NBSIR 73-137 ^)

Systematic Analysis of Meciianical

Hazards from Toys

Bal M. Mahajan

Consumer Product Systems Section

Measurement Engineering Division

May 23, 1973

Final report 07/72 - 02/73

Prepared for Bureau of Product Safety

Food and Drug Administration

Bethesda, Md. 20016
I
NBSIR 73-137

SYSTEMATIC ANALYSIS OF MECHANICAL

HAZARDS FROM TOYS

Bal M. Mahajan

Consumer Product Systems Section

Measurement Engineering Division

May 23, 1973

Final report 07/72 - 02/73

Prepared for Bureau of Product Safety

Food and Drug Administration

Bethesda, Md. 20016

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

ABSTRACT

The information necessary to establish criteria for differentiating

between hazardous and non-hazardous toy components consists primarily of (1) levels of severity beyond which mechanical injuries are

unacceptable, (2) knowledge of various injurious objects that may be

found as toy components and their injury potential and (3) the reasonable ranges of loading conditions for various child-toy interactions.

Mechanical injuries are described and classified into six levels

of severity, and a procedure to decide on the level of severity beyond

which injuries are unacceptable is suggested.

The various injurious objects that may be found as toy components

and loading mechanisms probable from various child- toy interactions are

identified. Some of the procedures for determining the injury potential of such objects are outlined.

Pertinent studies required to obtain other needed information

are recommended.

TABLE OF CONTENTS

Page

INTRODUCTION 1

BACKGROUND 1

MECHANICAL INJURIES 4

Descriptive Classification 4

Severity Classification 9

INJURIOUS OBJECTS 12

LOADING MECHANISMS 13

INJURY POTENTIAL ..... 15

HAZARD CRITERIA 24

CONCLUDING REMARKS • • 26

REFERENCES 28
LIST OF FIGURES

Figure No. Page No.

1 Typical cross-section of human skin. 31

2 Schematic cross-section of human skin. 32

3 Schematic representation of loading

condition which may lead to lacerations. 33

4 Schematic loading which may lead to

penetrations. 34

5 Various loading mechanisms, injurious

objects and probable resulting injuries, 35

6

" Geometric characteristics. 36

7 Postulated experimental injury threshold

curve for lacerations by points. 37

8 Postulated experimental injury threshold

curve for laceration by edges. 38
LIST OF SYMBOLS

A contact area

B bulk modulus = E/3(1-2V) of skin tissue

C compressibility = 1/B of skin tissue

D base diameter or base dimension of interacting object

E modulus of elasticity of skin tissue

F force

g geometric variables of interacting object

G shear modulus of elasticity of skin tissue

h height above the supporting surface of projection, point or edge

I. P. imjury potential

K.E. kinetic energy

1 length of v;ound

Lo initial gage length

L final gage length

M mass

P pressure = F/A

Pr^^ properties of injurious object

Pr^ properties of human tissue

r tip radius of sharp point tip

s resistance to shearing or cutting

T thickness of skin tissue

t contact duration
velocity

modulus of resilience = ^ /2E = ^o eo /2

energy absorbing distance or resilience distance of skin

tissue with the backing material intact

tip included angle or angle of impact

elastic limit strain

stress F/A

elastic limit stress

viscosity

Poisson's ratio

roughness of edge

Subscript

1 interacting object _ /

2 human body and its various tissues

n normal component

h horizontal

elongation or extensibility
Systematic Analysis of Mechanical Hazards from Toys

INTRODUCTION

This study was undertaken by the Consumer Product Systems Section

in support of the Toy Safety Program of the Bureau of Product Safety,

Food and Drug Administration. The objective of this study was to

recommend pertinent procedures and studies required to obtain information necessary for establishing criteria to differentiate between

hazardous and non-hazardous toys or toy components so that mechanical

hazards can be minimized.

For the purpose of this study a mechanical hazard* may be defined

as any toy, toy component, or product that presents a risk of unacceptable mechanical injury during normal use or reasonably foreseeable

abuse (or misuse) of the toy. Mechanical injury is the injury likely

to be inflicted on the human body by any type of mechanical loading.

Whether an injury is acceptable or unacceptable is determined primarily

by its severity. The severity of injury is dependent upon many factors

and is discussed in the section entitled Mechanical Injuries.

BACKGROUND

Many investigations have been conducted over the past three

decades to study the biophysical response of the human body to various

types of mechanical loadings. Human tolerance to the applied loads

have been variously defined and different researchers have established

different end points as criteria. Several methods to measure, calculate and estimate human tolerance have been devised. These methods

^Hazards resulting from performance failure of toys are not included

in this study.
- 2 -

utilize data from sources such as clinical reports of accidents,

experiments with cadavers, living animals and human and animal

tissue in vitro, and mathematical and mechanical models. Each contributes to our overall knowledge, although each, by itself, presents

problems and imperfections.

A number of attempts have been made to bring human tolerance

data together into summary form in order to permit predictions of

ranges of injury for any specified mechanical loading condition. An

excellent discussion of the subject and a comprehensive list of

references may be found in papers by Snyder \J and 2/, VonGierke 3/,

and Benjamin et al. kj , Also, some injury scales have been developed

to provide a universal means of assessing and evaluating human tissue

damage _5 / , 6^/, l_l , and 8^/. Nearly all of these developments fall short

of their intended objectives, primarily because the weight given in

each respective criterion varies significantly in individual judgements.

Unfortunately, until all the parties (or individual researchers) concerned agree with each other, diversity of subjective elements cannot

be eliminated.

The injury criteria and threshold or tolerance limits established

by these studies may not be applicable to the Toy Safety Program

because most of these studies were mainly concerned with impacts which

occur in vehicular accidents and in some other loading conditions

which do not relate to toys. However, data from some recent papers ^/

to 15 / and some recent studies 16 / and Y}_l shed some light on the

injury process and provide some information on the biomechanical properties of human tissue.
- 3 -

During the past few years mechanical hazards associated with

toys were given a great deal of attention by the National Safety

Council, Toy Manufacturers Association, Underwriters' Laboratories,

etc. However, little research has been directed to the systematic

assessment of mechanical hazards from toys and to assess the injury

potential of various objects which may be found as toy components.

Recently some studies dealing with these subjects have been conducted

by the Consumer Product Systems Section, Product Evaluation Technology

Division of the National Bureau of Standards 18 / to 21/

For establishing safety regulations to minimize mechanical

hazards from toys (or consumer products in general) one should have

the information necessary to differentiate between hazardous and nonhazardous components of toys or products. The acquisition of such

information requires knowledge of injurious components of toys, the

injury potential of these components, and the level of severity beyond

which injuries are unacceptable. The injury potential of any object

is defined as the type and severity of injury such an object is capable

of inflicting on the human body for any probable loading condition.

The present study deals with these subjects. It describes and classifies mechanical injuries and suggests procedures to determine an

unacceptable level of severity. It identifies most of the injurious

objects which may be found in toys and probable loading mechanisms

involving these objects. In addition, this report identifies the factors influencing the injury potential of injurious objects and

recommends pertinent procedures and studies to assess their injury

potential.
_ 4 -

v. ', ' " ; MECHANICAL INJURIES

Descriptive Classification

As stated in the Introduction, injuries inflicted on the

human body by any type of mechanical loading are termed mechanical

injuries. Because of the probable loading conditions (loading mechanism and load magnitudes) probable from various child- toy interactions,

most injuries sustained by children are injuries involving skin and

soft tissue damage and damage to the eyes. Impact loads under certain

conditions may also cause damage to the bone, ligament, muscle, tendon,

etc., and internal organs. However, impacts leading to these types

of injuries probably are less likely to occur under most forseeable

conditions. - • . ,

. .

This section of the report is an attempt to describe various

mechanical injuries and the damage mechanism responsible for producing

them. For this purpose, the mechanical injuries are placed in the

following three groups: 1) injuries involving damage to the skin and

adjacent soft tissue; 2) injuries involving damage to bones, ligaments,

muscles, etc.; and 3) injuries involving damage to the internal organs.

Injuries to the eyes will not be discussed in this report. Ocular

injury potential by blunt toy projectiles is discussed by Fischler

and Mahajan 18 /

Skin and Adjacent Soft Tissue Injuries

Injuries involving damage to the skin and soft tissue are described

below. (A typical cross-section of human skin is shown in Figure 1,

while Figure 2 shows a simplified schematic cross-section of human skin

required to define various levels of severity of skin injuries.)
- 5 -

Blisters . A blister represents collection of fluid in the

epidermis causing elevation of the horny upper layer and its separation from the underlying parts. A blister may be caused by pinching

and impact, but is often due to persistent friction.

Contusions or bruises . Contusions or bruises are superficial

injuries resulting from impacts that damage the soft tissue without

breaking the epidermis. A bruise may lead to blistering and swelling.

They are caused by excessive compressive loads with failure ranging from

crushed or torn tissue to vessel or nerve damage. Injuries of this

type usually result from impacts involving the human body and relatively

blunt objects. The severity of contusions varies depending upon their

location and other factors; but in general, they are not considered

serious.

Shallow lacerations . Lacerations represent tearing or cutting

of the skin. A laceration usually occurs when a sharp point or sharp

edge, pressing down on the skin, is pulled across the skin. The sharp

point or edge, by pressing down on the skin cross-section, pierces the

skin (probably by tension or shear) and starts the tearing process.

This type of loading conditions occur in such phenomenon as abrading

scraping, scratching, etc. Figure 3 schematically shows some loading

conditions that may result in laceration.

Penetration wounds . Penetration wounds are tissue damage caused

by either puncture or localized crushing of the skin and soft tissue.

Puncture is a piercing of the skin by a sharp object (such as a needle,

nail, etc.) when the applied load is essentially directed along the

longitudinal axis of a sharp point (see Figure 4) . The epidermis and
- 6 -

upper part of the dermis provide very little resistance to puncture.

Most of the resistance to puncture is provided by the fibrous part

of the dermis known as the reticular layer and 22/ (see Figure 2) .

Puncture injuries are discussed in a greater detail by McGuire and

Moore 19 /

. Penetration wounds caused by localized crushing of the skin and

soft tissue may be considered as contusion combined with lacerations

or punctures or both. This is so because in this type of injury the

insulting object breaks and penetrates the skin tissue while in contusion epidermis is not broken. Injuries of this type are probably

caused by a combination of excessive compressive stress and tensile

and shear stresses. These injuries usually result from impacts with

moderately blunt objects involving those parts of the body where

soft tissue is backed by bone. For example, a projectile impacting

the buttocks or stomach with energy just enough to cause a bruise may

penetrate the skin tissue by crushing when impacting the forehead,

elbow or knee with the same energy. This difference in the resulting

injury may be attributed to the following reasons: 1) the impact force

developed during impact with the forehead, etc., is greater than that

developed during impact with the buttocks or stomach, since the latter

locations provide a longer stopping distance; 2) the properties of the

skin vary with body location, with locations such as the forehead,

elbow and knee offering less resistance to puncture and laceration

than the buttocks and stomach. The information (data) concerning the

variations in the biomechanical properties of the human skin may be

found in references 17/, 19/ and 22/.
- 7 -

Injuries to Bone, Ligament, Muscle, etc.

Injuries Involving damage to the bone, ligament, muscle, tendon,

etc. are of numerous variety. Although these Injuries are mechanical

Injuries, their description is beyond the scope of this investigation.

This is so because a large variety of such injuries do not involve

mechanical hazards from toys. For example. Injuries such as sprains,

dislocations, pulled ligaments, muscles or tendons are usually caused by

unusual muscular efforts or movements.

However, some injuries, representing damage to these anatomical

body components, may be caused by Impact loads involving certain toys

and their injurious components. Some of these injuries are discussed

below.

Deep penetration wounds. Puncture of bones, muscles, etc. can

be caused by impact with a sharp point (or sharp projectile such as

a dart, arrow, etc.), when the impact velocity is essentially directed

along the longitudinal axis of the sharp point. Since the sharp point,

puncturing the bone, must first puncture the skin and soft tissue

covering the bone, the impact load (momentum) required to puncture the

bone is considerably larger than that required to puncture only the

skin. Such high momentum impacts probably are not likely to occur

under reasonable conditions. Therefore, the likelihood of such injuries resulting from child-toy Interactions is probably negligible.

Bone fracture. Fractures occur when the ultimate strength of

bone is exceeded. The applied load required to exceed the ultimate

strength of bones in vitro will vary with body location and thickness of

the soft tissue and skin covering them. Depending upon the contact area

during impact, bone fracture can occur by bending, compression or
- 8 -

shearing. For examplej Hodgson et al. 10/ , studying the fracture

behavior of the skull frontal bone against cylindrical surfaces,

found that for impacts with 10 ft/sec velocity the curved surface of

a 1-inch radius cylinder behaved as a blunt surface and produced

linear fracture (by producing excessive tensile stress due to bending)

while the curved surface of a 5/16 inch radius cylinder behaved more

like a sharp area surface and produced local elliptical fracture (by

producing excessive localized compressive or shear stress or both).

In most situations, bone fractures are accompanied by injuries

to skin and soft tissue. However, under certain loading conditions

bone fracture may occur without breaking the skin. For example,

Hodgson and Thomas 9^/ found, while dropping human cadaver heads against

several surfaces, that in a few cases involving a 10-inch drop onto a

flat plate, the skull was fractured with no apparent indication of

skin rupture. 'vj. ::v

Skull and facial bones are the most susceptable to fracture

because of their fragility and vulnerability, especially in automobile

accidents involving the instrument panel and windshield 23/

Injuries to internal organs . Injuries to internal organs can

include contusions, laceration, and ruptures arising from the various

types of stresses and strains produced by impacts to different parts

of the human body. Internal head injuries (brain damage) probably

occur more frequently than the injuries to other internal organs.

The most frequent causes of such injuries are vehicular accidents,

free falls, and impacts occuring in various sports.
- 9 -

Severity Classification

Mechanical injuries may be classified in a number of ways, but

classification by severity is best suited for the assessment of hazard.

Severity of injury inflicted on the human body is determined primarily by such considerations as the recoverability of damage, time of

rycovery, need of hospitalization, body part injuried, seriousness

of permanent disability if any, psychological factors, etc. However,

it is difficult to develop a universally acceptable injury classification because of the presence of subjective elements and the intended

use of the classification. For example, a wound that leaves a scar

on the forehead, face, or other parts of the body that normally is

not clothed may be considered by a cosmetologist to be of higher

severity than a similar wound that leaves a similar scar on the upper

arm, buttocks, or on those parts of the body which are normally

clothed

The classification of injuries based on severity considerations

given below may be used for the assessment of mechanical hazards from

toys and for the purpose of defining or establishing acceptableunacceptable types of criteria for various injurious objects. It

differs only slightly from the injury classification recently reported

by Mahajan 21/, but differs considerably from other injury classifications or injury scales _5/ , ^/ , IJ and 8^/ present in the literature.

Injuries involving damage to the skin and adjacent soft tissue make up

the first four of the six levels of severity of the injury classification.
- 10 -

Level 1

Insignificant Injury . Such injuries can cause considerable pain

and some tissue damage, such as blisters or bruises involving only

crushed or torn tissue. (Bruises involving vessel or nerve damage is

placed in the second category.) Injuries of this type do not provide

ease of entry to harmful bacteria and are fully recoverable.

Level 2

Slight injuries . Slight injuries include contusions involving

damage to vessels or nerves and injuries when the injurious object

completely damages the epidermis but barely damages the dermis by

lacerating, puncturing or crushing the tissue. These injuries (with

the exception of contusions) may cause slight external bleeding and

provide ease of entry to harmful bacteria. However, these injuries

heal easily and do not leave scars.

Level 3

Minor injuries . Minor injuries include those in which there is

damage to epidermis and dermis by lacerating, puncturing or crushing

of the tissue, but the damage does not extend beyond the reticular

layer of the dermis. These injuries will cause some bleeding and do

provide ease of entry to harmful bacteria which can cause tetanus, or

other infections. These injuries, however, heal easily but may leave

scars

Level 4

Moderate injuries . Moderate injuries represent damage to all

three layers of the skin (by lacerating, puncturing or crushing of

the tissue) . These injuries present all the problems described in
-lithe above category and in addition require a longer time to heal and

usually leave scars.

L^yel 3

Serious injuries . Serious injuries represent damage to ligament,

muscle, tendon, bone, etc. or contusion of various internal organs.

These injuries may require hospitalization for treatment, take a long

time to heal, and may leave some permanent disability.

Level 6

Critical injuries . Critical injuries include those in which

there is rupture or laceration of internal organs puncture of the eye,

contusion of vital areas such as the brain, amputation of a finger,

a toe or a limb. Such injuries require hospitalization, take a long

time to heal, and usually leave some sort of permanent disability.

Injuries of this type may result in fatality.

Unacceptable Level of Severity

The determination of level of severity beyond which injuries are

unacceptable is a highly controversial issue, primarily because

subjective factors must be included in the decision. Concensus of

opinion of physicians, parents, etc. obtained by using the severity

classification given above and carefully planned questionnaires should

prove very useful for a conclusive settlement of this issue.

Consideration of the ranges of children's activities during

various play conditions involving toys; the relative seriousness of

various levels of severity; and discussions with a few parents, one

histologist, and a few colleagues, led the author to make the following suggestions concerning the levels of severity beyond which
- 12 -

injuries are unacceptable: 1) during normal use of toys, injuries

beyond level 1 (insignificant injuries) should not be acceptable;

and 2) during reasonably foreseeable abuse of toys, injuries beyond

level 3 (minor injuries) should not be acceptable. However, these

suggestions are derived from a very limited and informal analysis

and cannot substitute for the kind of careful and comprehensive

investigations described in the previous paragraph.

INJURIOUS OBJECTS

Due to a large variety of toys present on the market and a large

number of new toys manufactured each season, the number of injurious

toy components is enormous. The injurious objects include (1) components with sharp points, edges, corners, etc., and (2) such components

as blunt and sharp projections, chains, belts, springs, etc., each

having a variety of different configurations and material properties.

This makes it extremely difficult and hopelessly impractical to provide for the specific testing and evaluation of the injury potential

of each of these objects. Nevertheless, the consideration of only a

few basic objects having generic characteristics may adequately cover

most of the important ones.

Studies should be made of the following components.

1. Sharp points and projections. A few simple basic shapes of

points to represent nails, pins, staples, wire-ends, splintery

wood, corners, etc.

2. Edges. A few simple basic shapes of edges to represent thin

or sheared metal, burrs, screws, fractured brittle material,

etc.
- 13 -

3. Blunt projections. A few simple basic shapes such as

cylinders on their ends and sides, and spherical surfaces

to represent unprotected ends of axles, actuating levers,

shafts, decorative features, etc.

4. Missiles. A few basic shapes of toy projectiles, and

points, edges and projections to represent toy projectiles,

darts, arrows, ejected broken parts of toys, ejected wind

up springs, etc.

5. Pincers. A pincer with simple configuration to represent

chains, belts, springs, pincers, closing boxlike toys, etc.

Figure 5 represents in summary form a number of these injurious

objects along with the loading mechanisms of their involvement and

probable resulting injuries.

LOADING MECHANISMS

A tremendous variety of child-toy interactions can result from

the activities of children associated with the normal use or reasonably foreseeable abuse of the toys. Some of these activities are:

1) normal use - unpacking, handling, holding, operating and occasionally assembling the toys; and 2) reasonably foreseeable abuse -

squeezing the toys, stepping or sitting on toys, rolling over the

toys, falling onto the toys, sliding or rubbing toys on various parts

of the body, grabbing or snatching a toy while it is held by another

child or resting on the floor, kicking toys, throwing toys for playing

catch or in anger at other children, inserting fingers, toes and

other parts of the body in various openings or springs of certain

toys, shooting toy projectiles at other children, being hit by broken

ejected parts, dismembering the toys, etc.
- 14 -

In all of the probable child-toy interactions, mechanical loads

are applied locally to the body surfaces by different loading mechanisms. Each situation involves physical contact with the toys or

their various components. However, each situation is different, each

having a unique set of loading conditions (i.e. loading mechanisms,

ranges of load magnitude, interacting objects, body parts, etc.). The

child- toy interactions, apart from being tremendous in variety, are

also very complex and extremely difficult to simulate. Nevertheless,

a large number of child-toy interactions may be adequately simulated

by the following loading mechanisms.

Compression . This involves interaction with sharp points and

edges, and occurs in situations where the applied force is essentially

directed along the longitudinal axis of the sharp point (interacting

object). This may result in injuries such as contusions or punctures.

See Figure 4.

Abrading, cutting, scraping, scratching, etc . This loading

mechanism involves interaction with points and edges and occurs in

situations where the interacting object, pressing down on the skin,

is pulled across the skin. In this loading mechanism the resultant

load essentially has two components, one directed along the longitudinal

axis of the interacting object passing through the point of contact

and the other parallel to the skin cross-section. See Figure 3.

This may lead to lacerations of variable severity.

Impact . Impact loading occurs in two different types of child-toy

interactions. First, in situations where the child or any part of the

child's body is hit by a missile. Second, in situations where a child
- 15 -

(or any part of the child's body) hits the toy, such as when the child

falls onto a toy or kicks a toy. Interactions involving impact loadings

can lead to all six categories of injuries discussed in the section

entitled Mechanical Injuries.

Pinching (compressing or shearing) . This loading mechanism is

typical of certain types of toys including closing-box and scissorlike toys, and toys possessing chains, belts, springs, gears, etc.

The child-toy interaction involving pinching loads can result in

injuries to skin, soft tissue and bones.

INJURY POTENTIAL

Having identified various injurious objects and loading mechanisms

involved in child-toy interactions in the previous sections of this

report, an attempt will now be made to identify the various factors

which influence the injury potential of these objects and to outline

the procedures needed for the determination of injury potentials. As

stated in the introduction, the injury potential of any object is

defined as the type and severity of injury such an object is capable

of inflicting on the human body for any probable loading conditions.

The determination of injury potential of various objects involved

in child-toy interaction is affected by many factors including characteristics (mechanical properties and geometry) of the injurious object,

the part of the body involved and its biophysical properties, the

loading mechanism, and the magnitude, direction, distribution, and

duration of load. In addition, certain physiological factors such as

age, sex, and physical and mental condition of the individual involved

have been known to affect the outcome of accidents even though the

manner of their influence is not completely understood.
- 16 -

The variability of biophysical properties of human tissue from

person to person as well as from part to part within the same person

make it difficult to determine the injury potential of injurious

objects for universal use, even for stipulated loading mechanisms

and sets of loading conditions. The presence of several possible

modes of injury, involving different tissue failure mechanisms, further complicates the problem.

Until the influence of physiological factors on the resulting

injuries is better understood and our knowledge of biophysical properties of the human tissue is greatly improved, the exact solutions to

the problems described above are improbable. Nevertheless, data obtained

by carefully planned experiments may still allow us to differentiate

between hazardous and non-hazardous toy constituents. These experiments

should be aimed at determining the various combinations of relevant

geometric characteristics of injurious objects and ranges of loading

conditions that produce unacceptable injuries. This will require

experimenting with cadavers, living animals, and human and animal

tissue in vitro and using various injurious objects and loading mechanisms. The validity of data thus obtained, however, may always be

questioned because animal tissue and dead tissue do not have the same

biophysical properties as those of living human tissue.

Experimental procedures to obtain the desired data, for each of

the loading mechanisms, are outlined below:

Compression . This involves interaction with points, edges, and

corners, and represents situations where the applied force is essentially directed along the longitudinal axis, passing through the point
- 17 -

of contact of the interacting objects and is perpendicular to the skin

cross section. Because the applied load is essentially pressing down

on the skin, it is therefore termed compression loading. This can

result in two types of injuries, contusions or punctures, depending primarily upon the applied force, contact area, and body location. Contusions

are usually caused by high compressive stresses while punctures are generally caused by high tensile or shear stresses. However, punctures can

also take place along with contusions, and once the skin is punctured

it is difficult to determine whether a contusion has occurred or not.

According to Gadd et al. 11/ , under this type of loading, skin

tissue fails from a combination of: 1) tensile stress arising from the

downward stretching of the skin by the advancing interacting object,

and 2) a "pinching off" action as the indentation produced by the interacting object has reached a certain depth (in the case of Gadd's

experiment, as the interacting object closely approaches the platen, i.e.,

the rigid background of the tissue), the effects of which combine to produce a sudden cleavage of the skin tissue in a plane essentially

perpendicular to the applied force.

Deck 17/ observed essentially the same skin failure mechanism under

this type of loading, while puncturing the skin with points having a

contact area less than or approximately equal to that of Gadd's tips,

even though Deck's points had different geometric characteristics than

Gadd's points. However, points having larger contact areas (i.e. the

cross-sectional area contacting the skin) did not puncture the skin in

a similar manner; instead the skin failed by a combination of crushing

and piercing of the tissue.
- 18 -

Deck 17 / and McGuire et. al. 19 / also observed that the tips with

larger contact areas required a larger force to puncture the skin.

However, probably due to difficulties associated with measuring the

contact area, the applied pressure required to puncture the skin was

not calculated. An examination of their data indicates that even with

the same sharp point a different force was required to puncture the

skin at different body locations, apparently because of variations in

the biophysical properties of the tissue.

Estimates made from the data provided by Deck Yl_l show that the

pressure required to puncture the skin completely (i.e. to produce

moderate or level 4 injuries) varies from 8000 to 60000 psi depending

upon the body location and tip geometry. The pressure required to

produce minor or level 3 injuries (i.e. to produce punctures not to

penetrate beyond the reticular layer of dermis) varies from 1300 to

10000 psi depending on the body location and tip geometry. No data

is available to determine the pressure or the force required to produce

lower level injuries.

These studies show that the injury potential of points, corners,

or edges is dependent upon applied force, body location, and the interacting objects geometry, and that the geometry (especially at the

contacting area) of the interacting object also affects the damage

mechanism. .

Hence, for this type of loading, the injury potential

I. P. = f(F, A, Pr^, Pr^) (See list of symbols) (1)

and if the interacting object is harder and tougher than the skin, as

it usually is for the objects, of interest to us for this study, the

properties of the interacting object (Pr ) can be omitted from equation
- 19 -

The biophysical properties of human tissue (Pr^) of interest include:

C, E, G, s, T, W, X^, e^, g"^, m .

The contact area (A) depends primarily upon the geometry of the

interacting object although the skin tissue properties, such as resilience, also exert some influence. See Figure 6 for geometric variables.

Therefore, Equation 1 may be rewritten as follows:

I. P. = f(F, A(g), Pr^) (2)

Skin puncture potential of points and corners under essentially

static conditions has been adequately studied by McGuire et al. 19/

The skin puncture potential of edges under this type of loading can be

determined by procedures similar to those used by McGuire et al. 19/

to study injury potential of points.

Abrading, cutting, scraping, scratching, etc . This loading

mechanism represents children's interactions with edges and points

that may result in skin tissue lacerations. As stated previously, this

type of loading occurs in situations where the applied load essentially

has two , components . One component is directed along the longitudinal

axis of the interacting object passing through the point of contact.

This component is usually perpendicular to the skin cross-section and

for the purpose of this study may be considered as a concentrated force

(F^) or pressure (P^) • The second component of the applied load is

directed in a direction perpendicular to the first one. It is usually

parallel to the skin cross-section. In some cases this may be a pulling

force that causes the interacting object to move across the skin, and

in other instances it may be a body motion that causes the tissue to be
- 20 -

dragged across the interacting object. In any event, the second

component of the applied load may be represented by a horizontal force

(F^) between the skin and the interacting object.

In some cases a sharp edge or point, due to load component F^,

punctures the skin and starts the tear process. The tear is then

lengthened (i.e. the cut is made larger) by the' second component of

load F in the direction of pull. In other situations the interacting

n object, due to the normal component of load F^, just indents the skin

but cannot puncture it. The indented skin may then be torn by the

interacting object, due to the horizontal component of load F^.

Situations v^hich occur in real life are not as simple as described

above. The injury mechanism is very complex and not completely understood. The various loads acting simultaneously on the tissue, induce

certain comb illations of stresses and strains that excite the damage

mechanism and cause injury. The injury potential of various injurious

objects obtained by sim.ple experiments in accordance with the loading

mechanism described above will, however, be adequate for our purpose.

The injury potential of a point or an edge, for this type of

loading, primarily depends upon the applied loads (F^,

^^i^

> the mass

and velocity of the moving object, the geometric characteristics of

the interacting object, the biophysical properties of the skin tissue

involved, contact duration (t), and angle of attach G i.e. the angle

made by the longitudinal axis of the injurious object with the skin

cross-section. (See Figure 3 for Sand Figure 6 for geometric characteris tics .

)
- 21 -

Mathematically

,

I. P. = f(F^, F^, M, V, g(a, D, r, h, ^) , Pr^, t, 6) (3)

If the contact areas A iF and A, i. F^ were measurable, the n n ii h

' number of variables present in Equation 3 could be greatly reduced

and Equation 3 could be rewritten as follows:

I. P. = f(F^, F^, M, V, A^, A^, Pr^, t) (4)

Furthermore, if the damage mechanisms were known, the application

of dimensional analysis techniques could further simplify Equation 4.

For example:

a) when both the load components and the velocity of moving

object (tissue or injurious object) are known, injury potential

may be expressed as;

I. P. = f(Fnno /A r, F,V,t/A,(ls) nhn or Fnnt/A,u , etc.) (5)

and b) when F is known and F, is not known, but V, and M of the

n h h

moving object are known, the injury potential of the injurious

object may be expressed as;

I. P. = f(Fnno /A ^ , MV^/yA^ or MV^/A. (Is) , etc.) (6) h h h

Unfortunately, the determination of contact areas is very involved

and extremely difficult. One may roughly estimate the contact area A^,

because it is dependent primarily upon geometric variables of the object

and angle of attack G. However, even rough estimates of the contact

area A^ are highly improbable, because A^^, apart from being dependent

upon geometric characteristics of the object and angle of attack 6,

is also affected greatly by F and properties of the tissue involved.
-11-

Moreover, neither the damage mechanisms nor the biophysical properties

of human tissue are completely known. Therefore, at the present stateof-the-art such simplifications as described above are not justifiable.

Nevertheless, a knowledge of various combinations of F and V, with

n h

which a given injurious object can lacerate the skin tissue would

adequately serve our purpose. The basic data necessary for the acquisition of the aforementioned knowledge may be obtained by the experimental

procedures outlined below.

A given injurious object, with a constant force and a constant

velocity V^, should be brought into contact with a stationary skin

tissue specimen to observe whether it lacerates the skin or not. In

tests where skin is lacerated, the size of the wound should be recorded.

A test series should be conducted with a constant value of force F and

n varying values of velocity V^, starting with = 0 and increasing it

in small increments until the velocity necessary to produce observable

laceration is reached. The experiment should then be repeated with a

different values of F^. After one injurious object is tested for the

desired ranges of F^ and V^, the experiment should be repeated with other

objects. The data for each object may be plotted on a rectilinear graph

paper with F as ordinate and V, as absicissa as shown in Figure 7. n h

The experiments can also be conducted by bringing the injurious

object, with Force F^, into contact with the skin tissue moving with a

constant velocity V, . Various combinations of F and V, , at which the

h n h

object can lacerate the skin can be found.

A small number of points and edges having simple basic shapes

(geometric characteristics) should be selected to represent injurious

objects. Some such experiments are already underway at the Consumer

Product Systems Section, INBS 24/
- 23 -

Impact

As stated previously, a child-toy interaction involving

impact can lead to all six levels of injuries. The injury potential

of a projection when impacted by a falling person is given by the

following equations 20/

Sharp projections - I. P. = f(h/X^ , MVy^iA) (7)

Blunt projections - I. P. = F(h/X^ , KE/ATO) (8)

The injury potential of projectiles impacting the human body is

given by equations similar to Equations 7 and 8.

The procedures to determine the injury potential of various

injurious objects outlined in references 18 / and 20 / are probably

adequate for the Toy Safety Program. Data obtained by Sorrells 24/

,

from his recent experiments, are in reasonable agreement with the

injury threshold curves postulated by Mahajan 20/.

Pinching (compression and shear)The injury potential of objects

involved in this mechanism depends primarily upon applied load, the

object's geometric characteristics, geometric characteristics of the

body part involved, and the biophysical properties of the tissue. For

example:

*

I. P. = f(F, g^, g^, Pr^) (9)

The geometric characteristic of both the injurious object (g-j^)

and the body part {g^ in Equation 7 can be easily replaced by contact area A. This is so because and §2'^ main influence on the

injury potential is the determination of contact area.

Hence,

I. P. = f(F, A, Pr^) (10)
- 24 -

The basic injury data collected for the other three loading

mechanisms can be easily used, by interpolations, to determine the

injury potential of injurious objects for this loading mechanism.

HAZARD CRITERIA

Any constituent of a toy that presents the risk of unacceptable

injury due to any child-toy interaction during normal use or reasonably foreseeable abuse of the toy is considered hazardous.

To establish criteria that can effectively differentiate between

hazardous and non-hazardous toy components (or toys) , one should have

a clearly defined level of severity beyond which injuries are unacceptable. Furthermore, since the severity of injury is dependent upon

loading conditions, a set of loading conditions should be stipulated.

To define the level of severity beyond which injuries are unacceptable,

and to make a reasonable assessment of the ranges of loads that are

developed in various child-toy interactions, the studies indicated

below are necessary. Some such studies of limited scale have already

been made. "j- ^

1. Consensus of opinion . Consensus of opinion of physicians

• (such as pediatricians and surgeons) parents, etc, should

be obtained by means of carefully planned questionnaires

to define level of severity beyond which injuries are

unacceptable and to determine the parts of a child's body

that are most vulnerable to injury from various child-toy

interactions
- 25 -

Case studies . A complete and thorough study should be made

of child-toy interactions resulting in injury. These studies

should investigate the injurious objects (or toys) involved,

type and severity of injuries inflicted, the interaction

conditions, the part of the child's body injured, etc. For

such studies the cooperation of pediatricians, parents, and

children is essential.

Physical measurement of children . These measurements should

include the following: the effective mass of various parts

of children's bodies and their geometric characteristics;

the ranges of forces or energies children are capable of

exerting during their various activities; the ranges of

velocities for various motions of different body parts during

typical activities of children; ranges of velocities with which

different parts of a child's body can hit a toy or an injurious

constituent of a toy under reasonable fall conditions, etc.

Experiment determination of injury potential . Experiments

with animals in vivo, human cadavers, and human and animal

tissue in vitro should be conducted to obtain data on the

injury potential of various objects in terms of the relevant

geometric characteristics of the object and appropriate load

magnitude for various loading mechanisms.

Injury mechanisms . Experiments should be conducted to study

and understand the mechanisms of tissue failure during injury

processes, and to obtain data on the basic biophysical properties of the human tissue. This study requires a team effort

of histologists , rheologists, and engineers.
- 26 -

6. Correlation between the biophysical properties of living

human tissue and dead tissue . For a better assessment of

the injury potential of various injurious objects, correlations between the biophysical properties of living human

tissue and dead human tissue is essential. Such correlation

could probably be obtained by finding the correlations

between the biophysical properties of the living animal

• tissue and dead animal tissue and applying the findings to

human tissue by interpolation and scaling.

- When the level of severity beyond which injuries are unacceptable

is defined, and a reasonable range of loading conditions (especially

the load magnitudes in the ranges in which children are capable) are

known and the injury potential of various injurious objects is determined, it becomes possible to determine whether any given toy constituent (or toy) is hazardous or not.

CONCLUDING REMARKS

At the present state-of-the-art it is extremely difficult to

establish universally acceptable injury criteria that will differentiate between hazardous and nonhazardous objects. The major reasons are

that humans are complex and variable, and available techniques for

testing living bodies are limited. Furthermore, injury mechanisms are

not exactly understood, and the biophysical properties of the human

tissue are not completely known.

Nevertheless, from the data obtained by carefully planned

experiments for a given family of injurious objects a specified loading

mechanism, criteria to differentiate between hazardous and nonhazardous
- 27 -

objects can be developed. The criteria thus obtained have to suffice

until our knowledge about the injury mechanism and properties of human

tissue is greatly improved.
- 28 -

REFERENCES

1. Synder, R.G., "State-of-the-Art Human Impact Tolerance", Society

of Automotive Eiigineering, Inc., Paper No. 70039B, May 1970.

2. Synder, R.G.., "Occupant Impact Injury Tolerance for Aircraft

Crashworthiness Design," A.S.E. Paper No. 710406, March 24, 1971.

3. VonGierke, H.E., "Response of the Human Body to Mechanical Forces -

An Overview," Annals Nev; York Academy of Sciences, Vol. 152, P. 172,

1968.

4. Benjamin, T. , "Physiological Effects of Blast in Air and Water,"

German Aviation Medicine in World War II, U.S. Government Printing

Office, Wash., D.C., 1950.

5. AM/i., Comjnittee on Medical Aspects of Automotive Safety, "Rating

the Severity of Tissue Damage: The Abbreviated Scale," JA>IA

215:277-280, 1971.

6. AMA, Committee on Medical Aspects of Automotive Safety, "Rating

the Severity of Tissue Damage: II The Comprehensive Scale,"

JAMA 717, 1972.

7. States, J.D., "The Abbreviated and the Comprehensive Research

Injury Scales," Proceedings of the Thirteenth Stapp Car Crash

Confereiice, Society of Automotive Engineers, Inc., New York,

Paper No. 690810 (1969).

8. NEISS, National Electronic Injury Surveillance System.

9. Hodgson, V.R. and Thomas, L.M., "Breaking Strength of Human Skull

vs. Impact Surface Curvature," Wayne State University, final

report DOT-HS-800583 (1971).
10. Hodgson, V.R.; Brin, J.; Thomas, L.M.; Greenberg, "Fracture

Behavior of the Skull Frontal Bone Against Cylinderical Surface,"

Society of Automotive Engineering Paper No. 700909, 1970.

11. Gadd, C.W.; Peterson, F.J. and Lange , W.A., "Strength of Skin

and Its Measurement with Special Application to Trauma," American

Society of Mechanical Engineers Paper No. 65-VJA/HUF-8, 1965.

12. Bobrova, M.V. , "Topography of the Mechanical Properties of the

Human Skin," Soviet Neurology and Psychiatry, 4, 3, 1971.

13. Holzmann, H.; Korting, G.W.; Robert, D. ; and Vogel, H.G.,

"Mechanical Properties of Skin in Relation to Age and Sex,""

Orchiv. Fur Klinische and Experimentelle Dermotologie , 239, 255,

1971.

14. Grahme, R. , "A Method for Measuring Human Skin Elasticity in Vivo

with Observations on the Effects of Age, Sex and Pregnancy,"

Clinical Science, 29, 223-38, 1970.

15. Fazekas, I.G.; Kosa, F.; Basch, A., "Degree of Extensibility of

the Skin in Various Body Parts," Deutsch Z. Ges Gerichtl. Med.,

64, 62-92, 1968.

16. Fuller, P.M., "Skin Puncture Data from 48 Unembalmed Cadavers -

unpublished data," University of Virginia School of Medicine, 1972.

17. Deck, J.D.; "Skin Histology and the Effects of Injury - unpublished

data" personal communication. University of Virginia School of

Medicine, 1972.

18. Fischler, S.; Mahajan, B.M. "Ocular Injury Potential of ProjectileType Toys," NBS Report No. 10 893, August 1, 1972.
- 30 -

19. McGuire, B.J.; Moore, J.D., "The Skin Puncture Potential of

Points Associated with Certain Toys," National Bureau of Standards

Report No. 10 83.9, 1972.

20. Mahajan, B.M. , "Analysis of Injury Potential of Projections when

Impacted by a Falling Individual," NBS Report No. 10 906, Nov. 22,

1972.

21. McGuire, B.J.; Sorrells, J.R.; and Moore, J.D.; "Resistance of

Human Skin to Puncture and Laceration," NBS Report No. 10 952,

Feb. 1973. - ' ' '

^

22. Kenedy, R. , "The Mechanical Characteristics of Skin and Other Soft

Tissue and Their Modeling," Symposium on Biodynamics Models and

Their Applications, Aerospace Medicine Research Laboratory, WrightPatterson Air Force Base, Ohio, Dec. 1971.

23. Patrick, L.M. ; "Prevention of Instrument Panel and Windshield Head

Injuries," The Prevention of Highway Injury (M.L. Selzer, et al.

eds.). Highway Safety Research Institute, the University of Michigan,

Ann Arbor, 1967. x

24. Sorrells, J.R., personal communication, Product Systems Section,

NBS, 1973. - '-^Ar-
- 31 -

•

CO

o

UJ

TERMINAL HAIR

PORE

DOWNY HAIR

HORNY LAYER

ST RAT U M LU C I D U ^

GRANULAR LAYER

MUCOUS LAYER

BASAL LAYER

PAPILLARY CAPILLAR

NERVE

ELASTIN FIBERS

t'ir^'/^r? ^—^-7- COLLAGEN FIBERS

BLOOD VESSEL

FAT CELLS

7 Z"swEAT GLAND

L- SEBACEOUS GLAND

HAIR FOLLICLE

Figure 1. Typical Cross-Section of Human Skin
- 32 -

Figure 2. Schematic cross-section of human skin

to indicate reticular layer.
- 33 -

Figure 3. Schematic

which may

representation of loading

lead to lacerations.

conditions
- 34 -

Figure 4. Schematic loading which may result in

penetration wounds.
- 35 - u c Q QH c O

CO c\3

(30 bO c C

•H •H^ o rd c

•Hm

01

M

•H -H W tH i •HE m o

>^ c!

03 ^ ^ Oi

p. i S '-^ '-v j

60d

bO ^ C O

•HW

•U ci3

60 60 c c

•H .H

ft,

M V-i

O

XI o -u < W CJ co

•Hw

CO

<ueo

bO

C! •Ho

•H -H o o

4-) o

ft. >1 • u> a I w

•V 0) W ^

>.

60

O " W

d J-J to tio o

•H

d

Cw

W QJ -H 'H

M

W

O ft^ n3 -H

r-H 4:: a<

u o O O CO CO -u o

CO

CO OJ

0)

d 60

rH CO <u •H

•U ow ok •CO

CU

u 0 d

(Uu 4-1 0 d

CO •I-) cti CU •H CO CD 0 +J

t-i dJ

a to •H ft (/) •u CO (U u

CO

u

a ) d

CO >^u OJu 0 •H

•H 0 ) d 0

:2:

H X) ft tcJ ft ft

CO CO

(U60

d

d

ct

w 0

t/f >-> 1 (U M CJ iH QJ a CD ft 4-) 4J u U

cci

d QJ ct3 4-1 •H QJ to rH

ft< CO to to 0)

u

to )-l rH

u

CO QJ QJ 4-1 <u d d 0 i-t 4-1 •H CO •H

ft 10 0 to rH d a d CO CO CU •H

4J 1 rH !-i d rH (U I

CO QJ QJ •H •H i-l 0 1

4J >-i 4-> 0 rd •H 0 QJ ;:5 rO :a .:2 e u B

ino

,-3

60

to C3

4-1 •H a iJ

at

H •r~l 3

(0

OJ Pi

to

(U CO 0 rH 01 •H X> -H

>-i CO J-i d rCl 3 0 -r-i d d

60

COB

fd x(

dJd (U 0 rH

rClCO

J=l • 0

>-! ft.

to

d

d CO 0 to iJ0 d <D 0 •r-t •rH

4-1 COU CO +J d

<u 0 0 •H

(U V-l ft d

•0d » •H (^

rx . to

to

B

d to 0 • •H

•H CU

d

4-1 60 ce CO CO Xi ^ B u

QJ CO QJ U -T3 B

CO rH

d 60

CO

d

60 •H • U 13 CM 0 CO0

rH rH

to Cd

r—{ to 0 U to <v H QJ u

CO J-J :3 d

d

d

to

d

d 0 (J •H 0 • QJ

LPl 60d • Id CO H

rH

d r) 4-1

X CO 0 rH •H d U CO

CO CI) > 5-1

Ln

Q)U

60. •H

Ct4
- 36 -

DrBase Dimension

Diameter

Included

a z Angle

rrTip Radius

h -Height Above The

Supporting Surface

X

h

±

Figure 6. Geometric characteristics.
igure 7. Postulated experimental injury threshold curve

for lacerations by sharp p-oints.
Figure 8. Postulated injury threshold for 1

by edges.
FORM N8S-114A l\rlV

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICA I ION OR REPORT NO.

NBSIR 73-137

2. Gov't Accession

Mn

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Systematic Analysis of Mechanical Hazards from Toys

5. Publication Date

6. Performing Organization Code

7. AUTHOR(S)

Bal M. Mahajan

8. Performing Organ ization >TBSIR 7 3-137

10. Pro|cct/Task/'i'. ork Unit No. 4110410

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

11. Contract/Grant No.

12. Sponsoring Organization Name and Address

Bureau of Product Safety

Food and Drug Administration

Bethesda, Md. 20016

13. Type of Report & Period

Covered

Final 07/72--02/73

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliogiaphy or literature survey, mention it here.)

The information necessary to establish criteria for differentiating between

hazardous and non-hazardous toy components consists primarily of (1) levels of

severity beyond which mechanical injuries are unacceptable, (2) knois'ledge of

various injurious objects that may be found as toy components and their injury

potential and (3) the reasonable ranges of loading conditions for various childtoy interactions.

Mechanical injuries are described and classified into six levels of severity,

and a procedure to decide on the level of severity beyond which injuries are unacceptable is suggested.

The various injurious objects that may be found as toy components and

loading mechanisms probable from various child-toy interactions are identified.

Some of the procedures for determining the injury potential of such objects

are outlined.

Pertinent studies required to obtain other needed information are recommended.

17. KEY WORDS (Alphabetical order, separated by semicolons)

Analysis; child-toy; classification; description; determination; hazard; injury;

interaction; mechanical; object, potential; procedure; safety; toys

18. availability statement

unlimited.

XXEfOR OFFICIAL distribution. DO NOT RELEASE

TO NTIS.

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

21. NO. OF PAGES

20. SECURITY CLASS

(Tins PAGE)

UNCLASSIFIED

22. Price

USCOMM-DC 662 44.P7t