Interpretation ID: nht72-4.21

DATE: 05/01/72

FROM: AUTHOR UNAVAILABLE; Charles H. Hartman; NHTSA

TO: Rose Manufacturing Co.

TITLE: FMVSS INTERPRETATION

TEXT: This is in reply to your letters of March 23, 1972, and March 27, 1972, concerning our previous letter to you dated March 10, 1972.

We recognize your contribution to safety and your deep personal involvement in child harnesses. Harnesses, such as yours, offer many desirable features. The child is free to move about, and he is adequately restrained if the harness system is properly adjusted and anchored. Effective harness systems can probably be produced at modest cost.

There certainly can be no objection to the upper torso restraint provided by a good harness system. Indeed, this is a very important feature which is required because of the child's special skeletal structure.

On the other hand, restraints which are anchored to inadequate structures or which allow excessive motion of the child in a crash cannot be condoned. Actual thirty mile-per-hour, sixteen g dynamic sled tests of child harnesses anchored as you recommend have shown that a severe problem exists with the anchorage system. Quoting the University of Michigan Highway Safety Research Institute Report, Child Seat and Restraint Systems Test Program, DOT/MS-000-376, "In the test at 30 mph the adult seat back broke away due to the load imposed by the restraint system tether. This allowed the dummy to move forward far enough to cause potential contact with the vehicle interior." This test was conducted using a heavy duty Bostrom truck bucket seat and utilized only the thrity-pound, three-year-old child dummy, restrained by a Sears small harness. The present typical seat back strengths are, thus, inadequate to support a harness system which depends upon the seat back. It is our intention to encourage improvements in seat back strength for automobile production by future rule making action.

Since your harness is recommended for children up to fifty pounds and since most passenger car seats are not as strong as the test seat, we expect the situation to be even more serious in realistic usage conditions which also normally encounter appreciably higher load levels in thirty mile-per-hour crashes. This is why we object to your system of anchorage. Thus, our position is as stated in our previous letter to you.

We hope that you will consider other methods of anchoring your child harness which will prevent seat back failure and resulting excessive occupant excursions.

We appreciate your sincere interest and concern in this matter. We emphatically do believe that child harnesses play a vital role in child restraints.