NBSIR 74-509

Strength and Stability Testing

of High Chairs

Daniel J. Chwirut

Engineering Mechanics Section

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

June 1974

Final Report

Prepared for Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, Maryland 20016

NBSIR 74-509

STRENGTH AND STABILITY TEST^G

OF HIGH CHAIRS

Daniel J. Chwirut

Engineering Mechanics Section

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

June 1974

Final Report

Prepared for Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, Maryland 20016

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

NATIOrylAL BUREAU OF STANDARDS, Richard W. Roberts. Director

STRENGTH AND STABILITY TESTING OF HIGH CHAIRS

Daniel J. Ghwirut

Accident reports from hospital emergency

rooms were surveyed to determine the probable

causes of accidents involving high chairs.

Possible test methods for determining if the

characteristics of the high chairs leading to

the accidents are present in a given item were

investigated, including the test methods re- commended in the Juvenile Products Manufacturers

Association Voluntary Safety Standard for High

Chairs, These tests included tests for tray

strength, chair static strength, foot rest

strength, restraining strap strength, and

stability. These test methods and performance

characteristics are intended to supply information leading to federal safety standards.

Key Words: Accident reports; high chairs;

infants; safety standards; stability and

strength; test methods,

1.0 INTRODUCTION

Accident reports received through the National Electronic Injury

Surveillance System (NEISS) at the Bureau of Product Safety (now

part of the Consumer Product Safety Commission) listed many injuries

to 8-24 month old children as a result of accidents involving high

chairs. These injuries included mostly lacerations, contusions and

abrasions, and a few fractures. The injuries resulted from a variety

of causes, including finger lacerations in oversized tray adjustment

holes, falls from the high chair, a child pulling the chair over

onto himself from the floor, failure of folding mechanisms, and

overall instability (chair tipped over with child in it). An investigation

was undertaken at the National Bureau of Standards to determine

what characteristics of the high chairs possibly contributed to

injury producing accidents, to determine if these characteristics

were present in most or only a few of the items on the market, and

to determine appropriate test methods and performance characteristics

which might be written into federal safety standards. Tests performed

included tests for tray strength, chair static strength, foot rest

strength, restraining strap strength, and stability. In addition,

some dimensional measurements important to the safety of the high

chairs were taken. Some tests were variations of the tests recommended

in the Voluntary Safety Standard for High Chairs sponsored by the

Juvenile Products Manufacturers Association (JPMA), draft dated

October 17, 1972. These tests are presented in the Appendix,

1
2.0 TEST SPECIMENS

Nine high chairs were purchased from local retail stores. These

included both tubular frame and wooden chairs, some folding and

some non-folding. These nine covered the range of styles available

during the period of this investigation. These chairs were designated

as test specimen numbers 101 through 109 inclusive.

3.0 TEST PROGRAM

3.1 Falls From the Chair

Many injuries resulted from the child falling from the chair,

although the specifics of the accident sequence are not known. One can envision four possible causes for these falls: 1) The tray

and/or restraining strap were not used or in^roperly adjusted, allowing

the child to slide out or stand and fall, 2) Although the tray was properly latched, too much clearance between the tray and the seat

back allowed the child to stand if not strapped in, 3) The tray

latch mechanism failed and 4) The restraining strap failed. The

solution for the first case is to educate the parents about the

importance of proper usage, either through government publications

or manufacturers' instruction manuals. The second case is a human

engineering design problem that must be considered. The tray must

be capable of being positioned so as to prevent the child from standing.

Table 1 shows the tray-to-seat back clearance with the tray adjusted

to the tightest position for nine high chairs. Possibly the human

factors experts can determine if these distances are acceptable

in proportion to the sizes of infants who use the chairs. The third case involves a structural design requirement. The tray latch mechanism

must be capable of withstanding the forces exerted on it by the

child. Child strength data gathered by Brown et al (ref. 1) at NBS

indicate that the 95 percentile push force applied by a 2 year old

male is about 23.5 Ibf (104 N), The forces exerted by a child in

a high chair may be higher since the child can brace himself against

the chair back. Test 2a in the JPMA standard requires that the tray

withstand a 20 Ibf (89 N) horizontal force applied at the front

center and side center. All nine high chairs, when tested as shown

in fig, 1, met these requirements. They also passed the same test

with a test load of 50 Ibf (22 N), All chairs also passed test 2B

of the JPMA standard, which requires the chairs to withstand 20

Ibf (89) vertical forces applied independently at the front and

back center of the tray (fig, 2), These tests were repeated with

a test load of 50 Ibf (222 N) and all chairs passed except specimen

number 102, v^ich failed by uncoupling of the tray latch mechanism

when the force was applied to the front center. Two additional tests

related to the mechanical integrity of the tray, a drop test and

a static load test (JPMA test numbers 3 and 4,3) were performed.

The tray from specimen number 104, a wooden chair, broke into two

pieces when dropped. All others passed this test. All chairs passed

2
the tray static Load test (fig. 3) when 50 Ibf (222 N) was applied,

but specimen number 102 failed when 100 Ibf (445 N) was applied.

All others passed with the higher load. The fourth case also involves

a structural design requirement. The restraining strap must have

sufficient strength to hold the child in the chair if the tray is

not attached. Only five of the nine chairs tested were equipped

with restraining straps (see table 1), These five were subjected

to JPMA test number 6, with a test load of 22 Ibf (98 N), and all

passed (see fig. 5), With a test load of 50 Ibf (222 N), specimen

numbers 106 and 107 failed because the belt slipped more than 1 in (25 ram) in 30 seconds.

The results of all of these tests are summarized in table 2,

3.2 Stability

The JPMA test for stability (JPMA test number 5) concerns itself

with the chair tipping over with the child in it, although the origin

of the specific loads, e.g. 25 Ibf (111 N) weight and 5.5 Ibf (24 N)

applied force, are not obvious. All nine chairs passed when subjected

to this test (fig, 4, table 2). The forces tending to tip an occupied

chair are external forces, such as from the child pushing or pulling

on a table or counter, or inertial forces from the child's movements.

No work was done in this investigation on the latter case since no human factors information on the forces generated by the movements of

a child in a high chair could be found. However, some consideration

can be given to the problem of a child pushing or pulling. The

locations of the centers of gravity for five high chairs were determined. The weight of an average 2 year old child was taken to be

30 lb (14 kg) (ref. 2). For a 30 lb (14 kg) child seated in the center

of the seat, the horizontal forces at tray height required to rotate

the chair forward were calculated. These values ranged from 11«2 to

17.2 Ibf (49.8 to 76.5 N). Similar values would be obtained for sideways rotation. Again referring to Brown's data (ref. 1), the 95 percentile pull strength of a 2 year old is about 38 Ibf (169 N) which is

well above the force required to rotate the high chairs tested in this

investigation. Of course other factors must be considered, such as distances from the child to the counter. However, once It has been

determined that the child could reach the counter, the forces a child

could apply are much larger than those applied in the JPMA recommended

test

.

The problem of a child pulling the chair over onto himself is a difficult one. The moments required to tip over unoccupied chairs

were calculated for five chairs. These values ranged from 66 to 176

Ibf-in (7,5 to 19,9 N-m), with the higher values corresponding to the

heavier chairs. Children in the 1-2 year old range can easily apply

this moment to even the heavier chairs by grasping a leg brace and

pulling or falling. Increasing this required moment could make the

chairs infract ically large and/or heavy. Some improvements in design

3
that could lessen the frequency and severity of injuries are:

1) minimize the use of cross braces between legs that children can pull on or climb on, 2) minimize the chair weight to lessen the injury

potential if the chair does fall, and 3) pad certain elements of the

chair similar to what is now done on some playpens and porta-cribs,

3,3 Lacerations Related to Oversized Holes

The JPMA standard restricts hole diameters to less than 0.125

in (3.2 mm) or greater than 0.375 in (9.5 ram). Strangely, all six

of the chairs that had tray adjustment holes failed this requirement

with hole diameters being 0.19, 0.25, or 0.31 in (4.8, 6.4, and

7,9 mm)

.

3.4 Other Static Load Tests

All high chairs passed the seat and footrest static load tests

in the JPMA standard (test numbers 4.1 and 4.2).

4, DISCUSSION

The performance of the nine chairs as determined by the JPMA tests

and modified tests are summarized in table 2. The test configurations

recommended by JPMA appear to be suitable for testing the overall static

strengths of high chairs. However, based on a limited amount of data on the strengths of children, the test loads recommended by JPMA appear

to be inadequate in several cases. The application of larger loads

more consistant with the strengths of infants produced failures in

a tray latch, a tray, and two restraining straps that had passed the

JPMA tests.

The JPMA test for stability appears to have no relation to the

push or pull strengths of infants. However, the human engineering

aspect of occupied chair stability are very inportant and should be

considered in any stability test. The problem of unoccupied stability can be eased somewhat with sin^jle design changes.

The test methods described in the appendix, with increased load

values determined by appropriate human factors studies could probably

be used as a basis for writing a strong federal safety standard.

Additional work in the areas of occupied stability, fatigue resistance,

and abuse testing should also be considered.

4
5. CONCLUSIONS

The test configurations recommended by the JPMA Voluntary Safety

Standard for High Chairs appear to be suitable for strength testing

of high chairs. However, larger applied loads, more consistant with

the limited available infant strength data, produced failures in four

high chair elements that had passed the JPMA tests. Additional test

methods for stability, fatigue resistance, and abuse testing should

be developed,

6. REFERENCES

1« Brown, W, C, , Buchanan, C, J,, and Mandel, J»: A Study of the

Strength Capability in the Two Through Six Year Old Age Groups,

NBSIR 73-156 (1973).

2. Fryer, B,, et al.: Growth of Pre-school Children In the North

Central Region, J, Amer, Diet. Assn. , 60: 30-37, 1972,

5
APPENDIX

TESTS IN JPMA STANDARD

TEST NO. 2A

Tray - Horizontal Force Test

Step 1« The chair is to be affixed securely (all legs on the

floor! so it cannot move in the direction the force is being applied.

Second, a pulley is affixed at a location in front of the chair at

a height whereby a rope or cord passing over it is horizontal with

the chair tray. Third, a pull scale capable of measuring at least

25 pounds of force is attached to the center front of the tray in

such a way that it would not affect the natural shape of the tray

when force is applied at that point. Next, a nylon cord is passed

over the pulley and weight or force applied gradually to the end of

the cord until the scale indicates 20 pounds for 30 seconds.

Step 2. Make a similar test under the same conditions as Test No. 2A but with the chair affixed in a position so that the

horizontal force of 20 pounds is gradually applied perpendicular to

the center of each side of the tray for 30 seconds each,

TEST NO, 2B

Tray - Vertical Force Test

Step 1, The chair is to be affixed securely in its normal

standing position so that all legs stay in contact with the surface

on which they rest. Second, a pulley is affixed in a location above

the chair at a position so a nylon cord passing over it is perpendicular with the front center of the tray. Third, a scale capable of

measuring at least 25 pounds of force is attached by one end to a nylon cord and the other in whatever manner possible to the front

center of the tray in such a way that it would not affect the natural

shape of the tray when force is applied. Now a vertical up force of

20 pounds is gradually applied by the means of pulling on the nylon

cord for a period of 30 seconds.

Step 2. Perform the same test as Test No. 2B but with the chair

positioned so that the 20 pound vertical force is gradually applied

perpendicular to the rear center of the tray.

6
TEST NO. 4

Static Load Test

Step 1, Seat Test. The chair is placed in an upright position

with all legs on the floor. Next, a total weight of 100 pounds will

be placed on the center of the seat and be distributed over an area

of 36 square inches upon a six-inch by six-inch wood block nominally

one-inch thick. The load shall be applied for a 60-second period.

Step 2. Step or Footrest Test. The chair is placed in an upright position with all legs on the floor. If the step or footrest is adjustable, adjust to low position. Next, a total weight of

at least 50 pounds will be placed on the center of the step or footrest and be distributed over an area of 18 square inches upon a threeinch by six-inch wood block nominally one-inch thick. The load shall

be applied for a 60-second period.

Step 3. Tray Test. The chair is placed in an upright position

with all legs on the floor. If tray is adjustable, adjust the tray

to middle position.* Next, a total weight of at least 50 pounds

will be placed at the center top surface of the tray distributed over

an area of 18 square inches upon a three-inch by six-inch wood block

nominally one-inch thick. The load shall be applied for a 60-second

period.

TEST NO. 5

Stability

Step 1. The chair is placed in an upright position with all

legs on the floor. The tray is attached, if adjustable, in middle

position." Then a weight of 50 pounds is centered on the seat upon

a six-inch by six-inch wood block and affixed to the seat in such a way so that it will not tip in the direction of the force when the

force is applied. Then an angle or bar will be placed on the floor

against the legs or leg closest to the force in such a manner as to

prevent the chair from sliding on the floor, but not to prevent it

from tipping. Next the force will be applied horizontally with

reference to the floor by pulling on the scale. The chair will be

tested for stability in the following instances:

1. Front - Horizontal pull applied at center front edge of

tray at the height of the tray.

''Relates to trays that have an odd number of positions. If there is no middle position, then adjust to the next colsest position to the back.

7
2, Sides - Horizontal pull applied at the center of each of

the arms at the height of the tray,

3, Rear - Horizontal pull applied at center of back at the

height of the tray.

In all directions the force must equal or exceed 11 pounds without

vertical displacement of more than one-fourth inch.

Step 2. Under the same conditions as Test No. 5 but with a 25

pound weight affixed to the seat instead of 50 pounds. In all

directions the force must equal or exceed five and one-half pounds

without vertical displacement of more than one-fourth inch.

TEST NO, 6

Restraining Strap Pull Test

The chair is to be affixed securely so it cannot move in the

direction the force is being applied. Second, a pulley with a nylon

cord is affixed in a position so that a nylon cord passed from the

pull scale over it will be four inches above the top of the seat of

the chair, and approximately in the center of its width. Third, a cylinder eight inches in diameter by eight inches in height is placed

in the seat with the restraining strap placed across it in the

engaged position. A nylon cord is attached to the cylinder above and

below the safety strap and both ends attached to a pull scale capable

of measuring at least 25 pounds of force. The other end of the scale

shall be attached to the nylon cord that passes over the pulley. Now

a force of 22 pounds is gradually applied to the cylinder by means

of pulling on the nylon cord. The force shall be applied for a 30

second period.

8
Table 1 - Tray-to-seat back clearance with tray adjusted to the tightest

position.

Specimen number Clearance Restraining strap

in cm

101 4.75 12.1 No

102 5.88 12.9 Yes

103 8.00 20.3 No

104 5.00 12.7 No

105 7.50 19.0 Yes

106 4.75 12.1 Yes

107 4.75 12.1 Yes

108 4.75 12.1 Yes

109 8.75 22.2 No
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N8S-1 I4A (REV. 7-73)

U.S. Q£PT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. inihi.u;ATioN OK ki-.I'or r no. NBSIR 74-509

2, Gov't Accession

No.

3. Recipient's .Accession No.

4. i i ri.i; .\:\n suin i'i li:

Strength and Stability Testing of High Chairs

5. I'ublication Date June 1974

6. Performing Organization C-odc

7. AUTHOR(S)

Daniel J. Chwirut

8. Performing Organ. Report No. NBSIR 74-509

9. PERFOR.MING ORGAMZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Projecr/Task/Work Unit No. 2130449

11. Contract/Grant No.

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

Consumer Product Safety Commission

5401 Westbard Avenue

. Bethesda, Maryland 20016

13. Type of Report & Period Covered

Final

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.)

Accident reports from hospital emergency rooms were surveyed to determine

the probable causes of accidents involving high chairs. Possible test methods

for determining the characteristics of the high chairs leading to the accidents were investigated, including the test methods recommended in the Juvenile

Products Manufacturers Association Voluntary Safety Standard for High Chairs,

These tests included tests for tray strength, chair static strength, foot rest

strength, restraining strap strength, and stability. These test methods and

performance characteristics are intended to supply information leading to

federal safety standards.

17. KEY M'ORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Accident reports; high chairs; infants; safety standards; stability and strength;

test methods.

13, AVAILABILITY \jC Unlimited

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