Excel Tribometers, LLC

For Dry and Wet Testing

ASTM F1677 is for the Brungraber Mk II (a/k/a Portable Inclinable Articulated Strut Tribometer or PIAST), which is used for both dry and wet testing.  This standard has been officially withdrawn by ASTM, but it is still available for sale and distribution by ASTM.

ASTM F1679 is for the English XL Variable Incidence Tribometer (VIT), which is used for both dry and wet testing.  This standard has been officially withdrawn by ASTM, but it is still available for sale and distribution by ASTM.

ANSI A1264.2 is for Provision of Slip Resistance in the Workplace, which originated with ANSI and is primarily oriented to workplaces rather than public walkway areas. The standard specifies a threshold of safety of 0.50, and references several of the ASTM F13 standards (including F1679 for the XL VIT) as means of measuring performance and suggests some means of mitigating slippery conditions.

NFPA 1901 Standard for Automotive Apparatus, 15.7.4 recognizes only the VIT and the PIAST for testing wet surfaces.

For Dry Testing Only

ASTM F609 is for the Horizontal Pull Slipmeter (HPS), an early electrically-operated dragsled meter.  The standard does not permit wet testing.  It is important to note that F609 applies only to the HPS and is not applicable to the Model 80, ASM 725 or any other device.

ASTM F1678 is for the Portable Articulated Strut Tribometer (PAST) also known as the Brungraber, Mk I. Because of its sticktion problem, it is not useful for wet testing.  This standard has been officially withdrawn by ASTM, but it is still available for sale and distribution by ASTM.

ASTM C1028 for the Horizontal Pull Dynamometer is for factory quality assurance testing of ceramic tile. It is a 50-pound drag weight that is pulled by a hand-held force meter, and the COF number is calculated using the H/V formula. As with all dragsleds, this tester is not capable of valid wet testing, nor has a satisfactory precision and bias study ever been completed.

ASTM D2047 is for testing floor polishes for slip resistance under laboratory conditions. It involves the James Machine, a leather friction pad, and specifies that all testing must be performed dry. It cannot be used on a floor since it is not portable. There are four iterations of the James Machine, with representations that results are interchangeable, although no precision and bias substantiation has been published.

UL410 is for rating of various materials and surfaces as "slip resistant."  Any material or coating can be listed by Underwriters Laboratories as slip resistant if it achieves an index on 0.50 or higher on a James Machine with a leather pad. This is the original slip resistance standard. Its limitations are similar to D2047.

Other Related Standards

Some codes and standards incorporating the "slip resistant" terminology include ASTM F1637 Practice for Safe Walking and the Uniform Federal Accessibility Standards and Americans with Disability Act Accessibility Guidelines (ADAAG) as well as the regional building codes (BOCA, UBC and Southern, and now the Universal Building code).

NFSI B101.1 is a recent standard developed by the National Floor Safety Institute that presents a ranking system for walkway surfaces based on measurement of “wet static coefficient of friction.”  The NFSI B101.1 standard is a separate stand-alone document that does not replace, negate, supplant, or diminish the requirements of any of the established standards and codes, particularly those detailed above.

The Letter of Interpretation in the NSFI B101.1 standard currently recognizes the BOT 3000 as the only approved device based primarily on the ability of a device to measure “wet static coefficient of friction,” and some other listed proprietary features that may be irrelevant to the validity of a slipmeter.  The Letter of Interpretation says that none of the widely accepted tribometers in the world meet the criteria of the NFSI, and specifically lists the English XL VIT, the Brungraber Mark I, Brungraber Mark II, and Brungraber Mk III, the Wessex Pendulum, the Sigler Pendulum, the Munro Skid Resistance Tester, and other pendulum-based devices as those well-established tribometers that are neither recognized or approved by the NFSI.

Accepted science and extensively published authoritative sources support the principal that “wet static coefficient of friction” has nothing to do with a human heel landing from the swing phase element of a stride.  The heel would have to land and be stationary for static friction to be significant.  Slips and falls do not occur when people’s feet are stationary when considering the preponderance of injury slip events related to walkway safety, as is readily evident to the most casual of acquaintances with the sciences of human ambulation and walkway safety.

Recent correspondence from the secretary of the NFSI clarified that “The ANSI/NFSI B101.1-2009 standard and the LOI (Letter of Interpretation) do not reference human ambulation studies nor attempts to mimic such.  It simply sets forth the method by which wet SCOF can be measured.  The ANSI/NFSI B101.1-2009 standard does not set forth to discuss or define any relationship between wet SCOF measurements and human ambulation.”  There is no dispute that the English XL VIT is a valid tribometer for measuring slip resistance representative of human ambulation.  There is no dispute that the NSFI B101.1 standard is simply based on measuring “wet static coefficient of friction,” with no representations relative to human ambulation.

The XL VIT remains unchallenged as an established, recognized, accepted scientific instrument that mimics significant biomechanical parameters of the human walking gait.  The machine angle and velocity of the leg operating mechanism, and the size and shape of the test foot, were developed to replicate the heel strike of a human walking; the machine has a functional ankle.  The leg of the XL VIT is free to accelerate once a slip occurs, as with a real-world human slip event.  The phenomenon of “sticktion” produces misleading results with respect to slip resistance when the walking surface is wet with any tester that has residence time before the slip dynamics are applied.  The dynamics of the English XL VIT specifically permit measurement of slip resistance in wet conditions because there is no residence time.

Notwithstanding the numerous challenges to the validity or significance of the NFSI B101.1 standard and the Letter of Interpretation; rather, in spirit of cooperation for the advancement of floor safety, an addendum to the EXCEL TRIBOMETERS, LLC., XL VIT User Guide has been developed to satisfy the “requirement” of NFSI B101.1 to measure “wet static coefficient of friction,” so that XL VIT can be included in the NFSI “recommended or approved” device list.  Simply put, to measure “wet static coefficient of friction” with the XL VIT, incline the mast to a sufficiently low slip index, gently hold the test foot actuating cylinder against the mast with your finger, depress and hold the actuating button to create a condition where the test foot is static on the wet test surface in sticktion, release your finger from the test foot cylinder while continuing to hold down the actuating button, then carefully decline the mast/increase the slip index by turning the thumb wheel while holding the instrument steady, and slip will eventually occur at the “wet static coefficient of friction.”

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