Floors, walking surfaces and slip resistance

The floor is where every slip and trip begins. A floor that is suitable for its use, correctly installed, kept in good repair and cleaned properly prevents most same-level falls before anyone needs to think about footwear or warning signs. A floor that is too smooth for wet conditions, uneven, damaged or poorly maintained creates hazards that no amount of caution will fully control. This lesson looks at the properties of walking surfaces, how slip resistance is measured, how to choose and maintain floors for different areas, and how to find and fix trip hazards such as changes in level, holes and damaged coverings.

What makes a floor slip resistant

Slip resistance depends on the interaction between the floor surface, the shoe sole and anything between them. On a clean, dry floor, most common flooring materials offer more than enough friction for normal walking. The problem arises when a contaminant such as water, oil, grease, food or dust gets between the shoe and the floor. A liquid film can separate the two surfaces, like a tire hydroplaning on a wet road, and dramatically reduce friction.

Two features of a floor surface help it resist slipping when wet. The first is surface roughness at a small scale, called microroughness: tiny peaks that can break through a thin liquid film and make direct contact with the sole. The second is texture at a larger scale, called macroroughness or profile, such as grooves, studs, embossing or aggregate, which gives the liquid somewhere to go and lets the sole make contact. Smooth, glossy surfaces such as polished stone, glazed ceramic tile, sealed concrete with a high-gloss coating and vinyl with a polish build-up can look attractive but become very slippery when wet. Matte, textured and gritted surfaces generally perform better.

Roughness wears down with traffic and cleaning, and it can be filled by dirt or by polish and sealers. A floor that tested well when new may be much more slippery a few years later. This is why slip resistance should be checked over the life of a floor, not only at installation.

Static and dynamic friction

Friction is usually described by two coefficients. The static coefficient of friction (SCOF) is the ratio of the force needed to start an object sliding to the normal force. The dynamic coefficient of friction (DCOF), sometimes called kinetic friction, is the ratio of the force needed to keep it sliding. For most materials, DCOF is lower than SCOF. Modern slip resistance research favors dynamic measurements because a slip involves the foot already moving across the floor at heel strike. Older test methods and guidance often used static values, which is one reason published numbers can be confusing.

How slip resistance is measured

Several types of instruments, called tribometers or slipmeters, measure slip resistance. They work in different ways and give different numbers, so a result means little unless you know which method was used.

ANSI A326.3, American National Standard Test Method for Measuring Dynamic Coefficient of Friction of Hard Surface Flooring Materials, is widely used for tile and other hard flooring in North America. The 2021 revision introduced different minimum values for different conditions: 0.42 for level interior spaces expected to be walked on when dry or occasionally wet, and higher values for interior spaces that are frequently wet, exterior areas and areas exposed to oils and greases, ranging up to about 0.55. These values are for the product as tested in a laboratory with a specified test liquid; they do not guarantee performance after installation, contamination and wear. ASTM F2508 sets a procedure for validating tribometers against reference surfaces so that results can be trusted.

OSHA does not set a numeric coefficient of friction requirement; section 1910.22 requires floors to be kept free of hazards. Older guidance often cited a static coefficient of 0.5 for level walking surfaces, and an appendix to the ADA guidelines once recommended 0.6 for accessible routes and 0.8 for ramps, but these values are advisory and based on older test methods. Courts and experts now usually refer to ANSI A326.3, ANSI/ASSP A1264.2 and ASTM standards.

Choosing floors for each area

The right floor depends on the use of the area, what contaminants are likely and how the floor will be cleaned. Designers and facility managers should think about the worst foreseeable condition, not the best. A lobby that is dry in summer may be soaked with melting snow in winter. A kitchen floor will meet grease, water and food every day.

Coatings, polishes and treatments

Floor finishes, sealers and polishes can increase or decrease slip resistance. Some high-gloss polishes leave a smooth film that is slippery when wet, while slip-resistant floor finishes include additives designed to maintain friction. Polish applied too thickly, or built up over many applications without stripping, can fill the texture of the floor. Ontario's industrial establishments regulation specifically prohibits applying a finish to floors that makes them slippery. When choosing a finish, ask the supplier for slip resistance test data, and follow the manufacturer's instructions for application and maintenance.

Several treatments can improve the slip resistance of existing floors: chemical etching of tile or stone to create microroughness, slip-resistant coatings containing grit, anti-slip tapes and strips for stair edges and ramps, and grinding or shot-blasting concrete. Each has advantages and drawbacks. Etching can make floors harder to clean, coatings wear and need renewal, and tapes can lift and become trip hazards if not maintained. Test the floor before and after treatment and keep monitoring it.

Changes in level and trip hazards

A trip happens when the toe or heel catches on something the person did not expect or did not see. Because toe clearance is so small, quite minor defects can cause trips. Common trip hazards in floors include raised edges between floor coverings, lifted tiles, cracked or heaved concrete, holes, gaps around drains and covers, loose or curled mats and carpet, thresholds, small steps that are hard to see and expansion joints.

Accessibility standards provide useful benchmarks for acceptable changes in level. A change of up to about 6 millimeters (1/4 inch) can generally be left vertical. A change between about 6 and 13 millimeters (1/4 to 1/2 inch) should be given a bevel with a slope no steeper than 1 in 2. A change of more than about 13 millimeters should be treated as a ramp or step, with suitable slope, marking and handrails. These benchmarks come from accessibility standards (such as CSA B651 in Canada and the ADA Standards in the US) and are good practice for all walking surfaces.

A single step, or a step of unusual height, is particularly dangerous because people do not expect it. Where a single step cannot be removed, mark its edge with a contrasting nosing strip, improve the lighting, add a handrail and consider a ramp. Abrupt changes in floor surface from high-friction to low-friction material, for example stepping from carpet onto polished tile, can also cause slips because the walker does not adjust their gait in time. Transition strips, matting and consistent materials help.

Maintaining floors

Floors need planned maintenance as well as cleaning. A maintenance program should include regular inspection for damage, wear and changes in slip resistance; prompt repair of holes, cracks, lifted tiles and loose coverings; stripping and refinishing on a schedule; replacement of worn mats and stair nosings; and periodic slip resistance testing in high-risk areas. Repairs should be made safely: guard the area, use barriers and signs, and do not leave a damaged area unprotected overnight. Repairs to floor structures should be done by competent people.

Temporary trip hazards, such as hoses, extension cords, tools and stock during deliveries, need just as much attention as permanent defects. Lessons 10 and 11 cover cords, clutter and housekeeping.

Setting up a slip resistance testing program

For sites with high-risk floors, such as hospitals, food plants, shopping centers and commercial kitchens, a simple testing program helps catch problems before they cause injuries. Choose one validated test method and stay with it so that results can be compared over time. Test new floors after installation to establish a baseline, then retest at set intervals, such as annually, and after any change in cleaning products, finishes or methods. Test in the locations where people actually walk and slip, such as entrance zones, around sinks and fryers, and along main traffic routes, and test both dry and with the contaminant most likely in that area. Record the results on a floor plan, and set trigger values that lead to action, such as deep cleaning, a change in finish or replacement.

Testing should be done by a trained person following the instrument manufacturer's procedures, because technique strongly affects results. Many flooring and cleaning suppliers offer testing services, and independent consultants can provide testing where results may be used in legal disputes.

Gratings, metal plates and special surfaces

Some walking surfaces need particular attention. Steel plates, manhole covers, drain grates, trench covers and diamond plate can become very slippery when wet, oily or icy. Serrated bar grating, perforated plank and abrasive-coated plates provide much better grip on industrial platforms and walkways. Painted lines and floor graphics on concrete can be more slippery than the surrounding surface unless a slip-resistant additive is used in the paint. Wooden decks and boardwalks grow algae and moss in damp, shaded locations and may need anti-slip strips or regular cleaning. Temporary surfaces on construction sites, such as plywood over openings, must be secured, marked and strong enough for the loads, and openings must be covered or guarded as covered in the working-at-heights course.

Buying flooring well

Most of the long-term slip performance of a floor is decided when it is specified and bought. Purchasing staff and designers should ask suppliers for slip resistance data for the intended conditions, check that the cleaning method recommended by the flooring manufacturer matches what the site can actually do, and involve the people who clean and work on the floor in the decision. Life-cycle cost, including cleaning effort and replacement, often favors a slightly more expensive surface that stays safe longer.