CO NBS TECHNICAL NOTE 895

°»£AU Of

U.S. DEPARTMENT OF COMMERCE/ National Bureau of Standards

An Overview of

Floor Slip-Resistance Research

With Annotated Bibliography

c, a.
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2 1976 An Overview of Floor Slip-Resistance Research

A

c^

3 With Annotated Bibliography

C>

Robert J. Brungraber

Structures, Materials and Safety Division

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

This paper was prepared by the author while he was an

Intergovernmental Personnel Act Appointee in the Building Safety Section, on leave from Bucknell University,

Lewisburg, Pa.

U.S. DEPARTMENT OF COMMERCE, Rogers C. B. Morton, Secretary

James A. Baker, III, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

U& NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Issued January 1976
National Bureau of Standards Technical Note 895

Nat. Bur. Stand. (U.S.), Tech. Note 895, 113 pages (Jan. 1976) CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OEFICE

WASHINGTON: 1976

For sale by the Superintendent of Documents, U.S. Government Printing Office. Washington, D.G. 20402 (Order by SD Catalog No. CI 3.46:895). Price $2.30 ,. (Add 25 percent additional for other than U.S. mailing
TABLE OF CONTENTS

Page

Introduction 1

Gravity of the Problem 2

Kinesiology and Anthropometry 3

The General Study of Friction k

Critical Appraisal of Past and Current Methods for

Determining Floor Slip-Resistance 5

Guide for Selection of Slip-Resistance Criteria 7

Legal Aspects of the Floor Slip-Resistance Problem and

the Present Status of Floor Slip-Resistance Specifications . . 8

APPENDIX

An Annotated Bibliography on The Slip-Resistance of Floors. . 10

Section A - Analytical Determination of the Required Minimum

Value of Coefficient of Friction Needed for Safe

Walking, Considering Anthropometry and Kinesiology.. 11

Section B - Experimental Studies of Kinesiology or Human Locomotion, With Specific Measurement of Normal and

Tangential Forces So that Limiting Values of

Coefficient of Friction Can Be Established 15

Section C - General Treatments of Kinesiology or Human

Locomotion 21

Section D - Methods and Results of Tests for Floor SlipResistance 3^

Section E - General Discussions of Floor Slip Resistance .... 70

Section F - Legal Aspects of the Floor Slip-Resistance Problem

and the Present Status of Floor Slip-Resistance

Specifications 78

Section G - Basic Principles of Friction 93

Section H - An Alphabetical Listing of all I terns in the

Bibliography 99

iii

An Overview of Floor Slip-Resistance Research

With Annotated Bibliography

Robert J. Brungraber

Slips and falls in the home as well as in public buildings have

reached serious proportions (8,000,000 accidents per year in the

home, resulting in 9,600 deaths and 1,600,000 disabling injuries).

This paper reviews the literature relating to this problem. Based

on studies of kinesiology and anthropometry, the coefficient of

friction between foot surfaces and floor surfaces is found to be

a significant parameter controlling slips and falls. A review of

the general study of friction and a critical appraisal of methods

for determining the coefficient of friction on slip-resistance of

floors leads to a guide for selection of slip- re si stance criteria.

The paper concludes with a. discussion of the legal aspects of the

problem and the present status of slip- re si stance specifications.

Key words: Building safety; floor surface friction; occupancy

safety; slip- resistance; slip-resistance testers; walking friction.

Introduction

The seriousness of the problem of slips and falls (8,000,000 accidents

per year in the home, resulting in 9,600 deaths and 1,600,000 disabling

injuries) has prompted the Building Safety Section of the National

Bureau of Standards to initiate a program to investigate the contribution

of floor slip-resistance to this problem. The ultimate aim of this

study is the development of a method for the evaluation of floor slipresistance and the establishment of criteria for the safe control of it.

This second of a planned series of reports describing the results of the

study is based on an extensive search of the literature relating to

slip-resistance in general and floor slip-resistance in particular. The

report consists of a general discussion of the slipperiness problem and

the results of past efforts to address it, followed by an annotated

bibl iography.

The bibliography is organized in sections for ready reference by the

reader to specific areas of the slip-resistance problem. Significant

portions of many of the references are abstracted so that a reader

interested in subject and scope only wil 1 not have to go to the source. Also material directly applicable to the establishment of slip-resistance

standards has been abstracted. Section H of the appendix is an alphabetical list of all the bibliography items.
Since this report is a product of the Building Safety Section it concentrates on background material that could be useful to the building owner

in his efforts to control slip-resistance, for example, by his selection

of flooring materials and treatment products and processes. Thus such

topics as shoe materials and construction and psychological factors of

the walker are treated only insofar as they relate to the development of

test methods for evaluating flooring materials and treatment products

and processes.

Gravity of the Problem

Injuries resulting from slips and falls, particularly as they are related

to the relative slip-resistance of shoes and flooring surfaces, result

in serious human discomfort and loss of life as well as significant

financial losses.

For example, the 1974 edition of "Accident Facts," published by the

National Safety Council, indicates that annually 8,000,000 falls occur

in the home, resulting in 1,600,000 disabling injuries and 9,600 deaths;

most of the deaths occurring among the aged, older than 65. Further,

Rodstein in 1963 (E-9)* reported that the combined general liability

experience of three la-rge department store. chains for a three year

period showed a total of 8,637 accidents with losses of $665,000. Fully

a third of these accidents were falls on stairways and floors with 17%

of them, resulting in 20% of the loss, being falls on floors. Schuster,

in a German paper of 1966 (A-3), reports accident statistics for one year of 2,508 falls, 93% of them on level surfaces; the rest on stairs.

For falls on level surfaces slip or slipperiness was usually considered

the most important factor. In 1964 Esmay and Segerlind (D-10) quoted

the National Safety Council in reporting that in 1959 alone more than

2200 farm people died as a result of falls. About one third of these

accidents occurred on steps and stairways.

The seriousness of this problem has resulted in continuing research by

the manufacturers of floor waxes and polishes (A-2, D-3, D-15, D-38, D39) many shoe manufacturers (D-4, D-26) and users (D-40); insurance

laboratories such as that maintained by the Liberty Mutual Organization

(D-13, D-22, D-23); numerous government laboratories (state, federal and

foreign) such as the National Bureau of Standards' efforts dating back

to the 1920's (B-5, D-2, D-20, D-34, D-36). It is the purpose of this

paper to assemble this material to serve as a starting point for yet

another attempt to bring increased understanding to this complex problem.

*Alphanumeric designations in parentheses refer to items in the attached

bibliography.
Kinesiology and Anthropometry

A complete understanding of all causes of slips and falls would necessitate a thorough knowledge of kinesiology, the study of the principles of

mechanics and anatomy in relation to human movement. However, from the

standpoint of the building owner or his designated agent only the material and the geometrical layout of the walking surfaces of the building

is under their control. It is clear that a walking surface can be too

slippery to permit safe walking. It may also be that a walking surface

could be too slip-resistant to permit safe, convenient walking. Thus

cleaYly the slip-resistance of the shoe-floor surface interface is a significant factor in the slip-fall equation. For this reason some means for evaluating and controlling the slip-resistance of floors is

essential. However, this means of evaluating slip-resistance must be

based on a study of kinesiology to the extent that the value of slipresistance is such and is measured in such a way as to relate to actual

walking. Essentially the following questions must be answered: (1)

which coefficient of friction, static or dynamic is of importance to the

slip and fall problem and; (2) under what circumstances should it be

measured.

The numerous studies of kinesiology (sections B and C of the bibliography) dating back to 1872, have revealed that in "normal walking" there

is no relative movement of the foot with respect to the floor, during

the period when the foot is in contact with the floor. This is particularly well demonstrated by the report of the Berkeley group (B-3, B-7)

where their lapsed time photography and other methods reveal no slipping

of the shoe during normal, straight-line, walking. Thus as was claimed

by James (D-24) the most significant parameter controlling the slipresistance of floors is the static coefficient of friction.

Some of the experimental studies of kinesiology made use of a force

plate to record the time variations of the forces developed between the

floor and the feet of walking subjects. In the cases (section B of the

appendix) where the normal component, V, and the tangential or horizontal

component, H, were recorded separately, thus permitting the calculation

of the ratio, H/V, the results can be used to establish a lower limit

for the coefficient of friction needed to permit safe walking.

Considerations of anthropometry, the study of human body measurements,

as it describes the geometry of the human stride (section A of the

bibliography) permits yet another determination of a lower limit for the

coefficient of friction needed for safe walking. The geometry of the

human stride can be translated into resulting force components in the

legs from which critical values of H/V can again be calculated.
The General Study of Friction

Although, starting with Leonardo da Vinci, some very famous scientists

have studied friction over the centuries (Section G of the bibliography)

it still remains one of the most familiar and yet least understood

facets of mechanics. This stems largely from the circumstance that its common occurrence has prompted the need for simple rules describing it

while it is in fact not a simple phenomenon at all. Drawing on the

deceptively simple yet clear treatment by Rabinowicz (G-10) we find the

three basic rules of friction: that the friction force (1) is proportional

to the normal force and thus (2) is not affected by the contact area or

(3) by the rate of movement. Rules (1) and (2) are borne out by tests

within + 10% in most cases, except for two readily deformable surfaces

rubbing together. But rule (3) is frequently violated, particularly at

extremely high and extremely low rates of motion. Fortunately for

considerations of the slipperiness of floors, high velocities are of no interest and extremely low velocities are of only academic interest.

Just as the ancient Greek philosopher, Heraclitus, claimed that everything

flows, as indeed it does if you adopt a long enough time frame; and just

as the proportional limit of a supposedly elastic material tends toward

zero as the precision of the strain gage is increased; so does the

static coefficient of friction tend towards zero as the rate of loading

is decreased. However, within the time frame of a normal step the

static coefficient of friction will not be zero, but actually greater

than the dynamic coefficient of friction. Rabinowicz (G-10) summarizes

this in the four curves, reproduced as Fig. 1, which depict the history

of the development of our knowledge of friction vs. velocity.

A friction problem more directly related to floors is the increase in

the static coefficient of friction with the increase in time delay

between the application of the normal loads and the tangential or sliding

load as noted by Braun and Roemer (D-3) and Gavan and Vanaman (D-15).

According to Gomer & Smith (G-7), Moore (G-9) and Rabinowicz (G-10) this

is caused by adhesion which in many cases is enhanced by the presence of

water between the sliding surfaces. This may very well be the explanation

for the increase in coefficient of friction of leather soles by wetting

that has been observed by many investigators (D-6, D-20, D-23, D-33, D34). This points up the need for a friction measuring device that

closely approximates the time delay that is representative of a normal

step and that is generally repeatable. Most of the presently available

friction testers introduce a time delay that is of indeterminate length

but generally much longer than the time needed to execute a normal

step.
Critical Appraisal of Past and Current Methods for Determining Floor

Slip-Resistance

Most of the methods currently used for the determination of floor slipresistance have been thoroughly described in Section D of the Bibliography

and summarized in E-l and E-3. They can best be considered in three

categories:

(1) A drag type meter . This consists of a weight of known value, having

a facing of a certain shoe sole or heel material, which can be drawn across a floor surface in such a way as to permit the measurement of the

forces needed to incipiate motion (static friction) and maintain motion

(dynamic friction);

(2) A pendulum type meter . This consists of a pendulum, faced with a certain shoe sole or heel material, which can be adjusted to sweep a path across a flooring surface so that the contact pressure between the

facing and the floor follows a predetermined time-dependency. The

resulting loss of energy of the pendulum is claimed to be a measure of

the dynamic friction;

(3) An articulated strut . This applies a known vertical force to a shoe

faced with a certain sole or heel material and then applies an increasing

lateral force until slip occurs. The ratio of lateral force at slip to

the known vertical force is the static coefficient of friction.

Examples of the drag type meter are the Horizontal Pull Slipmeter (D22), the TOPAKA (D-39), and more sophisticated devices such as that

described by Braun and Roemer (D-3).

Some researchers claim that the drag type meter can measure both static

and dynamic friction. However Irvine, the developer of the Horizontal

Pull Slipmeter, has found that the dynamic and static coefficients are

both seriously influenced by the velocity at which the meter is pulled

and thus has found it necessary to supply a capstan head motor to pull

the meter at a constant velocity. Even then, as has been demonstrated

by Braun & Roemer, dynamic effects seriously influence both the static

and the dynamic readings. The static reading is affected by the force

required to accelerate the weight which supplies the normal load and,

since this is the weight of the entire device, the error can be significant. In measuring the dynamic friction the phenomenon of stick-slip

frequently develops and this has been found to be a function of the

elasticity of the device, particularly portions of the prime mover such

as the string of the capstan-headed motor of the Horizontal Pull Slipmeter

and the TOPAKA.

The pendulum type, as represented by the Sigler (D-34, D-35) and The

British Portable Skid Tester (BPST), (D-16, D-21 , D-36) measures only

the dynamic friction and this as some sort of integrated function resulting in a measured energy loss of the pendulum. This makes the adjustment
of this device quite critical and, as has been shown above, the dynamic

coefficient of friction is not of prime importance in controlling slipresistance. Slow motion films of some BPST tests conducted at the

National Bureau of Standards as well as some tests made on bond paper

over a sheet of carbon paper (D-25) show that the contact pressure

varies erratically with time so that it would be difficult,, if not

impossible, to relate friction directly to the energy loss. The British

Portable Skid Tester is intended to simulate a 30 mph skid which is

hardly representative of maneuvers of the feet that occur during normal

wal king.

Finally the articulated strut device, as represented by the James (D-24)

and Hunter (D-20) machines, is based on the direct and fundamental

principle of the resolution of forces. The Hunter device has the disadvantage that it measures the dynamic friction since, the shoe is pulled

across the floor until uncontrolled slip occurs, at which time the

tangent of the resulting angle of the strut is measured. Thus the shoe

is actually in motion when the measurement is taken. The James machine

does measure static friction but for some reason, not explained in

James 1 article (D-24), the final version of his device is strictly a laboratory machine suitable only for evaluating flooring materials, not

floors. From the description of his device in his 1944 paper, tests

could be made directly on floors with the initial design but as is the case for the Hunter, the surcharge is 75-80 lbs. and this makes the device

portable only with difficulty (a portable version of the Hunter machine

was developed by Gurney [D-18]). Many investigators have shown that,

within rather broad limits, the coefficient of friction between typical

shoe and flooring materials is not sensitive to variations in contact

pressure (D-20, D-24, D-38). Thus it would seem that one of the major

reasons for employing such large surcharges on the Hunter and James

machines is to reduce the errors arising from the internal friction in

these devices.
Guide for Selection of SI ip-Resi stance Criteria

Considering that the slip-resistance can be controlled by specifying

values of the static coefficient of friction, how should these specified

values be selected? There are three sources of information that can be

used to select these values; (1) experimental kinesiology or measurement

of the forces exerted by the shod foot upon the floor, (2) anthropometry

or the geometry of the walking body, and (3) friction measurements made

on walkway surfaces having known safety records. In setting recommended

values for floor slip-resistance or static coefficient of friction it

may yery well be that for certain walking maneuvers the friction could

be too high and thus the recommendation should be in the form of both

upper and lower limits.

Of the many references on experimental kinesiology (sections B & C of

the bibliography) only a few (section B) report both the normal force,

V, and the tangential force, H, so that required values of H/V or y can

be established. These relate to normal walking in a straight line,

walking around a curve and walking up and down ramps, for both normal

people and people with artificial limbs.

There have been several studies of anthropometry, or the geometry of the

walking body, some of these also include consideration of the forces

needed to accelerate the body (section A). These studies indicate that

for the longest stride likely to be taken in walking the required minimum

static coefficient of friction would be 0.5. For running, the same study (A-l) indicates that a static coefficient of friction of 1.1 would

be needed to prevent slip.

Finally there have been many friction measurements made of flooring

surfaces (section D). Unfortunately the only fundamental evaluations of

the static coefficient of friction have been made with the James machine

and thus were made on flooring materials, not floors, and under controlled

laboratory conditions, not in the field. Most field measurements have

been made with either pendulum devices, such as the Sigler or the British

Portable Skid Tester or with drag type devices such as the Horizontal

Pull Slipmeter.
LEGAL ASPECTS OF THE FLOOR SLIP-RESISTANCE PROBLEM AND

THE PRESENT STATUS OF FLOOR SLIP-RESISTANCE SPECIFICATIONS

.There are several industries interested in the leqal aspects of floor

slip-resistance; the flooring manufacturers, the shoe manufacturers, the

underwriters who insure buildings and the floor wax and polish manufacturers. Out of this interest have developed several papers on the legal

aspects of floor slip-resistance (F-5, F-9, F-22); the development of

several floor slip-resistance testers, the James machine and the Horizontal Pull Slipmeter; and the development and promulgation of slipresistance standards. In addition the government, the Department of

Defense as well as the General Services Administration, has been

interested in the development of slip-resistance specifications.

The government specifications have been primarily developed by the

military (F-6, F-10, F- 11, F- 12) and are quite stringent, requiring that

\i be as high as 0.7 in some cases. The other major contribution to

floor slip-resistance specifications has been a combined effort of

Committee D21 of ASTM and the Scientific Committee of the Wax Division

of Chemical Specialties Manufacturer's Association (CSMA). There has

been considerable common membership in these two bodies and a great

deal of cooperation between them. Merscher's paper (F-8) nicely summa- rizes their efforts, culminating in the recently published revision of

"Standard Method of Test for Static Coefficient of Friction of Polish

Coated Floor Surfaces as Measured by the James Machine" D2047-75. This

version now states "Floor polishes having a coefficient of static friction,

as measured by this method, of not less than 0.5 traditionally have been

recognized as providing nonhazardous walkway surfaces. This value of not

less than 0.5 meets the requirements for compliance to Rule 5 on 'The use

of terms slip retardant, slip resistant or terms of similar import, 1 of

the Proposed Trade Practice Rules for the Floor Wax and Floor Polish

Industry as issued by the Federal Trade Commission on March 17, 1953."
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APPENDIX

An Annotated Bibliography on the Slip-Resistance of Floor s

The discussions of, and direct quotations from, the entries have been

limited to those relating to the subject of the slip-resistance of

floors even though many of the entries, such as those on friction, have

a much broader coverage.

The designation numbers, A-l etc., are used for reference in the text as

well as cross referencing in the bibliography.

10
ANALYTICAL DETERMINATION OF THE REQUIRED MINIMUM VALUE OF COEFFICIENT

OF FRICTION NEEDED FOR SAFE WALKING

CONSIDERING ANTHROPOMETRY AND KINESIOLOGY

A-l Barrett, G. F. C. "Observations on the Coefficient of Friction of

Shoe Soling Materials," Rubber Journal, Dec. 1, 1956.

Nice analytical development of the required y for walking >_ 0.497 or running >_ 1.077. In both cases an estimate of the acceleration

forces is included. A typographical error but not significant to the

results.

Static \i Dynamic y Classification

> static safe and rising

above 1 .

1

< static safe but falling

= static safe

> static potentially safe

0.5-1.1 < static potentially slippery

— static intermediate

> static slippery but rising

below 0.5 < static slippery but falling

= static slippery

Developed a neutrally suspended table to measure y and y ,. Used an 11# wt. on a 2" X 4" specimen yielding a pressure of 2 oz/in.'

2 Found no change in results for higher pressures up to 10 #/ in.

= approx. pressure for a man's foot.

Velocity of movement not controlled.

Surface tested dry and with a layer of water.

On dry surfaces leather is slippery but rising except on smooth concrete and polished linoleum,

wetting the walking surface improves y On dry surfaces rubber is safe or potentially safe, more variation on wet surfaces; potentially slippery on stone,

concrete, and varnished wood.

On dry surfaces crepe rubber is safe, but intermediate or potentially slippery on most wet surfaces.

Resin rubber and microcellular rubber is slippery or potentially so on wet surfaces.

Much more variation among sole materials on dry surfaces,

wetting tends to make them perform more nearly alike and on frozen surfaces everything is equally slippery.

11
Although natural rubber has higher y both wet and dry than

leather the significant decrease of y when wet for rubber,

and increase for leather may make leather less likely to

yield surprises.

"An ideal general purpose soling material might thus have

a coefficient of static friction between 0.6 and 0.7 and

a coefficient of dynamic friction between 0.7 and 0.8 under

all normal dry and wet conditions."

A-2 Ekkebus, C. F. and Ki 1 ley, W., "Measurement of Safe Walkway Surfaces,"

Soap/Cosmetics/Chemical Specialties for Feb. 1973.

Good brief description of the mechanics and biology of walking.

Review of the history of y ^ 0. 5 requirement. Theoretical

justif ication., using anthropometry, of 0.5 as being a conser- vative but reasonable restriction on y to provide slip

resistant surfaces; based on leg lengths and stride lengths of

a group of 16 people that were studied. They would have to

execute an unnaturally long stride to slip on a 0.5 floor during

normal walking.

Supports the use of the James Machine. "The swinging pendulum

type of machine does not measure static y. These machines

measure dynamic energy absorption which, by calculations, can

be converted to dynamic y. It has been suggested that a dynamic

y measurement is needed to relate to people moving across a floor. However, the foot is static in relation to the floor

in walking. A dynamic measurement would only be valid after

the foot has started to slip and therefore, cannot relate to

normal walking conditions."

This paper is also available in a preprint form and as part of

the Proceedings of CSMA 57th mid-year meeting, May 1971.

12
A-3 Schuster, K. "Slip - An Investigation of Practical Accident Prevention," Die Berufsgenossenschaft/Betriebssicherheit/ September

1966.

Accident statistics for one year 2,508 falling accidents 93%

(2,340) occurred on level ground, the rest on stairs. For

accidents on level ground, slip or slipperiness was usually

considered the most important factor.

Author rejects tests with live people as being unsafe and eliminating the element of surprise.

Uses a mechanics study instead. "It is hardly necessary to mention

that the slip resistance necessary for safe movement is a function

of this angle of contact. The smaller the angle of contact the

larger the required slip resistance. On ice we use only an angle

of contact which is very close to the vertical, since only a small

slip resistance is necessary. If we want to slide, however, we make the angle of contact smaller." "The slip resistance is almost

identical with the physical word friction." Then gives the few

exceptions, like walking in sand. Then a discussion of which friction, static or dynamic or rolling. "Moving friction is only of

secondary importance for normal propulsion. This result was obtained

by comparing the length of the sole of a walking or running person

with the length of the sole imprint on the floor. The greatest

difference in size, if at all noticeable,, measured only a few millimeters. Running friction therefore is only important when the

static friction is not sufficient or in other words when the foot

is already slipping -when safe locomotion becomes impossible. For

practical accident prevention it is therefore sufficient to consider

only or at least mainly, the static friction."

13
Then makes a static analysis including centrifugal forces from

curve negotiations. Argues that dynamic forces are small except at

start or stop and then are compensated for by shortening steps and

increasing contact angle. While walking a constant speed, dynamic

forces are counteracted by counter accelerations of arms etc.

While walking, angle of contact = 67° corresponding to crotch or walking angle of 45°. While running rear contact angle becomes 60°

and forward contact angle approaches 90°. Finally finds that y >_ 0.6 is necessary for safety in running around a curve of 3 meter

radius at 3 meters/sec. which is equal to double walking speed.

This results in y only about 5% greater than that required for

straight walking. Concludes that slip is not an important factor

on stairs because both legs are nearly vertical when there is yery

much weight on them.

Then describes a tester, a more sophisticated version of the technical products tester. The use of this tester investigating many

cases of slipperiness complaints showed that a slipperiness complaint

was always for a u < 0.6 and if u > 0.6 there was a feeling of

safety. Found that u ^0.6 on inclined planes resulted in safe

walking up and down 15% grade and safe running up a 1% grade.

Stresses the need to make measurements in the field. Describes two

versions of the tester, one with a scale to yield u directly, and

one with a go, no-go pair of lights. Both versions incorporate an electronic readout.

14
EXPERIMENTAL STUDIES OF KINESIOLOGY OR HUMAN LOCOMOTION, WITH

SPECIFIC MEASUREMENT OF NORMAL AND TANGENTIAL FORCES SO THAT

LIMITING VALUES OF COEFFICIENT OF FRICTION CAN BE ESTABLISHED

B-l Amar, J. "Trottoir dynamographique," Compt. rend., Acad. d. Sc.

163:130-132, 1916.

Vertical force, lateral shear and fore and aft shear of floor

reaction on foot measured by a force plate. Mechanical devices

using spring deflection.

B-2 "Complex Analysis Produces 'Signature' of Human Step," Product

Engineering, July 1, 1968.

A general discussion of some force plate tests made at the Picatinny

Arsenal, Dover, N. J., for the purpose of improving land mines.

They used a force plate similar to that of Bresler and Frankel , C-6

plus some photocells to measure velocity. Only two subjects were

tested and they were instructed to contact the force plate with

either the heel or the sole but not both. Only one set of curves

is presented but these are similar to other investigations and

clearly show that the lateral forces do not assume significant

values until the vertical forces are nearly a maximum.

B-3 Cunningham, D. M., "Components of Floor Reactions During Walking."

Prosthetic Devices Research Project, Institute of Engineering

Research, University of California, Berkeley. Advisory Committee

on Artificial Limbs, National Research Council, Series II, Issue

14, November 1950.

A series of charts that extends the data of "Fundamental Studies of

Human Locomotion and Other Information Relating to Design of Artificial Limbs." June 1947 report to Committee on Artificial Limbs of

15
= .25-. 33

= < .15

= < .15

= < .3

—

< .4

the National Research Council (B-8). Major extension is to measure- ment on a ramp. Shows that variation of normal force is only

slightly out of phase with tangential force. Generally they

increase and decrease together. When fore and aft shear is at a maximum normal force is just a little over half maximum when heel

is being placed and just a little less than full maximum when toe

is about to be 1 ifted.

Normal subjects walking level y req

Normal subjects walking upstairs y req

Normal subjects walking downstairs y req

Normal subjects walking up ramp y req

Normal subjects walking down ramp y req

Lateral shears are generally less than half the fore and aft

shears.

Similar results for amputees, more variation among subjects.

B-4 Cunningham, Don M. and Brown, Wayne G., "Two Devices for Measuring

the Forces Acting on the Human Body During Walking," University of

California, Berkeley, Proceedings of the Society for Experimental

Stress Analysis, Vol. 9, No. 2, 1952.

Describes a load measuring pylon which was substituted for the

shank of a prosthesis and a force plate which measured the floor

reactions on a normal or artificial foot. Only a few results

reported to properly discuss the devices.

B-5 "Electronic Step.-Meter Reveals Mechanics of Walking." National

Bureau of Standards Technical News Bulletin, 1951, 35(4), 50.

Plate similar to the Berkeley plate, described in C-6, but instrumented with springs and electronic mutual -inductance micrometers.

16
Limited test results reported but statement that a minimum y of

0.2 is essential if slipping is to be avoided.

Actually the single plot in the article of V vs. time, H vs. time

and H/V vs. time shows that u ^0.2 is essential in<the initial

part of the step (on the heel) and u >_ 0.4 becomes necessary for

the latter part of the step, (on the toe). The published results

were for a 247# 6'4" man wearing shoes with large rubber lugs on soles and heels, but the article indicates that the other 12 subjects, ranging from 107-247#, 5'2" - 6'4", 27-60 yrs. and both men and women were similar. The women had low, medium and high heels

and the foot wear included rubber and leather heels and soles.

B-6 Elftman, Herbert, "The Measurement of the External Force in Walking,"

Science 88:152-153, 1938.

Mechanical, spring balanced, force plate to measure three compon4 ents of the floor reaction on the foot; vertical force, lateral

shear, fore and aft shear.

As reported in B-4 "Dr. Elftman' s force plate was probably the most

direct and accurate device for measurement of forces. However, its

accuracy was limited by relatively large deflections of the walking

surface and by the inertia of the plate and friction in the recording linkages." Also see following references.

Elftman, Herbert, Anatomical Record, Vol. 59, p. 481 (1934)

Elftman, Herbert and Manter, J., Science , Vol. 88, p. 152 (1938)

Elftman, Herbert, Arbeitsphysiologic, Vol. 10, p. 485 (1939)

17
•7 "Fundamental Studies of Human Locomotion and Other Information Relating to the Design of Artificial Limbs." University of California,

report to U.S. National Research Council, 1947.

Referred to in B-8 as having a detailed bibliography on dynamics of

the human body. This material was intended to improve the design

of artificial legs and concentrated on the study of the relative

movement of the various parts of the body (particularly legs) and

contributes little to the study of slip or other relative movement

of the leg and the floor. However, in chapter IV, "Locomotion Study

Using Interrupted Lights," there are several lapsed time photographs

and diagrams that show there is little if any, relative movement of

the foot and the floor while the foot, or any part of it is in

contact with the floor, thus there is no slip shown during walking.

This indicates that the dynamic u is not the most significant with

respect to walking. The Glass Walkway Studies of Chapter V also

show that there is little if any slip occurring during normal

walking. Only studies of walking, level floor, stairs, ramp, with

and without prostheses. No data on running. Chapter 8, "Force

Plate Studies," gives data of most value to the study of floor slipresistance. Both the vertical and the fore and aft shear loads are given in terms of % of body wt. and maximum values of both kinds of

loads are given. However, no direct data on both loads at a common

time are reported. Thus it is difficult to establish the value of

\i needed.

However, this is no doubt the same or similar data reported in B-3

and B-4 so that the limiting value of u developed is „ 0.4, when

descending a ramp. A fairly detailed study of the curves of forces versus time reveals that y of as much as 0.5 might be needed just

after the heel comes in contact with the floor and while the heel

is tending to oppose forward motion.

18
Center of pressure data demonstrates that normal walking has the

center of pressure progressing more or less uniformly from back of

heel to ball and toe of foot, and staying in vicinity of ball and

arch when ascending or descending stairs. Rotation of the various

segments of the limb about the long axes as revealed in Chapters I,

"Study of Rotation During Locomotion, Using Pins," V, "Glass Walkway

Studies," and VIII, "Force Plate Studies" is believed to be of major

importance for normal gait, and finally is manifested by the torque

developed in the force plates. It may yery well be that the upper

limit for p may be dictated by the limit of torque permissible

which will overly restrict their rotation. It may equally as well

be that there must be sufficient u to develop the torque needed to

generate these rotations.

There is data to demonstrate that there is or needs to be some twisting slip between the foot or shoe and the floor, at least for

normal walking in a straight line at any rate. "The limb is wound

up, as it were, about its long axis in a medial direction to be

suddenly unwound in the opposite direction at the completion of the

phase of full weight-bearing."

B-8 Harper, F. C, Warlow, W. J. and Clarke, B. L. "The Forces Applied

to the Floor by the Foot in Walking," National Building Studies

Research Paper #32, Department of Scientific and Industrial Research

Building Research Station, London 1961.

Interested in shoe wear, thus studied forces, concentrated on H, V,

and H/V = \i. Plate much like that of reference B-4.

Measured contact areas by photographing thru a glass plate. H is

resultant of all components in plane of floor. Maximum H/V occurs

as toe is about to leave the floor. Studied straight walking and

19
walking around a corner, a right angled corner. Limiting values of

H/V for 87 males and 37 females were obtained statistically by

using Pearson curves at the 1/1,000,000 point and the incomplete 3 function.

The limiting values of H/V obtained were 0.36 for straight walking,

0.40 for turning on the left foot and 0.36 for turning on the right

foot. Actually only the 87 male subjects were analyzed statistically

because of the larger sample, but in general the female tests

resulted in lower or comparable values of H, V, and H/V. Max. foot

pressure 7-44 psi., max. heel pressure 14-840 psi.

20
GENERAL TREATMENTS OF KINESIOLOGY

OR HUMAN LOCOMOTION

C-l Abrahamson, E., "Zur Kenntnis der Mechanik des Mittelfusses," Skandinav, Arch. F. Physical. 51: 175-234, 1927.

Studied pressure distribution on the foot using steel shot pressed

against a lead plate.

C-2 Basler, A., "Kinematographische Aufnahmen mit gleichzei tiger

Registrierung von Kraeften," Arbeitsphysical . 8: 585-590, 1935.

Pressure on small areas of the foot was determined using a series

of para! lei rods.

C-3 Basler, A (1935) - Abderhalden. "Handbuch der biologischen

Arbeitsmethoden. " Abt. V. Organfunktionen. pp. 559-74. (Urban and

Schwarzenberg: Berlin).

Indicates that results are not for subjects normally shod walking

on ordinary floors.

C-4 Beely, F., "Zur Mechanik des Stehens," Arch. f. Klin. Chir. 27: 457-

471, 1882.

Studied pressure distribution on the foot using plaster-of-paris

impressions.

C-5 Bernstein, N. A. and others, "Biodynamics of Locomotion," Vol. 1,

Moscow, 1935.

An extension and improvement of Fischer's technique and evaluation

of results (see C-l 4 and 15).

21
C-6 Bresler, B. and Frankel, J. P. "The Forces and Moments in the

Leg During Level Walking" Transactions of the ASME Vol. 72, No. 1,

January 1950.

An excellent discussion and bibliography on the Human Gait. Gives no indication that there is any data on the forces between foot and

floor in their papers. The early investigators had no satisfactory

way to measure forces and thus their work is largely confined to

the study of chromophotography and other techniques for analysing

the kinematics of human locomotion. Only Elftman, (B-6) measured

forces and his device generally permitted such large displacements

as to bring Heisenberg's uncertainty principle into play. Paper

shows a few results of force plate measurements but there is much

more data in B-7, B-3 and B-4.

G-7 Bresler, B. and Berry, F. R., "Energy Characteristics of Normal and

Prosthetic Ankle Joints," Prosthetic Devices Research Project,

Institute of Engineering Research, University of California, Berkeley,

Advisory Committee on Artificial Limbs, National Research Council,

April 1950.

Experimental study of several artificial ankle joints.

Seems to be of little value to the study of floor slipperiness.

C-8 Bresler, B. and Berry, F. R., "Energy and Power in the Leg During

Normal Level Walking," Prosthetic Devices Research Project, Institute

of Engineering Research, University of California, Berkeley, Advisory

Committee on Artificial Limbs, National Research Council, May 1951.

Only very indirectly related to the study of floor slipperiness.

22
C-9 Carlet, M. G., "Essai Experimental sur la Locomotion humain, Etude

de la Marche." Ann. d. Scien. mat. Zdol . 16:1-92, 1872.

First measurement of the vertical force on the foot, using a pneaumatic cell in the sole of the shoe.

C-10 Carlsoo, Sven "How Man Moves, Kinesiological Methods and Studies,"

Heinemann:l_ondon , 1972.

A brief but thorough treatment of the subject including description of the various experimental devices used. Chapter 5 "The

Gait" and a portion of chapter 7 "Kinesiological Analyses in

Sports and Work" on "slipping and the risk of slipping in the

factory" are of most interest to the researcher in floor slipresistance.

Fig. 41, "Schematic representation of the pattern of movement of

certain body parts in walking projected in the sagital plane,"

presumably obtained from chromocyclographs, shows no slip between

the foot and the floor.

From chapter 7 "Slipping is one of the most common causes of

accidents on the job. It is particularly in the food industry and

food trades that such accidents are serious, elusive problems.

"However, considerable efforts have been made in recent years to

prevent these accidents. In this context, studies have been made

of the friction between footwear and floor under various conditions.

A consistent finding has been that the friction which exists prior

to the slip is of critical importance for the occurrence of slipping

Thus, static friction is the critical value."

23
A nice succinct discussion of friction, including the point. "The

fractional force may also be independent of the normal force if

there is a liquid between the slip surfaces and if the rate of slip

is low -- only low rates are involved in the present context. In

physics this is known as fluid friction and the frictional force is

considered to be proportional to the rate of slip."

Reports tests of about 100 persons when H & V were measured with a force plate as a function of time. Then H/V was calculated and

plotted as a function of time. Maximum values of H/V=f , and thus

the greatest likelihood of slip occurred at the start and the end

of the step, f is the required static coefficient of friction to

prevent slip and for the 100 subjects had a mean value of 0.23.

Describes an "artificial lower leg with heel," attached to a three

wheeled cart used to measure static friction between heels and

floors. The angle of attack of the heel could be varied independently

of the angle of the leg which was set at some fixed value before

each test. Thus the evaluation of a single location on a floor

required the conduction of several tests, each with a different

length of leg and resultant angle of inclination of the leg. The

device was developed because they found existing devices to have

the following shortcomings: "In the first place, it is not at all

clear which magnitudes characterize a risk of slipping and what the

measurements imply in purely physical terms. In the second place,

most of the measurements can only be made in the laboratory and not

at places of work, while in the third place many of the methods do

not give reproducible measurements and consequently call for statistical processing of a series of data."

Using a rubber heel on the above mentioned device, measurements

were made in a meat factory. They found that f = u varied from a

24
low of 0.10 in front of a preserving table to a high of 0.64 near the mixer. They judged that the risk of slipping was very great

where u < 0.30 and practically non-existent where p > 0.50.

Some additional tests were made under more controlled conditions

using both wooden and rubber heels with similar results. A wooden

heel was found to be "safer" when wet than when dry, but as is the case with most testers, there was an opportunity for water to be

extruded from beneath the heel before the test commenced.

C-ll Carl sob, Sven, "A Method for Studying Walking on Different Surfaces."

Merely describes a force plate and their initial efforts at using

it. No results as yet available.

A nice description of the human gait. "In the human gait the

equilibrium is lost and regained with every step; lost with the

take off of the propelling foot when the body's center of gravity

momentarily lies beyond the anterior border of the supporting

surface. It is regained as soon as the swinging leg is extended

forward and its heel touches the ground. The horizontal component

of the force applied by the foot when it touches the floor acts

forward and is counteracted in ordinary walking by a friction force

which is just as large but acts in the opposite direction. It is

this play of forces which reestablishes the momentarily lost balance

at each step. But if the friction force is less than the horizontal

force applied by the foot, the foot skids along the floor and we

slip."

C-12 Elftman, Herbert; "A Cinematic Study of the Distribution of Pressure

in the Human Foot," Anat. Rec. 59:481-490, 1934.

Studied pressure distribution on the foot using photographic means.

25
Includes a summary of previous work. C-17 indicates that these

tests are not on subjects normally shod walking on ordinary floors.

C-'13 Elftman, H. (1939) -- Amer. J. Physiol, 125:339-56.

C-17 indicates that results are not for subjects normally shod

walking on ordinary floors.

C-14 Fischer, 0., "Der Gang des Menschen, I. Thiel:

Versuche am unbelasteten und belasteten Menschen, Abhandlungen der

Mathematisch - Physischen Classe der Koniglich Sachsischen." GeselV

schaft der Wissenschaften. Classe 21, p. 153-322, Leipzig, 1895.

C-15 Fisher, 0., "Der Gang des Menschen, II. Thiel: Die Bewegung des

Gesammtschwer punktes und die ausseren Krafte, Abhandlungen der

Mathematisch - Physischen Classe der Koniglich Sachsischen." GeselV

schaft der Wissenschaften. Classe 25, p. 3-130, Leipzig, 1895.

B-4 refers to this as follows: "The forces acting on the body have

also been determined indirectly from three dimensional space-time

relationships for the various body segments. In 1895 Fischer

determined these relationships for the component parts and the

center (of) (sic) gravity of the body as a whole. A thorough

analysis of one subject was made by means of still photographs

taken while Geisler tubes fastened to the body segments flashed

intermittently. Fischer's work still remains the classical example

of the method.

C-16 Fung, Y. C. & Anliker, M. "Biomechanics, Its foundations and Objectives," edited by Y. C. Fung and M. Anliker. Published by PrenticeHall, Inc., Englewood Cliffs, New Jersey, 1972.

26
This volume is the edited symposium on Biomechanics, Its Foundations

and Objectives, which was held in La Jolla, California, from July

29 to 31, 1970. This Symposium was sponsored by the University of

California, San Diego, and the United States Navy, Office of Naval

Research.

This symposium is a series of papers, only one of which appears to

be of any value to floor slip-resistance, paper #20 entitled, "Biomechanical Compatibility of Prosthetic Devices," by J. P. Paul, J. Hughes, and R. M. Kenedi.

This is a rather brief paper, but does a nice job of covering the

mechanics of prosthetic devices, primarily legs. However, it

pretty much limits itself to the forces or pressures that occur within the joint, rather than the forces that occur between the

foot and the floor. Thus, it is of limited interest to floor

slipperiness.

C-17 Holden, T. S., and Muncey, R. W., "Pressures on the Human Foot

During Walking," Aust. J. App. Sci., 1953, 4(3) 405.

Used a pressure sensitive cell in the shoe, thus measured only the

vertical component. Thus of little value in studying the friction

requirements of the floor surface.

"Instantaneous pressures developed on the sole of the foot during

walking in ordinary shoes on any floors can be measured with the

equipment described. Large variations in the shape of the pressuretime curve occur from one person to another, but the step-to-step

variations of any one person are very much less. Variations in the

rate of walking changes the ordinates and abscissae approximately

in inverse proportion. Variations due to changes in floor surface

27
are almost nonexistent, the only noticeable effect being the disappearance of a small impact peak when the subject changes from

ordinary floors (concrete, wood) to lawn."

Referenced in D-8 and quoted that "A study conducted by Hoi den & Muncey showed that pressures exerted on the heel by most of the

subjects in walking ranged from 20 to 30 pounds per square inch

with an overall average of 25 pounds."

C-18 Klopsteg, P. E., Wilson, P. D., et al . Human Limbs and Their

Substitutes . New York, 1954, McGraw Hill .

Referred to in B-8 as having a detailed bibliography on dynamics of

the human body.

C-19 Marey, E. J., "De la Locomotion terrestre chez les bipedes et les

quadrupedes," J. de L'Anat, et de la Physiol. 9:42-80, 1873.

One of the first examples of the measurement of the vertical force

on the foot, using a pneumatic cell in the sole of the shoe.

C-20 Rehman, I. (1947), - Arch. Phys. Med. 28:749-56.

C-17 indicates that results are not for subjects normally shod

walking on ordinary floors.

C-21 Schwartz, R. P., Heath, A. L., and Wright, J. N. "Electrobasographic

Method of Recording Gait," Archives of Surgery, Nov., 1933, Vol. 27-

C-22 Schwartz, R. P., Heath, A. L., Miziek, W., and Wright, J. N.,

"Kinetics of Human Gait" The Journal of Bone and Joint Surgery,

Vol. XVI, No. 2, Apr. , 1934.

28
C-23 Schwartz, R. P., and Heath, A. L., "The Definition of Human Locomotion on the Basis of Measurement." (1947) The Journal of Bone and

Joint Surgery, 29:No 1, 203-14., Jan. 1947-

Discusses the workings of an oscilloscope designed and built in

1939 and the home-made piezoelectric pressure gaqes. They used

individual gages to measure the pressure or force at six distinct

locations on the plantar surface of each foot. Found that in spite

of the fact that individuals can often be recognized by the sound

of their gait, normal gaits are remarkably similar and in fact vary

no more from person to person than from time to time for the same

person. By summing the six individual traces to a single line plot

they got the same double humped curve as have other investigators,

such as the Berkeley group. They reported several infirm gaits as well as the normal ones. No measure made of H so that H/V could

not be considered. They put the lie to the concept of everyone

walking differently.

C-24 Schwartz, R. P.; Heath, A. L.; Morgan, D. W. and Towns, R. C; "A

Quantitative Analysis of Recorded Variables in the Walking Pattern

of 'Normal' Adults," The Journal of Bone and Joint Surgery, Vol. 46-

A, No. 2, pp. 324-334, March 1964.

Presents data similar to that of C-23 on three men and one woman. Again shows that there is as much gait variation with time for one person as there is among different "normal" people; particularly

when speed of gait or height of heel, for a woman, is varied. Thus

in spite of the fact that we can sometimes recognize certain gaits

by sound there is really yery little difference between "normal"

gaits. No measurement of H so that H/V cannot be considered.

29
C-25 Steindler, A., "Mechanics of Normal and Pathological Locomotion in

Man," by Arthur Steindler, M.D. F.A.C.S., Professor of Orthopedic

Surgery, State University of Iowa, Iowa City, Iowa. Published by

Charles C. Thomas, Springfield, Illinois, and Baltimore, Maryland,

1935.

Referred to in B-8 as having a detailed bibliography on dynamics of

the human body.

Chapter 27 entitled, "The Mechanics of the Human Gait," and Chapter

28 entitled, "Graphic Description of the Gait," is pretty much the same material as appears in Steindler 1 s more recent book, C-26.

C-26 Steindler, A. "Kinesiology, of the Human Body, Under Normal and

Pathological Conditions," by Arthur Steindler, M.D. (Hon.) F.R.C.S.,

Eng. F.A.C.S., F.I.C.S., Professor Orthopedic Surgery, Emeritus,

State University of Iowa, Head of Orthopedic Department, Mercy

Hospital, Iowa City, Iowa. Published by Charles C. Thomas, Springfield, Illinois, 1955.

There is an interesting, but somewhat sketchy, historical treatment

up to the early fifties on the mechanics of the gait. It misses

some significant references such as those of Sigler and others in

the National Bureau of Standards. In his discussion of alternating

bipedalism, which follows his discussion of first the quadrupedal

gait and then bipedalism in general; he states "the human gait,

therefore, can be described as an alternating play between the two

extremities, one in touch with the ground producing in sequence

restraint and propulsion, while the other swinging freely carries

with it the forward momentum of the body. At the completion of the

swing the leg again touches the ground, first restraining the body

in its forward path and then again assuming the role of propulsion.

The moment the center of gravity of the forward moving body has

30
passed beyond the supporting base the balance is lost and remains

lost during the entire propulsion phase of the standing leg. It is

only regained as the heel of the other leg touches the ground and

the leg exercises a restraining function. It is quite proper,

therefore, to designate the human gait as a constant play between

loss and recovery of the equilibrium."

He gives no credit to this statement and thus it would seem that it

is original with him. This statement is, however, quoted, usually

without credit, by many later authors.

The remainder of this chapter which he entitles "Lecture 37 on the

Mechanics of the Gait," pretty much describes the kinematics; that

is the displacement, velocity and acceleration. He uses fairly

primitive ways to get the velocity and acceleration; by differentiating the displacement curve to get the velocity curve and in

turn differentiating that to get the acceleration curve.

Differentiating experimental curves generally leads to sizeable

inaccuracies. There are no direct measurements of forces or pressures, although he does make some calculations of the work done

during movement.

C-27 Strasser, H., Lehrbuch der Muskel und Gelenk Mechanik , 4 Vols,

Berlin, 1908-17.

Referred to in B-8 as having a detailed bibliography on dynamics of

the human body.

C-28 Sussman, A., and Goode, R. , "The Magic of Walking."

Delightful treatment of walking describing its history, its benefits,

its proponents and places to do it.

31
Chapter entitled "Engineer's Delight" states that the body is

ideally designed only for walking, certainly not for sitting or standing. "Walking, the human design comes into its own. Form

blends with function and the result is harmony and perfect performance. The body is built for action, and the action for which it is

specifically built is walking.

"Consider what happens to the body structure when we walk. The

flexible spine yields and springs back with each stride; the

spring like forms of the arched feet dissipate the impact of weight

meeting surface as effectively as any fluid suspensions designed by

General Motors engineers.

"And see what use is made of the body's peculiar distribution of

weight. The top-heavy torso now reveals its true value in twolegged locomotion: The forward pull of its weight becomes the

motive power for its progress. With each stride we are falling

forward, and one or the other leg is swinging out on its ball-andsocket hip joint to catch us.

"In terms of its mechanics, walking is nothing more than a series of

stumbles caught in the nick of time, a continuous rythmic loss and

recovery of balance. Gravitation, no less, is the force that we harness to our service when we walk.

"If we need any proof of this, we have only to remember that when

the astronauts go 'walking' weightless in space, they need a little

jet-propulsion gadget to move them - because they do not have the

help of gravity .

Chapter 3 "Engineer's Delight" and Chapter 7 "The Science and Art

of Walking" present excellent general descriptions of the mechanics

of walking and are frequently stolen and/or referred to by other

authors.

32
Chapter 7 "to describe walking as a successive loss and recovery of

balance is mechanically accurate, but it gives us the image of a herky-jerky gait that is nothing at all like the smooth flow of

natural walking style. Our minds-eye picture is closer to the fact

when we see it as a continuous ripple of motion flowing up and down

through muscles and joints. From head to toes and back, without a break anywhere along the line.

"The motion is smooth because the successive transactions with

gravity are bridged by forward momentum. The body moves flexibly,

but all at once. To take a step, it tilts slightly forward, but

not head and shoulder first, or abdomen first, or bent at the hips

to push the torso ahead. It tilts forward by bending slightly at

the ankles. Try it. Shift from an erect standing position to

walking position in slow motion, and you will see that it is your

ankles that tilt you forward, or rather the ankle of the standing

foot, because the other is already lifting to take your weight in a forward step. The knee of the standing leg does not bend, but

rather straightens, at the same time as the heel lifts and the foot

muscles push off from the toe.

"The knee of the forward leg does bend, to lift and again to take

the weight as it lands. In a good walking style, the body tilts

forward just far enough to keep the center of gravity moving forward in the right mechanical relation to the individual's natural

length of stride. We don't need a slide rule to figure this out.

Fortunately because if we give it a chance the body figures it out

pretty much for itself.

"Once the body finds its proper angle, it does not jerk forward and

back with each stride. It keeps the angle unaltered within the

fluid forward motion, as long as it is going along at the same pace

and the ground is level."

33
METHODS AND RESULTS OF TESTS FOR FLOOR SLIP-RESISTANCE

D-l "Bell System Practises, Measurement of Slip-Resistance of Resilient

Floors. Principles and Evaluation," section H51.119 (Aug. 1958)

AT&T Company Standard .

Describes an instrumented floor polisher used to measure

slipperiness by AT&T and Public Buildings Service, GSA.

D-2 Boone, T. H. & Auld, C. W. "Standard Measurements of Slipperiness

on Walkway and Roadway Surfaces," Progress Report 1, NBS Report 7510,

21 May 1962.

Factors Affecting Friction of Rubber

Adhesion: Caused by intimate contact between the two surfaces at

individual points. Thus proportional to the "actual" contact area which may be proportional to the "average" contact area.

Hysteresis: energy loss owing to the mechanical interaction of the

surfaces. Proportional to the hysteresis value of the rubber and

deformation it undergoes. Could be independent of contact area,

for smaller areas more work per area because of increased pressures.

Cohesion: "It is likely that cohesion, as such, has wery little

effect on friction, but contributes indirectly by augmenting

adhesion and hysteresis resistance." There may also be viscous

drag in any lubricating layer that is present but "any viscous drag

is also negligible if the lubricating film remains thick enough and

the sliding velocity is not excessive." Then describes two models

of the Sigler tester and the British Portable Skid Tester.

34
Ran a series of tests comparing synthetic rubber and natural rubber

sliders. "With the exception of the stainless steel surface, the

SR sliders gave higher readings than the NR sliders," "on the steel

surface, where the hysteresis and cohesive forces of the rubber were of less significance, the softer NR with its greater surface

contact gave higher results." In addition to the stainless steel,

an epoxy and three different concretes were evaluated.

In an attempt to establish reference surfaces for floors, six

asphalt tiles, four vinyl asbestos tiles, cork, linoleum, cork/vinyl

tiles and vinyl were tested dry and wet, unexposed and after exposure

to four years of pedestrian traffic. All but one of the asphalts

and all but one of the vinyl asbestos tiles showed reduced slip

resistance caused by four years of wear. Generally the other

materials showed increased slip resistance caused by wear. Finally

7 British Portable Skid Testers were compared and found to yield

reasonably consistent results.

D-3 Braun, R. and Roemer, D. "Influence of Waxes on the Static and

Dynamic Friction," Soap/Cosmetics/Chemical Specialties, Dec. 1974.

Reproducible results required replications & statistics. In general polishes increased y, suggests an optimum value above which

no gain and below which danger. "An analysis of the walking process

shows that at the beginning and towards the end of a step, the

horizontal force between the foot and the floor reaches a maximum.

This has to be compensated for by the static friction. The dynamic

friction is also important since it must prevent the sliding process

from developing into slipping. ...We realize that other kinds of

motion can occur during running and walking; however, it is not

practical to design a measuring procedure which will cover all cases imaginable. On plastic films as well as on floors, the friction

does not follow the Coulomb-Amonton law which states that the

frictional coefficients are not dependent upon the pressure of

35
contact and the speed. In addition, a great number of other

parameters, such as temperature and humidity are important, and

static friction depends on the contact time which starts when the

test shoe is placed on the floor and ends when the actual test

begins." The James machine is unsatisfactory "since contact pressure

is only approximated and the contact time prior to testing cannot

be enumerated at all." A device developed by K. Schuster consists

of a sledge with a built-in dynamometer that is pulled over the

substrate by hand. In this case, the test data are strongly dependent on the individual doing the testing. The Topaka is an improvement because of the motor drive. "With this device only the dynamic

friction can be measured for reasons which will be obvious later

on."

The Hoechst device, developed by Braun and Roemer, uses three

symmetrically placed, chromium plated shoes that are mechanically

lapped, u occurs in the moment the shoe starts moving. This can

be established when a, v or s = o. "However a simple calculation

shows that a is most suitable to determine this moment." For — — 2 —

example if a is proportional to t then v increases as t and s as

3 _

t . Thus a at time t = o is easiest to evaluate. It is necessary

to measure y @ a = o since "when the movement starts, the mass force necessary for speeding up the shoe is measured in addition to

the friction." They found that Fmax "near" the start of motion

could be as much as twice the F needed to initiate motion. This

s points up the need to have a fairly light shoe relative to the

normal weight. The James device has this feature. "To determine

dynamic friction, only the force necessary for maintaining constant

speed has to be measured. There is a stick-slip problem, caused by

small irregularities in the surface, causing oscillations in the

force and speed. They are most noticeable at the start and tend to

damp out. A non-elastic drive arrangement would help but would be

hard to achieve. Another way to approach the problem is to average

36
over a long period of time, by integration or by damping the oscilloH graph." Got good reproducibility with chrome plated shoes, in

contrast to leather, rubber or PVC. Normal foot pressure about 7 psi, but found that y & y, varied yery little in range of pressure

of 3.6-7.3 psi, thus used about 3.5 psi. In general y increases

slightly with p but not with all polishes, y as a function of v is not very sensitive. A decisive quantity for y is t , the

standing time.

"One quantity which is decisive for the static friction is the

standing time, t , between putting down the shoe on the substrate

and the start of the test run. At first y shows a remarkable

increase with t and reaches a limiting value only after a prolonged time." They used t = 1 second.

Fairly sophisticated statistical analysis of data revealed the need

to make 6 replications. Found that generally y > y , but only

slightly, vJv^ = 1.1- The substrate had a greater effect on y or

y , than the polish.

"Cases in which the dynamic friction exceeds the static friction

essentially are only of theoretical interest since a high y , damages the polish-film during sliding."

D-4 Bunten, J. "Friction Measurements on Soles and Heels, With Particular

Reference to Women's top-piece Materials," SATRA, Shoe and Allied

Trades Research Association, SATRA House, Kettering, Northants SATRA

Memorandum, T. M. 1355.

Nice general discussion of the problems of measuring friction of

shoe soles and heels.

Claims y varys with pressure & velocity. Describes the SATRA ramp

test for floor si ipperiness, first reported in a SATRA bulletin for

37
August 1950. Mentions many serious limitations, particularly that

the natural action of walking on level ground is not closely reproduced particularly at the important instant when the heel first

touches the ground. Describes devices of the same type as the

Horizontal Pull Slip Meter and the British Portable Skid Tester.

Results on clay quarry tiles are given, wet & dry, on ramp, HPS & BPST. "The differences between wet and dry conditions are most

consistent for the BPST, with the wet friction always lower than

the dry. The HPS method appears to give higher wet than dry y for

the hard materials and higher dry than wet for the soft. The ramp

tests show no consistent difference."

Measurement on polished vinyl tiles, wet, using the BPST gave very

low results on almost all materials tested. Apart from microcellular rubber, at 0.18, all u's were in the range 0.09-0.11. In other words this sort of surface can be dangerous in itself, what- ever the soling and top piecing used.

D-5 "Coefficient of Friction (Slip) Measurements," G-63-10 Fixture,

Instron Corp., Canton, Mass.

D-6 Day, S. S. - Bowen, H. D.; & Hader, R. J. "Skid Resistance of Floor

Surfaces and Finishes" Resilient Floor Coverings, Hard Floor

Surfaces and Wood Floor Finishes, Tech. Bui. No. 200, North

Carolina Agricultural Experiment Station In Cooperation with

the School of Home Economics. The University of North Carolina

at Greensboro, Dec. 1970.

Error in tables 13-16

Extensive paper describing a series of MS theses that evaluated a series of floors & shoe materials using the Bowen Friction Tester.

The BFT is a table that rotates with several flooring surfaces

under a shoe of any desired material. Based on results of a study

38
at Michigan State the rotational velocity was such as to yield a linear velocity of 15 ft./min. at the shoe. Thus only a dynamic

coefficient was measured. A "mechanical" recorder was used.

Investigation One : Various heel materials and new and worn resil

ient floor materials.

1. By far the biggest effect on u is that of the heel

material

2. Second largest effect is condition of floor, y generally being lower for worn floors.

39
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Heel

. 2 size, in. 5#

Stacked 0.74 6.76

Cuban 1.50 3.33

Child's 5.23 0.96

Man 's 10.00 0.50

Investigation two : Effect of size of heel or normal load on the heel

Four different heel sizes and five different surcharges were used,

resulting in the following range of contact pressures.

load on heel

11# 18. 5# 26# 33. 5#

14.86 25.00 35.14 45.27

7.33 12.33 17.33 22.33

2.10 3.54 4.97 6.41

1.10 1.85 2.60 3.35

For Leather .296 <_ u <_ .327, for rubber .516 <_ y £ .716

Rubber has a much higher y than leather. Increasing weight increased y for rubber but not for leather. Increasing heel size increased y for

leather and decreased y for rubber.

Investigation Three : Three materials: Leather Nylon Rubber

Av. y .245 .567 .605

and three manufacturers of each.

Material has the greatest significance, but material manufacturers and

flooring materials have some significance.

Investigation Four : The effect of floor polishes in both dry and wet

conditions on resilient floor coverings.

1. Heel materials show a greater effect on skid resistance

than resilient floor materials or brands of floor polish

41
but interact with them. Low y's are obtained with leather

and relatively high y's with rubber, neoprene-cord and

crepe heels in a dry condition.

2. Moisture reduces y for all heel materials except leather

and for all floor materials, though for linoleum the

reduction is smal 1

.

3. In a dry condition different floor materials exhibit

different y's but not so when wet.

4. Both polish type and brands within polish type show

significant differences of y, those within types only

slightly smaller than those between types.

5. Dry tests showed skid resistant polish superior to

ordinary & clear polishes, but wet tests reversed the

order of polishes in terms of y, ordinary-highest and

skid resistant-lowest. Polished floors generally lower

than bare floors & worn floors.

Investigation of Skid Resistance of Hard Floor Materials

The rank order of the dry floor materials differed from that of the same materials wet; aggregate, glazed ceramic tile and concrete

were best dry and poorest wet, while terrazzo, quarry tile and

unglazed ceramic tile were poorest dry and best wet, as a class

they decreased only 10-24% by wetting. Heel materials showed

greater variation than floor materials or polishes, leather being

poorest and crepe the best. y for leather was 43-70% less than for

other heel materials. Moisture reduced y except for leather on quarry tile or unglazed ceramic tile; significantly so for all

heels on concrete, aggregate or glazed ceramic tile. Polish reduced

y in all cases except terrazzo, dry. Type of polish had little

effect dry but wet the skid resistant polishes were worst, compared

to clear and ordinary polishes. Application of moisture reduced y in all cases, particularly on polished floors. Wearing the floor

tended to increase y and polishing tended to decrease y, except for

crepe soles.

42
Investigation of the Skid Resistance of Wood Floor Finishes

Heel material has the greatest effect, leather poorest, crepe best.

On bare finishes moisture decreased y except for penetrating seal.

On dry wood flooring, all finishes, all heels except leather yielded

y >_ 0.40 with moisture some were < 0.40. Waxing lowered y except

for the self-polishing, y for bare and self-polishing was usually : 0.50. Dry the paste- skid resistance was as good as self-polishing,

but wet it was more like the other waxes. Generally y >_ 0.5 would

pass most heels on most dry surfaces, but it would take y >_ 0.2

to pass leather heels on all dry surfaces and about half the wet

surfaces

.

D-7 Day, S. S. ; and Hodges, M. B. "Factors Affecting Skid Resistance

of Hard Floor Surfaces," Hospitals, J.A.H.A. April 16, 1967, Vol.

41.

This material is presented more completely in D-6 but there appears

to be an error in tables 13-16 of D-6.

D-8 Day, S. S. & Shamburger, E. "Factors Controlling Skid Resistance

of Resilient Floor Coverings," Hospitals, J.A.H.A., April 16, 1965,

Vol. 39.

Results reported in bar chart form that are also reported in tabular

form in D-6. Heel material had greatest effect; for leather, dry & wet, 0.15 £ y <_ 0.40, wet better than dry; for rubber dry & wet

0.30 <_ y <_ 0.95, dry much better than wet: 0.30 <_ y <_ 0.50 wet

0.40 <_ y < 0.95 dry

Skid Resistant polishes generally improved y for leather dry, but

in this one case leather wet showed a decrease in y. Skid resistant polishes also gave best y for rubber dry but for rubber wet

43
all polishes were equally bad. For crepe 0.5 ^y < 1.2 dry,

0.15 <_ y <_ 0.8 wet. Generally on dry floors, polish helps, skid

resistant the most. On wet floors the polish frequently is more slippery than a bare floor, particularly for the skid resistant.

Recommendations for Floor Safety

1. Keep floors clean and dry. Wipe up any spilled or tracked-in

liquids immediately.

2. Use a floor polish that has been tested for skid-resistant

characteristics under both dry and wet conditions.

3. Avoid the use of different types of polishes having different

y's on the same floor or if practicable on adjacent floors.

4. Block off floor area that is being cleaned or polished and

allow the floor to dry thoroughly before opening it to

traffic.

5. Place floor mats at entrances to prevent tracking water into

the building during wet weather.

D-9 Day, S. S., Tuten, F., Trogdon, J. and Bowen, H. "Measurement of the

Skid Resistance of Resilient Smooth Floor Surfaces." Journal of

Home Economics, Vol. 56, No. 10, Dec. 1964.

Describes work conducted at University of North Carolina at Greensboro,

see reference D-6.

D-10 Esmay, M. L., and Segerlind, L. J., "Analysis of Frictional Characteristics of Stairway Tread Covering Materials," Transactions of

the American Society of Agricultural Engineers, Vol. 7, No. 2, 1964.

44
Have discussed the difficulty experienced in obtaining a true

determination of friction coefficient between two elastic materials

"In 1959 alone, more than 2200 farm people died as a result of

falls. About one third of these accidents occurred on steps and

stairways (National Safety Council, 1959). In 1959 approximately

700 farm people died as a result of falls which occurred on steps

and stairways.

"The coefficient of friction was measured on a machine having a movable table under a stationary holder. ...The vertical load on the shoe soles was applied by placing weights at the end of an arm which rested on the holder. The tread materials were placed on the

table and moved under the holder containing the shoe sole at a controlled uniform rate of speed. ...A vertical force of 117 lb. was used. ...The table moved at a constant speed of 14.6 fpm.

...The horizontal forces required to pull the shoe sole materials

over the tread-covering materials were thus recorded on the oscillograph.

"New and worn specimens of six different tread materials and six

different sole materials were used. The different sole materials were duplicated for two different sole sizes; 16.4 and 10.7 sq. in.

The tread materials used were wood, linoleum, a non-skid type

paint, abrasive strip, varnish and rubber mat.

"The sole materials investigated were neoprene, neolite, crepe,

leather, ripple, and hard-surfaced sole made by B. F. Goodrich...

"The coefficient of friction for the abrasive strip and rubber mat

materials was higher than the coefficients of friction of the other

tread materials for most all of the soles investigated. Wood,

varnish and paint generally showed a decrease in the coefficient of

friction with use, while linoleum increased with use. The ripple

sole had the highest coefficient of friction values for any of the

45
sole materials studied. The crepe sole was the only sole which

consistently had a higher coefficient of friction value on the new material than on the worn material."

Only averages of results were reported, with the large soles yielding values of y , from just below 0.5 for leather and B. F. Goodrich

to nearly 1.0 for the ripple. The small soles yielded similar

results except that the leather was about 0.3 for new sole and

about 0.4 for worn sole.

D-ll "Evaluating the Slip Resistance of Floor Waxes, The Significance of

Friction Measurements," ASTM Bulletin, Sept. 1958.

This is nearly a verbatim quote of Weirich's paper, D-38, which was presented at CSMA, May 1958.

D-12 Ewerdahl , S. "Hal ksakerhet Hos Golvbelaggningsmaterial ," Byggmastaren,

1938, 17, 447-451, N:r 39 1938, Innehall. Investigations of Various

Floor Materials in Relation to Slipperiness.

Although an English translation of this paper is not available, the

figures and charts report the results of tests for both static and

dynamic coefficient of friction of leather soles against a variety

of flooring materials using a series of testing rates varying

between and 1.0 meters/sec. The device used was similar to the

Horizontal Pull Slipmeter. Sometimes the static y exceeds the

dynamic y and other times the reverse is true, this phenomena

appearing to be affected by the test rate.

The tabulated results indicate that y varies from 0.33 to 0.87 and

y varies from 0.18 to 0.65.

46
D-13 Frederik, W. S., "Description of a New Portable Slip Testing Machine,

44th Mid-year Meeting Proceedings of the Chemical Specialties

Manufacturer Association Inc., N.Y., May 1958.

Describes the design and operation of the Frederick machine.

Incorporates a shoe, W2, that is twice as heavy as the surcharge,

Wl . Thus v = W tan a = Wl tan a = 1/3 tan a . Where

Wl +W2 3W1

,

tan a is the tangent of the angle between the leg and the vertical.

This means that to evaluate y near 1.0 say you would have to let

the articulated leg get pretty close to the floor.

Statistics: "The combined general liability experience of three

large department store chains, for a period of three years, showed

a total of 8,637 accidents, with losses of $665,000; 'falls on stairways' and 'floors' accounted for 33 percent of the accidents,

38 percent of the loss. Floor accidents, principally falls, alone

were responsible for 17 percent of accidents, 20 percent of loss."

D-14 Gavan, F. M., Discussion of C. H. Irvine Paper, "A New Slipmeter

for Evaluating Walkway Slipperiness," Materials Research & Standards,

Vol. 7, No. 12, December, 1967.

Questions the use of the HPS at least without a complete recognition

of its precision limitations.

D-15 Gavan, F. M., & Vanaman, J. B., "Significant Variables Affecting

Results Obtained With the James Friction Machine," Materials Research

& Standards, Vol. 8, No. 11, November, 1968.

U. L. Standards, from "Accident Automotive and Burglary Protection

Equipment Lists" of Sept. 1966, page 16, "Listed floor coating and

47
finishing materials are of three classes: FTM, Floor Treatment

Material; OGA, Oil and Grease Absorbents; and WCM, Walkway Construction Materials. The materials listed have been found to have slip

resistance characteristics of not less than 0.5 as determined by

the static friction test method of Underwriter's Laboratories,

Inc."

Systematic investigation of the variables in the James Machine

Test. Found the following variables to be particularly significant:

1 . The operator (two)

;

2. The time under a load before the start of test (immediate

or after 1 min. )

;

3. The rate of application of the load (the vertical load)

sudden (dropped from 1/2 in) or slowly;

4. The direction of the substrate (machine direction or across MD)

.

The three parameters that were much less significant were:

1. Speed of table (fast or slow);

2. Dry position (MD or AMD);

3. Cleaning of sensor (cotton or camel's hair brush).

Of the 64 tests run only one failed to meet the UL minimum of 0.5.

Table 5 - Qualification of Means:

Mean Coefficient of Confidence

Static Friction Level (X%)

0.6991 99

0.6577 95

0.6419 90

0.5000 50

Based on the variance of the 64 tests performed in this study.

48
Conclusions "From the results obtained it is apparent that this

test is greatly affected by several common variables that may be

overlooked. This is likely in these days of exploding technology

and transient personnel. Industrial qualifications tests should be

foolproof to the testing conditions. This work is published to

call attention to a situation pertinent to a rather simple test and

to bolster our caution about the adoption and widespread use of

such tests." There was insufficient detail in the report of the

test results to permit the determination of just how the various

variables considered affected the results of the James Test.

D-16 Giles, C. G.; Sabey, B. E. and Cardew, K. H. F. "Development and

Performance of the Portable Skid Resistance Tester." Rubber Chem.

Technol. 38,840(1965)

.

Reprinted from "Symposium on Skid Resistance" Special Technical

Publication 326, American Society for Testing and Materials (1962).

Originally published by Department of Scientific and Industrial

Research, Road Research Laboratory, as Road Research Technical

Paper No. 66, and available from Her Majesty's Stationery Office,

London.

The definitive paper on the development of the BPSRT. Gives credit

to the Sigler tester as the model for the BPSRT.

"The portable skid-resistance tester can carry out a wide variety

of measurements. It is particularly well adapted for use on the

more rough-textured surfaces. The design also makes the readings

of the instrument independent of gradient, camber, or crossfall on the surface under test.

49
"The instrument gives readings that correlate well with the results

of tests made with patterned tires skidding at speeds of 30 mph.

The readings have also been correlated with the risk that accidents

involving skidding are likely to occur on any stretch of road.

...The calibration is based on the effective weight of the pendulum

arm, the distance over which the slider is in contact with the

surface under test, and the nominal load on the slider. Checks

made on the 150 or so machines in use show that with this kind of

absolute calibration all the machines agree within an accuracy of +

3 percent.

"In attaining this degree of accuracy, the physical properties of

the rubber used for the slides have an important role (as they do

in any apparatus for studying skidding problems). A detailed

specification gives the resilience and hardness properties of the

slide rubber that will ensure this high standard of consistency in

the readings."

D-17 Gough, V. E., "Simple Direct-Reading Friction Meter," Journal of

Scientific Instruments, Vol. 30, No. 10, October, 1953.

A complete description of the device used in D-32 and an improved

version of it, which made use of relatively large discs joined

together with shafts and belts.

The device is essentially a means of determining the direction of a resultant force, which when acting on a flat surface can be read

off as a friction coefficient. The method of application of the

normal and tangential forces is optional with the user. Unless

this is well controlled one has the same problem as with other drag

type friction meters.

50
D-18 Gurney, S. W., "Is the floor too Slippery?" National Safety News,

1940, Aug. 22. Referred to in B-8 as discussing evaluation of

slipperiness.

Gurney was Laboratory Director, Loss Prevention Department, Liberty

Mutual Insurance Company.

Describes a portable version of the Hunter machine where a 3" X 3"

maple shoe loaded through a 10" long articulated strut is pulled across a floor until slip occurs and the angle of the 10" strut is

recorded. This is probably measuring y , just as Hunter did.

1. Found that y < 0.20 was slippery and y > 0.25 was non slip.

2. Found that the more resilient the substrate the more effective

(> y ,) was the wax or polish on it.

3. Where there is considerable foot traffic, a freshly waxed

surface is more slippery than one that has been walked on for

several days, largely owing to the dust, street dirt and

similar abrasive materials which are tracked onto the surface.

D-19 Hartley, Owen, "How to Use a Floor Slip Tester," The Executive Housekeeper Vol. 15, No. 11, Dec. 1968.

Suggests the use of some slip tester in public buildings to demonstrate concern in the event of law suits.

In Memorial General Hospital, Las Cruces, N. M., they use a 10# bag

and a fish scale, with a pull chain and a drop chain to be certain

that their pull is horizontal at all times. They routinely check

12 places throughout the hospital, each time they freshly wax and

any time they are told an area is slippery. They have found that worn terrazzo can be as slippery as tiles and thus should be waxed.

"Ludox" is an ingredient in many floor polishes which causes little

51
bubbles to form on the floor, thus making it slip resistant.

Traffic breaks these bubbles down and reduces the slip resistance.

D-20 Hunter, R. B. , "A Method of Measuring Frictional Coefficients of

Walkway Materials" Journal of Research , NBS, Vol. 5, p. 329 (Aug.

1930), RP204.

Describes the Hunter Machine. The Hunter Machine is similar to the

James machine in that a 3" x 3" shoe is loaded vertically with

80# through a 10" long articulated strut; the angle of which is

increased and monitored until slip occurs. The Hunter machine

differs from the James in that the shoe is dragged across the

walkway specimen until slip occurs; thus, since the shoe is already

sliding when uncontrolled slip occurs, the value measured is likely

to be y. rather than y . Hunter found that variations in pressure,

8.3 - 16.7 #/in , had very little effect but that "polishing" in

repeated tests reduced y. Increasing humidity decreased y between

leather and leather but usually increased y between leather and

walkway surfaces. He found that leather is a fairly consistent

material, y increases for leather on wet and/or oily surfaces.

Hunter believes this is caused by a vacuum formed between the

leather and the walkway surface. Hunter attempted to eliminate the vacuum by lifting and dropping the shoe to simulate what he believed

to occur in walking on wet or oily surfaces.

D-21 "Instructions for Using the Portable Skid-Resistance Tester," Road

Research, Road Note No. 27, Department of Scientific and Industrial

Research, Road Research Laboratory, London: Her Majesty's Stationery

Office: 1960 .

D-22 Irvine, C. H. "A New Slipmeter for Evaluating Walkway Slipperiness ,"

Materials Research and Standards, MTRSA, Vol. 7, No. 12, Dec. 1967

pp. 535-541.

52
Compares the Horizontal Pull Slipmeter (HPS) with the Frederik

Tester (FSTM). HPS uses 3.93 "/min and 10.5 psi. with the Contact

sensor sanded with 6/0 grit finishing paper before each series of

tests.

It was found that HPS and FSTM gave essentially the same results

but there are problems of consistency between operators and between

different days for the same operator. Used as floor surfaces;

teflon, vinyl asbestos, rubber, linoleum, vinyl plastic and asphalt.

Teflon results in y - 0.2 others result in y * 0.5 - 0.6.

Also found that stainless steel is not a suitable material to use

as a replacement for leather as a test sole or sensor for the HPS.

D-23 Irvine, Charles H., "Shoe Sole Slipperiness on Structural Steel,"

ASTM Materials Research and Standards, Vol. 10, No. 4 April 1970.

Refers to Accident Facts, ACFAA, National Safety Council, Chicago,

111.', 1968.

Discussion: Sole leather, when dry, becomes hard and slippery; when

wet, it turns softer and tends to adhere to surfaces. On unpainted

steel, y dry - 0.98, y wet = 0.72. Other material such as GRS,

Neoprene (foamed), Hypalon (solid) also showed increased slip

resistance against bare steel when wet. Foamed hypalon, PVC (solid),

rippled neoprene (solid or foamed) and solid neoprene showed decreased

slip resistance when wet. The rippled design did not help slip

resistance. Foamed neoprene, foamed G.R.S. & Solid Hypalon showed

increased slip resistance on painted steel but water affected it

adversely for the GRS & hypalon. Cold structural steel, 21°F in

78°F room, thus frosty, had reduced slip resistance for the materials tested, solid neoprene, solid hypalon, foamed neoprene, foamed

G.R.S.

53
D-24 James, Sydney V., "What Is a Safe F.loor Finish?" Soap and Sanitary

Chemicals, Oct. 1944.

This appears to be the only article published by^Sydney V. James.

It presents a general discussion of the interest of U.L. in floor

slip-resistance and the biomechanics or kinesiology of human locomotion. He concludes "The essential point of this process, it seems

to us, is that the shoe is in stationary contact with the floor

during the walking action. • There may be spme difference of opinion

as to this. It would be extremely interesting to see 'slow-motion'

moving pictures of the walking process. I think we should see clearly that the shoe, although it may rock or roll slightly during

the step, is essentially in stationary contact with the floor. If

a person tries to take too long a step on a slippery floor, the

leading foot may slip because, in attempting to transfer the weight

to it, the angle of the leg is too great and the friction at the

shoe contact will not keep the foot from slipping. Similarly

letting the leg take too great an angle backward may also result in

slipping. Think of a person walking on stilts. On a slippery

floor short steps are necessary, while on a rough floor long strides

become possible.

"Another point which should be considered is that the friction

between two bodies in stationary contact is greater than if the

bodies slide relative to each other. We believe that it is necessary

to take this into account when analyzing the walking process."

James then developed a test method for floor slip-resistance by

considering and rejecting previous methods such as: the variably

inclined plane since the normal force varies; a dragged shoe since

this is generally dynamic friction; a propelled shoe, measuring the

stopping distance, which is again dynamic and a non-constant velocity;

54
and the pendulum which is again dynamic and a non-constant contact

pressure or velocity. He then describes his machine which was based on the Hunter machine, as to 3" X 3" shoe and 75# force,

resulting in 8 1/3 psi , which is less than that for a man but he

claimed that for pressures above 6 psi the y was not affected by

pressure. His description of his device would indicate that it was intended for testing in-place floors as well as flooring materials,

yet the devices bearing his name are only suitable for testing

samples of materials.

"Summing up the matter, therefore, our method of answering the

question 'what is a safe floor finish?' is to compare the surface

friction of the finish-coated floor with that of the untreated

floor and then if the coefficient of friction of the treated or finished surface is no less than that of the untreated surface, the

finish is regarded as being a safe finish. This is a relative or comparative method. It is based on the assumption, amply justified

by experience, that the various forms of commonly used floors and

floor coverings are safe enough for use without any finish material

being appl ied.

D-25 Johnson, Bayard S., "A Discussion of Some Factors Influencing Slip

Resistance Measurements," CSMA, Proceedings of the 44th Midyear

Conference, May 1958.

Refers to NBS slipmeter tests. He assumed a shoe contact area of

2 15 in. and thus postulated contact pressures of 10 psi from 0.1

second after impact to 0.6 second after impact and then falling

rapidly to zero. James and HPS approximate this. He further

postulated that in the first part of a step, on a new sharp edged

2 heel the pressure on 0.2 in. could be as much as 375 psi. He mentioned

"A limited number of tests on certain types of floor wax formulations

shows that the static coefficient of friction decreases under high

pressure, probably due to plastic flow of the wax composition."

Then suggests the y needed for normal walking is not high, possibly

55
not greater than 0.2. Then discusses the need for higher values of

y and possibly a relatively high ratio of y d /u

s to control stumbles,

losses of balance, slips etc.

Then discusses an evaluation of the Sigler machine on bond paper

over a sheet of carbon paper. With a hard heel against a hard

substrate, asphalt tile, the carbon paper revealed a nonuniform

contact pressure trace. For the same heel on a soft substrate,

rubber, the trace was much more uniform, also for soft leather

shoes. This throws doubt on the Sigler values.

D-26 Kellett, P. H. "Modern Solings in Wear," SATRA Information Publication I. P. 16, SATRA Symposium on Injection Moulding, June 28,

1968.

Describes the ramp test, angles > 15° are preferred but sole or floor surface is not considered dangerously slippery unless the

slip angle is below 10°. Measurements are made both wet and dry.

Ramp appears to be about 12' long and the upper end is elevated by

means of a rope hoist.

Gives some slip results for rubber & PVC, against clay and vinyl

tiles, wet and dry.

1. Rubber is generally less slippery than PVC.

2. Both rubber and PVC are dangerously slippery on wet surfaces

when their hardness is less than 55 IRHD.

3. PVC's of 80 IRHD or over are wery slippery on wet and dry

surfaces.

IRHD is a measure of hardness of PVC or rubber, etc. Polyurethane was found to behave much as rubber as to slip and wear. Thermophastic SBR soling has excellent skid resistance. Ethylene Copolymers have satisfactory skid resistance.

56
Tests of top pieces (heel taps for women's heels)

Slip resistance

Rubber (NR & SBR)

Rubber (nitrile)

Polyurethane (cast)

Polyurethane ( In j . Mid.)

Nylon

Polyformaldehyde

Hard PVC

Surlyn 'A' Thermophastic SBR

Steel

= Satisfactory

= Dangerous

D-27 "Measurement of the Slipperiness of Walkway Surfaces," Rubber Age,

Vol. 62, Dec. 1947, pp. 296-297. No author, but it appears to have

been written by Percy Sigler.

Describes efforts of National Safety Council to collect data regarding accidents to make a statistical study and efforts of NBS to

measure slipperiness. Questioned earlier devices on grounds that

they were concerned with starting rather than sliding friction and an appreciable area of contact between sole and floor surface was generally used. Thus more representative of a person standing than

of someone in the process of walking, when most slips and falls

occur.

This is where the delay between application of vertical load and

tangential load becomes vital. Discusses concealed camera observations of walkers and study of worn heels and development of the

Sigler Tester. Does not claim that the "antislip coefficient" is a coefficient of friction.

57
Describes in general terms some tests of concrete blocks, ground

with carborumdum and worn from 25 years of service; rubber tile

with and without alundum grit; a rubber matting with cotton fibers;

floors at Walter Reed and the Pentagon. Some general conclusions

but very little specific data.

D-28 "Model 80 Floor Friction Tester," Promotional Literature, Technical

Products Co., 264 Park Ave., N. Caldwell, N. J. 07006.

Describes a slip-resistance tester consisting of a 10# weight and

non-linear spring balance that permits low drag forces to be measured with the same relative precision as larger forces. The sensor area is 3 1/2" <j> leather buttons disposed much the same as

on the Horizontal Pull Slipmeter.

D-29 Modern Sanitation and Building Maintenance , Vol. 11, No. 7, p. 6

(1959)

Describes use of 10# bag of lead shot pulled by a fish scale, on two layers of cheese cloth;

Force less than 3# implies slippery

Force greater than 5# implies safe

Research Department of the Hospital Bureau Inc.

D-30 "Progress Report to the National Safety Council Committee on Safe

Walkway Surfaces," Oct. 1, 1949 - Mar. 31, 1950.

Reports a large number of tests of floors with what is presumed to

be the Sigler Tester. Generally a rubber heel is less slippery

than leather and dry is less slippery than wet, for both rubber and

leather. Wet leather can go as low as y = 0.14 on floors maintained

58
with solvent type wax, and dry leather can go as low as y = 0.24 on the same floors. Wet rubber can go as low as y = 0.15 on the same floors while dry rubber has a low y of 0.47 on the same floors.

The highest y in any case is y = 0.95 for dry rubber on a linoleum

corridor scrubbed, cleaned, waxed and not polished, with silica.

Force plate tests of 7 men and 5 women revealed that the maximum

required value of y was y = 0.2 on the heel and y = 0.5 on the toe

except for one 140# man, 5'8", 27 years old who developed y = 0.75

on the toe just at the end of his stride.

This is essentially the same as reference B-5 except that this has

more data.

D-31 "Proposed Method of Test for Measuring the Static Coefficient of

Friction of Waxed Floor Surfaces," and "Proposed Method of Test for

Measuring the Dynamic Coefficient of Friction of Waxed Floor Surfaces,"

ASTM Bulletin, No. 196, Feb. 1954.

The first was adopted as ASTM D2047-72, The James Test. The second

describes the Sigler Tester and was apparently never adopted.

D-32 Robinson, W. H. and Kopf, R. E., "Evaluation of the Horizontal Pull

Slipmeter," Materials Research and Standards, Vol. 9, No. 7 American

Society for Testing and Materials, July 1969.

Points up the need for a device to measure the static y of actual

in-use floors. Paper deals only with the static y's. For "the

Horizontal Pull Slipmeter (HPS) variations of speed between 2, 3.93

and 5 "/min. had little effect on the test results.

59
The Instron machine demonstrated that the HPS gives reliable static

results. The Instron was used to pull the HPS and both the Instron

and the HPS loads were read. The James Machine gave consistently

higher results than the HPS. For ten repeated HPS tests, S varied

between 0.012 and 0.056. For 4 repeated James tests S varied

between 0.015 and 0.060, where S is the standard deviation.

D-33 Schjodt, R. "Measurements of Human Reaction to Hardness of Floor

Covering," ASTM Bulletin No. 247, July, 1960.

Mostly recorded normal forces, but a bit on coefficient of friction

measured by pulling a weighted sole along the floor as described or specified in G-8. "In some cases special test floors could be

tilted so that the friction angle could also be measured directly."

Last two tests were included to check why, in the lobby of a research institute it was found necessary to put up warnings. Fine

sand appeared to lubricate the limestone but not terrazzo.

Author claims that the results show that the kinetic u ought to be

not less than 0.20 and not more than 0.4 for leather soles. In some cases, dry on rubber and sheet vinyl, kinetic y for rubber is

greater than the static y.

60
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D-34 Sigler, P. A. "Relative Slipperiness of Floor and Deck Surfaces."

U. S. National Bureau of Standards, Building Materials and Structures Report, B.M.S. 100.

Recommends the Sigler test for dry and wet floors, dirty, clean

soapy, even oily.

Most materials satisfactory when dry but dangerous when wet.

Was concerned by the previous findings that y static for wet sur- faces was frequently higher than for dry surfaces. Thought that

this was because the Hunter or James machine made just too large an area in contact, one more representative of standing, than walking.

Max. vel . of heel at strike - 500 ft./min.

Avoids reference to a dynamic coefficient of friction, but merely

calls it "antislip coefficient."

Tested in an environment of T = 72°F RH = 65%

clean = exceptionally clean floor

dirty = china clay sprinkled on the floor = very dirty

soapy = 0.5% solution = a maintenance procedure using

a yery strong soap solution and no rinsing.

Wear of stone floors was simulated by grinding with 180 grit,

excessive oil yields low y, excessive oil wiped away yields

same y as wet.; oily y increased slightly by sprinkling china

clay.

62
A wealth of data, no mention of number of replications

Suggested limits

Antislip value Leather heel Rubber heel

(classification) (antislip coefficient) (antislip coefficient)

poor < 0.15 < 0.25

fair 0.15-0.30 0.25-0.40

good > 0.30 > 0.40

Rubber heels are more likely to create surprises on wet surfaces.

Leather heels are more likely to slip on dry wax.

D-35 Sigler, P. A., Geib, M. N, Boone, T. H. "Measurement of the Slipperiness of Walkway Surfaces." J. Res. National Bureau of Standards,

1948, 40, 339. Also Research Paper RP 1879, May 1948.

"Slow motion pictures of people walking were taken with concealed cameras so that the subjects were unaware of being photographed and

were thus likely to be walking naturally. These pictures reveal

that the leg slows down at the termination of its swing and then

appears to vault onto the walkway, the other leg being used as a pole. They also show that the foot is first placed upon the walkway so that only the rear edge of the heel contacts the walkway

surface during the early stages of the retarding phase of a step.

The other foot remains in contact with the walkway, thus bearing

part of the vertical load, until the heel rocks forward and the

foot is fully planted. Then follows a survey of worn heels and

motion pictures which shows that probable angles that heels make

with a walkway surface at the first instant of contact vary from

11° - 33° with an average of 19° - 26°.

63
"According to the literature (Elftman B-6) the horizontal component

of the force exerted by the leg on a walkway surface reaches a maximum in the forward direction shortly after the heel makes

contact with the walkway, decreases rapidly at first and then

slowly as the foot deploys, and rapidly reaches a maximum in the

backward direction as the ball of the foot prepares to leave the

walkway. These horizontal components are the forces that must be

counteracted by friction in order to avoid slipping." Then a justification of the need for a portable device. Then a description

of the design and use of the Sigler machine.

Here the claim is made that the max. linear velocity of the heel

from a release ht. of 10" is 150 ft./min.

"In general, lower antislip coefficients were obtained with increase

in the pressure." "Therefore, the antislip coefficients obtained by

this method should be considered as relative rather than absolute

values and the establishment of a minimum antislip coefficient for

walkway surfaces as a specification or code requirement would have

to be based on a definite method of test."

The results of this test, considered in relation to slip-resistance

as actually experienced, indicate that a slippery condition does or does not exist, according to whether the measured coefficient is

less or greater than 0.4.

A large number of test results.. . "All the walkway surfaces gave

relatively high antislip coefficients with dry rubber heels, and

thus good traction should be experienced with such footwear. In general, much lower coefficients were obtained with dry leather

heels, the values ranging from one indicating poor traction, 0.30,

to one indicating good traction, 0.50."

64
D-36 "Standard Method of Test for Measuring Surface Fractional Properties

Using the British Portable Tester," ASTM Designation E303-69.

D-37 "Tentative Test Method for Qualitative Determination of Slip Resistance of Floor Polishes," CSMA Committee "N" CSMA Bulletin No. 117-

68, May 7, 1968.

Describes the shoe on paper, subjective test of floor slip-resistance

This was later revised in July 22, 1970, to become CSMA-Bulletin

No. 245-70; CSMA Tentative Method, Comparative Determination Slip

Resistance of Floor Polishes. See F-4.

D-38 Weirich, C. L., "Static Coefficient of Friction, Significance of

Test Results," Clarence L. Weirich, presented before the CSMA, May,

1958.

Found that variation in the weight bearing down on the shoe does

not affect the readings (within experimental range).

For steel on steel the above is generally true.

For a leather shoe on bare asphalt tile for top wts. from 19.3-

131. 0# and shoe sizes of 0.5 in.

2

, 1 in.

2

, 4 in.

2 and 9 in. the

results were \/ery consistent. For wts. of 17.3 & 19. 3#, p was too

high, probably caused by excessive friction in the machine.

For a leather shoe on waxed asphalt tile or on waxed TOTAT, fairly

2

consistent results were obtained for areas 4 and 9 in. and all top

wts. There was some indication of high readings for low top weights.

2

But for the small areas, 0.5 and 1.0 in. the results were much

65
lower, as much as 1/3 lower, indicating that at these high contact

pressures something is happening to the wax-leather interface to

make it less slip resistant.

A general discussion of "Evaluating the Slip Resistance of Floor

Waxes." Generally reservations on the usefulness of available

machines in other than laboratory conditions. Reference to other

causes of slips; trash on floors such as flower debris in hospital

rooms, the tendency of people to change gait when stepping onto a shiny floor, etc.

D-39 Williams, W. D., Smith, J. A. and Draugelis, F. J. "TOPAKA, A New

Device and Method for Measuring Slip Resistance of Polished Floors,"

Soap/Cosmetics/Chemical Specialties, July, 1972.

Claims that results of James machine do not correlate with foot

traffic experience in all cases. "We have had manufacturers of

polish tell us that their slipperiest polish gets the highest James

Machine Coefficient of friction."

Found good correlation with shot bag but too many uncontrolled

variables. CSMA test Method and Foot Evaluation,- CSMA uses a panel

of observers, using a piece of clean paper under the shoe.

5# total wt. with shot bag on 8 1/2" X 5 1/2" paper, 25% rag content

bond "Weston Bond Fluorescent." Shot bag ~ 5" X 8" Thus pressure -

1/8 psi. Windlass similar to Horizontal Pull Slipmeter except 110

volts, 3.3"/second, nylon cord.

Small portable sling psychrometer is routinely used.

Chatillon DPP5 push-pull spring scale with maximum load button.

For higher contact pressures used three 1/2" <f> gum rubber buttons,

2 A=0.59 in. thus pressi

man's walking pressure.

2 A=0.59 in. thus pressure - 8.5 psi. compared with 15 psi - average

66
On polymer products found pressure to have no effect, not as confident on all -wax products.

Found thai; the cheesecloth seemed to dig into all-wax products and

g i \/e results higher than actual foot feel wodld indicate. Paper

seems to give better correlation.

Tested 15 products with values of dynamic u varying from 0.300 to

0.158. Of the 15 materials only one had a statistically significant number of tests, 147; the others had from 2-4 tests. For the one with 147 tests n varied from 0.21-0.44. They concluded that y >0.24 implies slip resistant, 0.2 <_ y ^0.24 implies acceptable slip

resistance, u < 0.2 implies marginal slip resistance.

Findings:

1. The same polish acts differently on different types of

flooring.

'

2. The number of coats of polish influences the degree of

slip resistance.

3. Temperature, within reasonable limits, is not very

important.

4. Humidity is important: generally, higher relative humidity

will increase slip resistance.

5. Recoatability of polish is important; film disturbance,

crazing, can influence slip resistance.

6. Age of the polish film; as polish hardens with age and

traffic, slip resistance can change.

7. The last treatment of the floor is important; e.g. just

spray-buffed (and with what), just washed, buffed, etc.

8. The particular area of the floor where slip resistance

is measured is important too. High traffic areas versus

those with low traffic.

D-40 Wilson, Angus, and Mahoney, Patrick, "Measuring Frictional Properties

of Soles and Heels," Rubber World, March 1972.

67
Describes an inclined-horizontal test track and carriage designed

at the U.S. Army Natick Laboratories to study dynamic friction

between rubber soles and heels and typical floor surfaces. "In

evaluating sole and heel materials, we are concerned with the

retention of traction, or the prevention of skidding, and so sliding

friction is of interest. Loading, based on heel contact point

measurements, is calculated to be 88 psi. for a 150# man; speed is

taken as the 2.5 to 4 mph generally considered to be that of walking. ...The test specimen may be 1" or 3" wide and is flanged to

fit into a slotted holder angled at 15° to the horizontal. The 1"

specimen has a contact area of approximately 0.18 sq. in. A specimen loading of 16 lbs. or approximately 88 psi is achieved with a carriage weight of 30#.

"The carriage skid distance, measured from specimen contact point,

is used as a comparative measure of friction. In cases of yery low

friction, on wet tile for example, the average speed over the last

foot of horizontal track is measured using a micro switch and

millisecond timer." Found that a layer of floor dust, natural or artificial, consisting of whiting, talc, clay and carbon black,

increased skid markedly on tiles but only slightly on concrete;

making concrete the most skid resistant"which seems to agree with

more subjective evaluations.

Comparison with Portable Skid Resistance Tester (presumed to be the

British PSRT) resulted in the relationship:

r ... 138 Carriage skid = Port S kid Resist. Units

within + 2%

"Both apparatus show that clean smooth surfaces have comparatively

higher frictions and that wet or dry lubricating layers on such

surfaces drastically lower it. This can be explained by that

component of friction commonly designated as adhesion, attributed

68
to the attractive forces between the rubber and contacting surface.

On rough surfaces, like concrete, contact is poorer and the component

designated as deformation takes precedence, with the interfering

layer having less effect. ...In general, the results obtained from

the various tests show that it is extremely hazardous to try to

predict the frictional characteristics of a heel or sole compound

from other physical properties, or from the type of rubber used."

They must be tested specifically for friction.

69
GENERAL DISCUSSIONS OF FLOOR SLIP-RESISTANCE

E-l "Causes and Measurement of Walkway Slipperiness," Federal Construction

Council Technical Report #43, National Academy of Sciences - National Research Council Publication 899, Washington, D. C. 20418

A good basic report but somewhat out of date, 1961.

Objective to recommend performance tests, safety from slippage

only, primarily interior surfaces.

1. The causes of slipping

2. Methods of determining relative slip resistance

3. Need for standardized means of expressing degrees of slipresistance

4. Need for methods of measuring slip-resistance

A task group from six federal agencies

Conclusions

Existing test methods are good laboratory tests but are highly

subject to variable environmental conditions. Couldn't at that

time set standards, either a value or a method of measurement.

Suggested the establishment of standard surfaces and some simple

device for comparing field surfaces with the standards. Return the

standard surfaces for recal ibration from time to time.

70
Recommended Research Topics:

1. Establish standard surfaces

2. Develop a portable device for slip measurement

3. Conduct an extensive series of field tests

4. Determine a standard

Then classify and recommend materials and maintenance techniques

on the basis of their slip-resistance.

Discussion

Brief discussion of mechanics of walking

Factors influencing frictional requirements and floor safety

Floor Factors:

Layout and variety of floor finishes

Location of Surface

Physical shape of surface

Pedestrian Factors

Individual considerations

Psychological considerations

Amount of Traffic

Speed of Traffic

Type of Personnel

Footwear Factors:

Area of contact

Composition of heel and sole materials

Proper fit of the shoe

Then a discussion of the Fundamentals of Friction and methods

for measuring it including rolling and stopping friction

71
Discussion of Machines for Measuring Friction

Horizontal Track, including the Hunter, James and an instrumented

polisher

Inclined track or plane

Pendulum machines, Sigler and BPST, also wheels and a puck impeller

Evaluation with the foot

Problems with testers

1. Which type of friction, static, kinetic or stopping controls

the si ip of a foot?

2. Operator induced variables and variations in the conditions

of the machine

3. Elastic properties of the sliding materials

4. Geometry of the surface

5. Boundary film and matter prevailing at the surfaces of

contact.

A table comparing 11 methods of measuring floor slip-resistance is

included.

E-2 Chaffin, Don B. Private Correspondence from visiting professor,

Department of Industrial and Systems Engineering, College of

Engineering, University of Florida, Gainesville, Fla. 32611.

He suggests that "too much friction may be harmful to the musculoskeletal system" and that "the floor/foot interface is only one component which may influence the hazard potential of a given

man-task-environment system. Before seeking further opinions,

I would suggest a more open debate of experts to define the

broader system characteristics, so that any resulting measurement schemes are realistically defined to meet valid and logical

safety health criteria."

72
E-3 Cramp, A. P. and Masters, L. W.; "Preliminary Study of the Slipperiness of Flooring," National Bureau of Standards Report, NBSIR 74-613

E-4 Gutt, W. Private correspondence from Department of the Environment,

Building Research Establishment, Building Research Station,

Garston, Watford, WD2 7 JR.

He indicates that static friction measurements are usually favored

although the possible influence of dynamic friction, particularly

in turning maneuvers, is recognized. From their studies of the V and H forces they have concluded that a value of u J_ 0.4 is desirable. They have observed that lack of slip-resistance leads to

falls most often when there is heel only contact even though that

does not usually result in the maximum value of H/V. "Although

classical theories of friction are based on the concept that the

coefficient is independent of load this may not be true of floorings that are easily compressible. If one is measuring static

friction, I see no reason for simulation of normal walking behavior

but in situations where dynamic friction could be more important

then other considerations such as angular velocity need to be

considered." They use three contact materials: steel , leather and

rubber. "The results often indicate that with some materials the

floor is safe but with others it may produce a chance of slipping."

He comments on the effects of contaminants such as water, wax,

grease, etc., particularly water. "A fruitful source of investigation seems to be an examination of the behavior of water films on the flooring under different loading conditions and how moisture

might be transferred to the floor surface from contact with damp

(not wet) footwear."

E-5 Heath, Arthur L. Private correspondence with Associate Director,

Myodynamics Laboratory, The University of Rochester, School of

Medicine and Dentistry and Strong Memorial Hospital, 260 Crittenden

Boulevard, Rochester, N.Y. 14620.

73
His letter gives a good discussion of the variation of force and

pressure under the foot when walking, referring to two of his

published papers; C-23, C-24.

E-6 Hopkins, S. K. "Elusive Factor in Falls: the Shoe Sole," National

Safety News, NSANA, Nov. 1966, pp. 34-39.

Referenced in D-23 and quoted "The reason for this neglect (safe

shoes) is lack of information. Almost no valid research relating

to slip resistance of shoe soles and heels has been published.

Recommendations of shoe and shoe sole makers are at best very

general, often vague, and sometimes conflicting. There is no generally accepted method of measuring the slip resistance of shoe

soles or heels on various surfaces."

Followed in the same journal by "How an Antislip Sole was Born."

French Testing and design research led to a tread unlike anything

in the U.S.

This describes a tester which subjected a pair of shoes to a normal force of 45-350# in 45# increments and applied a gradually

increasing lateral force until slip occurred. The average u for

each direction of pull on a given surface was determined by averaging the u's obtained with different loadings..

E-7 Jablonsky, R. D., Private correspondence from Truesdail Laboratories,

Inc., Chemists, Microbiologists, Engineers, 4101 N. Figueroa Street,

Los Angeles, Cal . 90065.

He believes that friction between the shoe and the floor is only

one of many factors that relate to slipping and falling. He feels

that efforts to invent yet another new instrument for measuring

floor friction are not justified by the present state of the floor

74
slipperiness art. He implies that Truesdail uses the Sigler machine

with a value of u , >_ 0.3 indicating that the floor is not a significant contributor to slips and falls. He supports the use of ASTM,

D2047 with an attempt to correlate the results with actual falls.

This, of course, is hard to do since D2047 is not suitable for

field use. He recommends the use of the Sigler test as a field

test until some device is developed that is suitable for both

laboratory and field use. Believes that it is important to standardize on a field test method as quickly as possible so that all

interested parties will be using the same test method. He suggests

interim measures such as a high safety factor on required p until

more is learned in a scientific way. He cites the successful use of the British Portable Skid Tester for evaluating pavements as a demonstration of the value of a Sigler type machine. Finally he

notes that from their many investigations of slip and fall accidents

a large percentage occurred under circumstances other than normal

walking.

Thus it may well be necessary to evaluate a variety of stride

patterns and other maneuvers. He also listed such other factors in

the slip and fall equation as: condition and types of shoes and

materials; size, shape and stride of the individual; surrounding

environmental conditions; and the physiological and psychological

conditions of the individual at the time of the fall.

E-8 "Keeping Employees on their Feet," National Safety News, Sept.

1970.

Discusses safety of various types of shoe soles and shoe sole

materials including the squeegee shoe developed in France. Quotes

the significant results from D-23.

75
E-9 Rodstein, Manuel, MD, Accidents Among the Aged," 1963, National

Safety Council, 425 N. Michigan Avenue, Chicago, 111. 60611 4pp.

Falls of persons occur more frequently and have more serious

results, on the whole, than any other type of accident in com- mercial establishments. Then quotes the accident statistics from

D-13. Falls of persons on floors is an especially acute accident

problem in stores, hotels, restaurants, and theaters, because their

clientele frequently includes a large percentage of older persons,

and these older persons are usually more susceptible to serious

injury from this type of accident than are younger people.

E-10 Waters, E. H.; "Some Special Problems of Floor Design From the

Safety Aspect," Report No. L10, Division of Building Research Commonwealth Scientific and Industrial Research Organization, Commonwealth

of Australia, Melbourne, 1960.

A general description of floor hazards, including insufficient

slip-resistance and some general guidelines of what to do. No

mention of any quantitative way to evaluate slip-resistance.

E-ll Wilson, Angus F., Private Correspondence from Chief, Polymer Applications Group; Polymers and Organic Materials Br.; Materials Applications Division; Clothing, Equipment and Materials Engineering

Laboratory, U. S. Army Natick Laboratories, Natick, Mass.

Suggests that both static and dynamic friction should be measured,

under the range of loads likely to be encountered in real situations. Believes that testing must be a compromise between the

practical desire for a simple, reproducible test procedure and the

need for reproducing actual field conditions with all the variables

that are likely to be introduced. "As an example, our previous

testing showed that with compounds of 9 different base rubbers the

76
dynamic friction was higher on clean floor tiling then on concrete.

Our experience tells us this is not true. The addition of a layer

of dust to the tiles reverses the situation so that it is in accord

with our experience and more representative of reality. In my

opinion this aspect has not been properly taken into account in

most of the work that has been done on evaluation of floor slip

properties. The effect of water is often evaluated but this is

only one material found on floors. Selection of others, or mixtures of others, as representative of real situations is extremely

difficult, but I feel that it should be considered."

77
LEGAL ASPECTS OF THE FLOOR SLIP-RESISTANCE PROBLEM AND

THE PRESENT STATUS OF FLOOR SLIP-RESISTANCE SPECIFICATIONS

F-l Chemical Specialties Manufacturers Association, "CSMA Procedure for

Products Classified as to Slip Resistance" CSMA Bulletin #308-70,

December 8, 1928.

Adopts the value of y >_ 0.5 as the criteria to determine if a product should be classified as slip resistant, anti-slip, or terms of

similar import. Implies the use of the James machine to determine

y. Thus p = the static coefficient of friction.

F-2 CSMA Bulletin No. 245-70, July 22, 1970, Waxes, Polishes and Floor

Finishes Division

Exact same wording as F-24. Documents the passage of the tentative

Standard CSMA Test Method by the Wax Scientific Committee, the Wax

Executive Board, and the Board of Governors of CSMA at the 56th

mid-year meeting in May, 1970.

F-3 CSMA Bulletin No. 308-70, December 8, 1970. CSMA Procedure for

Products Classified as to Slip Resistant, signed by John D. Conner,

General Counsel & W. S. Jessop, Chairman Standards and Specifications

Appraisal Committee. Reports the adoption of the resolution on F24 by CSMA Board of Directors.

Quotes Rule 5 of the Proposed Trade Practice Rules for the Floor

Wax and Floor Polish Industry, published March 17, 1953.

This includes both the James Machine test with u >_ 0.5 and the

Sigler Test with y , >_ 0.4; actually the Sigler Test is referenced

first.

78
Then refers to section 5 of the FTC Act which prohibits any unfair

trade practice and points out that FTC never promulgated the proposed

rules in final form because the legal significance to have dbne so would be to make the rules evidence in a proceeding for violation

of Section 5 of FTCA of the practices which the industry considered

to be unfair. Although the proposed rules were not promulgated in

final form, they have been considered by the industry as broad

guidelines of acceptable practices.

Then claims that U.L. and CSMA certification procedures are the same except that U.L. demands that all tests be performed in their

laboratory and specifies the frequency. "If a member of the industry

wishes to make a claim that his product meets the CSMA standard, he

must assume the responsibility for conducting the necessary tests

to assure that the product does meet this standard. This testing

may be done either in independent testing laboratories or in companyowned laboratories, or in both." 'Then limits the wording of the

claim a manufacturer can use and presents several examples that are currently in use.

F-4 CSMA Tentative Method, "Comparative Determination of Slip Resistance

of Floor Polishes," CSMA Bulletin No. 245-70, July 22, 1970.

Presents the revised form of that on D-37.

Approved in Chicago May, 1969.

F-5 Doering, R. D., "Defining a Safe Walking Surface," National Safety News,

August 1974.

Some good references to the legal aspects of the floor slip-resistance

problem.

79
A yeoman effort to force the problem into a matrix formulation, not

very effective. A direct quote from D-35 on the mechanics of

walking and the importance of the angle between the heel and the

floor. A reference to the possibility of dictating the shoe in some cases such as for kitchen workers on wet-greasy quarry tiles.

A comparison of available Friction test instruments.

Referred to Federal Test Standard 501A Method 7121 for use of

Sigler Machine. Referred to D-35 "That a slipping condition does or does not exist according to whether the measured coefficient is

less than or greater than 0.40."

Studies time dependent degradation of surface of polyurethane

matrix and crushed glass as to y (Sigler), dry and wet, with and

without a sealer.

Test machines considered: Sigler, James, Frederik, Shot Bag, Topaka,

Horizontal Pull Slipmeter, Foot Evaluation.

F-6 Fed. Spec. RR-G-1602, July 10, 1970, Federal Specification Grating,

Metal, Other Than Bar Type (Floor, Except for Naval Vessels).

Specifies Antislip by including the following table. The equivalent

values of coefficient of friction have been introduced by the

author.

3.6 Friction when specified (see 6.2), the minimum friction for

foot traffic shall be as shown in Table II.

80
110# 0.76 105# 0.73

11 0# 0.76 95# 0.66

80# 0.55 75# 0.52

95# 0.66 75# 0.52

108# 0.75 95# 0.66

Table II Antislip values

Condition Minimum Antislip Values (pounds)*

steel u Aluminum y

Dry

Mud

Ice

Grease

Detergent

* Minimum force in pounds, acting to prevent a 145 lb. weight

from si ipping.

F-7 Federal Trade Commission, Washington; "Proposed Trade Practise Rules

for the Floor Wax and Floor Polish Industry." For release in morning

newspapers of Tuesday, March 17, 1953.

This is the only officially published version of these rules,

including Rule 5 "IMPROPER USE OF THE TERMS f SLIP RESISTANT», 'SLIP

RETARDANT,' 'ANTI-SLIP,' ETC."

"It is an unfair trade practise to use the terms 'slip resistant, 1

'slip retardant,' 'anti-slip,' or terms of similar import, as descriptive of any industry product which does not contain slipresistant properties sufficient to assure that a floor surface to

which the product is applied will be substantially safe for walking.

"Note : Subject to the development and acceptance of improved testing

methods, either of the following tests with resultant coefficients

of friction may be employed for the purpose of determining compliance

with this rule:

"(1) A coefficient of friction of not less than 0.40 as determined

by averaging the results of four separate Sigler tests of different

areas of the surface. The Sigler test shall be made at room temperature (73 1/2° + 2°F.) with relative humidity of 50% + 4%. Four

81
tests shall be made using a leather test piece of hard, firm, sole

leather conforming to Federal Specification KK-L-261c (leather;

sole, vegetable-tanned, factory) except that the compressibility of

the leather shall be restricted to 6% + 2%."

(2) A coefficient of friction of not less than 0.05 as determined

by the test for slip-resistance as used by the Underwriters' Laboratories, Inc., at the time of promulgation of these rules.

This rule is preceded by: Rule 4 - IMPROPER USE OF THE TERMS "SLIPPROOF," "NON-SLIP," "NON-SKID," ETC.

"In the sale, offering for sale, or distribution of any industry

product it is an unfair trade practice to use the terms 'slip

proof,' 'non-slip 1

, 'non-skid,' or terms of like import, as descriptive of such product unless it will completely prevent slipping on any floor surface to which it is applied for the duration of the

product thereon."

Note . It is the judgment of the industry that no industry product of

present commercial manufacture is qualified to be designated as "slip proof," "non-slip," or "non-skid."

A notice of hearing and of opportunity to present views, suggestions, or objections to these proposed rules appeared on page 1513 of the

Federal Register, Tuesday, March 17, 1953.

F-8 Merscher, John H. "The 1972 Revision of ASTM Standard Method of

Test for Static Coefficient of Friction of Polish Coated Floor

Surfaces as Measured by the James Machine." Presented at C.S.M.A.

Meeting, December 1972.

Describes differences and similarities of ASTM D21 & Scientific

Committee of CSMA's Wax Division. There has been close cooperation

since the organization of D21 in 1950.

82
Describes the development of D2047-72, particularly the improvement

and limitations of the James machine and the limitations of other

tests for slip-resistance.

F-9 Messner vs. Webb's City, Inc., Florida, 62 SO. 2D; 66, 67. (See

Hall vs. Holland, Florida. 47 SO 2D;889).

The rule is that the owner of premises is charged with the duty of

exercising ordinary care to keep his premises in a reasonably safe

condition for the purposes to which they are adapted. He is responsible for injuries to his invitees due to latent or concealed

perils, known to him or which in the exercise of reasonable care,

should have been known to him and which were by the invitee unknown

or by the exercise of due care could not have been known to such

invitee, and, of course, in the absence of a warning by the owner

as to such dangers.

F-10 MIL-D-0016680C (SHIPS) Military Specification for Deck Covering

Magnesia Aggregate Mixture. Has a section 4.5.9 Non-slip properties

which is similar to section 4.5.8 of MIL-D-18873B (see F-ll) except

that the oil to be used is SAE10W and the load to be applied uniformly

over a 2 by 4 inch specimen is 22 pounds.

F-ll MIL-D-18873B - Military Specification for Deck Covering Magnesia

Aggregate Mixture.

"3.10 Nonslip properties. The covering shall show coefficient of

friction not less than that shown in table I when tested as specified

in 4.5.8 and after 1,500 revolutions of the wear test machine

specified in 4.5.9.1

.

83
Table I. Nonslip Properties

Contacting surface conditions

Dry Wet Oily

Coefficient of static friction

Leather 0.30 0.50

Rubber 0.60 0.60 0.50

Coefficient of sliding friction

Leather 0.30 0.40

Rubber 0.60 0.60 0.30

"4.5.8 Nonslip properties. The coefficient of friction of the deck

covering against leather and rubber respectively, shall be determined

The leather shall be oak-tanned sole leather which has been sanded

smooth with grade garnet paper. The rubber shall be a vulcanized

compound with a hardness range of 60 to 80 durometer 'A

1 . Tests

shall be made with the contact surface dry, wet with a solution of

4 percent sodium chloride in water and oiled, using oil conforming

to Symbol 3042 of Specification MIL-L-15016. A load of 33 pounds

shall be applied uniformly over the 2 by 4 inch specimen. The

determination of static and sliding friction may be made by the

inclined plane method or by determining the pull on a spring balance

required to start the test piece from rest and then to maintain a constant velocity. The factor of friction shall be the average of

four readings."

F-12 MIL-D-3134F Military Specification for Deck Covering Materials.

"3.11 Nonslip properties - When tested as specified in 4.7.6, the

deck covering shall show factors of friction not less than shown in

Table I.

84
Table I - Factors of Friction

Contacting Factor of static Factor of sliding

Surface friction condition friction condition

Dry Wet Oily " Dry Wet Oily

Leather 0.60 0.50 -- 0.30 0.40

Rubber 0.60 0.70 0.30 0.40 0.70 0.10

"4.7.6 Nonslip properties Two specimens 2 by 4 inch prepared as specified in 4.7.1 shall be used ..." The rest of this is similar

to section 4.5.8 of MIL-D-18873B (See F-ll).

"4.7.1, Preparation of Specimens - Specimens of the sizes as specified in the following tests shall be made by preparing the deck

covering in accordance with the manufacturer's instructions. The

deck covering shall be troweled on 1/8 inch thick clean steel

plates to a thickness of approximately 1/4 inch. The specimens

shall be allowed to cure for 96 hours at room temperature before

conducting tests.

"Type I materials shall be ground smooth with a power sander using

No. 60 paper without water, unless the manufacturer specifies

another abrasive paper or procedure. All tests shall be conducted

under atmospheric conditions at a temperature of 70° to 75° Fahrenheit^), and a relative humidity of 50+2 percent. For specimens

intended for immersion tests where corrosion of the steel may

occur, areas not covered by the deck covering compound, except the

1 inch strip specified in 4.7.15 may be protected by a suitable

anti -corrosion coating."

F-13 Report of Committee D-21 on Wax Polishes and Related Materials,

Presented at the Fifty-fourth annual meeting of ASTM, June 18-22,

1951.

85
Under subcommittee IV on Performance Tests is the first mention in

ASTM of the James Tester. It is referred to as the UL machine and

a cooperative test program was in progress to "investigate the

usefulness of the Sigler Pendulum Impact machine and UL machine for

determining the slip resistance of waxed floors."

F-14 Report of Committee D-21 on Wax Polishes and Related Materials -

1961 Proceedings of ASTM.

Announced that subcommittee IV on Performance Tests "is completing

a revision of the proposed method of test for static coefficient of

friction of waxed surfaces, which was published in 1954 as information

only."

John Merscher in F-8 states that there is no news of the next three

years but it was finally approved as a tentative method in 1964,

after 10 years.

F-15 Report of Committee D-21 on Wax Polishes and Related Materials -

1966 Proceedings of ASTM

Established policy of submitting all standards of Committee D-21 to

the American Standards Association for approval as American Standards.

F-16 Report of the Scientific Committee 50th Annual Meeting CSMA, Dec.

10, 11, 12: 1963.

Written by Perry, Lloyd H.

States that a new subcommittee on Slip Testing was established

under Herb Green to: (a) establish limitations for present test

methods of measuring slip; (b) explore possible new approaches that

may be used for measuring this.

86
F-17 Report of Waxes and Floor Finishes Division Proceedings of CSMA

39th Annual Meeting. December 8 & 9, 1952.

Division Chairman D. M. King reported "that there has been formed a group which has met with Mr. Fitzsimmons of the UL to help develop new test methods for slip resistance. This group last met in

September and has made considerable progress although there is

nothing yet that they are ready to disclose. That is not of course

a CSMA -function. Issuance of any results of the work of this group

will come from the UL group rather than from this body." In F-8

Merscher reports that as of Dec. 1972 there was still nothing that

they were ready to disclose.

In a sub report by Dan Schoenholz the James Machine is discussed

with particular reference to the difficulty of getting a standard

piece of leather that works properly. To get two or more pieces of

leather to behave in a similar fashion may require checking as many

as 10 or 20 pieces.

F-18 "Shoe Sole Slipperiness Standard Status," Aug. 1974 National Safety

News.

Essentially a repeat of D-23.

F-19 Soap & Chemical Specialties, May 1971.

This journal contains an article "Candy Does Own Polish Slip

Resistance Testing" and an editorial referring to the article,

"Seal-an Alternative" that describes and publicizes how "A private

label floor polish manufacturer, who declined to renew his UL

contract after 25 years, has just announced a program of slip

resistance testing and reporting of his own. — Such a program is

a sensible alternative to what seems to us to be the high-handed

and uncompromising attitude adopted by UL."

87
Editorial mentions UL refusal to accept toxicity test results

performed by any other laboratory and their insi stance on rating

all aspects of the product to obtain the organization's seal.

F-20 "Standard Method of Test for Static Coefficient of Friction of

Polish Coated Floor Surfaces as Measured by the James Machine," ASTM

D2047-72, soon to be revised to ASTM D2047-75.

This specification defines the design and use of the James Machine.

The 1975 version will include the following additions:

"2. Applicable Documents

2.2 Other Standard

Proposed Trade Practice Rules for the Floor Wax and Floor

Polish Industry, issued March 17, 1953, by the Federal

Trade Commission.

"3. Significance

3.1 Floor polishes having a coefficient of static friction,

as measured by this method, of not less than 0.5 traditionally

have been recognized as providing nonhazardous walkway surfaces.

This value of not less than 0.5 meets the requirements for com- pliance to Rule 5 on the use of terms slip retardant, slip

resistant or terms of similar import of the Proposed Trade

Practice Rules for the Floor Wax and Floor Polish Industry as issued by the Federal Trade Commission on March 17, 1953."

F-21 Underwriter's Laboratory Re-examination Service - Floor Coating and

Finishing Materials, North Brook, 111. 60062.

F-22 "Waxed Floors Are Safe," a Panel Presentation presented before the

Waxes, Polishes and Floor Finishes Division, Chemical Specialties

Manufacturer's Association Inc., 47th Mid-year meeting, Drake Hotel

Chicago, 111., May 15, 16, 17, 1961.

88
This has become the "bible" of lawyers on floor slip cases.

1. "Legal Principles of Liability Resulting From Slippage on Waxed Floors," Conner, John D., "The Standard of care is

measured by the 'status' of the person who happens to be

on the premises." Highest = invitee, next = licensee,

lowest = trespasser. To be protected against possible

litigation one must consider the highest.

Owner can wax and polish floors but must exercise "reasonable

care"; that typical of a "reasonably prudent man." Must watch for: wax or polish build up, use of wrong material, floor not being

completely dry, improper use of wax and soap, etc.

2. "The Technical Aspects of Alleged Negligence from the Use of

Floor Wax," Steinle, J. Vernon.

Part I, a general discussion wherein it is claimed that "in general,

it can be stated that the coefficient of friction of waxed floors

as compared to the same floor covering unwaxed shows only small

differences. It is particularly noteworthy that in a wery large

number of cases the coefficient of friction for the unwaxed surface

is lower than for the same surface waxed, that is, the unwaxed

surface is slipperier."

Quotes ASTM D-21 from their published conclusions on the Significance

of Coefficient of Friction Measurements in Evaluating the Slip

Resistance of Floor Waxes. "It is now generally accepted by those

engaged in this study that machine measurements of the coefficient

of friction can not correlate in all cases with foot tests on the

floor or with safety in use.

89
"There are presently no standards of floor safety that can be expressed

in terms of accident frequency, coefficient of friction or subjective

foot tests in the field."

The UL labs of Chicago for many years used as their criteria for

inclusion on their list of "antislip materials" the requirement

that the u for the waxed surface be greater than y for the unwaxed

surface. More recently their listing included any material for

which m was greater than 0.5 when the material was applied to an asphalt tile. "Most commercial waxes are included on the UL list."

The Principal Factors involved in slipping and falling:

A The floor surface

1. y, floor vs. the sole of the shoe

2. Presence of foreign substances on the floor; water, trash, etc.

3. Condition or state of repair of the floor; presence of a ramp,

damaged or missing section of the floor covering.

B The individual's shoe

1. y - the sole of the shoe vs. the floor.

2. Presence of foreign substance on sole or heel of shoe.

3. Condition or state of repair of the shoe; spike heels,

run-down heels, etc.

C Physical features of the individual

1

.

Method of walking.

2. Distribution of forces.

3. Physical condition; lameness, etc.

D Mental condition of the individual

1. Sanity.

2. Psychology (most important, author) e.g. gloss = slipperiness

in the minds of many.

3. Proneness to accidents.

90
Check list for floor maintenance

1. Follow directions of manufacturer of any product used."

2. Keep traffic off a freshly waxed floor till it is dry

and/or pol ished.

3. Wax the entire floor; for psychological reasons.

4. Use the right kind of wax for the floor involved.

5. Do not wax ramps or stairs; again psychological.

6. Do not use heavily oiled mops on waxed floors.

7. Do not wax outside surfaces which are exposed to

ra i n

.

Also

1. Keep floors clean and dry and free of all foreign matter.

2. Post warnings of any existing danger.

3. Keep floors well lighted.

4. Inspect and maintain all floor areas regularly.

Check list for floor safety

1

.

Walk -- don' t run.

2. Face in the direction you are walking.

3. Be extra cautious on waxed f.loors.

4. Don't read while walking.

5. Keep to the right of center in corridors.

6. Keep far to the right in turning corners, especially

blind corners.

7. Enter corridors from offices, stairways and elevators

with caution.

8. Don' t crowd or push.

9. Avoid horseplay.

10. Wear a practical type work shoe.

Part II of paper

A checklist for expert witnesses

Part III of paper

1. The attitude of the manufacturer to alleged negligence

due to waxing floors.

2. Pointers for the expert witness.

F-23 "Write to Cancel U.L. Contracts," an editorial in Soap and Chemical

Specialties, Dec. 1970.

91
Describes the "new" U.L. contract as "calls for 'classification' of a product unless all of its safety aspects, including slip-resistance,

are checked by U.L. If a product is merely 'classified' as to

slip-resistance, it cannot be 'listed' and bear the U.L. seal. The

new contract for a listing also involves agreeing to unannounced

factory inspections, delisting without a hearing, and a greatly

increased contract fee."

Then suggests that manufacturers must take positive steps to drop

their contacts or they will legally remain in force, that many of

the large manufacturers are dropping and suggest that there is no reason not to drop.

F-24 Zdanowski , R. E., Report of the Scientific Committee, - Waxes,

Polishes and Floor Finishes Division - Proceedings of CSMA 56th

mid-year meeting, May 17-20, 1970.

Report of subcommittee N, by Chairman Arthur Blake, adoption by

unanimous vote "that CSMA adopt as the tentative Standard CSMA Test

Method, ASTM D-2047-69( . .

. ) with the further provision that any

floor polish when tested by this method and has a static coefficient

of friction equal to or greater than 0.5, may be considered to meet

the requirements of Rule 5 (improper use of the terms 'slip resistant,' 'si ip-retardant, ' 'anti-slip,' etc.) of the proposed Trade

Practice Rules for the Floor Wax and Floor Polish Industry as published by the Federal Trade Commission on March 17, 1953."

Cognizance was made of the fact that the precision of the method is + 0.05. The method has subsequently been approved by the Scientific

Committee, The Executive Board of the Waxes, Polishes and Floor

Finishes Division and finally by the Board of Governors. It is now ready to be bulletinized as a tentative standard CSMA procedure.

92
BASIC PRINCIPLES OF FRICTION

G-l Amontons, M. "De La Resistance Causee dans Les Machines"

Histoire de L'Academie Royal e des Sciences , p. 206 (1699).

Early effort to measure friction by measuring F and N directly and then calculating F/N = y

Or see "Memoires de Mathematique et de Physique" 1699 pp 259-286.

G-2 Bowden, F. P. and Leben, L. "The Nature of Sliding and the Analysis

of Friction." Proceedings of the Royal Society of London, Eng. Vol.

169, 1938-1939, pp. 371-391.

A fundamental paper on friction (dynamic) between "clean" metals,

similar and dissimilar. Use of a carefully designed tester to

eliminate dynamic effects found sticks! ip occurring; violent for

dissimilar metals and more subdued and regular for similar metals.

Found signs of localized welding and tearing of the surface so that

sliding involves material below the surface and is not just a surface phenomenon, even when lubricated. Temperature measurements

showed a wild fluctuation of surface temperature during sliding

with a sudden temperature "flash" at the instant of slip. The

exact behavior depends upon the relative physical properties of the

metals, particularly on the melting point, and there is evidence

that three distinct types of sliding may occur, relating to three

distinct types of metallic junctions. "The detailed analysis of

the frictional force shows that the classical laws of friction can

be regarded only as crude approximations. Earlier theories have

assumed that sliding is continuous and that only the surface atoms

of the solid are involved. It is clear that neither of these

assumptions is correct."

93
G-3 Bowden, F. P. and Tabor, D., The Friction and Lubriction of Solids , Parts I and II, Oxford at the Clarendon Press, 1964.

This is a monumental treatment on the subject of friction and

contains a particularly complete treatment of the history of the

subject. Not too surprizingly most of the material is on friction

between two metallic surfaces, with particular emphasis on the

effects of lubricants. There is material on the friction of wood

and of lubricated rubber, but there is very little data relating

directly to shoe and flooring surfaces. Chapter XXIV, "Some Early

Work on Sliding and Rolling Friction," traces the history of the

understanding of friction, starting with the Egyptians, as early as 1900 B.C., and extending up to modern times.

G-4 Conant, F. S. and Liska, J. W., "Friction Studies on Rubberlike

Materials." Rubber Chem. Technol. 33,1218 (1960).

Extends the work of Bowden and Tabor (G-3) to rubber and rubberlike materials. A \/ery comprehensive paper including an extensive

bibliography, 165 items. Indicates that for the pressure and

velocities likely to occur in normal walking the "laws" of Amontons

and Coulomb are likely to hold reasonably true.

G-5 Coulomb, C. A. "Theory of Simple Machines," Memoire de L'Academie

Royale Sciences , Vol. 10, p. 161 (1781).

First well-known systematic compilation of values of y.

G-6 Ernst, H. and Merchant, M. E. "Surface Friction of Clean Metals - A

Basic Factor in the Metal Cutting Process." Proceedings on Friction

and Surface Finish, MIT, June, 1940, pp. 76-101.

94
G-7 Gomer, Robert and Smith, C. S. Structure and Properties of Solid

Surfaces, A conference arranged by the National Research Council,

Lake Geneva, Wisconsin, Sept. 1952. The University of Chicago

Press, 1953. A series of papers with chapter VI "The Adhesion of

Solids" by F. P. Bowden and P. Tabor being of most interest to

floor slip-resistance investigators.

"Although these adhesive forces (at junction of asperities) are very strong, the normal adhesion between surfaces that have been

pressed together is usually very small. This is due mainly to the

effect of released elastic stresses or other types of stress concen- tration which rupture the junctions as the joining load is removed.

For this reason frictional measurements may provide more information

about the nature of surface adhesion than the direct measurement of

adhesion itself.

"In some cases liquid films produce strong adhesive forces between

solid surfaces, but these are essentially due to surface tension

and viscous forces. On the other hand, contaminant films which

separate the surfaces by more than a few angstroms can produce a profound reduction in the adhesion. In the limit, if the surface

film completely prevents solid-solid interaction, the adhesive

strength at the interface is primarily determined by the strength

of the contaminant film itself."

G-8 Graf, Otto Handbuch der Werkstoffpriifung , Vol III, 2nd. Ed.,

Berlin, Chapter XXII (1957).

G-9 Moore, D. F.; "A History of Research On Surface Effects," WearElsevier Sequoia S. A., Lausanne, 13(1969) 381-412.

"A historical survey of surface texture effects ranging from pipe

flow roughness factors to molecular roughness concepts is presented.,

95
— Techniques for measuring surface features are classified according to whether the scale of roughness lies in the macro-or micro

roughness ranges, and the methods are tabulated. —It is suggested

that at least five parameters are required to uniquely and completely

specify surface features in the general case. The effects of

texture design on adhesion, hysteresis, lubrication and squeeze

films are given, and the subject of macro-el astohydrodynamics has

received special emphasis, —." This paper has an extensive bibliography, 83 items.

Moore indicates that the interaction between two surfaces, for

example friction, is intimately related to the surface texture of

the two surfaces and to how they are affected by any intervening

foreign material, such as a lubricant. Most of the work to date

has been confined to pairs of rigid surfaces, such as metals, but

resilient surfaces, such as leather, rubber, linoleum etc. are also

of interest, where the surface is likely to deform under the normal

pressures present. He goes on to discuss some of the techniques

that have been used to evaluate the surface character of a variety

of materials, demonstrating that there is much yet to be learned of

surface features and that the learning will require considerable

experimental effort.

G-10 Rabinowicz, Ernest; "Stick and Slip," Scientific American, May 1956,

Vol 194, No. 5.

A popularly written article that outlines the historical development of our knowledge of friction and how our improved knowledge

has resulted in an understanding of stick slip. "The two types of

force that are met most frequently in mechanics are gravity and

friction. The former has been studied by great men of science in

e^jery age. The latter has been largely neglected, it being assumed

that the sliding process holds little intrinsic interest and that

96
three simple laws, all discovered before 1800, adequately describe

the force of friction. —-The three laws describing the force of

friction say that when one solid body slides over another thefrictional force (1) is proportional to the load, or pressure of one against the other, (2) is independent of the area of contact,

and (3) is independent of the sliding velocity. The first two laws were stated by Leonardo da Vinci and rediscovered in the 1690' s by

Guillaume Amontons, a French engineer working under the sponsorship

of the French Royal Academy of Sciences. The third law was first

expressed in 1785 by Charles Augustin de Coulomb, the French physicist better known for his researches in electrostatics.

"If the three laws are correct, friction depends only on the applied

load, and the coefficient of friction (the ratio friction-force-toload) for any given materials should be constant under all conditions

The first two laws generally hold true, with no more than 10

percent deviation. But it has been known for some time that friction

is not independent of sliding speed. The coefficient of friction

between two bodies may vary as much as 30 to 50 percent according

to the speed of motion. In 1835 0. Morin of France proposed that,

since the frictional force resisting the start of sliding for two

bodies at rest was obviously greater than the resistance after they were in motion, there should be two coefficients of friction: a static one, for surfaces at rest, and a kinetic one, for surfaces

in motion. Today, as a result of work by a number of investigators, we know that both the static and the kinetic coefficients themselves vary. The kinetic coefficient drops off as the sliding

speed increases. And the static coefficient depends to some extent

on the length of time the surfaces have been in contact. —Thus

the only satisfactory way to represent the friction coefficient for

any pair of surfaces is by two plots, one of the static coefficient

as a function of time of contact, the other of the kinetic coefficient as a function of sliding velocity.

97
" —In any adhesive process the bond becomes stronger the longer it

is left undisturbed. This is why the static coefficient of friction

increases with time of contact. In the case of sliding surfaces,

the period of contact between points on the two surfaces is, of

course, longer when the surfaces slide slowly than when they move

rapidly. Consequently, if the slide of one surface over another

slows down, friction increases. This is the situation that favors

stick slip. However, laboratory tests have developed the unexpected

finding that at extremely slow speeds the situation is reversed: as friction increases the sliding velocity also increases." He ascribes

this to creep. "These considerations present us with the paradoxical conclusion that there is really no such thing as a static

coefficient of friction for most materials. Any frictional force

applied to them will produce some creep, i.e. motion." The author

presents four graphs of friction versus velocity that depict the

evaluation of the friction concept from the late 18th century up to

the present. These graphs are duplicated in the body of the paper.

G-ll Swindells, A., "Simple Instrument for Measuring Friction,"

Journal of Scientific Instruments, Vol. 28, No. 7, July 1951.

An ingenious little device for measuring dynamic coefficient of

friction between a plate and the rounded tip of a rod. Not suitable for slip-resistance of floors. The plate must be inclined at some angle with respect to the horizontal and then pulled along one of its horizontal edges.

6-12 Tomlinson, G. A., "Moleculer Theory of Friction," Philosophical

Magazine, Vol. 7, series 7, pp. 905-939.

98
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100
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101
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Surface Finish, MIT, June 1940, pp. 76-101.

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Friction Measurements," ASTM Bulletin, Sept. 1958.

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1938, 17, 447-451, N:r 39 1938. Innehall; Investigations of

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44th Mid-year Meeting Proceedings of the Chemical Specialties

Manufacturer Association Inc., N.Y., May 1958.

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102
D-14 Gavan, F. M., Discussion of C. H. .Irvine Paper, "A New Slipmeter for

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D-15 Gavan, F. M. & Vanaman, J. B. , "Significant Variables Affecting Results

Obtained with the James Friction Machine, "< Materials Research & Standards, Vol. 8, No. 11, November, 1968.

D-16 Giles, C. G.; Sabey, B. E.; and Cardew, K. H. F. "Development and

Performance of the Portable Skid Resistance Tester." Rubber Chem.

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G-7 Gomer, Robert and Smith, C. S. Structure and Properties of Solid

Surfaces, A Conference arranged by the National Research Council,

Lake Geneva, Wisconsin, Sept. 1952. ! The University of Chicago

Press, 1953. A series of papers with chapter VI "The Adhesion of

Solids," by F. P. Bowden and P. Tabor being of most interest to

floor slip-resistance investigators.

D-17 Gough, V. E., "Simple Direct-Reading Friction Meter," Journal of

Scientific Instruments, Vol. 30, No. 10, October, 1953.

G-8 Graf, Otto, Handbuch der Werkstoffpru'fung , Vol. Ill, 2nd Ed., Berlin,

C h a p te r XXII (19571.

D-18 Gurney, S. W. , "Is the Floor too Slippery?" National Safety News, 1940,

Aug. 22.

E-4 Gutt, W. Private correspondence from Department of the Environment,

Building Research Establishment, Building Research Station, Garston,

Watford, WD2 7JR.

B-8 Harper, F. C; Warlow, W. J.; and Clarke, B. L. "The Forces Applied to

the Floor by the Foot in Walking," National Building Studies

Research Paper #32, Department of Scientific and Industrial Research

Building Research Station, London 1961.

D-19 Hartley, Owen, "How to Use a Floor Slip Tester", The Executive Housekeeper

Vol. 15, No. 11, Dec. 1968.

E-5 Heath, Arthur L. Private correspondence with Associate Director,

Myodynamics Laboratory, The University of Rochester, School of

Medicine and Dentistry and Strong Memorial Hospital, 260 Crittenden

Boulevard, Rochester, N.Y. 14620.

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Walking," Aust. J. App. Sci., 1953, 4(3) 405.

103
E-6 Hopkins, S. K. "Elusive Factor in Falls: The Shoe Sole," National Safety

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Road Research Laboratory, London: Her Majesty's Stationery Office:

1960.

D-22 Irvine, C. H. "A New Slipmeter for Evaluating Walkway Slipperiness,"

Materials Research and Standards, MTRSA, Vol. 7, No. 12, Dec. 1967

pp. 535-541.

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Los Angeles, Cal . 90065.

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Chemicals, Oct. 1944.

D-25 Johnson, Bayard S., "A Discussion of Some Factors Influencing Slip

Resistance Measurements," CSMA, Proceedings of the 44th Midyear

Conference, May 1958.

E-8 "Keeping Employees on their Feet," National Safety News, Sept. 1970.

D-26 Kellett, P. H. "Modern Solings in Wear," SATRA Information Publication

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104
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Aggregate Mixture.

F-ll MIL-D18873B - Military Specification for Deck Covering Magnesia

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Products Co., 264 Park Ave., N. Caldwell, N.J. 07006.

D-29 Modern Sanitation and Building Maintenance , Vol. 11, No. 7, p. 6 (1959).

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Sequoia S. A., Lausanne, 13 (1969) 381-412.

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Surfaces," Oct. 1, 1949 - Mar. 31, 1950.

D-31 "Proposed Method of Test for Measuring the Static Coefficient of Friction

of Waxed Floor Surfaces," and "Proposed Method of Test for Measuring

the Dynamic Coefficient of Friction of Waxed Floor Surfaces," ASTM

Bulletin, No. 196, Feb. 1954.

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194, No. 5.

C-20 Rehman, I. (1947) - Arch. Phys. Med. 28:749-56.

F-13 Report of Committee D-21 on Wax Polishes and Related Materials,

Presented at the Fifty-fourth annual meeting of ASTM, June 18-22,

1951.

F-14 Report of Committee D-21 on Wax Polishes and Related Materials - 1961

Proceedings of ASTM.

F-15 Report of Committee D-21 on Wax Polishes and Related Materials - 1966

Proceedings of ASTM.

F-16 Report of the Scientific Committee 50th Annual Meeting CSMA, Dec. 9, 10,

11, 12: 1963.

F-17 Report of Waxes and Floor Finishes Division Proceedings of CSMA 39th

Annual Meeting. December 8 & 9, 1952.

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105
E-9 Rodstein, Manuel, MD, "Accidents Among the Aged," 1963, National Safety

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Covering," ASTM Bulletin No. 247, July 1960.

A-3 Schuster, K. "Slip - An Investigation of Practical Accident Prevention,"

Die Berufsgenossenschaft/Betriebssicherheit/September 1966.

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of Recording Gait," Archives of Surgery, Nov. 1933, Vol. 27.

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National Bureau of Standards, Building Materials and Structures

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D2047-72, scon to be revised to ASTM D2047-75.

106
C-25 Steindler, A., "Mechanics of Normal and Pathological Locomotion in Man,"

by Arthur Steindler, M.D. F.A.C.S., Professor of Orthopedic Surgery,

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D-37 "Tentative Test Method for Qualitative Determination of Slip Resistance

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Vol. 7, series 7, pp. 905-939,

F-21 Underwriter's Laboratory Re-examination Service - Floor Coating and

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F-22 "Waxed Floors Are Safe," A panel presentation presented before the Waxes,

Polishes and Floor Finishes Division, Chemical Specialties Manufacturer's Association Inc., 47th Mid-year meeting, Drake Hotel,

Chicago, 111., May 15, 16, 17, 1961.

D-38 Weirich, C. L., "Static Coefficient of Friction, Significance of Test

Results," Clarence L. Weirch, presented before the CSMA, May 1958.

D-39 Williams, W. D., Smith, J. A. and Draugelis, F. J. "T0PAKA, A New Device

and Method for Measuring Slip Resistance of Polished Floors," Soap/

Cosmetics/Chemical Specialties, July 1972.

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Soles and Heels," Rubber World, March 1972.

107
E-ll Wilson, Angus F. Private correspondence from Chief, Polymer Applications

Group; Polymers and Organic Materials Br; Materials Applications

Division Clothing; Equipment and Materials Engineering Laboratory.

U.S. Army Natick Laboratories, Natick, Mass.

F-23 "Write to Cancel U.L. Contracts," an editorial in Soap and Chemical

Specialties, Dec. 1970.

F-24 Zdanowski , R. E., Report of the Scientific Committee - Waxes, Polishes

and Floor Finishes Devision - Proceedings of CSMA 56th mid-year

meeting, May 17-20, 1970.

108
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. DIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS TN-895

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

An Overview of Floor Slip-resistance Research with Annotated

Bibliography

5. Publication Date January 1976

6. Performing Organization Code

7. AUTHOR(S)

Robert J. Brungraber

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as 9.

13. Type of Report & Period Covered Tech Note

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary ol most significant information. If document includes a significant bibliography or literature survey, mention it here.) Slips and falls in the home as well as in public buildings have reached serious

proportions (8,000,000 accidents per year in the home, resulting in 9,600 deaths

and 1,600,000 disabling injuries). This paper reviews the literature relating

to this problem. Based on studies of kinesiology and anthropometry, the coefficient

of friction between foot surfaces and floor surfaces is found to be a significant

parameter controlling slips and falls. A review of the general study of friction

and a critical appraisal of methods for determining the coefficient of friction

on slip-resistance of floors leads to a guide for selection of slip-resistance

criteria. The paper concludes with a discussion of the legal aspects of the problem

and the present status of slip-resistance specifications.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Building safety; floor surface friction; occupancy safety ; slip-resistance;

slip-resistance testers; walking friction.

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