Interpretation ID: aiam3715
Sr. Project Engineer - Vehicle Regulations
Mack Trucks
Inc.
P.O. Box 1761
Allentown
PA 18105;
Dear Mr. Robson: This responds to your recent letter requesting an interpretatio 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 subject 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-dut 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 requried loading (paragraph S4.2). The upper seat sections and adjusters of 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 its adjusted position during loading.; The answer to your specific question, the seat must remain in it adjusted position when tested to 20 times the weight of the entire seat, as required by paragraph S4.2 of the standard. We would agree with you, however, that with a seat configuration such 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 adjusters 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 yo 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 components 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, Frank Berndt, Chief Counsel