AMA - "Slip Resistance" Is more always better? Expert Breakdown
We're back for another "Ask Me Anything" instalment and this time we're addressing slip-resistance. It's one area of specifications that is filled with grey areas but often considered in binary terms causing heaps of confusion and often ends in dissatisfaction for the client.
To understand slip-resistance isn't easy and because of that, and the fact that it's a safety consideration, most opt for the solution of more is better. Like anything important in life though, there is a fulcrum for balance where more or less to one side means sacrifices somewhere else. We'd like to help you understand the choices you're making with slip resistance better so you can weigh the costs before you find yourself in a situation of dealing with the unforeseen and suffering the costs.
This is a long and technical post that is intended as a reference to be referred to. For those that just want the Cliffsnotes, here's the TLDR:
The perception of a standard for slip resistance came from an OSHA publication following the ADA in 1991. This recommendation was flawed from the outset because it referenced a SCOF value of 0.6 but failed to specify a testing method. The recommendation was subsequently removed in 2004.
Current standards in North America follow ANSI 326.3 specifying DCOF testing with BOT3000E tribometer and suggest a minimum of 0.42 DCOF for interior areas that are occasionally wet.
There are no further recommendations for other environments like outdoors, ramps or pool decks in the current ANSI standard.
Current standard is not based on slip-and-fall testing with human test subjects and the standard itself specifically states that the test method and recommended minimums specified does not predict the likelihood that a person will slip or fall.
There are multiple ways manufacturers can increase the tile surface's friction but all of them result in adding texture to the surface, visible or not.
Increased friction works on dirt and dust as well as feet. A higher DCOF tile will often require more frequent and aggressive cleaning.
Increasing the DCOF past the necessary for the client can have a negative impact on comfort and cleanability. There's balance in everything and in this case, it's a balance between liability and livability.
Q1: So what are the actual slip-resistance values reported and required in Canadian specifications?
Well, for us here in Canada and our neighbours south of the 49th, the standard and test method largely quoted and considered in specifications is DCOF, or Dynamic Coefficient of Friction, thanks to its inclusion in ANSI standards A137.1 and A326.3. The former being the primary basis for the 09300 specification and installation handbook published by our industry association, the TTMAC (Tile, Terrazzo & Marble Association of Canada), the latter being a more general hard-surface floor coverings category standard, not confined to ceramics alone. Since 2017 the general hard-surface standard, A326.3 is the single-overarching standard as 137.1 references it in regards to slip-resistance testing methodology. This standard and test method, specifically requires the use of the BOT 3000E tribometer, developed and manufactured exclusively by Regan Scientific Instruments in Carrollton Texas.
Since first publication in 2012, this standard is also referenced in the International Building Code (IBC) - stating that tile being installed indoors in occasionally wet situations shall have a DCOF value of at least 0.42. It does not provide a minimum value for outdoor or ramped installations.
It's important to note that despite widespread adoption of DCOF, the preceding test method ANSI B101.3 that paved the way for global adoption's safety recommendations were based on actual slip and fall research carried out by the National Floor Surface Institute (NFSI) in a laboratory under controlled conditions using numerous human subjects. The modified test currently in use, outlined in ANSI A137.1/A326.3 is not. The NFSI's accreditation to develop floor and safety standards for ANSI was terminated in 2020 leaving their previous standards & research defunct and unable to be renewed.
So, where does that leave us when we need to select a safe floor? There is a recommended value of 0.42 DCOF measured with a BOT3000E tribometer for indoor flat flooring applications of ceramic tile in areas that may be wet. That's all. Remember that this is a measurement of coefficient of friction against a moving object, not precisely a value of slip-resistance though.
Q2: Ok, so is 0.42 DCOF measured with the AccuTest as specified in A 137.1 slip-resistant or not?
The answer here, frankly, is that there isn't one. Despite our collective desire to dot I's and cross T's so that we're not left holding the bag in the case of an accident - it's not so easy to develop a blanket standard for something like slip resistance. There's just too many variables - average footwear of users, consistency and viscosity of normal contaminants, average age & dexterity of users, level of traffic and corollary surface deterioration... the list goes on and on. But since we now know the prevailing North American standards only reference the value of 0.42 for indoor occasionally wet environments, that recommendation is no longer based on a study of human subjects and further, does not specify different value recommendations for other situations like outdoors or ramps, we must look further afield for guidance.
Much of the confusion surrounds the switch from SCOF (Static Coefficient of Friction) to DCOF as the testing method in 2012. Prior to 2012, the 1991 ADA (Americans with Disabilities Act) published a recommendation (for the first time affecting the hard-surface flooring industry) that all flooring specifications meet a minimum 0.6 SCOF value but in a fatal error, failed to specify a testing method. Subsequently, this Occupational Health and Safety (OSHA) recommendation was later removed from both ADA and ABA (Architectural Barriers Act) guidelines in 2004. After 13-years of influence, the industry had long conformed to making products to fit these perceived standards due to the universal demand of design professionals. So when the new standard came into effect in 2012, the recommended value of 0.42 DCOF was this time, written directly into the testing method's standard. The number of 0.42 wasn't just picked out of thin air, instead multiple comparative results were taken from previously acceptable samples achieving 0.6 SCOF tiles finding an average DCOF value of 0.38. It's important to note that despite these results, there is no parity between the tests and as such, no possible equation to parse a relevant value in the other scale without re-testing. For more information on studies and the implementation of DCOF, see the Tile Council of North America's (TCNA) 2013 document.
Further, despite now being the prevailing standard commonly taken for slip-resistance, ANSI Standard A326.3 states that this test "can provide a useful comparison of tile surfaces, but it does not predict the likelihood a person will or will not slip on a tile surface."
Q3: How do tiles achieve higher DCOF results?
Since the OSHA recommendation in 1991, the industry has been focused on creating flooring products that satisfy the design community's perceived needs for slip-resistant product. Most products intended for floors (that aren't polished) achieve 0.42 or higher DCOF today. If it's not perceived as "safe" it's just not going to sell. Standards, more specifically the preferences they instil, affect industry trends and market-availability to a large degree.
There are a few different methods manufacturers use to achieve higher values from the BOT3000E tribometer. Given that it is a test of the surface's coefficient of friction, the end goal is to increase the friction created by the surface against a moving object. It's important to understand that most tile we specify today is glaze and that the majority of a glaze surface is comprised of fused silicates and flux, or more commonly, glass. Since glass is inherently smooth, everything we do is aimed to fight against that and increase the roughness of the surface. Here's a few ways the industry has approached increasing slip-resistance.
Corundum glaze additives: Largely out of use except in quarry tiles made specifically for industrial, abattoirs and commercial kitchens. Corundum is a naturally occurring crystallized aluminum oxide compound that is MOHS hardness scale 9 (one less than diamond). Because of its jagged crystalline structure and extremely high melting point, corundum is ideal for adding heavy texture to ceramic surfaces. The resulting surface is similar to sand paper - overkill for a lot of areas.
Nano-Frits: Frits are pre-glass compounds of silicates, flux and mineral compounds. Different mixtures of silicates and minerals produce varying degrees of smoothness when sintering (hardening after liquifying in the kiln). Today, it is possible to have tiles that look and even feel smooth but are quite jagged when viewed under magnification. The more microscopically jagged the surface is, the "dryer" the surface feels. Many of the In-Out or multi-use glazes today are made in this way. The way surface tension works in water, many of these micro-variegated surfaces actually can create more friction when wet than dry.
Surface and/or edge texture: Clefted surfaces & irregular edges of the tile itself, provided the modules are smaller than our feel and each step will include crossing a joint, create point-based increases in friction. Adding texture to your tile, or simply a lot of smaller modules so the joint and edge structure is impactful. Yet another way to keep the glaze smooth but potentially decrease the potential of a slip/fall occurrence.
Q3: So why not just specify the highest DCOF I can find for all my floors?
There's balance in everything in life. Without understanding the details, we tend to go with "more is better" tactics and while that may seem like the safe path - knowledge and understanding is far more powerful in the long run than overcompensating for one variable to the exclusion of others. Increasing the tile surface's friction, is directly correlated to increasing the surface's texture. This creates peaks and valleys, however small, for dirt to collect in. The rougher textures created by these peaks and valleys also make the surface harder to clean and require more frequent and labour-intensive cleaning.
As a good rule of thumb, the "dryer" a surface feels to your hand, the higher the DCOF... but that comes with more effort to keep it clean. An increase in friction doesn't just work on your feet, it also works on dust, dirt and other normal contaminants.
Understanding your client's safety concerns, average use-cases and desired maintenance processes/frequencies will allow you to select tile that meets their expectations for both liability and livability. Understanding the industry standards and practices in meeting those standards gives you the background to make a savvy decision. Working with a supplier partner that can support you and provide the right knowledge and options ensures everyone gets what they need rather than what they thought they wanted in a vacuum.
- The Centanni Tile Team