Measurements and Testing

AuthorCharles E. Turnbow
Measurements and Testing
§500 Introduction
§510 Coefficient of Friction and Slip Resistance
§511 Commonly Used Measurements
§512 Measurement Techniques
§512.1 Laboratory Testing
§512.2 Field Testing
§512.3 Portable Articulated Strut Tester (PAST)
§512.4 Portable Inclinable Articulated Strut Tester (PIAST)
§512.5 English XL Slip Resistance Tester
§512.6 Other Testing Methods
§512.7 American Society for Testing and Material Standard Changes
Picture: The English XL Variable Incidence Tribometer
§513 Errors in Measurement
Table: Standard Deviations in Measurement
§514 Correlating Methods
§515 Acceptable Coefficients of Friction
§515.1 Special Requirements
§515.2 Standard Practice for Safe Walking Surfaces
§516 Standard Setting Procedures
Table 516A: ASTM Standard Methods for Measuring Coefficient of Friction or
Slip Resistance
Table 516B: ASTM Standards for Reporting and Interpreting Test Data
§517 Typical Questions and Answers Regarding Slip Resistance
§520 Dimensional Measurements
§520.1 Types of Measurement Devices
§521 Stairway Dimensions
§521.1 Treads and Risers
Picture: Storefront Theater Stairs
Picture: Rise and Run Violations
Picture: Sloping Landing
Figure 5.1: Combination Square
§521.2 Handrails
Picture: Covered Handrail
§521.3 Headroom
§521.4 Slope
Picture: Non-Conforming Stairway
§521.5 Single Risers
§522 Ramp Measurement
§522.1 Slope
Figure 5.2: Ramp Slope
Picture: Electronic Level
§522.2 Handrails
§522.3 Markings
§523 Typical Questions and Answers
Picture: School Playground Ramp
§524 Typical Questions and Answers—Single Risers and Thresholds
§530 Lighting
§531 Terminology
§532 Testing Instruments
§533 Acceptable Values of Incident Light
§534 Statutory Standards
§535 Industry Advisory Standards
Table: Light Intensity Values
§536 Glare
§540 Shoes and Footwear
§541 Coefficient of Friction
§542 Shoe Material
§543 Straps and Construction
§544 Shoe Design
Figure 5.3: Toe and Heel Spring
Figure 5.4: Woman’s Shoe Heel
§550 Field Testing Checklist
Sample: Field Testing Checklist
§560 Expert’s Report
Sample: Liability Evaluation Report
Picture: Stairs With Missing Baluster
Picture: Water Damage
Picture: Urethane Cleavage
Picture: Unworn Tread
§500 Introduction
To document the hazard in a pedestrian fall accident case, the
expert must determine and analyze the physical properties of
the walkway surface. Generally, slipping and tripping hazards
can be measured and quantified, providing an objective basis
for the expert’s opinion. The types of testing and measure-
ment, as well as the limitations of these techniques have been
the cause of extended scientific and legal debate. The tests
are designed to determine the physical characteristics of the
accident site so that the conditions may be compared to rec-
ognized standards or specifications.
§510 Coefficient of Friction and
Slip Resistance
The relative slipperiness of a floor surface is determined by
measuring the amount of friction generated between the shoe
and the floor. The ratio of the amount of force necessary to
cause an object to begin a slide across a surface divided by
the weight of the object is called the coefficient of friction.
In standard methodology this is now called “slip resistance”
when measured by devices that are specifically designed
to simulate the force patterns occurring during the human
stride. This is the most commonly encountered technical term
in slip and fall cases. Organizations such as the American
Society of Testing and Materials (ASTM) and Underwriter’s
Laboratories (UL) have established recommended levels of
coefficients of friction for different types of walkway sur-
faces. The coefficient of friction is a numerical expression
used to describe the amount of traction or friction that is
generated between two rubbing surfaces. Generally the coef-
ficient of friction is expressed as a decimal fraction between
zero and one. The higher the number, the less slippery the
surface. For example a floor with a coefficient of friction of
0.80 is substantially less slippery than a floor with a value of
0.30. This data can be determined by using a number of differ-
ent testing techniques. The American Society of Testing and
Materials (ASTM) promulgated a series of standard methods
of testing floor and shoe materials. These methods are referred
to below by their numerical designation (i.e., ASTM F-609-
96). Copies of the standards may be obtained directly from
ASTM at a nominal charge. For further information, contact
American Society of Testing and Materials, 100 Bar Harbor
Drive, West Conshohocken, PA 19428 or visit their website
§511 Commonly Used Measurements
The static coefficient of friction describes the relation-
ship between the weight of an object and the force
necessary to cause the object to slide across a surface.
Static is defined as “not moving or stationary.” When
an object starts at rest, the calculated value is called the
static coefficient of friction. If the object is pulled until it
starts to slide, the amount of force necessary to continue
the slide results in a calculated value called the dynamic
coefficient of friction. The current trend in referring to
the amount of available traction existing between two
surfaces is to use the term slip resistance in preference
to coefficient of friction. In ASTM Standard Method
F-609-95, the procedure defines Static Slip Resistance
as the force required to cause one body in contact with
another to begin to move. Throughout this standard
method, the reference is to slip resistance instead of
coefficient of friction. Standard Method F-695-95 relates
to the evaluation of test data from the measurement of
slip resistance of footwear. This designation considers
the totality of conditions which can affect the safety of a
walkway surface. The newest standard methods for test-
ing floor surfaces and revisions of the older ones have
used the term slip resistance to quantify the amount
of traction between the shoe and the floor. The James
Machine standard method ASTM F-2047-93 defines slip
resistance as that property of a floor surface which is
designed to prevent slipping. A surface having a static
coefficient of friction of 0.5 or greater as measured in
accordance with this test method is considered to be a
slip-resistant surface. In the ASTM F-1637-95, Standard
Practice for Safe Walking Surfaces, there is no mention
of the coefficient of friction, but slip resistance is defined
as the relative force that resists the tendency of the shoe
or foot to slide along the walkway surface. Slip resis-
tance is related to a combination of factors including the
walkway surface, the footwear bottom, and the presence
of foreign materials between them.
The term slip resistance is often used by those reporting
data obtained by using the pendulum impact device such
as the Sigler Machine (Federal Test Standard 7121 Method
501), or the British Portable Skid Resistance Tester
(ASTM E-303-93). Both of these methods measure the
amount of energy lost when a rubber specimen is rubbed
across a test surface. Sigler preferred to call the numbers
derived from his instrument the antislip coefficient but
calculated and referred to the data as coefficient of fric-
tion. The British Portable Skid Resistance Tester reports
data as BPN (British Portable Numbers) which have a
range of values from 0.0 to 1.0 similar to those tradition-
ally assigned to coefficients of friction. A controversy still
rages between European safety professionals and those
in the United States. Europe and Britain believe that the
dynamic coefficient of friction more closely replicates the
movement of the foot during the stride and therefore is a
better indication of the relative slip resistance of the floor
surface. ASTM and ANSI have adopted standard methods
of testing which determine the amount of traction provided
when the foot is at rest on the surface for the static coef-
ficient of friction.

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