Slip Coefficient of Friction
Flooring systems used on industrial, commercial, and residential floors should provide a safe walking surface in both wet and dry conditions. By measuring the coefficient of friction (COF), a quantitative number can be used to express the degree of slip resistance of a floor surface.
The following is a compilation of facts regarding slip-resistance of floor finishes: The slip resistance of floor finishes (coefficient of friction) is measured on an apparatus known as a James Machine. The results of the James Machine, when compared to actual floor condition, becomes somewhat nebulous, but it still remains the best test available. The readings measure the static coefficient of friction (slip resistance) and give a numerical rating of 0.1 to 1.0 with 0.5 being the figure set as the limit of safety. Readings higher than .5 are progressively less slippery and hence safer. Numbers progressively lower than 0.5 are more slippery and considered unsafe.
A newer generation slip resistance apparatus is the Sellmaier tester unit which measures dynamic coefficient of friction (slip resistance). An unfinished or unwaxed floor is very often faster (more slippery) than a finished or waxed floor. In most cases the application of finish or wax actually controls slip.
When the coefficient of friction is measured from a resting position, it is called the “static coefficient of friction” (SCOF). When it is measured when the surfaces are in relative motion, it is called the “dynamic coefficient of friction”. Measuring the dynamic COF is difficult and requires a strict laboratory environment for accurate results. The James Machine would be used in this situation under the ASTM D-2047 standard. Almost all portable and laboratory meters measure only the static COF and most measuring devices (slip meters) refer to static COF based off the ASTM C1028 standard.
The James Machine is a laboratory only device for dry testing only under standard F489. This makes field testing impossible.
The Sellmaier slip test meter measures both Static and Dynamic coefficient and provides a digital printout and audit trail.
For decades, manufacturers of floor finishes and polishes have relied upon the ASTM D-2047 (UL-410) standard for determining the slip-resistant properties of their products. This test method divided products into two categories, those whose dry Static Coefficient of Friction (SCOF) was equal to or greater than a 0.5 value and those whose SCOF was below the 0.5 value. Products that met the 0.5 or greater value were classified as slip resistant, while products whose SCOF was below the 0.5 value were simply not classified. For many, this pass-fail approach created the perception that products meeting the 0.5 value were “safe” while those that did not were “unsafe.”
The higher the "Static Coefficient of Friction" the less slippery the surface
Conventional spray buffing is a major factor affecting slip-resistance. Spray buffing hardens the finish and thus speeds up the floor. There is a definite correlation between hardness and slip. Conventional spray buff (a mix of finish, water and cleaner) lowers the coefficient of slip by about 0.025 points thus speeding up the slip on the floor. Today's modern spray buff and mop on dressing compounds will control the slip on a floor. After using a Spray Buff or Mop on Restorer on a finished floor, the slip index will usually read 0.05 0.075 higher on the James scale; slowing down the floor (making less slippery).
Spray buffing is a valid and economical method of floor maintenance and is here to stay, but the proper choice of chemical compounds is important in relation to safety.
Water spillage on floors creates an extremely hazardous condition. Water acts as a lubricant between the floor substrate and the bottom of the shoe. Spilled water, condensation, food and drink should be cleaned up immediately using an safety spill kit. Good quality walk off mats should be placed at entranceways to prevent rain and snow from being brought in by foot traffic.
Residual mop treatment film or residue from furniture polish, metal cleaner and lubricating sprays will greatly increase the slip on the floor surface.
Avoid overspray onto floor. Clean up residues promptly using a good heavy duty cleaner/ degreaser. Dust created by burnishing or dirty floors will cause a floor to become more slippery. Sweep or damp mop floors on a regular basis.