NBSIR 77-1294

POWER LAWN MOWERS:

Evaluation of Anthropometric

Foot Probes

J. J. Persensky

A. M. Ramey

Human Factors Section

Product Systems Analysis Division

Center for Consumer Product Technology

Institute for Applied Technology

National Bureau of Standards

May 1977

Final Report

Prepared for U.S. Consumer Product Safety Commission

NBSIR 77-1294

POWER LAWN MOWERS:

EVALUATION OF ANTHROPOMETRIC

FOOT PROBES

J. J. Persensky

A. M. Ramey

Human Factors Section

Product Systems Analysis Division

Center for Consumer Product Technology

Institute for Applied Technology

National Bureau of Standards

May 1977

Final Report

Prepared for U.S. Consumer Product Safety Commission

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Table of Contents

Page

List of Tables iii

List of Figures v Acknowledgements ix

Abstract xi

1.0 Introduction 1

2.0 Methodology 4

2.1 Participants 4

2.2 Apparatus 4

2 . 3 Procedure 7

3.0 Results 9

3.1 Data Reduction 9

3.2 Data Analysis 9

4.0 Discussion 22

References 35

Appendix A- -UK Probe Design Rationale 37

Appendix B--NBS Evaluation of Foot Probe 39

Appendix C--Foot Length Data 49

Appendix D--Research Consent Form 51

l
" r
List of Tables

Number Title Page

1 Generic Probe Data 11

2 Foot Data 12

3 Percentage of Sample Protected by

Generic Probes 22

4 Percentage of Sample Protected by

the 95th Percentile Data 23

5 Sample Correlations 29

6 Shoe Probe M I" Data 30

7 Percentage of Sample Protected by

Shoe Probe "I” 34

i i i
i . ' , ; ;/ ie2 \ P?
2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

List of Figures

Title Page

Proposed CU Foot Probe 2 UK Foot Probe 3

ANSI Foot Probe 5 Test Fixture Schematic 6

Comparison of Lawn Mower to Simulator ... 8

Diagram of Triple Exposure Foot Image ... 10

Safety Envelopes -Generic Probes,

6 cm Housing Height 13

Safety Envelopes -Generic Probes,

8 cm Housing Height 14

Safety Envelopes -Generic Probes,

10 cm Housing Height 15

Safety Envelopes -Foot Data - With Shoe,

6 cm Housing Height 16

Safety Envelopes -Foot Data - Without Shoe,

6 cm Housing Height 17

Safety Envelopes -Foot Data - With Shoe,

8 cm Housing Height 18

Safety Envelopes -Foot Data - Without Shoe,

8 cm Housing Height 19

Safety Envelopes -Foot Data - With Shoe,

10 cm Housing Height 20

Safety Envelopes -Foot Data - Without Shoe,

10 cm Housing Height 21

Safety Envelopes -Comparison Data,

6 cm Housing Height 24

Safety Envelopes -Comparison Data,

8 cm Housing Height 25

Safety Envelopes -Comparison Data,

10 cm Housing Height 26

v
.

j

-

'
List of Figures (Continued)

19 Proposed Modification of UK Probe 27

20 Safety Envelopes -Shoe Probe "I" Comparison,

6 cm Housing Height 31

21 Safety Envelopes -Shoe Probe "I" Comparison,

8 cm Housing Height 32

22 Safety Envelopes -Shoe Probe "I" Comparison,

10 cm Housing Height 33

Vll
.
Acknowledgements

The authors of this report wish to acknowledge the

assistance of V. J. Pezoldt in data collection and

Barbara Stanton, Addie Stewart and Pam Murray for their

aid in data collection and reduction. Thanks are also

due James Huckeba for equipment implementation, Harry

Appleby for equipment construction, and Kim Leaman and

Bonnie Matteson for secretarial support.

ix
.
ABSTRACT

This document is the final report for the Consumer

Product Safety Commission of an evaluation of the adequacy

of existing generic foot probes. The Human Factors Section

at NBS compared the dynamic characteristics of three generic

probes with those of potential lawn mower users' feet.

Horizontal and vertical insertion distances for the

generic probes and the foot data were used to develop

safety envelopes for various simulated housing heights.

Inspection of the safety envelopes at 6, 8, and 10 cm

housing heights indicates that, of the three generic probes,

the UK probe most closely approximates the foot data,

since only the UK probe passes through the area above

the horizontal plane formed by the bottom edge of the

housing

.

However, a comparison of each individual '

s

data (rather

than aggregate data) was made with each generic probe

to determine the percentage of participants who would

be completely protected by each generic probe. These

data indicate that at least one point of each individual's

foot movement data would fall outside of the safe region

defined by the generic probe envelopes. Therefore, a lawn mower meeting the criteria of any of the generic

foot probes would not completely protect any of the participants in the study.

Recommendations for a modification of the UK probe

and for further research are discussed.

xi
.

'

'

mm

.

.

•

.

.
Power Lawn Mowers

:

Evaluation of Anthropometric

Foot Probe

1.0 Introduction

"Power Mowers", a 1976 Product Profile (1) prepared

by the U.S. Consumer Product Safety Commission (CPSC) , indicates that an estimated 178 000 power mower -related

injuries occurred in 1975. It was estimated that the

associated annual costs exceeded 70 million dollars.

Over half the total injuries were from body contact with

the blade, acdording to the National Electronic Injury

Surveillance System data. The Product Profile also stated

that: "Hands and feet were the body parts most frequently

injured." In an attempt to reduce the number of blade

contact injuries, the CPSC has been considering a proposed

safety regulation prepared by Consumers Union (CU) (2)

under Section 7 of the Consumer Product Safety Act. The

proposed regulation includes two items which are directed

at reducing blade contact injuries: a requirement for

a dead-man control and a test which utilizes an anthropometric

foot probe. The dead-man control requires that the operator

maintain continuous contact with the control at the operator

po.sition in order to power the blade rotation.

The second requirement, the foot probe test, is intended

to protect feet from blade contact by describing a region

under the housing through which the blade must not pass.

The test assumes two points: first, that the probe or

foot simulator is5 representative of lawn mower users’

feet; and second, that the probe test will accurately

measure the potential for foot contact with the blade.

CU proposed a probe design (Figure 1) which was an

adaptation of an Underwriters’ Laboratory (UL) probe.

According to telephone conversations with UL personnel,

the probe was originally proposed by representatives of

lawn mower manufacturers in consultation with shoe manufacturers. The UL representative further indicated that

UL modified that probe in an attempt to "make it more

severe." CU further modified the probe by adding 1.9

cm to its width.

An evaluation of foot probes by the Human Factors

Section of the National Bureau of Standards in the fall

of 1975 (3) compared the proposed CU probe with two other

generic probes. These were the United Kingdom (UK) probe

(Figure 2) designed by the British Standards Institute
Figure 1. Proposed CU Foot Probe

2
Figure 2. UK Foot Probe

3
[See Appendix A for Rationale of design.] and the American

National Standards Institute (ANSI) probe (Figure 3) . The generic

probes were compared with nine shoe probes which utilized shoes

representing the range of foot sizes from the 5th percentile

11 year old to the 95th percentile adult male. Shoe size

data were found by comparing shoe manufacturers' data (4)

with foot length data from anthropometr i'c surveys (5, 6,

7, 8). The results of this evaluation were submitted to

CPSC in a memo dated October 24, 1975 (See Appendix B)

.

Based on that evaluation, the UK fixture was selected by CPSC

as the most representative probe, should a static probe

be used for the blade contact test.

In September of 1976 the CPSC requested NBS to develop

a further rationale to justify the choice of the UK probe

from among the existing foot probes. NBS supported this

concept and proposed an effort to compare the existing generic

probes (UK, ANSI, and CU) with a sample of lawn mower operators'

feet. This report describes the comparison of characteristics

under dynamic conditions and the results.

2.0 Methodology

2.1 Participants

The participants in this study included 127 males

and 74 females ranging in age from 9 to 66 years (X = 32.1,

S.D. = 14.9). The mean height was 166.4 cm (S.D. - 13,7 cm).

Foot., length and breadth measures were taken for the right . foot of each participant, both with the shoe on and shoe

off. The average foot length without shoe was 25.2 cm

(S.D. = . 2 cm) while the breadth averaged 9.3 cm

(S.D. = 0.8 cm). With shoes on, the length averaged

27.2 cm (SrD. =“3.1 cm) and breadth averaged 9.8 cm

(S.D. = 1.0 cm). The foot length data without shoes

were compared to those collected by other researchers for

specific populations (See Appendix C) . This comparison

demonstrated that the present sample represented the range

of foot sizes but not necessarily a statistically representative sample of the frequency various foot sizes would be

found in the population of lawn mower users.

2.2

Apparatus

A schematic of the apparatus used in the study is

presented in Figure 4. It consisted of two parts: first, a camera and strobe mounted on a platform and focused on a gray4
Figure

3.

ANSI

Foot

Probe
STROBE

Figure

4.

Test

Fixture

Schematic
on-black, measured graph backdrop. The second part of

the apparatus was a frame with a movable metal partition

15.0 cm wide which could be adjusted to allow vertical

openings of 6 to 10 cm in 1 cm increments to simulate

different housing heights. Perpendicular to the frame

was the scaled backdrop. The base of the apparatus was

plywood, covered with a 0.5 cm thickness of cushioned carpeting. This test fixture was considered to be an accurate

simulator of possible lawn mower configurations (Figure

5 demonstrates the relationship of the simulator to a lawn

mower housing). A simulator was chosen to ensure generalizability to lawn mowers as well as other products whose safety

or performance might be dependent on foot movement envelopes.

Simple anthropometric scales were used to obtain

height and foot length and breadth data.

2.3 Procedure

After signing the appropriate consent forms (See

Appendix D) , participants removed their shoes, and their

height and right-foot length and breadth measures were

taken. The sex and age of each subject were also recorded.

The participants then put a white nylon stocking

over their right foot to increase image contrast. Participants

were then instructed to:

- Insert their right foot under the metal panel as

far in and to the left as comfortable, keeping

the foot flat on the base. Then,

- Rock the foot back on its heel, lifting the front

of the foot as far off the base as possible, curling

the toes upward, yet keeping foot as far in as

possible

.

- Keeping the front of the foot elevated and toes

curled up, pull the foot out from under the partition

until the base of the toes contacted the metal

panel

.

At each of the three positions described above, a picture

was taken, creating a triple exposure print and negative.

For each participant, foot dimension measurements

were taken both with the shoes on and shoes off. Also,

triple exposure photographs, one at each of the five housing

heights (i.e., 6, 7, 8, 9 and 10 cm), were taken both

with shoes on and shoes off. This procedure resulted

in ten triple exposure photographs, one exposure at each of

the three positions described above, for each participant.

7
8

Figure

5.

Comparison

of

Lawn

Mower

to

Simulator
3.0

Results

3.1 Data Reduction

Photographic negatives were placed in an enlarger

and projected onto a work board below. For each triple

exposure negative, lines on the work board were aligned

with reference lines on the photograph created by the

scaled backdrop. Next, map pins were placed at the height

of the longest point of each of the three positions.

(Position 1 was foot flat on floor; Position 2 was foot

raised and toes curled; and Position 3 was base of toes

contacting the partition.) Map pins were also placed

at the point corresponding to the length of the highest

point on each image, within 3 cm horizontally of the point

described above. There were, therefore, two sets of coordinates for each position or a total of six per negative

(housing height) . This is illustrated graphically in

Figure 6.

Once the map pins were in position, the x and y coordinates (horizontal insertion distance and vertical insertion

distance, respectively) for each point were recorded.

The same procedure was repeated for each participant at

each housing height, both with shoe on and shoe off, resulting

in a total of 60 sets of coordinates per participant.

3 . 2 Data Analysis

It became apparent that data from 6, 8, and 10 cm

housing heights would provide adequate information to

evaluate the generic probes. For that reason, the 7 and

9 cm housing height data were neither reduced nor analyzed.

Horizontal and vertical insertion distances for the

generic probes are presented in Table 1. Table 2 contains

the insertion distance data for the foot data. (Refer

to Figure 6 for interpretation of column headings.) The

foot data are presented in terms of Median, 5th percentile

and 95th percentile for the actual sample, not statistically

derived. Other percentiles can be derived from raw data

if desired. These data were used to develop safety envelopes

for each housing height and for shoe-on and shoe-off data

individually. The envelopes are presented in Figures

7 through 9 for the generic probes and Figures 10 through

15 for the foot data. In addition, the 95th percentile

foot data are compared with the generic probes in Figures

16 through 18. It should be noted that the 5th percentile

x coordinate data were used in all cases when graphing

position 3H (See Figure 6) in order to demonstrate the

most severe safety envelope; thus, the discrepancies between

Table 2 and the Figures 10 through 18.

9
10

ground

line
Generic

Probe

Data 0 o VO p- to o LO o 00 to

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11

Refer

to

Figure
Table 2

Foot Data (cm)

Position* 1 L H

X Y X Y Housing Height

6 cm with shoe

5th %ile 5.2 0.8 4.0 2.8

median 8.0 2.1 6.5 4 .

95th %ile 10.3 4.7 9.2 6.8

6 cm without shoe

5th %ile 7.5 0.5 5.4 1.7

median 10.2 1.6 8 .

2.7

95th lile 12.0 4.4 10.8 5.5

8 cm with shoe

5th %ile 7.4 1.4 5.8 3.5

median 10.4 2.3 8 .

4.4

95th %ile 12.7 4.4 10.6 6.5

8 cm without shoe

5th %ile 9.5 1 . 2 7.0 2.3

median 13.4 1.9 10.9 2.9

95th %ile 15.1 4.0 12.6 5 . 3

10 cm with shoe

5th %ile 9 .

0.9 6.9 3.3

median 13.4 1.8 11.1 4.4

95th %ile 16.1 3.2 13.7 5 .

10 cm without shoe

5th %ile 12.3 1 .

9 .

2.1

median 15.7 1.6 12.9 2.9

95th %ile 17.8 2.4 15 . 5 3.7

* Refer to Figure 6.

Position 2 Position 3

L H L H

X Y X Y X Y X Y

4.3 2.4 2.8 4.5 2.3 2.3 0.8 4.8

7.1 4.6 5.2 6.7 5.2 4.7 3.1 6.6

9.3 7.7 7.5 9.5 8.0 8.1 5.7 9.6

4.3 4.0 3.1 5.4 1.5 5.7 0.4 7.0

7 .

6.8 6.0 8 .

3.8 7.7 2.5 8.9

9.9 10.5 8.6 11.5 6.1 11 . 2 4.6 11.8

6.6 3.8 4.4 6.0 2.9 5.1 1.1 7.4

9.3 6.0 7.0 8 .

5.9 7.0 3.5 9.0

11.4 9.2 9.2 10.6 8.0 9.5 6.0 10.6

6.7 5.4 5.6 6.6 2.0 7.7 0 . 7 OG oo 10 .

7.2 9.7 8.5 4.0 9.8 2.6 10.9

13.4 10.0 12.3 11.0 6.5 11.7 5.5 12.7

oo 4.0 4.6 6.4 3.1 7.5 1 . 2 10 .

11.8 7.2 9.5 9.4 6.2 10.3 3.7 1 i . 9 15.0 10.6 12.5 12.4 9.1 12.2 6.6 13.7

8 .7.4 6.6 9.8 2.1 10.6 0.9 11 .

11 .11 . 7 10.0 12.9 3.9 12.2 2 .

13.4

14.4 13.6 13.0 14 .

6.0 13.8 4.7 15.0

12
o

ANSI

PROBE

AUK

PROBE

CU

PROBE

O

Uul

CJ>

CO

CO

1^1

M 33NV1SI0 N0I1U3SNI 1V3I1H3A

13

Figure

7.

Safety

Envelopes

-

-Generic

Probes

- 6

cm

Housing

Height
IG'6

‘O

il

X

co

T- OO

r^i

(uio| 3QNV1SIQ N0I1U3SNI 1V3I1M3A

14

Figure

8.

Safety

Envelopes

-

-Generic

Probes

- 8

cm

Housing

Height
|

18

5.

, 10

0. |

I

I

\i

o

M 30NV1SIQ N0I1U3SNI 1V0I1U3A

O

•Hu

<L> c

<D U

tno

Cl, O

rH

CD>

a

w

•M

<D

4-1rt inO

<DD

bfl •H

Uh

15

Probes

-

10

cm

Housing

Height
o

95th

PERCENTILE

•

MEDIAN A

5th

PERCENTILE

(wo) 33NV1SIQ N0I1H3SNI 1V3I1U3A

16

HORIZONTAL

INSERTION

DISTANCE

(cm)

Figure

10.

Safety

Envelopes

-

-Foot

Data-With

Shoe

6

cm

Housing

Height
(WO) 30NVJLSIQ NOI1U3SNI 1VDI1H3A

17

HORIZONTAL

INSERTION

DISTANCE

(cm)

Figure

11.

Safety

Envelopes

-

-Foot

Data-Without

Shoe

6

cm

Housing

Height
(92., 106. )

18

Figure

12.

Foot

Data--With

Shoe 8

cm

Housing

Height
(ui3) 3QNV1SIQ N0I1H3SNI TV3I1H3A

19

HORIZONTAL

INSERTION

DISTANCE

(cm)

Figure

13.

Safety

Envelopes

-

-Foot

Data-Without

Shoe

8

cm

Housing

Height
(

12

5.

, 12

4. )

x

CD

CNJ CO

1

LT3

(«io) 30NV1SI0 N0IW3SNI 1V0I1H3A

20

HORIZONTAL

INSERTION

DISTANCE

(cm)

Figure

14.

Safety

Envelopes

-

-Foot

Data-With

Shoe

10

cm

Housing

Height
(iua) 33NV1SI0 N0I1H3SNI 1V3I1H3A

21

HORIZONTAL

INSERTION

DISTANCE

(cm)

Figure

15.

Safety

Envelopes

-

-Foot

Data-Without

Shoe

10

cm

Housing

Height
In addition to comparing envelopes defined by the

aggregate foot data with the generic probe data, a comparison

of individual participant's data was made with each generic

probe to determine the percentage of participants who

would be completely protected by each generic probe.

This result is presented in Table 3. These data indicate

that at least one point of each individual ’ s foot movement

data would fall in the hazardous region as determined

by the corresponding point of the generic probe data.

There fore 3 none of the three generic probes would completely

protect any of the participants in the study.

Table 3

Percentage of Sample

Protected by the Generic Probes

Housing Height

6 cm 8 cm 10 cm

Shoe

Condition

With Without With Without With Without

Probe

ANSI 0 0 0 0 0 0

CU 0 0 0 0 0 0

UK- 0 0 0 0 0 0

4.0 Discussion

Inspection of the safety envelopes indicates that

of the three generic probes, the UK probe most closely

approximates the foot data at 6, 8, and 10 cm housing

heights. However, the percentage of the sample protected

is far less than the 95th percentile envelope for real

feet --which is recommended as the lower bound for an adequate

safety regulation. If a probe were designed using the

95th percentile data, theoretically 95 percent of the

tested population would be protected from blade contact.

Conversely, if the probe were designed based on the 5th

percentile or Median data, only 5 or 50 percent, respectively,

of the population would be protected.

22
Inspection of Figures 10 through 15 indicates that

in all cases the Median and 95th percentile envelopes

pass through a region higher than the bottom edge of the

housing position. However, Figures 7 through 9 indicate

that the UK probe is the only probe which passes through

the region above the bottom edge of the housing. In this

respect, only the UK probe might provide protection for

the operator, but that protection is very limited. Further,

inspection of Figures 16 through 18 demonstrates that

none of the probes approaches the vertical insertion distances

achieved by the 95th percentile foot data. The CU probe

exceeds the other probes and the foot data in terms of

horizontal insertion distances; however, in accordance

with existing standards, the blade is required to rotate

above the lower edge of the housing. Consequently, CU's

longer horizontal insertion distance does not result in

any added protection of the operator from blade contact.

If the UK probe is selected by CPSC for inclusion

in the Standard, one minor modification is suggested as

a means to assure repeatability of the test. That is,

the back of the heel of the probe should be flat and parallel

to the front of the toe (Figure 19) . This will allow

for consistent vertical rotation, not now possible.

It must be noted that a serious problem is still

present with all of the existing generic probes. Namely,

the comparison of the individual participant data with

the generic probe data indicates that none of the participants

would be completely protected by any of the probes. In

contrast, a probe based on the 95th percentile data would

protect a larger percentage of the population, as indicated

in Table 4

.

Table 4

Percentage of Sample

Protected by 95th Percentile Data

Housing Height

Shoe

Condition 6 cm 8 cm 10 cm

With 77% 82 % 14 % Without 80% 78% 73%

Table 4 shows that the 95th percentile data protects

less than 95 percent of the population, as might be assumed.

However, the percentile data is an aggregation over all

participants and is not directly related to any one particular foot. The dynamic characteristics of feet under a barrier do not conform to normal statistical assumptions.

To further demonstrate this, a sample of correlation

23
•

ANSI

PROBE

CU

PROBE

AUK

PROBE

95th

PERCENTILE

w/o

SHOE

LxJ

M 30NV1SIQ N0I1H3SNI 1VOIJLU3A

X

to

24

HORIZONTAL

INSERTION

DISTANCE

(cm)

Figure

16.

Safety

Envelopes

-

-Comparison

Data

6

cm

Housing

Height
M 3QNV1SIQ N0I1H3SNI 1V0I1H3A

25

HORIZONTAL

INSERTION

DISTANCE

[cm)

Figure

17.

Safety

Envelopes

-

-Comparison

Data

8

cm

Housing

Height
(wo] 33NV1SI0 N0I1U3SNI 1V3I1H3A

26

HORIZONTAL

INSERTION

DISTANCE

(cm)

Figure

18.

Safety

Envelopes

-

-Comparison

Data

10

cm

Housing

Height
27

Figure

19.

Proposed

Modification

of

UK

Probe
coefficients (9) were calculated for some of the data;

these are presented in Table 5. Inspection of Table 5

suggests that there are at least two factors affecting

the foot movement envelopes. The first may be referred

to as length, or horizontal insertion, and is demonstrated

by the high positive relationships between 1LX and 2LX.

The second factor might be referred to as flexibility,

or vertical insertion, and is demonstrated by the high

positive relationships between 2HY and 3HY. These two

factors do not appear to be systematically related to

each other, as demonstrated by the correlations 1LX-2HY,

1LX-3HY, and 2LX-3HY, or may even be negatively related

as indicated by the correlations between 2LX and 2HY.

A more thorough analysis of these data was beyond the

scope of the present project. However, the data indicate

that such analyses should be done in the near future along

with the data from the 7 and 9 cm housing heights.

The scope of the present project was to evaluate

the existing generic probes. However, in an attempt to

demonstrate the possible effectiveness of alternatives

to the generic probes, one of the shoe probes developed

for an earlier study (3) was tested using the simulator.

The probe selected was Shoe Probe "I", which was constructed

from the 95th percentile size adult female shoe. The

results are presented in Table 6 and graphically in Figures

20, 21, and 22. It should be noted that this shoe probe

passes through more of the region above the housing plane

than even the UK probe. Further, the data from Shoe Probe

"I" was compared against the individual foot data to determine the percentage of the sample protected. The results

are presented in Table 7.

As can be seen in Table 7, the results associated

with Shoe Probe "I" are not particularly impressive when

compared to the 95th percentile data although they exceed

the protection offered by any of the generic probes.

It should be noted that Shoe Probe "I" is not, at this

point, being recommended for inclusion in a standard.

Rather, this demonstrates only one of many possible alternatives to the proposed generic probes.

It is clear from all of the above that further research

should be performed to develop a more protective probe.

The present data clearly demonstrate that none of the

existing generic probes comes close to matching a safest

case for foot data. A determination of adequacy of the

sample with regard to population demographics and distribution

is warranted. If required, a larger and more diverse

sample should be tested. A probe or probes could be developed

to match the data collected and validation of those probes

accomplished

28
Table 5

Sample Correlations

Housing Height

With Shoe Without Shoe

Correlates 6cm 8cm 10cm 6cm 8cm 10cm

FL** -1LX .32* .37* .57* - .05 .06 .46*

FL-2LX .17 .30* .46* - .24* .04 .46*

FL-2HY .24* .24* - .04 .50* - .07 -.15

FL-3HY .19* .09 .10 .33* .12 .23*

1LX-2LX .86* .92* .90* .75* .80* .73*

1LX-2HY .19* .02 .01 -.15 .12 .14

1LX-3HY . 23* .14 .42* 0 .03 .39*

2LX-2HY .14 .23* - .34* -.57* - .51* -.32*

2LX-3HY .13 0 .26* -.29 .22* .07

2HY-3HY .75* .53* .29* .75* ,55* .37*

* p

< .05 FL With Shoe - FL Without Shoe r = . ** Foot length

29
Table 6

Shoe Probe "I" Data

Position 1*

Housing

Height X

L

y

H

x y_

6 cm 11.3 2.8 9.4 4.5

8 cm 13.6 2.4 11.1 5.6

10 cm 15.6 5.3 11.9 8.3

Position 2

6 cm 10.6 5.3 8.7 6

8 cm 12.3 8.0 9.4 10,

10 cm 14.1 10.3 10.9 12,

Position 3

6 cm 7.1 4.3 5.2 6.

8 cm 8.1 6.0 4.9 8.

10 cm 9.2 10.9 5.7 13.

*Refer to Figure 6

30
•

ANSI

PROBE

CU

PROBE

UK

PROBE

(uia) 3QNV1SIO NOI1U3SNI 1VOIIU3A

31

X

bn

HORIZONTAL

INSERTION

DISTANCE

(cm)

Figure

20.

Safety

Envelopes

-

-Shoe

Probe

I

Comparison

- 6

cm

Housing

Height
|W3) 3GNV1SIQ N0I1H3SNI lV3liH3A

32

HORIZONTAL

INSERTION

DISTANCE

(cm)

Figure

21.

Safety

Envelopes

Shoe

Probe

I

Comparison

- 8

cm

Housing

Height
X

I

HORIZONTAL

INSERTION

DISTANCE

(cm)

Figure

22.

Safety

Envelopes

-

Shoe

Probe

I

Comparison

-

10

cm

Housing

Height
Table 7

Percentage of Sample

Protected by Shoe Probe "I"

Housing Height

Condition 6 cm 8 cm 10 cm

With shoe 14% 14% 46%

Without shoe 1% 1% 4%

34
References

1. U.S. Consumer Product Safety Commission. Product Profile:

Power Mowers , October, 1976.

2. Consumers Union of United States, Inc. Proposed Safety

Standard for Power Lawn Mowers , Submitted to the u. S.

Consumer Product Safety Commission, July, 1975.

3. Persensky, J.J. Memo: Evaluation of Proposed Lawn Mower

Safety Standard, October 24, 1975. (Appendix B)

.

4. National Shoe Manufacturers Association. The Foot Inside

the Shoe .

5. Van Cott, H.P. and Kinkade, R.G. (eds) . Human Engineering

Guide to Equipment Design. U.S. Government Printing

Office, 1972.

6. MIL-STD-1472B . Military Standard, Human Engineering Design

Criteria for Military Systems , Equipment and Facilities , December , 1974.

7. McCormick, E.J. Human Factors Engineering , McGraw-Hill:

New York, 1964"!

8. Snyder, R.G., Spencer, M.L., Owings, C.L., Schneider, L.W.

Physical Characteristics of Children as Related to Death

and Injury for Consumer Product Safety Design . Final

Report to the U.S. Consumer Product Safety Commission

,

May, 1975.

9. Baggaley, A.R., Intermediate Correlational Methods . John

Wiley and Sons"! New York, 1964

.

35
• «*j»dfot30 ,

'

!

.

.

.

:
APPENDIX A- -UK Probe

l>r J J Persensky

Human Factors Section

Product Systens Analysis Division

United States Department of Commerce

National Bureau of Standards

Washington, D.C. 20234

Design Rationale — - —— - British Standards Institution

'‘JnrorporaU’d by Koval Charter

2 Purl* Si rcct LONDON WIA 2KS

Tckrphone: 01-629 WXX)

TfU-a: 26693rUHSI LONDON) Head Offir. 23218 (STANLMKUS LUN) Sales U Accounts

Your ref

Our tel cst/rcf 375* AGE/20

Date 12 October 1976

Dear Sir

BS 5107: POWERED LAWNMOWERS

With reference to your letter of 9 September, we set out below comments from the

-Chairman of the Technical Committee responsible for BS 5*107 on your enquiry regarding

the development of the test probe shown in Fig 3 of the Standard:

•The foot probe referred to originated with the Technical Committees

of B.S.I. dealing with lawnmowers and in fact I myself prepared the

original drawing of it, based on initial criteria set by the committee.

-The committee first considered whether the object should simulate an

adult foot, a child's foot, or should attempt a compromise between the

two. While adult and child feet do present somewhat different problems,

experiments with several different types of sample lawnmowers appeared

to indicate that in practice, few machines which were acceptable when

tested with an adult foot were unacceptable with a child's, whereas the reverse was not the case. When tested with a probe having an adult

side view but a width in plan view designed to simulate a child's foot,

-some machines were found unacceptable which were, however, acceptable

to both the adult and the child sized probes complete. On this basis,

-and bearing in mind that the operator of a mowing machine is more likely

to be an adult male than any other class, the committee decided that this

was the type of foot to be simulated.

In preparing the detailed design, I had informal consultations with members

of the shoe manufacturing trade, to ascertain the size of shoe most commonly

worn by adult males, and its approximate dimensions. There was of course a considerable variation in dimensions depending on styling etc., and I adopted

some deliberate distortions to make the test as searching as possible while

still reasonably realistic; such distortions include making the toe section

untypically long and low. and the instep also low. A leg section was included,

at an angle of ACT to simulate the limb being thrust well forward to give the

maximum penetration of ary guarding positioned at a fairly high level from the

ground.

37

/see over
Appendix A, Page 2

n

I would not pretend that this process was equivalent to a fine

analysis of anthropometric data, but I do consider its use a

sufficiently close approximation for the purposes intended. *

Yours faithfully

Cl

Group Manager

Mechanical Department

cha/sew/fm

cc: MSI

r

38
APPENDIX B- -NBS Evaluation of Foot Probe

/ v

\ W/

UNITED STATES DEPARTMENT OF COMMERCE

National Bureau of Standards

Washington, D.C. 20234

,Octobcr 24, 1975

MEORANDUM FOR John MeGahan

Office of Consumer Product Safety

From: J. J. Persensky y

Consumer Behavior and Information Section

Subject: Evaluation of Proposed Lawn Mower Safety Standard

Three of the tests proposed by CU were evaluated by this office: Test

jj - Foot probe test, Test kk - Terrace test, and Test 11 -Obstruction

test. The tests relate to requirements 1205.18 and 1205.19 which discuss

-guards, shields, and grass catchers for rotary mowers. Tests kk and 11

are specific to walk-bchind rotary mowers, while Test jj relates to

both walk-behind and ride-on mowers. Figures 4 (Foot Probe), 13 (Terrace

Test), and 14 (Obstruction Test) describe the fixtures used in these tqsts.

The tests are considered separately below, but it must be remembered

that Tests jj and kk utilize the same foot probe so that comments

related to the probe are common to both tests.

Test ii - Foot orobe test

1. The requirements associated with this test appear reasonable

.and adequate and are more stringent than earlier standards

with regard to the blade contact hazard.

2 . The test conditions are reasonable and are easy to achieve.

However, a consistent method for measuring the lowest oosition

of the blade should be stated in order to assure repeatability.

3. Section 1205.21 ( j j ) (2) (i) should be rewritten to clarify

th3t the probe should be inserted slowly and pivoted in the

vertical plane several times prior to maximum insertion.

Also, it is not clear as to whether the 18 newton (4 lb.)

force is to be measured at lateral insertion or when the

probe is pivoted.

4 . The materials and fixtures for the test are easily obtainable

or constructed.

5. Two testers arc necessary to adequtcly nerform this test,

i.c., one to insert and observe the probe and one to move

the mower blade.

39
Appendix B, Page 2

"* 2

-

6. In order to evaluate this test it was necessary to validate

the probe design. To accomplish this, several probes, in

addition to the proposed probe were tested.

These were: A. CU adaptation of the UL probe (proposed

by offeror)

,

B. ANSI probe (currently used to detemine

compliance to ANSI B71. 1-1972),

C. United Kingdom probe (drawings Attachment A)

,

and nine shoe probes constructed with

shoes representing the population of lawn

mower users. These were:

D. Male, 95th percentile adult, wide, leather

shoe,

E. Male, 95th percentile adult, narrow,

leather shoe,

F. Male, 95th percentile adult, soft last shoe,

G. Female, 95th percentile adult* wide,

leather shoe,

H. Female, 95th percentile adult* narrow,

leather shoe,

I. Female, 95th percentile adult, soft last shoe,

J. 11 year old, 5th percentile, vide leather

shoe

,

K. 11 year old, 5th percentile, harrow

leather shoe,

L. 11 year old, 5th percentile, isoft last shoe.

Each of these probes was used to perform Test ji on 6 walk-behind mowers

"and 4 ride-on mowers. The results are presented in Attachment B. Analysis of the data (Attachment C) indicated that of three generic

probes (A, B, and C) the United Kingdom probe was most valid when compared

with the shoe probes. Also the CU proposed nrobc is more stringent than

the ANSI probe. Based on the data the United Kingdom probe should be

considered for inclusion in the final standard instead of the nrobc

proposed by the offeror.

Test kk - Terrace test

1. The requirement associated with this test is intended to

provide additional (with relation to 1205.18) blade contact

protection for the operator at the rear of the mower. This

is a new test not present in voluntary standards. It also

provides n means to assure that a rear trailing shield will

not be damaged

2. The test conditions appear reasonable and are easily achieved.

The test fixture can be constructed readily, however, the

overall length and width measurements should be stated. It should be noted that the fixture must support the weight of

the mower and tester. Also, since the critical area is the

curvature of the terrace a simplified and smaller fixture

might lie constructed so as to maintain the radius of curvature

but without t he long slope and terrace. Finally, there is

question as to the appropriateness of the proposed radius of

40
Appendix B, Page 3

-3-

curvature. There' is no rationale stated for this value.

The final value might he based on a survey of actual terrace

faces using the smallest existing radius.

3 . Procedural ly, there is no statement of force for insertion of

the probe. On the mowers tested there was a clear differentiation among mowers which met the criteria and those which

did not (see data Attachment D) . Some force is required to

-lift a trailing shield by inserting the probe. Those mowers

which failed to meet the criteria had trailing shields

which were constructed of material which was rigid enough

to lift off of the surface of the fixture allowing blade

contact. Other shields could not be raised without considerable

insertion force. The test should state a maximum insertion

force

4 . Comments regarding the foot probe are stated in the discussion

of Test jj and apply to Test kk.

5. TVo testers are necessary to perform this test.

Test 11 - Obstruction test

1. Test 11 is designed to prevent any loss of protection from

guards or shields when the mower passes over an obstruction

or over a depression in the mowing surface. Further, the

-intent is to reduce the probability that a rear trailing

shield will be removed because of its nuisance value if

the shield catches on obstructions.

2. The test conditions appear reasonable and easy to achieve.

The test fixture can be easily constructed, however, overall

length and width measurements should be stated. There is

no rationale for the criteria values selected for the

obstructions

3. Procedurally a problem exists in that there is no statement

as to forces or speeds for moving the mower over the obstructions. In the course of testing it was observed that, with

sufficient SDccd all mowers would fail to meet the criteria

because the mower would bounce, but when nulled across the

obstructions slowly only -a few mowers failed the test. The

4ata presented below was based on fast, slow, and medium

speeds, where t ho medium speed was a little faster than

walking. The data arc from six walk-behind mowers.

41
- 4

- Appendix B, Page 4

Test 11

Number of mowers which fail or meet test criteria

Criteria • Depression Obstruction

Fails 4 2

Meets 2 4

From this data it can be seen that most mowers do not meet

the criteria for Test 11.

SUNMARY

Three major suggestions are presented in the above discussion for

alternatives to tests jj, kk, and 11.

1. Test jj - The United Kingdom foot probe should be required

by the safety standard rather than the proposed modification

of the UL probe.

2. Test kk - A maximum force should be stated for insertion of

the foot probe. The United Kingdom probe should be used.

3. Test 11 - A force or speed should be stated for movement of

the mower over the obstructions.

'Cc: John Donaldson

Attachments : A - Drawing of United Kingdom probe

B - Data, Test jj

C - Analysis of data from Test jj

D - Data, Test kk

42
Appendix B, Page 5

Attachment B

Data, Foot Probe Test

Data from foot probe insertion for six walk-behind mowers and four rideride-on mowers as per Test jj.

Probe

Walk-behind Ride-on Blade

Contacts

No Blade

Contacts

Blade

Contacts

No Blade

Contacts

A 3 3 4 0

B 0 6 0 4

C 5 1 4 0

D 4 2 4 0

E 5 1 4 0

F 5 1 4 0

G 3 3 2 2

H 5 1 4 0

I 5 1 4 0

' J 5 1 3 1

K 4 2 4 0

L 6 0 4 0

43
Appendix B, Page 6

-Attachment C

Analysis of Data from Test jj

In order to determine the "best" generic probe (CU, ANSI, or United

Kingdom) an attempt was made to compare those probes with shoe probes

which were assumed to be representative of the population of lawn

mower users, i.e. , 95th percentile adult male to 5th percentile 11

year old. The analysis was performed using the following assumptions

and data collected as per Test jj.

Assume

1. The population of lawn mower users ranges from the 95th

percentile adult male to the 5th percentile 11 year old.

2. The shoe probes tested are representative of that population.

3. The "ideal" probe would duplicate the entire population

of shoe probes, both with regard to blade contact and misses.

Six walk-behind and four ride-on mowers were tested using the three

generic probes and nine shoe probes. Data were accumulated on blade

contact for each probe on each mower. The following table is based on the number of agreements between each generic probe and each shoe

probe. That is, if a generic probe and a shoe probe both contacted

the blade a point was scored, or if both failed to contact the blade

a point was scored. If only one of the pair contacted the blade there was no agreement, i.e., no point scored. Each cell has a maximum value

of six.

Table 1.

-Number of agreements between each generic probe and each shoe probe

for six walk-behind mowers.

Generic Probes

Foot

Probes A B C

D

' 5 2 5 E 4 1 6

F 4 I 6

G 4 .5 4

11 4 1 6

1 4 1 6

J 4 1 6

K 5

0 5

1. 5 n 5 Toi .i 1 Agrivwm s 12 10

44
Appendix B, Page 7 Attachment C

Page 2

Assume further that the ideal probe would agree perfectly with all

shoe probes for a Total Agreements of 6 x 9 or 54.

Now, to test the statistical significance of these data the standard

error of proportion is appropriate for each nair assuming a noDulntion

of 54.

First compute the proportion of each total agreements.

Probe A - .68

Probe B - .22

Probe C - .91

The significance of the proportions is computed by

^1 ~ ^2

/P

x

(l - i^) + Is (l - P

2

) V J*a

+ N

2

cohere = proportion of group 1 ~ proportion of group 2

Nj = number of entries in group 1

N

2 = number of entries in group 2

So, for comparisons

AB

AC

.68 - .22

2 = /- 68 (1 - . 6S) + .22 (1 - .22)

54 + 54

7.66 p< .01

.68 - .91

2 = /.68 (1 - .68) + .91 (1 - .91)

54 + 54

2 * 4.37 p< .01

.22 - -.91

BC 2 = /. 22 (1 - .22) + .91 (1 - .91)

V 54+54

2 * 14.24 p< .01

Therefore, all probes are significantly different from each other.

Further, the absolute values indicate that the United Kingdom nrobc

is most similar to the shoe probes.

• 45
Appendix B, Page 8 Attachment C

Page 3

When performing these calculations for the four ride-on mowers it

was determined that probes A and C were equivalent and nrobc B

was significantly different. See data in Table 2.

Table 2

Total agreements between each generic probe and all shoes probes.

Probe ABC

total

Agreements 33 3 33

Proportion .92 .03 ,92~

46
Appendix B, Page 9

Attachment D

Data, Terrace Test

Data from foot probe insertion in six walk-behind mowers as per Test kk.

Blade No Blade

Probe Contact Contact

A 2 4

B 2 4

C 2 4

D 2 4

E 2 4

F 2 4

G

n4* 4

H 2 4

I 2 4

J 4* 4

K 1 5

L 2 4

47
.
APPENDIX C

Foot Length Data

Presented below are foot length data presented in

various Human Factors Handbooks and the data from the present

study.

Percentile

Source 5th 95th

Van Cott and Kinkade (5)

Adult Male

Female

23.9

22.1

29.5

26.2

Military Standard 1472-B (6)

Adult Male

Female

24.4

22.2

29.0

26.0

McCormick (7)

Adult Male

Female

24.8

22.7

28.6

26.1

University of Michigan (8)

11 years old Male 19.7 23.3

Female 19.0 23.0

Present Study

Male 23.1 29.3

11-65 years Range 19.3 30.5

old Female 21.4 25.4

Range 19.8 - 26.2

49
'
APPENDIX D--Research Consent Form

| NfcS-783 U.S DEPARTMENT OF COMMERCE

117.71, NATIONAL BURLAU Of STANDARDS

' RESEARCH PARTICIPANT AGREEMENT

3. (. •»*.! (.Itllll'l

i. umtitin/SiiLlioii 4. LOCal lO'

Dr. J. J. Persensky 441.02 3QC Gaiineraiiuip

| b. U(ieHn«nt Coo* |X Omar Ibwh iln Foot Simulator Evaluation (Probes) Local school

I L. Lraacnoiion cl iaftfcirnari: The purpose of this research is to determine how far a foot can be pushed

under an opening and then tilted upward. It is being done so that protective

shielding for consumer products (such as lawn mowers) can be evaluated. Tne

equipment will be a box- like rig and a camera. Tne participant will place

his/her foot through the opening in the box and turn the foot upwards . While the

foot is in the box photographs will be taken.

1 7. Atsas to Particioan-. No accidents are expected.

| £. AesDonsiOnmes of Parncipan*.

i Tne participant, with informed consent, will follow instructions , answer

i questions about age and sex, and allow the investigator to weigh them and

| measure their height and feet.

i i

j S. fcesDonsioiiiues o' investipatot is

I The investigator will (1) fully explain the test procedure, (2) explain

the purpose of the test, (3) ensure safe test conditions, and (4) keep personal

information confidential.

i

IP. IT IS UNDERSTOOD THAT EITHER TnF PRINCIPAL INVESTIGATOR. THE PARTICIPANT. OR THE PARTICIPANT'S PARE NT OR GUARDIAN MAI

TERMINATE THE PARTICIPANT'S INVOLVEMENT IN THE RESEARCH A1 ANY TIME KITHOUT INCURRING LEGAL LIABILITY E OR SUCh

TERMINATION.

I El. I n»t«bv CPtliiv in* i my participation u voluntary ane mm • m»i iwo ana acc*n ina irmi ol mis apraamant.

| Participant, p Paiant p Guardian fAipnaiw/r; Data

EC. Piinripai invattipaim ISiaaaturr. Oatr

I EJ. Early Eamufwrlran try IlifMli Uair

r 1
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 77-12942. C»ov *t Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE 5. Publication Date

Power Lawn Mowers:

May 1977

fcvaluation of Anthropometric

Foot Probes

6. Performing Organization < ode

1

7. AUTHOR(S)

J. J. Persensky 5 A. M. Ramey

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Pro ject /Task/Work Unit No. 441-1423

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Consumer Product Safety Commission

5401 Westbard Avenue

13. Type of Report & Period Covered

Final

Washington, D. C. 20207 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

bibliography or literature survey, mention it here.) This document is the final report for the Consumer Product Safety Commission of an evaluation of the adequacy of existing generic foot probes. The Human Factors Section

at NBS compared the dynamic characteristics of three generic probes with those of potential lawn mower users’ feet.

Horizontal and vertical insertion distances for the generic probes and the foot

data were used to develop safety envelopes for various simulated housing heights. Inspection of the safety envelopes at 6, 8, and 10 cm housing heights indicates that of

the three generic probes, the UK probe most closely approximates the foot data. Only

the UK probe passes through the area above the plane of the housing opening.

However, a comparison of each individual * s data (rather than aggregate data) was made with each generic probe to determine the percentage of participants who would be

completely protected by each generic probe. These data indicate that at least one point

of each individual’s foot movement data would fall outside of the safe area defined by

the generic probe envelopes. Therefore, a lawn mower meeting the criteria of any of the

generic foot probes would not completely protect any of the participants in the study.

Recommendations for a modification of the UK probe and for further research are

discussed.

I 64341

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

)

Consumer products; generic probes; human factors; lawn mowers; safety; standards

18. AVAILABILITY Unlimited

uz For Official Distribution. Do Not Release to NT1S

|

1 Order I' rom Sup. of Doc., U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. CU

1

! Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

l!NC LASSII II.

D

21. NO. OF PAGES

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