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Education Article

Preventing Slip and Fall: Mastering Wet COF Measurement

Nu-Safe can provide coefficient of friction testing throughout the U.S/Canada & Islands. With over 15 technicians trained on the BOT 3000, Nu-Safe can conduct coefficient of friction testing on any type floor surface. Our testing services are used by several major insurance companies, insurance brokerage firms, resorts, restaurants, and Timeshare organizations, across the U.S. Please contact us for further information.

Why do slip-and-fall accidents occur? Technically speaking, a slip occurs when the Coefficient of Friction or COF between the shoe material and the walking surface does not provide sufficient resistance to counteract the forward, resultant forces at the point of contact. This happens most commonly on wet floors or surfaces.

Why? Water, unlike air, does not easily compress, and when trapped between shoe and floor can form a continuous film leading to hydroplaning. Of course, hydroplaning is more common in environments where water is regularly present (i.e., entranceways during inclement weather, shower rooms, lobbies, and kitchens or food service areas).

According to the U. S. Department of Energy (DOE), a study of workers at DOE facilities who experienced injuries from slips and falls showed that approximately three-fourths of the indoor slip/fall events reported involved water.

Since a floor that is slip-resistant when wet will generally be slip resistant when dry, taking measurements of the condition of floors by benchmarking the wet COF (see Sidebar, “COF - Coefficient of Friction”) - a number or range indicating how slip-resistant the floor surface is when it is wet or contaminated - is an important starting point to raise safety levels.

Measurement Overview

There are three steps to slip/fall prevention involving wet COF Measurement and data collection: 1) measuring and recording the condition of floors, 2) improving then maintaining that condition to a desired benchmark level through effective treatments and routine care, and 3) regularly evaluating / documenting the state of floors over time to help ensure (and demonstrate) the proper degree of due diligence, care, and compliance with safety norms.

According to Dave Ludwin, Director, General Liability Risk Control, CNA Insurance Companies: “It’s important to know what the starting slip resistance is on the floor materials in your facility. These numbers provide a baseline when considering changes to cleaning and floor maintenance practices. Then, going forward, have flooring COF audited periodically to determine slip resistance.”

Measurement Devices

The Binary Output Tribometer or BOT-3000 is a portable robotic device for both laboratory and on-site testing of dry and wet static and dynamic coefficient of friction. Since the BOT is an automated unit that can be calibrated in the field, user error or variability is minimized.

The BOT meets ASTM’s rigorous precision and bias requirements. It is also recommended by a major insurance carrier, and other expert groups.

Interestingly, early in 2006, Southlake, TX-based Regan Scientific Instruments, Inc. (fka Universal Walkway Testing, LP) - manufacturer of the BOT - submitted a BOT-3000 digital tribometer to Wuppertal University in Germany to study the correlation with the stationary German Ramp, Europe’s de facto standard for measuring slip-resistance.

According to Peter Ermish, principal of RSI: “The German Ramp Method (DIN 51130) is an established benchmarking test method in Europe and other countries for analyzing the slip resistance of footwear, floor surface materials, and coatings. Results to date show a close correlation between both devices/methods using a standardized test shoe material.”

Measurement Benchmarks

Slip and fall prevention, and COF measurement science, have greatly progressed in recent years. Until recently, the goal was to achieve and maintain a .5 Static Coefficient of Friction (SCOF) on a dry floor surface. However, laboratory and field research have led to new, emerging and more practical benchmarks, since it is now clear that slips occur most often on wet floors in dynamic “in motion” environments.


ANSI B101.1 - “Test Method for Measuring Wet SCOF of Common Hard-Surface Floor Materials” – now in final development recommends a SCOF of .6 on wet floors.

The German Ramp Test (DIN 51130) sets an “in motion” Dynamic Coefficient of Friction (DCOF) target threshold of 0.45 or higher on a wet surface (see Sidebar, “German Ramp Test”).

Thus, wet DCOF is becoming the new gold standard in slip/fall prevention measurement.

What to Do About Slippery Surfaces - Products and Treatments

If an existing wet floor's DCOF demonstrates that it is slippery, consider applying a specialized treatment or product to the surface that increases wet slip resistance.

Two product categories have proven effective in raising slip resistance on wet surfaces, and thus provide an excellent means to help ensure floor slip safety in general:

1. Surface modifiers that raise traction levels of mineral containing floors (concrete, ceramic tile, stone, quarry tile, etc.)

2. Mop-on cleaner/treatments that raise traction on finished and other floors.

Surface Modifiers

Surface modifiers use chemical processes to alter the physical properties of an unfinished mineral-containing floor or surface improving the DCOF. The process creates micro-pores or imperceptible tread patterns rendering tile and stone floors safer to walk on when wet. Applying a penetrating sealer makes the surface more resistant to soil. Slip resistance lasts several years with proper regular cleaning. Application should be handled by professionals. Surface modifiers are also very effective on porcelain or ceramic tubs and showers.

Mop-on Cleaner/Treatments

Mop-on cleaner/treatments are high performance pH-neutral cleaners with ingredients that raise the slip resistance of finished and other floors. Though recommended dilution ratios must be followed, relatively unskilled employees can apply these water-based treatments for routine cleaning and maintenance of slip resistance.

Follow Up Testing and Documentation

The initial DCOF test should form the basis and reference point for all future recordkeeping and follow-up testing. This information should ideally be available both electronically and in hardcopy formats and should be readily available. The results of all future slips tests should be added to the existing file the day the tests are performed or shortly thereafter.

According to CNA’s Ludwin:

“A walkway auditing program can help identify trends within your facility that can result in reduced slip resistance to flooring surfaces. To be effective, the testing should be completed in a consistent, periodic manner and include more than a single set of measurements.”

Documentation should also include a guide and logbook (See Sidebar, “Floor Safety Guide”) outlining all standard cleaning procedures; the cleaning materials and equipment that are used; and enabling the recording of any slip/fall incidents - and the surrounding circumstances - that occur in the building.

(Author: Kenneth Fisher is Vice President of Nu-Safe Floor Solutions. He serves on the ANSI B101.1 committee, which is establishing a test method for measuring wet Static Coefficient of Friction (SCOF) of common hard floor materials, and is chairman of the ANSI B101.2 sub-committee, which is developing a standard for chemicals and treatments for hard tile surfaces. He also served on ASTM's F-15 committee dealing with slip/fall issues.)


COF – Coefficient of Friction

COF – Coefficient of Friction is a scientific numerical measurement indicating the degree to which a floor is slip-resistant. The COF is determined with an instrument (such as the Binary Output Tribometer or BOT) that physically senses the slip resistance of a surface. Both static and the dynamic coefficient of friction measurements are useful in determining floor safety.

STATIC COEFFICIENT OF FRICTION (SCOF) is the ratio of the horizontal force needed to start an object moving to the vertical force pressing an object to the surface.

DYNAMIC COEFFICIENT OF FRICTION (DCOF) is the ratio of the horizontal force needed to keep an object moving to the vertical force pressing an object to the surface.


German Ramp Test

In Germany and much of Europe, floors are usually tested for slip resistance using the Ramp Test. The test is performed on an inclined plane or ramp with liquid contamination brushed onto the surface. Two persons walk with test shoes with half-step gaits up and down the ramp while it is raised by the drive unit. If slipping occurs, safe walking limits are determined by precise measurements taken during ascent and descent.


Floor Safety Guide

A written and enforced floor safety policy and procedures guide will improve floor safety, while demonstrating management commitment to prevention. The policy/guide should address common causes of slips and falls such as poor worker training, lack of weather contingency planning, inconsistent hazard identification, inappropriate footwear, and improper cleaning of floors, among other factors. It should thoroughly detail how to perform - and document - wet COF measurement, improvement and maintenance of floors.


Employees are Critical

Employees responsible for floor care must be properly trained regarding the slip/fall program, which includes establishing safety standards and cleaning procedures. Employees should be familiar with all cleaning products and equipment used, and should also understand proper storage of these items.

Employee cleaning regimes should include vacuuming, dust mopping and other floor care according to an established schedule. Mops that are treated with ingredients that could contribute to a slick surface, such as an oil-treated dust mop, should not be used, and employees must understand the importance of minimizing floor contaminants. Cleaning procedures and components of the slip/fall prevention program should be reviewed with employees at least on an annual basis.

Employees must understand the important role they play in properly maintaining a facility's floors, just as they should appreciate the importance of all work they perform. Employees can and should play an active role in identifying hazardous conditions such as a loose tile that is discovered during cleaning. They must be knowledgeable regarding both cleaning protocols and the mechanism for reporting hazards such as spills. Acknowledge employees for their proper cleaning efforts as well as their reporting of hazards and incidents. Individuals who believe they are an integral part of the team will provide a higher level of service and typically have greater job satisfaction – a win for both the facility and the individual.


Learn from Incidents

Learn from the incident when a slip or fall occurs. Document the conditions at the time of the event – the floor's condition, whether an obstruction was present, and the type of footwear that was worn by the individual involved in the incident. Work to determine if the fall could have been prevented through any effort on the part of facility operations. Share and document the information that is compiled regarding the incident with appropriate employees so that everyone can learn from the event.


Some Recommendations from CNA Insurance Companies:

• Remove any unauthorized or incompatible cleaning products and educate staff of the potentially dangerous consequences using the wrong products can have on the slip resistance of flooring surfaces.

• Color coding materials can provide instant recognition for personnel using the wrong equipment in the wrong area of the facility.

• Maintaining open and clear communication between the staff, cleaning personnel and the walkway floor auditor is crucial to the identification of trends and elimination of factors that could reduce the slip resistance on floor surfaces.