by Nick Gromicko, CMI®
The slip resistance of floors and pavements is the measure of the ability of a surface to prevent accidental slipping by pedestrians in dry or wet conditions. InterNACHI inspectors, especially those who perform commercial inspections, can benefit from learning about the details of slip resistance, especially when the lack of it presents a serious safety hazard.
Slip resistance is important because it prevents against slip-and-fall accidents, which cause needless physical and emotional trauma -- as well as financial hardship through medical expenses and lost work -- to the injured person. The party found legally responsible – typically, the property owner – may face stiff liability payouts, legal defense costs, insurance premium hikes, increased administrative costs, and a damaged reputation within the community. All told, these accidents and their resulting lawsuits cost all parties enormous sums of money and inconvenience, and they’re common, too; according to the Occupational Safety and Health Administration (OSHA), they constitute the majority of general industry accidents and cause 15% of all accidental deaths. For these reasons, InterNACHI inspectors and their clients can benefit from learning the basics of slip-resistant flooring.
Critical to understanding slip resistance is a metric used to gauge the slipperiness of the floors in a building: the coefficient of friction (COF) represents the resistance to movement between two objects -- in this case, a human foot and a flooring material. Sophisticated devices, such as the James Machine,
obtain the COF by dividing the measured horizontal resistance to the vertical, downward force. High COFs indicate greater friction and less slipping. For example, ice, which has a COF of 0.3, is more slippery than dry, swept concrete, which has a COF of 0.8. Concerning the relationship between COF and safety, Purdue University states:
[P]eople can walk comfortably and safely on surfaces with a coefficient of friction greater than 0.4, but a floor with coefficient of friction of 0.5 or better is considered a Slip-Resistant Surface.
OSHA and the American Society for Testing and Materials (ASTM) agree, and each has set a standard of 0.5 COF or higher for flooring surfaces. However, the Americans with Disabilities Act (ADA) specifies a coefficient of friction of 0.6 on flat surfaces and 0.8 on ramps. Note that a COF beyond 0.8 does not significantly add to slip resistance, and a COF that's higher than 1 can actually impede a person’s ability to walk on that surface.
For a basic understanding of the inherent slip-resistance of some common types of flooring, refer to the following list:
- Porcelain tiles: This clay product is baked in a kiln at very high temperatures for superior density and strength. Porcelain tiles can be found in lobbies and vestibules and can simulate mineral floors, such as slate and stone. Textured varieties offer good slip resistance.
- Marble and granite: When wet, these materials offer little slip resistance.
- Terrazzo: Chips of marble, glass and other decorative materials are suspended in epoxy or urethane and poured in place. These types of floors are commonly found in retail stores and airports. Terrazzo has a COF of 0.64 when dry and 0.16 when wet.
- Quarry tiles: Common in restaurant floors and dining areas, this natural clay product offers good slip resistance when clean and wet, but poor slip resistance when dirty (especially greasy) and wet. For improved traction, some quarry tile comes with aluminum oxide grit, but this can wear down after a few years of foot traffic.
- Ceramic tiles: These clay products are baked with ceramic at high temperatures and come glazed and unglazed, sometimes with imbedded granules to enhance traction. Smooth glazed tiles offer little slip resistance when wet. With grit, ceramic tile offers COFs of 0.62 when dry and 0.34 when wet. Without grit, ceramic tile measures 0.7 when dry and 0.1 when wet.
- Vinyl composition tile: Very slippery when wet, this inexpensive tile is common in schools, hospitals and offices.
- Concrete: Unsealed concrete floors are hard to clean and commonly considered unattractive, but they offer good slip resistance, especially when broom-swept.
Flooring COF tested under laboratory conditions is limited in that it does not account for usage and maintenance practices employed after the floor is installed or the physical and mental condition of the walker or their stride. Therefore, a determination of slip resistance of floors under field conditions should use COF as one component in a larger analysis that may include the following considerations:
- Cleaning practices: Clogged pores will cause tiles to lose their slip resistance, so frequent cleaning is necessary. Mopping is generally advised against, as dirty materials are spread around and forced into the pores.
- Application: The choice of flooring material should suit its environment and purpose. For instance, a certain tile may not be appropriate if the floor is sloping, and areas that are often wet demand more slip-resistant materials than areas that are usually dry. Flooring near an entry or exit door should perform well under snowy and wet conditions.
- Floor sealants and waxes: Sealants and waxes fill in the pores in tiles that provide slip-resistance. Anti-slip coatings can also be ineffective, as they rely on an abrasive surface material that quickly wears away, exposing a slippery coating that can be expensive to remove.
- Maintenance and repair practices: Tiles can become cracked, broken or uneven by dropped loads, weathering and general use. They can also become “polished” by constant foot traffic, losing the slip resistance they had when they were installed. The effort taken to remedy these issues influences the chances that they will cause a person to trip or fall.
InterNACHI inspectors can inform their clients about how to avoid the personal and financial fallout that result from slip-and-fall accidents through the following corrective measures:
- Abrasive treatments, finishes and coatings: Rough finishes made from epoxy, urethane and paint may be applied to impart slip resistance to floor and stair applications. Silicon carbide and aluminum oxide are more durable grits, while garnets and sand are less durable to contaminants and high traffic.
- Chemical etching: Common in bath and shower areas, hydrofluoric acid is used to create ridges and valleys to increase surface roughness on marble, granite, concrete, and ceramic and porcelain floors. This etching may be lost if the floors are not frequently cleaned.
- Carpeting and mats: Carpeting and mats are used in high-traffic areas to increase slip resistance, especially near deep fryers, sinks, and other locations that are commonly slippery. Where installed, ensure the following:
- The slip-resistant surface should be present on both the top and bottom sides. If the mats become loose, they can themselves become a slip hazard. Ensure that area rugs and mats are securely tacked or otherwise secured to the floor. Elderly building occupants are vulnerable to falls from sudden underfoot movement of small, loose carpets on slippery floors.
- The surface should be adequately and regularly cleaned, as dirty carpets and mats are unhygienic and may lose their surface roughness.
- Mats and carpets should have beveled edges or a similar design to reduce the likelihood of guests or workers tripping on the mat’s edges. The mat should otherwise be in good condition.
- There should be some measure, such as slots, to allow for drainage and prevent the accumulation of water, snow, ice or grease in areas exposed to weather or prone to water leaks or grease accumulation.
- Cleaners and polishes: These may be applied daily when the floor is washed, but they must be re-applied whenever the floor is waxed. They wear away easily under heavy traffic or rewashing.
- Illumination: Pedestrians cannot anticipate the slip potential of a floor if they cannot see it, especially as one flooring material transitions to another.
- Guardrails: ASTM offers the following recommendations for guardrails:
- The guardrail should consist of a midrail installed halfway between the floor and a top rail, which should be connected by posts.
- The top rail should be smooth-surfaced throughout the length of the railing (the mid-rail).
- The ends of the rail should not overhang the terminal posts where such an overhang represents a projection hazard.
In addition to the aforementioned, InterNACHI inspectors can pass along the following safety tips to their residential and commercial clients:
- Use non-skid waxes and surfaces coated with grit to create non-slip surfaces in slippery areas, such as toilet and shower areas.
- Require employees to wear slip-resistant footwear.
- Dry floors promptly when they become wet.
- Make sure that floors are designed to have sufficient drainage and that floor drains are clear and unplugged.
- “Caution: Wet Floor” signs are available for use. Even where there is a comparatively small chance that anyone will actually slip, the placement of these signs is wise because it shows that the property owner is aware of the potential and has taken active steps to warning of its danger, which may decrease his liability if an accident should happen and matters proceed to court.
- Flooring should have a similar slip resistance when transitioning between different types of flooring, especially when liquids are present.
- Provide electrical receptacles at a low floor height for equipment to prevent the use of cords that may run across hallways and other footpaths.
- Temporary electrical cords that must cross aisles should be taped or anchored to the floor.
- Stretch and lay flay carpets and mats that have become bunched to prevent tripping hazards.
- Eliminate uneven floor surfaces.
- Make sure that floor drains, pits and other floor openings are covered or protected with guardrails.
In summary, property owners can reduce their liability and the slip potential of their floors by installing and maintaining slip-resistant flooring materials. InterNACHI inspectors can help their clients become aware of these potential hazards and simple preventative measures to help ensure safety in the workplace and other large properties.