Ceramic Tile Institute of America, Inc.
Endorsement of Portable Test Methods and Slip Prevention Standards for Existing
Flooring
Summary
The objective of this endorsement is to reduce
the human and financial costs of slips and falls on all types of flooring
materials. Such accidents cause some 1200 deaths, and in the workplace
alone about $4 billion in lost productivity and compensation costs,
in the United States each year.
The Slip Resistance Committee of the Ceramic Tile
Institute of America (CTIOA) hereby endorses the following:
(1) The variable-angle ramp human traction test method
as the primary standard for validation of portable slip-resistance
test methods
(2) The Tortus dynamic slip resistance measuring instrument, with
digital data acquisition, for wet testing, and the use of a trace of
Triton X-100 wetting agent in distilled or deionized water (three drops
per 250 milliliters) as the wetting liquid
The following minimum average dynamic coefficients
of friction for safety based on Tortus measurements with a Four-S rubber
slider on clean flooring, wet, with measurements in at least four directions,
each measurement direction having a preferred total path length of
20 cm (8 inches):
(a)
0.50 for level floors (i.e., not ramps) that may get wet in use
(b)
0.70 for bathtubs, showers and swimming pool decks
(3) The pendulum dynamic slip resistance measuring
instrument for wet testing (without wetting agent), and the use of
the pendulum test guidelines recommended by the United Kingdom Slip
Resistance Group
A minimum British Pendulum number, BPN, on wet
clean flooring, of
(a)
35, using a Four-S rubber slider, for level floors that may get wet
in use
(b)
35, using a TRRL rubber slider, for showers and pool decks
Use 3M 261X Imperial pink lapping film on float
glass (or a similarly smooth, flat surface) as a calibration check
surface for both Tortus and pendulum.
Preference is for the pendulum in locations where
some pedestrians (either adults or children) may reasonably be expected
to be running rather than walking. On level flooring, in case of conflict
between Tortus and pendulum findings, preference is for the pendulum.
Higher slip resistance minimums may be appropriate
in many situations, such as ramps, environments where lubricants other
than water are present, etc.
The two portable instruments are recommended because
they have achieved wide acceptance, and because data are now available
to show that they correlate well with tests of human traction, and
with well-simulated mechanical analogs of human traction.
The Tortus is less time-consuming per test than
the pendulum. The Tortus is therefore more suitable for periodic testing
of a floor (e.g. quarterly) and for checking uniformity of an area
using repetitions covering various zones across the area. The slider
speed of the pendulum is higher, making it possibly more conservative
in evaluating hydroplaning potential.
We request that manufacturers of hard and resilient
flooring offered for sale in the United States supply potential buyers
with pendulum test data for the manufacturers’ products by June 1,
2003. As a substitute for the pendulum test, manufacturers may use
any alternative slip test method, or combination of tests and calculations,
that is scientifically proven to predict the results of the pendulum
test or to be as good as, or better than, the pendulum test or the
variable-angle ramp test as an indicator of human traction potential
on wet flooring. Any such test device or method must be commercially
available so that field tests by other parties are feasible.
These portable tests are intended to replace the
horizontal pull-meter test, American Society for Testing and Materials
Method C 1028-96, that U.S. ceramic tile manufacturers currently use
for field testing of their products.
These test methods and the safety standards that
are based on the test results are useful in field testing of flooring
in ceramic tile, vinyl and linoleum, natural stone, terrazzo, concrete,
wood, and other common types of flooring.
This endorsement does not preclude use of other
existing or improved portable test methods as long as they demonstrate
a correlation coefficient R of 0.90 or higher, with human traction
measurements using the ramp method, on a population of at least 14
samples well-distributed over the ramp test categories R9 through R
13.
Buyers of new flooring should use the safety standards
endorsed by the Committee on September 19, 2001. Those standards are
based on laboratory tests using the variable-angle ramp method, which
is not suitable for field tests.
Introduction
The
Slip Resistance Committee of the Ceramic Tile Institute of America
(“the Committee”) is tasked to advance and disseminate scientific knowledge
of slip and fall issues in order to improve safety of walkway surfaces
in the built environment, including floors, stairs, and pedestrian
ramps.
Pedestrian slips occur from an unfavorable combination
of the person involved, the activity the person is involved in, the
environment, the footwear (if any), and the flooring. Most slip accidents
occur when the footwear or bare feet and/or the flooring are wet or
otherwise lubricated. Some manufacturers of flooring and floor coatings
presently offer as catalog information slip resistance test results,
dry and/or wet, based on test methods standardized by the American
Society for Testing and Materials (ASTM).
Experience with U.S. test methods and safety standards
for prevention of slip and fall accidents shows that improved test
methods and safety standards are necessary. National Safety Council
statistics indicate that some 1200 Americans die each year — an average
of one death every seven hours — as a result of slip-and-fall accidents
on the same level (not on a ladder, stairs, etc.). In the workplace
alone, in 1998 slips and falls caused 313,335 injuries (an average
of one every two minutes) and over $4 billion (or $340,000 per hour)
in workers’ compensation and lost productivity (Ref. 1). Too many floors
are potentially slippery under their normal conditions of use. The
requests and recommendations here are in the interest of public safety.
On
September 19, 2001 the Slip Resistance Committee approved “Endorsement
of Improved Test Methods and Slip Prevention Standards for New Flooring,” available
from the Ceramic Tile Institute of America (telephone 1-310-574-7800).
It endorsed a laboratory test method for rating slip resistance of
new flooring. However, that test is not suitable for field testing
of existing floors. The portable methods discussed here are suitable
for field testing.
We base the designation of portable test methods
on their correlation with measurements of human
traction as determined by the variable-angle ramp test. This test
assesses human traction on wet or otherwise lubricated surfaces through
repetitions of controlled walking by two or more human subjects on
a five-square-foot sample. The test determines the critical angle, for each flooring sample,
at which it is not possible to walk on that sample without slipping.
The larger the critical angle is, the greater is the potential for
human traction on that sample.
To be acceptable, trends that a portable test method
determines must give reasonable mathematical correlation with results
from the variable-angle ramp method. It’s not necessary that both methods
give the same numerical value as
output for a given sample. For instance, suppose that the critical
ramp angle for Sample A is 5 degrees and for Sample B is 10 degrees,
while the portable test output for Sample A is 0.40 and for Sample
B is 0.80. As long as the portable test results can be used to predict,
mathematically, the ramp test results to reasonable accuracy, the portable
test is deemed acceptable.
Portable
Test Methods
Portable test methods have several potential uses:
1. Periodic
checks on existing flooring to confirm safe condition and maintenance
(procedures and floor-care products) of the floor
2. Investigation
of accidents and of complaints
3. Routine
manufacturing quality control by flooring manufacturers
For slip resistance of all types of hard, resilient,
and wood flooring we recommend the Tortus method and/or the pendulum
method. Both, along with the variable-angle ramp method, are national
standards or final draft national standards for wet tests in many nations
(the pendulum in 21 nations, the Tortus in 19; Refs. 2, 3). They are
also both included in the International Standards Organization (ISO)
Draft International Standard 10545-17. The United States is a member
of ISO.
The two methods have different advantages. Testing
by Ceramics Research, Ltd. in Stoke-on-Trent, England, indicates that
both of these methods show good correlation with test results from
the variable-angle ramp test, which measures human traction potential
as assessed by human subjects in walking tests. (Statistical correlation
coefficients, R, of 0.90 or higher.) Both methods also show good correlation
(R of 0.93 or higher) with the SATRA STM 603 tester, a computerized
device which uses a complete shoe that moves with respect to the flooring.
The SATRA test is a realistic simulation of human traction, but because
it is done by machine it eliminates the element of human variability.
A
very fine abrasive film, 261X Imperial pink lapping film sheets from
3M Company, should be used as a high-end calibration check for both
instruments. This film, with a roughness of about three microns peak
to valley, has good quality control and so yields consistent results.
For testing, the film should be placed on float glass or similar smooth,
flat surface.
New
ceramic tiles are sometimes shipped with a protective waxlike coating.
Before testing, clean new tiles with Hillyard’s Renovator (Hillyard
Industries, St. Joseph, Missouri) at a dilution of one part Renovator
to eight parts warm water. Scrub using this solution and a soft brush,
then rinse thoroughly.
Tests on existing floors should include both high-
and low-pedestrian-traffic areas, and areas of visibly noticeable differences
in wear, texture, or color. For high-traffic areas, entrances, exits,
and zones where pedestrians make turns or accelerate are preferable.
Tortus
method. The Tortus
is a computerized, battery-driven cart about the size of a bathroom
scale. It has a 3/8-inch-diameter slider of
laboratory-grade Four-S rubber. The liquid for wet tests is demineralized
water with a trace (three drops per 250 milliliters) of Triton X-100
wetting agent (available from chemical supply houses; the wetting
agent is not used in pendulum testing).
The
Tortus is manufactured by Severn Science (Instruments) Ltd. in Bristol,
England. The Tortus crawls across the floor at 2/3 inch per second,
continuously measuring dynamic coefficient of friction (DCOF). It prints
a continuous trace of the DCOF together with a calculated average.
The Tortus was invented by Ceramics Research Ltd. and has a history
of over 20 years of use. In more recent years, digital data acquisition
has greatly improved the accuracy of Tortus test results.
The
Tortus is generally repeatable to 0.02 in coefficient of friction over
the same path. This is four percent of the level-floor safety standard
recommended here, and two percent of the safety standard for swimming
pool surrounds.
The
test method is given (except for use of the wetting liquid in wet tests)
in Ref. 3. The Tortus should be calibrated at each location where it
is used, immediately preceding the start of testing. At least once
a week when in use, the Tortus reading should be checked on 3M Imperial
lapping paper obtained from a reputable supplier. When testing flooring,
take an average of readings in at least four different directions (e.g.,
north, south, east, west). Each of these four readings should be an
average over a total path length of 8 inches (20 cm). This may be on
the diagonals of 8-inch-square tiles, or may combine measurements on
diagonals of smaller tiles.
Pendulum
method. The United
States National Bureau of Standards devised the pendulum method.
British researchers developed it further (Ref. 4), and the American
Society for Testing and Materials (ASTM) specifies the pendulum in
its Method E 303-93 (1998). Australia and New Zealand have established
the pendulum as the standard for wet testing and the Tortus for dry
testing. The pendulum test procedure we endorse is that specified
by the United Kingdom Slip Group (Ref. 5). The slider is three inches
wide, one inch wide in the direction of travel, and covers a path
five inches long.
Pendulums
are available from two companies in England: Wessex Engineering Ltd.
(located in Weston Super-Mare) and Munro Group (Woodford Green, Essex).
Comparison of Tortus and pendulum. The
pendulum’s rubber slider strikes the floor at eight miles per hour,
about 200 times faster than the movement of the Tortus slider. The
pendulum’s slider speed is close to that of a typical young adult’s
body when running at a sustainable pace. The Tortus’ slider speed is
typical of the speed of a person’s heel when it first lightly touches
down in normal walking. The Tortus’ slower speed might to some extent
be compensated for by the addition of a trace of wetting agent in the
water for wet testing. In addition to aiding in uniform wetting, the
wetting agent makes the water a better lubricant. This may make hydroplaning
possible at lower speeds on a smooth surface. Tests by CERAM in the
United Kingdom show good correlation (R = 0.94) between pendulum and
Tortus test results for ceramic tile (17 samples).
The operating procedure for the Tortus makes it
possible to conduct many more tests in a given amount of time. This
is an advantage in testing of areas for nonuniformity that results
from poor production quality control, wear, or inappropriate maintenance.
Some owners (or their agents) of commercial or industrial property
have their floors’ slip resistance tested quarterly to confirm that
the floors are safe despite possible changes in floor-care chemicals,
personnel, or procedures. We recommend that periodic Tortus tests,
with safe ratings or remedial action to restore the floor to safe ratings,
be accepted as due diligence for commercial and industrial property
owners with respect to documenting the safety of their floors. The
Tortus is also more suitable for testing curved surfaces, such as the
bottoms of some bathtubs.
The higher speed of the pendulum may make it more
suitable for areas where pedestrians may reasonably be expected to
run: airport concourses, subway, bus and railroad stations, lobby areas
where doors stand open during rainfall, swimming pools used by children,
etc.
In litigation it may sometimes occur that there
is a conflict between findings from the pendulum and the Tortus regarding
whether flooring was safe when wet. In such cases we recommend that
the pendulum take precedence. This is because of its acceptance by
the United Kingdom Slip Group and Standards Australia/Standards New
Zealand after extensive study. In the absence of pendulum results,
we recommend acceptance of Tortus data.
Both pendulum and Tortus should be calibrated at
least annually by an appropriate third party, preferably one with ISO
certification for calibrations.
This
endorsement does not preclude use of other existing or improved portable
test methods as long as they demonstrate a correlation coefficient
R of 0.90 or higher, with human traction measurements made using
the variable-angle ramp method, on a population of at least 14 samples,
This allows for advances in the state of the art within the constraint
that new measurements must be proven relevant to human traction.
Any form of curvefit may be used to derive an equation from which
to calculate R-squared; R is the square root of R-squared.
Values of R near 1 indicate that the curvefit is
very useful for making predictions of the critical ramp-test angle
for a sample using the results from the portable test method. Standard
textbooks on elementary statistics describe the parameter R and how
to calculate it. Widely-available software such as Microsoft Excel
makes it easy to calculate curvefits and R.
Safety
Standards
Different test methods yield different numerical results for the same sample,
even if the test results are all converted to coefficients of friction.
For instance, a sample that has a coefficient of friction of 0.60 (corresponding
to a BPN of 55; see Ref. 4) on the high-speed pendulum using Four-S
rubber gives a coefficient of friction of approximately 0.80 on the
low-speed Tortus using the same rubber. This means that safety standards
must depend on the test method that is used. Below are a few recommended
minimum safety standards. For certain situations, higher minimums than
these are appropriate; see Ref. 7.
Tortus. The
traditional Tortus dynamic coefficient of friction safety standard
of 0.40 minimum for most level floors is too low, and leads to passing
grades for unsafe floors. We recommend a minimum average of 0.50 for
any level floor that is likely to become wet. The average should include
measurements in at least four directions, each measurement having a
preferred path length of 20 centimeters (3 inches). No single 20-centimeter
path at any one location on a floor should have an average of less
than 0.38. This is based on the former safety criterion of 0.40, with
allowance for a measurement variation of 0.02.
For bathtubs, showers and swimming pool decks we
recommend a minimum average of 0.70 (Ref. 8). The high standard is
desirable because of soapy water in baths and showers; and presence
of suntan oil and body fats on swimming pool decks, as well as children
running.
Pendulum. Following the lead of the United Kingdom Slip Group
and Standards Australia/Standards New Zealand, we recommend a minimum
British Pendulum Number (BPN) of 35 (when testing with a Four S rubber
slider) for any level floor that is likely to become wet in use. For showers and swimming pool decks we
recommend a minimum BPN of 45
(Ref. 9) when testing with Four-S rubber. However, for barefoot areas
pendulum testing with TRRL rubber as specified in Ref. 3 is preferable,
and for showers and pool decks the BPN with TRRL rubber should be 35
or higher. Softer than Four-S rubber, TRRL rubber better simulates
bare feet.
Catalog
Data
We have previously requested that ceramic tile
manufacturers supply catalog data for slip resistance categories based
on the variable-angle ramp test or equivalent (Ref. 6). Pendulum data
could be substituted for, or could supplement, the ramp data. Pendulum
data can help manufacturers and building owners confirm that the tile
delivered conforms to the manufacturer’s specification. Such data can
also serve as a benchmark for future periodic testing.
We request that manufacturers of hard and resilient
flooring offered for sale in the United States supply potential buyers
with pendulum test data for the manufacturers’ products by June 1,
2003. (Tile manufacturers in leading tile-manufacturing countries China,
Spain, Italy, and Germany already offer such data.) As a substitute
for the pendulum test, manufacturers may use any alternative test,
or combination of tests and calculations, that is scientifically proven
to predict the results of the pendulum test or to be as good as, or
better than, the pendulum test or the variable-angle ramp test as an
indicator of human traction potential. Any such test device or method
must be commercially available so that field tests by other parties
are feasible.
References
1. Simpson,
R., “An Ounce of Prevention,” Flooring, August 2000, pp. 24–25.
2. “Ceramic
Tiles — determination of coefficient of friction,” European Committee
for Standardization CEN/TC 67 N. 161, February 1998, Milan, Italy.
3. “Slip
Resistance Classification of New Pedestrian Surface Materials,” Australian/New
Zealand Standard AS/NZS 4586:1999, Standards Australia, Strathfield,
NSW, 1999.
4. Giles,
C.G., Sabey, B.E., and Cardew, K.H.F., “Development and Performance
of the Portable Skid-Resistance Tester,” Department of Scientific and
Industrial Research, Her Majesty’s Stationery Office, London, 1964.
5. “The
Measurement of Floor Slip Resistance: Guidelines Recommended by the
UK Slip Resistance Group,” June 2000, ISBN No. 1-85957-227-8, Rapra
Technology Limited, Shawbury, Shrewsbury, Shropshire, United Kingdom.
6. Private
communication from William Walters, CERAM, Stoke-on-Trent, United Kingdom,
October 2001.
7. “Endorsement
of Improved Test Methods and Slip Prevention Standards for New Flooring,” Ceramic
Tile Institute of America, Culver City, CA, September 19, 2001.
8. Tyrrell-Roberts,
T., letter to Gray La Fortune of Ceramic Tile Institute of America,
from SDi Limited, Torpoint, Cornwall, England, November 19, 2001. Modified
following Refs. 6 and 9.
9. Bowman,
R., communication to G. Sotter of Sotter Engineering Corporation, Mission
Viejo, CA, dated November 22, 2001, CSIRO — Building Construction & Engineering,
Victoria, Australia.
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