Measurements and Testing

• Author: Charles E. Turnbow
• Pages: 156-207

5-1

CHAPTER 5

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

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SLIP AND FALL PRACTICE 

§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

5-3

 MEASUREMENTS AND TESTING §511

§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

at http://www.astm.org.

§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.