To All Persons Who Require Scientific, Performance Based Methods for Measuring the Slip-Resistance of Walkway Materials and Coatings
Re: Static Coefficient of Friction (SCOF) Test of Blue/White Coating on Plate Glass
I received one 8" x 8" x 1/2" thick plate glass panel coated with a blue (47N1) and white (47T17) coating mixture. The Technical Products Co., Model 80, Floor & Footwear Friction Tester requires a minimum 2 3/4" x 4 ¾" test area.
The SCOF of the coating and the uncoated plate glass of each panel were measured by rotating the panel in 90 degree increments through two revolutions for a total of eight readings, per ref. 1 Leather, Monarch EVA and 1/16" thick gray silicone rubber sensors were used per ref. 2. The leather and Monarch EVA pads were sanded before each set of measurements per ref. 1; the silicone rubber sensors were not sanded. The initial reading was discarded, and repeated., if it was greater than or less than the other readings.
Ref. 1 requires that both "standardized " leather and "standardized" Monarch EVA (rubber) be used dry and dry/wet SCOF testing respectively, in order to determine whether any walkway material is "slip resistant". A minimum SCOF of 0.45 for leather (dry), 0.50 for Monarch EVA (dry) and 0.35 (wet with distilled water) are the minimum SCOF requirements.
Ref. 2 uses 1/16" thick gray silicone rubber, to simulate bare feet, when wet testing swimming pool decks, in addition to the ref. 1 materials. This material was used since the subject material may be used in hotels where swimming pools may be present. The minimum required wet SCOF is the same as EVA: 0.35.
Ref. 3 uses the ref. 4, A382 Silastic rubber, to establish minimum SCOF requirements of 0.6 and 0.8 for level and ramped walkway surfaces. This sensor, 1 ½" x 3" x ¼" thick was used to test the ref. 8 samples. Ref. 8 lists the test results with this sensor material that is replaced by the 1/16" gray silicone rubber per ref. 2.
Ref. 4 uses the Brungraber Mark I SCOF friction tester with the A382 Silastic rubber sensor together with a soap solution to measure the SCOF of bathtubs and showers. The Brungraber Mark II and the English XL are both dynamic COF (DCOF or KCOF) friction testers recognized by both ASTM and ANSI ASTM F1677 (Brungraber Mark II) and ASTM F1679(English XL). Dynamic friction is not recognized as the criteria for measuring the slip-resistance of flooring or footwear in the United States.
Ref. 5 uses Neolite, a material used for lining tanks and not currently used in footwear, to measure the SCOF of ceramic tiles both dry and wet. There is no minimum SCOF requirement for a "slip resistant" surface. This standard lists average SCOF of 0.70 dry and 0.47 wet when testing the "Florida" calibration tile. This is the identical ceramic tile specified as the test surface used when standardizing the Monarch EVA pads in ref. 1. This test method uses a 50-lb. weight that is too heavy for use as a portable SCOF tester. The 3"x3" Neolite sensor, in addition to giving significantly higher SCOF readings than typical footwear material (Monarch EVA) has a sensor pressure of 5.6 psi which is less than the ref. 1 minimum 10 psi pressure required in order to have SCOF test results correlate with slip/fall accident rate (ref. 1, appendix ref. 12).
Ref. 6 uses leather and the non-portable James Machine for testing polish coated floor samples in a laboratory. Since any instrument for measuring SCOF must be able to be used in both the field and laboratory, this method should be discontinued. Although polishes can be evaluated on any substrate, the method specifies "Official Vinyl Composition Tile" (OVCT) as the substrate to be used when evaluating polishes since the substrate affects the SCOF measurements of polishes. This is the only ASTM slip resistance test method that is performance based . The minimum SCOF for a "slip resistant" polish coated surface is 0.5 when tested only by ref. 6.
Ref. 7 , appendix 1, "Index by Products Tested", lists 56 product categories. Voices of Safety International is the only NIST recognized organization for accrediting test labs for measuring the "slip resistance of coatings, footwear and walkway materials". This is very significant since the VOSI slip resistance test methods are the only Universal Specification/Test Methods that standardize the sensor materials in order to eliminate the variability of the sensors that are sanded between tests. In addition correction factors are used to correct readings to a 50% laboratory humidity condition (ref. 6) and gage correction factors are used in order to eliminate force gage errors. Laboratory operators of the Model 80 SCOF tester must be certified since this is a manual tester. Operator certification requires that the initial SCOF of standardized leather on the secondary standard polypropylene test surface must be within 0.02 of the record maintained by VOSI and the range of 8 valid measurements must be within 0.05.
Table 1 lists the uncorrected and corrected SCOF for leather Monarch EVA, and gray silicone rubber. The gage, sensor and humidity correction factors (ref. 1) were used to calculate the corrected SCOF for Monarch EVA and leather; only the gage correction factor was used for the silicone rubber,. The standard deviation, S.D. is also listed. Ref. 6 lists the test results with Neolite, which is replaced by Monarch EVA, and A382 Silastic rubber (ref. 4) which is replaced by the 1/16" thick gray silicone rubber (ref. 2).
The "Florida" ceramic tile, used for standardizing the dry and wet Monarch EVA, was tested both before and after completing the Table 1 tests in order to calculate the average "rubber correction factor" required for correcting the SCOF to "standardized EVA". The gray silicone rubber was also tested before and after the Table 1 tests .
Ref. 5 uses a 50-lb. drag type friction tester with a 3" x 3" Neolite sensor. The Table 2 "Florida" ceramic tile is the identical "calibration" tile specified in ref. 5 wherein the average dry and wet SCOF is 0.70 and 0.47 respectively compared with the 0.42 and 0.34 values in Table 2. SCOF varies inversely with sensor pressure. The Model 80 tester uses a 10 lb. Weight and three 7/16" diameter sensor pads which results in an average pad pressure of 21.9 psi. compared with 5.6 psi. for the ref. 5 tester; this results in lower Model 80 SCOF readings. The ref. 3 tester, the Brungraber Mark I, uses a 10-lb. weight and a 3" x 3" sensor resulting in a 1.1 psi. pressure. A minimum 10.0 psi sensor pressure is required to have SCOF measurements correlate with slip/fall accident rate.
Ref. 1 explains the use of the "Traction Index" (T.I.), the ratio of the actual SCOF to the minimum required SCOF for a "slip resistant" surface. Table 3 shows the T.I. for all sensors tested and the test condition, dry or wet, for each coating and the plate glass substrate.
The ratio of the coating T.I. to the plate glass provides the best indicator of the effectiveness of the coating in increasing the slip resistance of the uncoated surface. Table 4 lists this ratio for each coating.
Donald C. Meserlian,P.E. Ref:
NIST Special Publication 831 99ED "Directory of Professional/Trade Organization Laboratory Accreditation/Designation Programs"(Pg. 83) by Charles Hyer, Editor
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Ref: NIST Special Publication 831 99ED "Directory of Professional/Trade Organization Laboratory Accreditation/Designation Programs"(Pg. 84) by Charles Hyer, Editor
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