Slip Resistance

Falls are the dominant incident type leading to serious injury not only in public places but also in the workplace.

Because every fall has the potential for producing a serious injury, including the possibility of death, depending upon how the victim goes down, this category of incident is what is known among safety engineers as a ‘high potential’ loss type. Not all types of hazards lead to equally serious consequences, but because falls are such a problem in virtually every industry and public area, they have been selected for the primary attention of accident prevention professionals.

Slips result from inadequate friction on the shoe/floor interface. After over half a century of serious research on what slipperiness is and how it can be measured, rapid progress has been made in the decade of the 90s, but obsolescent ideas persist even in the scientific literature, partly because some investigators don’t read the existing literature, partly because some scientists presume to write about technology outside their area of competence.

Investigators still examining technology widely known to be invalid still don’t even seem to know that dry surfaces aren’t slippery nor that smooth hard surfaces are slipperier than ice when wet.

Designing for Slip Resistance

Slip resistance is affected by, floor material and finish, pedestrian shoe bottom material and texture, environmental surface contaminants and pedestrian gait dynamics. How the pedestrian performs his behavioral dynamics may be beyond our control and sometimes shoe characteristics are relatively uncontrollable, but floor construction and maintenance relative to surface condition and contamination are almost always controllable and therefore provide the greatest opportunities for responsible parties to affect slip resistance under foot.

The first consideration in floor design is the environmental conditions that may be expected or foreseen. Walkway features that will provide adequate traction in that environment should be specified, designed, constructed and maintained. This includes all walking surfaces such as floors, ramps, stairs, ladders and platforms, whether fixed or as part of mobile equipment.

The second consideration in slip resistance performance is maintenance. Sometimes environmental conditions or chemical processes affect slip resistance of a walking and working surface, and regular cleaning and maintenance materials and methods must be specified. Regular inspection and accountability procedures will also be required to maintain walking and working surfaces in a relatively safe condition.

The Physics of Slipping

The vast majority of slips and falls result from wet or otherwise lubricated surfaces. The property of a floor that makes it slip resistant in the presence of a lubricating contaminant, such as water or oil, is its surface roughness. That is, the surface roughness must be tall enough and sharp enough to extend upward through the lubricating film sufficiently to engage the shoe bottom in a manner not unlike sandpaper.

If a walking surface is found to be excessively slippery, either through accident experience or by measuring the slip resistance performance with a slip meter, consideration should be given to replacing the smooth surface with one that is sufficiently rougher to make it safer in the normal use environment. This can be accomplished by changing the existing surface properties by chemical treatment (such as Y-Slip Treatment or by using aggressive cleaners to remove hard films that ‘level’ the surface through build-up) or the surface can be abraded or textured by the use of mechanical equipment.

If such treatment is not practical or desirable, the floor surface should be replaced with a different material having pronounced surface roughness, by applying a suitable textured surface coating, or by laying a new floor.

Because of the variability of conditions and phenomena that may occur in a real world workplace or use environment that are different from what occurs under laboratory conditions, evaluations of prospective flooring materials, finishes or treatments must be tested under existent use conditions before specifying them for system wide application. The effectiveness of cleaning materials and methods under the control of the maintenance people who actually do the work are part of the evaluation of the performance of any flooring system.

Adequate slip resistance under lubricating conditions depends upon using flooring surfaces that are sufficiently rough to have micro peaks on the surface protrude upward through the hydrodynamic squeeze film so as to dig into the shoe bottom surface. The material, texture and tread pattern of the shoe bottom also affect slip resistance performance in contaminated environments; and where the footwear can be controlled, substantial improvements in pedestrian safety can be realised.

Making the best of Existing Flooring

Although much can be done in the design and construction of new facilities to make falls less likely, there are numerous times when operators acquire existing properties, thereby inheriting slippery flooring that can turn out to be an ongoing injury problem. Or walking surfaces that were once safe can become hazardous due to wear or changing conditions.

Floor Maintenance

The first step is to see if existing cleaning and maintenance procedures may have caused the slipperiness. For example, a slippery wax may have been applied or a relatively slip resistance floor finish may have become slippery by improper application or maintenance methods. An effective solution may be to simply strip the floor and apply a safer finish.

The first step towards an adequate maintenance programme is to determine what chemicals will be used to treat the floor, including both finishes and cleaners. Gain technical assistance from the chemical suppliers. Then any prospective process should be tested in actual operations to verify its effectiveness and that it can be made to work in the intended environment by the personnel who actually work there. Once the proper methods and materials have been decided upon, clear written instructions should be established.

Present the maintenance program to the operations management and devise effective training procedures. Training alone will not assure program success, there must be adequate monitoring and supervision to confirm compliance with the program without either there is no program.

Responsibility and accountability must be determined and assigned. A practical means of measuring slip resistance performance of floors under actual every day conditions, can help control quality. Our EXL Slip Tester is used to test under these conditions.

Other Maintenance

One recognised way of preventing slips and falls is to control leaks or spills that can make a floor slippery. It is always much more efficient to fix leaky pipes, clogged drains and faulty equipment promptly, before a fall occurs than it is to try to get by under hazardous conditions.

Remedial Floor Treatments

In places where slippery spills are to be expected, special precautions should be taken. Since spills are known to occur in these areas and since personnel will not be able to wipe every spill dry before a pedestrian slip and fall, supplementary control measures, such as mats or slip resistant surface treatments, may be helpful.

Warning signs posted near spills or at entrances during wet weather are of some help in making people aware to the slippery conditions, but they are not a substitute to taking adequate action to control hazards.

Mats Efficiency

Mats are devices for cleaning and drying pedestrians’ feet and may be used at building entrances or other locations where messy contaminants may occur to reduce the tracking of moisture or other lubricants over the surface of hard floors.

For mats to be effective as fall control devices, they must first of all lie flat and securely to the floor. Curled edges in particular will present a trip hazard and may well cause more trips than prevent. The absorbency and drainage of the mat is especially important where large amounts of moisture are to be encountered, as is the size of the mat to allow adequate removal of contamination. The advice of a qualified expert should be sought.

Other Floor Treatments

Several other methods can be used to rehabilitate smooth hard floors that have found to be slippery under use conditions.

Ceramic tile floors can have the surface roughness enhanced with propriety brands of surface treatment, which will increase the slip resistance of the surface, however it is best to seek professional advice. Contact us for more information.

In operations such as food service, where certain organic liquids are ubiquitous, polymerization can occur, if cleaning methods are not excellent. Such films contribute to the slipperiness by coating over the surface roughness and aggressive remedial cleaning techniques may be required. Contact BDI Solutions for more information.

Some kinds of Resilient Flooring can be quite slippery when lubricated and there are chemical coatings containing abrasive granules that may be very helpful in imparting slip resistance.

Other smooth hard surfaces such as concrete or metal plates can be coated with troweled on and paint finishes with varying degrees of hardness and roughness. Thought should be given for the need for chemical resistance and durability when selecting such coatings. It is important to select one that will adhere tenaciously to the substrate it is to be applied to, cleanability and durability should be considered.

Definitions

Static Coefficient of Friction is the force required to initiate relative motion between an object and a surface it is resting on. Dynamic Coefficient of Friction is defined as the force required to keep a sliding object in motion, once sliding has begun.

Since most clean dry surfaces are not slippery it is almost always necessary to investigate some contamination of the walking surface, in cases of pedestrian slips. We are looking at the ability of a rough surface to protrude through the contaminant and engage a shoe bottom. That is the study of Slip Resistance not Coefficient of Friction. There is another complicating phenomenon affecting slip meters known as Adhesion or as many investigators have termed it Sticktion (under wet conditions) Adhesion or Sticktion arises as a function of the slider pads residence time on the surface. If there is a delay between the instant of surface contact and the application of the horizontal force, adhesion will occur. On surfaces wet with water, residence times as short as .20 second can produce significant sticktion that can result in readings that would be higher under wet conditions than would be obtained on the same surface in a dry state.

All drag sled meters and all articulated strut instruments that do not apply the horizontal and normal forces simultaneously with initial surface contact are afflicted with disqualifying sticktion. In other words, you cannot take a valid reading on a wet surface with any drag sled instrument, regardless of what the testing standards say.

For more information about this article or to discuss, please do not hesitate to contact BDI Solutions.