Interpretation ID: 86-4.27

TYPE: INTERPRETATION-NHTSA

DATE: 07/31/86

FROM: AUTHOR UNAVAILABLE; Erika Z. Jones; NHTSA

TO: Hubert J. Thomiszer -- Senior Mechanical Engineer, Triodyne, Inc.

TITLE: FMVSS INTERPRETATION

TEXT:

Mr. Hubert J. Thomiszer Senior Mechanical Engineer Triodyne Inc. 5950 West Touhy Avenue Niles, Illinois 60648

Dear Mr. Thomiszer:

This responds to your letter asking about Federal Motor Vehicle Safety Standard No. 207, Seating Systems. You asked whether the 20 g acceleration requirement in the fore and aft direction through the center of gravity of the seat was based on a barrier impact test and, if so, at what speed. You also asked whether the 20 g acceleration was established taking into account the possibility that passengers who are unrestrained would impact the back of the seat in front of them on a frontal impact so as to add additional weight to the seat itself which would thereby increase the loading on the seat anchors. Your questions are responded to below.

The requirements to which you refer are set forth in section S4.2 of Standard No. 207. That section provides in relevant part:

S4.2 General performance requirements. When tested in accordance with S5., each occupant seat, other than a side-facing seat or a passenger seat on a bus, shall withstand the following forces.

(a) In any position to which it can be adjusted--20 times the weight of the seat applied in a forward longitudinal direction:

(b) In any position to which it can be adjusted--20 times the weigh; of the seat applied in a rearward longitudinal direction . . .

The basic requirement that occupant seats be able to withstand forces of 20 times the weight of the seat applied in both forward and rearward longitudinal directions was part of Standard No. 207 as that standard was established as one of the initial Federal motor vehicle safety standards. See 32 FR 2415, February 3, 1967. (The standard was later amended by revising certain other requirements, extending its application to additional vehicle types, adding requirements, and clarifying and restructuring the standard.)

As required by section 103(h) of the National Traffic and Motor Vehicle Safety Act, the initial Federal motor vehicle safety standards were promulgated under a tight statutory deadline and here based on existing safety standards. Standard No. 207 was based on the Society of automotive engineers' (207) Recommended Practice J879, Passenger Car Front Seat and Seat Adjuster (November 1963), and on the General Services Administration's (GSA) Federal Standard No. 515/6a, one of a number of standards which were developed for Government vehicles.

With respect to the requirements at issue, section 3.1 of SAE Recommended Practice J879 provided in relevant part:

3.1 Seat Adjusters and Seat Frame Combination--Each combination of seat adjusters and seat frame, together with their attachments, shall be capable of sustaining horizontal forward and rearward static load (L) equal to 20 times the weight of the fully trimmed seat. One-half of this load (L/2) shall be applied at points 8.00 in. above the seat frame rear attaching points as shown in Fig. 1. The 8.00 in. load application points represent the approximate vertical center of gravity of a fully trimmed passenger car front seat. . .

We have been advised by our technical staff that the requirement that occupant seats be able to withstand forces of 20 times the weight of the seat applied in both forward and rearward longitudinal directions was based on the forces involved in a 30 mph barrier impact test. Moreover, this requirement does not include any adjustment to take account of the increased loading on seat anchors that could result from passengers who are unrestrained impacting the seat in front of them in a frontal impact.

You may wish to contact the Society of Automotive Engineers for information concerning the development of their recommended practice.

I hope this information is helpful.

Sincerely,

Erika Z. Jones Chief Counsel

January 17, 1986

Chief Counsel Erika Z. Jones National Highway Traffic Safety Administration Room 5219 400 Seventh Street. S.W. Washington, DC 20590

Dear Erika Jones: I was advised by Mr. Steve Oesch to forward my request for information to your attention.

I would like to know two features of the Federal Motor Vehicle Standard No. 207.

1. Was the 20G acceleration requirement in the fore and aft direction through the center of gravity of the seat based an a barrier impact test and if so at what speed.

2. Was the 20G acceleration taking into account the possibility that passengers who are unrestrained would impact the back of the seat in front of them on a frontal impact so as to add additional weight to the seat itself which would thereby increase the loading on the seat anchors.

I will appreciate receiving this information as quickly as possible. there be any questions regarding this request, please call me collect at 677-V430.

Thank you for your cooperation in this matter.

Sincerely,

Hubert J. Thomiszer, M.E., P.E Senior Mechanical Engineer