance requirements. Negligence is the key word in litigation.
Slip resistance testing can be conducted in the laboratory or in the field, the latter of which may be required by some municipal building inspectors. The DCOF is not always what the manufacturer lists, since it may have been tested years before when raw materials and manufacturing conditions were different.
It is best for all concerned when the proper slip resistance is dictated by a legitimate and legally defensible specification and testing. After all, no one wants the headache of remediating the situation after installing the wrong flooring.
The ANSI A137.1 slip resistance test is conducted using only the BOT-3000E digital tribometer—a relatively recent slip test device made in the United States and backed up by human traction research carried out in Germany. However, it has no situation-specific safety standards (e.g. 0.42, 0.60, 0.80, etc.) for various circumstances.
What’s a specifier to do?
Fortunately, there are detailed situation-specific recommendations in Standards Australia (SA) HB 198:2014, Guide to the Specification and Testing of Slip Resistance of Pedestrian Surfaces, which has been in use Down Under, with minor modifications, since 1999. The authors believe this provides the best justification for a specifier to set guidelines.
The Australian standard uses a different instrument—the pendulum skid tester, which has been in use continuously for pedestrian slip resistance since 1970, and is now a national standard in at least 49 nations. (This is thanks to European Standard EN 13036-4, Road and Airfield Surface Characteristic–Test methods Part 4: Method for Measurement of Slip/Skid Resistance of a Surface: The Pendulum Test). It is employed for ASTM E303, Standard Test Method for Measuring Surface Frictional Properties Using the British Pendulum Tester, and has been endorsed by the Ceramic Tile Institute of America (CTIOA) for all types of flooring since 2001. (See CTIOA’s “Floor Safety Reports: No. 1, Portable Methods” from 2001).
The Australian standard recommends minimum wet pendulum test values (PTVs) for some 40 different situations, such as:
For reference, the ASTM standard for basketball courts—that is, Section 4.5 of ASTM F2772-11, Standard Specification for Athletic Performance Properties of Indoor Sports Floor Systems—specifies a dry PTV between 80 and 110. (Basketball courts are very slippery when wet, which is why considerable effort is devoted to wiping up sweat off the floor after a player falls.)
The authors believe using the Australian standards indicate a design professional has employed due diligence, best possible practice, and all that is reasonably practicable—in other words, he or she was not negligent. Many of the authors’ domestic and international clients have been using this test method for years in the United States to choose appropriate flooring, due to lack of any similar domestic safety criteria.
If installed flooring is found to have insufficient wet slip resistance, there are ways of remediating it—at least to some extent—in situ. However, safe flooring should really be specified and installed in the first place. Lubricants on indoor floors can include not only tracked-in rainwater and snow, but also spilled beverages, furniture polish, WD40, perfume, cooking oil, and debris (e.g. food, sauces, and dust).
Sustainable slip resistance
A major international fast-food chain found that in some cases where slip-resistant flooring was installed in a busy restaurant, wear from many thousands of shoes (and the soil on them) could destroy the wet slip resistance in a few weeks or months. This company spent years devising a test to indicate whether a flooring sample was likely to give good slip resistance after years of heavy wear.
The test involves measuring the wet PTV of the sample when new, then subjecting it to a standard abrasion, then testing the wet PTV after abrasion. (For more, see C.J. Strautins’ papers, “Sustainable Slip Resistance: An Opportunity for Innovation,” presented at the Spanish conference, Qualicer in 2008 and “Enhanced Test Method for Assessing Sustainable Slip Resistance,” at the 2007 International Conference on Slips, Trips, and Falls). The specification is the wet PTV must be 35 or higher after 500 cycles of abrasion using a standard abrasive pad loaded with 1 kg (2.2 lb). When the sample meets this, it is said to have “Sustainable Slip Resistance.” Other large property owners, including two major cruise ship companies, are now having their candidate flooring samples tested for this Sustainable Slip Resistance.
Another test worth noting was devised in Germany and adopted in modified form in Australia as AS/NZS 4586:2004, Slip Resistance Classification of New Pedestrian Surface Materials, Appendix C, “Wet/barefoot ramp test method.” This involves two technicians individually walking a wet 1-m (3-ft) long flooring sample in bare feet on a variable-angle ramp. The technician adjusts the ramp angle so he or she just barely can walk without slipping. Depending on the angle, the sample is classified as A, B, or C, with C having the greatest wet slip resistance. The A category is suitable, for instance, for locker rooms, while B is for swimming pool decks and C is for swimming pool ramps and steps leading into the water.
While the test is the most realistic one for barefoot situations, it is still a laboratory test and is impractical for checking quality of flooring after it has been delivered to the jobsite—or already installed. For onsite testing, the pendulum with a soft rubber slider is the preferred method of testing barefoot flooring.
A similar variable-angle test is used to rate flooring for industrial-type shoes having treads in oily situations, and is a standard in Germany and in Australia as the aforementioned AS/NZS 4586:2004 Appendices C and D (“Oil-wet Ramp Test Method”). However, the results are not applicable to general commercial situations where most pedestrians are not wearing shoes with effective treads.
When to test flooring
It is commonly assumed when a flooring sample is tested once, for instance for a catalog DCOF, that its slip resistance will always be the same. This has led to some expensive and embarrassing mistakes.
For a large project, experience has shown the flooring needs to be tested at four stages to protect the various parties involved:
The party being protected should normally be the one who pays for the test. Figure 1 shows when tests should be done and who should pay.
At present, IBC lacks a specific slip resistance requirement for outdoor surfaces. However, this does not mean there is no problem. In fact, outdoor surfaces should meet a higher standard because people are conditioned to believe they can run when outdoors—especially when it starts to rain or hail. Sidewalks and roads are normally slip-resistant when wet. Someone who would not think of running on a polished marble indoor floor might not hesitate to run on an outdoor tile surface. Just because it is not glossy does not mean it is not slippery.
The Australian standards can be very helpful for outdoor situations. Generally, a wet PTV of at least 35 is required, and for a ramp with slope steeper than 1 in 14 (i.e. 4.1 degrees), a wet PTV of 55 or higher (tested with a hard rubber slider) is required.
The ANSI A137.1 slip resistance test is unsuitable for outdoor surfaces because the BOT-3000E instrument used is low in speed, and does not simulate someone walking fast or running. The pendulum test is more suitable.
Good safety engineering practice involves designing to prevent hazards to the extent feasible. It is not good practice to create a hazard, and then post warning signs. For one thing, such signs are not always noticed; for another, they give the pedestrian a Hobson’s choice—should she try to negotiate the hazardous area to get to work, or go back home and return to work when it is not raining?
Maintaining slip-resistant flooring
The architect or specifier is generally not responsible for ensuring the flooring is properly maintained. Nevertheless, they might be among those blamed for a slip and fall if the carefully chosen flooring is poorly maintained so it loses its wet slip resistance. Would you recommend using a broom and dustpan for routine cleaning of carpet? Most people opt for a vacuum cleaner instead, because it takes the soil away instead of mainly spreading it around. Hard flooring is often cleaned using a dirty mop and dirty water. This is analogous to cleaning a carpet with a broom and dustpan. The best way to clean hard flooring is to use an autoscrubber. The machine lays down the detergent solution, scrubs with a pad or brush, and uses a double squeegee with vacuum to pick up the dirty water.
Pads for autoscrubbers are color-coded, with anything other than white indicating abrasiveness. Abrasive pads must not be used if a floor is to retain good wet slip resistance. Even better than using a white pad is to use a very soft brush, like a carpet brush. Brushes have a higher initial cost, but last much longer than a pad; further, they will not shear off the small, sharp asperities on the floor surface that give the floor good wet slip resistance. Most autoscrubber pads used for general cleaning tend to polish the floor, making it smoother and more slippery when wet, whereas a soft brush will ‘tickle’ dirt out of grout joints and low points within the flooring to clean more effectively than a pad.
Monitoring slip resistance
Slip resistance can change with time due to wear or inappropriate maintenance. It is beneficial for many large property owners to have slip resistance monitored periodically—quarterly for high-traffic areas, and perhaps annually for less busy areas. Testing should be both dry and wet, if the floor can get wet in use.
Having written proof a routine testing plan is followed, and that any problems discovered are promptly rectified, both prevents accidents and attention from plaintiff attorneys. An accident on a dry floor may have been due to the pedestrian’s footwear having poor traction, but this does not stop the injured pedestrian from potentially suing the property owner and everyone else connected to it. A slip-resistance monitoring program can help prevent losses from frivolous lawsuits.
By incorporating ANSI A137.1, the 2012 IBC explicitly puts responsibility for floor slip resistance in the hands of the Specifier. It sets a rather low bar for minimum wet DCOF, but points out meeting the minimum dynamic coefficient of friction requirement is not enough—numerous other factors must be considered. (Specifiers should make sure their insurance covers this added risk.) However, using the methods discussed in this article can help avoid accidents and build a strong defense against litigation.
|KEEPING SLIPPERY FLOORS DRY|
Most flooring, even if smooth and glossy, is slip-resistant when dry (to footwear having reasonable traction potential, anyway). Not all floors need be safe when wet—those slipperier surfaces can be used in places where the floor will be kept dry.
Here are some precautions to ensure a floor stays dry in use:
A BOT-3000E display after four runs using the procedure in American National Standards Institute (ANSI) A137.1, American National Standard Specifications for Ceramic Tile.
George Sotter, PE, PhD, is president of Sotter Engineering Corporation. His background includes rocket combustion research, air pollution control, and slip-fall prevention. He is a member of ASTM and is certified by the City of Los Angeles to test floor friction. Sotter authored the book, STOP Slip and Fall Accidents! He can be reached at firstname.lastname@example.org.
John Sotter is a graduate of the University of California at San Diego in Urban Planning. He has many years of experience in responsible safety work for the City of San Clemente, California, and trained in floor friction testing in the United States and the United Kingdom. Sotter has worked for 15 years in floor friction testing and treatment in North America and on the high seas. He can be contacted via e-mail email@example.com.
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