Interpretation ID: nht88-2.72

TYPE: INTERPRETATION-NHTSA

DATE: 07/14/88 EST

FROM: FRANK BERNDT -- CHIEF COUNSEL NHTSA

TO: S. ROBSON -- SR. PROJECT ENGINEER - VEHICLE REGULATIONS MACK TRUCKS, INC.

TITLE: NOA - 30

ATTACHMT: ATTACHED TO LETTER DATED 08/03/88 TO BARRY NUDD FROM ERIKA Z. JONES, REDBOOK A32(3), STANDARD 207, VSA 108; LETTER DATED 08/28/87 TO ERIKA Z. JONES FROM BARRY NUDD

TEXT: Dear Mr. Robson:

This responds to your recent letter requesting an interpretation concerning the test procedures of Safety Standard No. 207. You ask whether a seat in a heavy duty truck must remain in its adjusted position when tested with a load of 20 times the weight of the entire seat, if the seat has been tested and remains in its adjusted position when subjected to a load of 20 times the weight of the adjustable upper section of the seat.

This question arises because of the configuration of some heavy-duty truck seats which include suspension fixtures (pedestal structures) on which the upper seat section rests. Safety Standard No. 207 requires seats to withstand a load equal to 20 times their weight and requires the seats to remain in their adjusted position during the required loading (paragraph S4.2). The upper seat sections and adjusters or your truck seats are tested on rigid test beds by the seat manufacturer and reportedly comply with the adjuster provision of S4.2. However, when you test these seats in the actual vehicle (applying 20 times the weight of the entire seat, including pedestal), the center of gravity falls on the seat adjuster and the seat does not always stay in it s adjusted position during loading.

In answer to your specific question, the seat must remain in its adjusted position when tested to 20 times the weight of the entire seat, as required by paragraph S4.2 or the standard. We would agree with you, however, that with a seat configuration suc h as you describe, the adjusters and upper seat section would never experience a loading of 20 times the weight of the entire seat in an actual crash. Your problem appears to arise because the center of gravity of this seat happens to fall on the seat a djusters and the standard requires the

loading to be applied through the center of gravity. The purpose of this loading requirement, however, is to ensure the integrity of the entire seat as it is attached to the vehicle structure.

Therefore, it is our opinion that for a pedestal seat such as you describe, a manufacturer could establish due care through a combined test procedure which would load the seat adjusters and upper seat section to only 20 times the weight of those componen ts to determine if the seat would remain in its adjusted position, and which would load the seat as anchored to the vehicle structure to 20 times the weight of the entire seat, including the pedestal.

Please contact Hugh Oates of my staff if you have any further questions (202-426-2992).

Sincerely,