Sustainable Slip Resistance

Sustainable Slip Resistance is a particular floor friction testing method and selection criteria for use in choosing and sourcing slip-resistant flooring that maintains good tribological characteristics over its life cycle to minimize slip and fall accidents. Testing floors before and after they are in place on a property can assure a building owner that safe flooring has been chosen and installed for its intended use. This floor slip resistance testing method, developed by the McDonald's Restaurant chain and now specified by many other property owners (e.g. Westfield, Aldi, Toyota) assesses the effects of mild abrasion on wet slip resistance. This test identifies flooring that has a high propensity to lose its wet slip resistance.

Pendulum floor friction tester in action
Pendulum floor friction tester in action

The Need for Sustainable Slip Resistance

The widely accepted principle of safety by design, as well as U.S. laws and building codes, require that flooring be slip-resistant over its life cycle — not just at the time of installation. Safety criteria based solely on static coefficient of friction, often used in the U.S. for assessing safety, are too often misleading where flooring gets wet or otherwise lubricated in use.

Over 150 safety criteria have been adopted in Germany and Australia for specific situations — swimming pool decks, commercial kitchens, restrooms, etc. These are based on a laboratory test device, the variable-angle ramp, that is not readily portable. The pendulum tester is a portable ASTM method, has been used successfully since at least 1971 for assessing pedestrian traction potential, and is a national standard for pedestrian traction in 48 nations on four continents. Abrasion of a flooring sample, tested with the pendulum before and after, is being used to assess “Sustainable Slip Resistance.” Some architects and property owners are now combining this pendulum-based test with situation-specific safety criteria to specify and verify safe flooring. If flooring is in an area where it can get wet or otherwise lubricated (airborne deep-fryer fat, automobile grease, etc.), it needs to be slip-resistant under such conditions.

The Americans with Disabilities Act (ADA) requires that flooring accessible to disabled persons be slip resistant — not just when the building is constructed, but throughout its lifetime. Typical building codes in the USA require that "Every existing building, structure, premises or portion thereof shall be maintained in conformity with the code regulations and Department approvals in effect at the time of such construction and occupancy ... Every existing building, structure, or portion thereof shall be maintained in a safe condition and good repair … all physical elements of every existing building, structure or portion thereof shall be maintained … by restorative means, in a condition as close as reasonably feasible to their originally required and approved state."[1]

If a building owner can be confident that his or her new flooring will sustain its slip resistance for a period of years this can protect a considerable investment in the flooring and prevent business interruptions as well as protect the safety of the pedestrian. The stakes are even higher for hotels and cruise ships, which are occupied virtually nonstop with guests who will not tolerate the noise involved in changing out hard flooring.

Sustainable Slip Resistance (SSR) testing was developed by Strautins [2][3] in Australia for McDonald's Restaurants to identify flooring that is not highly susceptible to loss of its slip resistance from wear or some types of inappropriate maintenance. This test and appropriate selection criteria can help avoid investment in inappropriate flooring as well as prevent costly, life-altering accidents and increased healthcare costs. This article explains the method and how it can be used to improve flooring safety in the USA.

Test Methods and Safety Criteria

International test methods

Germany and Australia have for over 10 years had detailed flooring slip resistance standards based on some 150 specific situations — e.g. external walkways, swimming pool decks, swimming pool stairs, commercial kitchens, hospital operating rooms, etc.[4][5] Many architects elsewhere in Europe have informally adopted them. The slip resistance ratings are based on humans walking an oily or wet flooring sample in standard footwear and/or bare feet on a laboratory variable-angle ramp the repeatability of which was extensively documented.[6] However, the test results apply only to flooring before it is installed. In some cases initially good wet slip resistance is gone after the building has been open for only a few weeks. The ramp test can’t be used to assess safety of the flooring on site under the ambient conditions.

The United Kingdom has since 1971 had well-established slip resistance standards based on a portable test method, the pendulum. This test was developed for pedestrian traction by the U.S. National Bureau of Standards in the 1940s and further refined in the UK.[7] It was validated for pedestrian traction in 1971, together with its safety standards, in the UK over a period of 25 years by 3500 real-world public walking area tests and site accident records.[8][9] The test is an ASTM standard (E 303), slightly modified for pedestrian traction.

ASTM C 1028 vs. Pendulum

In the USA, architects and designers generally look for a wet static coefficient of friction of 0.60 or higher by ASTM method C 1028 to assess potential safety for wet areas of level floors. This can give deceptive results, applying “safe” ratings to some flooring samples that are in fact very slippery when wet.[10] The method is now acknowledged by ASTM,[11] Ceramic Tile Institute of America,[12] and Tile Council of North America[13] to be inadequate for assessing safety. See "external links" at the bottom of this page for more information on the inadequacies of the C1028 test. The ASTM C1028 test was finally and permanently withdrawn by the ASTM in 2014. It was replaced by an only slightly better dynamic coefficient of friction test specified by ANSI A137.1.[14] This test has been shown to correlate strongly with ASTM C1028, meaning the results can be very deceptive and a poor evaluator of slip risk.

The ASTM C 1028 method does not represent the most current state of knowledge about testing methods, but this is not widely known by American architects and property owners. A more useful test and safety standards (safety assessment) for due diligence is based on the pendulum. The pendulum is now a standard test method for pedestrian slip resistance in 48 nations (European Committee for Standardization EN 13036-4, 2003 names many of them) on four continents and has been endorsed by Ceramic Tile Institute of America since 2001.[12]

SSR Test Procedure

The SSR test procedure consists of an initial wet pendulum test; abrasion, wet, for up to several thousand cycles with a standard (100x100 mm 3M green Scotchbrite) abrasive pad under a standard load of 1 kg at 50 cycles/min; and another wet pendulum test after abrasion. Both hard and soft rubber pendulum sliders (or “test feet”) might be used if the area is walked on in both hard-bottom footwear and bare feet or soft-soled footwear. The abrasion is conducted either manually or mechanically using a Gardco 12VFI linear washability and wear tester.

Typically, about 85 percent of the loss in slip resistance after 5000 cycles has already occurred after 500 cycles.[2] Depending on the flooring buyer’s situation, the flooring might be considered to have Sustainable Slip Resistance for a level floor if (for example) the wet Pendulum Test Value (PTV) is 35 or higher after abrasion for 500 cycles. The 500-cycle result in the laboratory has been found by in situ pendulum tests to be roughly equivalent to 6–12 months of wear in customer areas at a busy McDonald's Restaurant. The 500-cycle specification was adopted by McDonald’s in Australia in October 2006. Other major property owners such as Aldi, Toyota, Westfield and a major cruise ship company have adopted similar specifications. In the USA, flooring with SSR is available in ceramic tile, natural stone, and resilient products. Abrasive-containing coatings, some transparent, are also available that have SSR.

In some cases, analogous to the variable-angle ramp test-related standards mentioned above, the SSR safety standards are situation-specific[15][16] rather than “one size fits all.” Thus a minimum pre-abrasion wet PTV of 35 might be required for hotel or hospital bathroom floors; a minimum of 45 (hard rubber slider) for stair nosings that get wet in use; and 54 (hard slider) for commercial kitchens and steep outdoor ramps. If the flooring is to be sealed after installation, the laboratory tests should be conducted with the correct sealer applied. Cleanability tests with expected contaminants (local mud, coffee, red wine, ketchup, etc.) by owners and/or other duty holders are also advisable before final selection of flooring. The methods of cleaning[17] should be planned. (A dirty mop with dirty water might not be adequate for slip resistant flooring, but abrasive pads can destroy wet slip resistance quickly.)

Experience has shown that what is specified and ordered is not always what is delivered, and it is prudent for property owners to verify that flooring meets their slip resistance specification both before installation and at turnover of the property for occupancy. Monitoring of slip resistance every 3–12 months after that can further protect pedestrian, owner, and other duty holders.

References
  1. City of Los Angeles Building Code, 2008, Chapter 81, Section 8104, based on 2007 California Building Code and 2006 International Building Code
  2. Strautins, C.J., “Sustainable Slip Resistance: An Opportunity for Innovation,” Qualicer 2008, Castellon, Spain
  3. Strautins, C.J., “Enhanced Test Method for Assessing Sustainable Slip Resistance,” International Conference on Slips, Trips and Falls 2007: from Research to Practice
  4. Sotter, G., STOP Slip and Fall Accidents!, 2000, 204 pp., amazon.com
  5. CTIOA (a), Ceramic Tile Institute of America, “Floor Safety Reports: No. 3, Endorsement of Improved Test Methods and Slip Prevention Standards for New Flooring,” ibid., 2001
  6. Jung, K. and Schenk, H., “Objectification and Accuracy of the Walking Method for Determining the Anti-Slip Properties of Floor Surfaces,” (in German) Zentralblatt for Industrial Medicine, Accident Prevention and Ergonomics, 39, No. 8, 1988, pp 221–228, Germany
  7. Giles, C., Saby, B, and Cardew, K., “Development and Performance of the Portable Skid-Resistance Tester,” 26 pp., Department of Scientific and Industrial Research Road Research Laboratory Technical Paper No. 66, Her Majesty’s Stationery Office, 1964, United Kingdom
  8. Greater London Council, GLC Bulletin No. 43, March 1971, London, United Kingdom, available in pdf form at SafetyDirectAmerica.com, “Testing and Instruments — Pendulum”
  9. Greater London Council, GLC Bulletin 145, February 1985, ibid
  10. Powers, C., et al., “Assessment of Walkway Tribometer Readings in Evaluating Slip Resistance: A Gait-Based Approach,” J Forensic Sci, March 2007, 52, No. 2, pp. 400-405
  11. ASTM, American Society for Testing and Materials subcommittee 21.06, meeting minutes, May 3, 2005, Orlando, Florida USA, 26 pp.
  12. CTIOA (b), Ceramic Tile Institute of America, “Floor Safety Reports: No. 1, Portable Methods,” ctioa.org, 2001
  13. Astrachan, E., “Installer Update: Updates to an American Method for Measuring Coefficient of Friction.” TileDealer, November/December 2007
  14. "ANSI A137.1 Tile Slip Test".
  15. Natspec Technotes guidance for consideration, “Slip Resistance Performance,” NTN Des 001, July 09, http://www.natspec.com.au/Technical/tndesign.asp, Australia
  16. Bowman, R., “Slip Resistance Testing: Zones of Uncertainty,” 24 pp., presented at Qualicer 2010, Castellon, Spain
  17. Tari, G., with contributions by Brassington, K., Tenaglia, A. Thorpe, S., and Engels, M., “SlipSTD Publicly Available Specification (SlipSTD PAS)”, Version 6, revised, July 2009.
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