SLIP
RESISTANCE - 'A BRIEF STUDY IN TIME'
lntroduction
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.
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.
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.
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.
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.
Taken from 'PEDESTRIAN SLIP RESISTANCE'
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