Interpretation ID: nht78-1.36

DATE: 05/11/78

FROM: AUTHOR UNAVAILABLE; J. J. Levin, Jr.; NHTSA

TO: Blue Bird Body Company

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your February 9, 1978, letter asking how to measure the head form contact area in Standard No. 222, School Bus Passenger Seating and Crash Protection.

In your first paragraph, you indicate that the National Highway Traffic Safety Administration (NHTSA) has allowed the knee form contact area measurement to be undertaken on or within a line 1 1/2 inches from the edge of the leg protection zone to ensure that the knee form will contact the entire surface. You ask that a similar line be established for the head protection zone contact areas.

As you know, the head form contact area requirements apply to more areas than do the knee form contact area requirements. The knee form contact area requirements apply only to seat backs and the backs of restraining barriers. The head form contact area, on the other hand, includes anything falling within a specified zone which might include the sides or tops of seats. Therefore, it is impossible to create fictional lines around the outer edges of objects that fall within the head protection zone for purposes of testing the compliance of those objects with the requirements. The agency notes further that it never stated that it would test knee form contact area on or inside a line 1 1/2 inches from the edge of a seat back or restraining barrier. The agency did state that it would test in a manner that "provides opportunity for the knee form to contact with the seat back or restraining barrier to the fullest extent possible." That interpretation can also be applied to the head form contact area requirements.

SINCERELY,

BLUE BIRD BODY COMPANY

February 9, 1978

Joseph J. Levin Chief Counsel National Highway Traffic Safety Administration

Dear Mr. Levin:

Reference: 1. W. G. Milby to Frank Berndt, December 20, 1976 2. Frank Berndt to W. G. Milby, February 23, 1977, N 40-30

Reference number 1 requests an interpretation that the centerline of the knee impact tests of FMVSS 222 only be required on or inside of a line 1 1/2" (same as knee form radius) from the edge of the leg protection zone. The reason for the request was to insure that it is physically possible to obtain the required contact area and to insure that enough padding of the correct composition is available for the knee form to contact.

Reference number 2 grants the request of reference number 1.

The purpose of this letter is to confirm our assumption that the same reasoning should be applicable to the head protection zone.

Thank you for your early response.

W. G. Milby Manager, Engineering Services