Interpretation ID: nht94-3.90

TYPE: INTERPRETATION-NHTSA

DATE: August 8, 1994

FROM: Jane L. Dawson -- Specifications Engineer, Thomas Built Buses, Inc.

TO: Chief Counsel, NHTSA

TITLE: Subject Request For Interpretation - FMVSS 210

ATTACHMT: Attached to 2/2/95 letter from Philip R. Recht to Jane L. Dawson (A43; Std. 210; VSA 108(b) (2))

TEXT: Dear Sir:

Thomas Built Buses, Inc. is in the process of releasing a school bus passenger seat that may eventually be used on school buses produced by all body manufacturers. Since this is a new product line for us, we have several concerns about certifying compli ance of our seat on other manufacturers' vehicles.

We know that NHTSA recognizes that in many instances due to cost considerations, manufacturers simulate test conditions when performing compliance testing by using test fixtures rather than testing in actual school buses. NHTSA addresses that fact in S5 of FMVSS 210 by requiring that anchorages be "connected to material whose breaking strength is equal to or greater than the breaking strength of the webbing for the seat belt assembly installed as original equipment at that seating position" and that "t he geometry of the attachment duplicates the geometry, at the initiation of the test, of the attachment of the originally installed seat belt assembly."

Traditionally, when we test seat belt anchorages on our own school bus passenger seat, the seat is attached to an actual 14 gauge school bus floor, and force is applied according to the testing requirements of FMVSS 210. As a result of the force applica tion, the floor undergoes a certain amount of buckling. As the floor begins to buckle, the angle of the belt relative to the seat frame changes from the belt angle that's present at the initiation of the test.

When the same test is conducted using a school bus passenger seat attached to a 1/2" steel plate test fixture rather than an actual floor section, there is no buckling of the floor, therefore, there is no change to the belt angle when the anchorages are subjected to the force requirements of FMVSS 210. Since there's no change to the belt angle, the use of a school bus bench seat mounted on a 1/2" steel plate test fixture doesn't necessarily duplicate the - conditions present when the bench seat is moun ted on an actual school bus floor.

Thomas Built Buses requests an interpretation on the following:

When a seat manufacturer certifies compliance with FMVSS 210 for installation in a school bus, do the requirements of FMVSS 210 allow the seat manufacturer's certification to be based on the seat's more rigid attachment to a 1/2" steel plate test fixture or must the seat manufacturer's certification be based on the seat's attachment to a typical 14 gauge school bus floor?

If the seat manufacturer uses a 1/2" steel plate test fixture, must the final stage school bus manufacturer who installs the seat retest using their own 14 gauge floor before compliance with applicable standards is certified?

Please contact me if you have additional questions or need additional information.

Sincerely