Search Interpretations

Interpretation ID: 86-4.45

TYPE: INTERPRETATION-NHTSA

DATE: 08/18/86

FROM: AUTHOR UNAVAILABLE; Erika Z. Jones; NHTSA

TO: Mr. Koji Tokunaga

TITLE: FMVSS INTERPRETATION

TEXT:

Mr. Koji Tokunaga Manager, Engineering Isuzu Motors America, Inc. 21415 Civic Center Drive Southfield, MI 48076-3969

Dear Mr. Tokunaga:

Thank you for your letter of December 19, 1985, to former Chief Counsel Prank Berndt, asking several questions about how the requirements of Standards No. 207, Seating Systems, 209, Seat Belt Assemblies, and 210, Seat Belt Assembly Achorages, apply to an airsuspension truck seat equipped with a safety belt and a tether belt. The diagrams you enclosed with your letter show that one end of the tether belt is connected to the floor behind the seat and the other end is connected to the frame of the air suspension seat. The safety belt is also connected to the frame of the seat. I regret the delay in our response and hope the following discussion answers your questions.

You first asked about which portion of the system is considered the safety belt anchorage for the purpose of Standard No. 210. S3 of the standard defines the term "seat belt anchorage" as "the provision for transferring seat belt assembly loads to the vehicle structure." Since, according to the diagram enclosed with your letter, the safety belt is directly attached to the seat, we would consider the attachment point on the seat to be the anchorage. It is that attachment point that transfers the seat belt load to the vehicle structure. Although not specifically discussed in your letter, we believe that the primary purpose of the tether belt is to hold the seat in position during a crash rather than to transfer the safety belt loads to the vehicle structure.

You next asked whether S4.2(c) of Standard No. 207, Seating Systems, would apply to the seat since the safety belt is secured to the seat. The answer is yes, S4.2(c) would apply. S4.2(c) sets requirements for any seat in which "a seat belt assembly is attached to the seat."

In your third question, you asked whether the seat would have to be tested to the requirements of Standard No. 210 if it meets the requirements of S4.2(c) of Standard No. 207. The seat must meet the requirement of S4.2(c) of Standard No. 207 and the seat belt anchorages must separately meet the requirements of Standard No. 210. As a manufacturer, your responsibility is to certify that the seat and safety belt anchorages will meet each of those requirements. You may not have to conduct two separate tests if you can demonstrate compliance to both sets of requirements when the seat and seat belt anchorage are tested in accordance with S4.2(c) of Standard No. 207.

In your fourth question, you asked whether the struts specified in S5.1.1 of Standard No. 207 can be used in testing the system. S5.1.1 provides that if "the seat back and the seat bench are attached to the vehicle by the same attachments," a strut can be secured on each side of the side for the purposes of securing a rigid crossmember used in loading the seat. In the case of your seat, the seat back and the seat bench are attached to the vehicle by the same attachments and thus use of the struts is permitted.

You then asked how the center of gravity of the seat is to be determined for the purpose of the test. You asked whether you are to determine the center of gravity of the entire system, including the seat stand with the air suspension and slide mechanism. In a July 14, 1983 letter to Mack Trucks, Inc., NHTSA addressed the issue of how to apply the loading required by Standard No. 207 to a heavy-duty truck seat which, as with yours, includes a suspension system and is mounted on a pedestal-like structure.

In its letter, Mack explained that it tests its seat in a two step process. First, the seat supplier for Mack mounts the seat cushion and the seat back on a rigid structure and tests the seat to the performance requirements of Standard No. 207 by applying 20 times the weight of the seat cushion and seat frame to the seat. Then, Mack conducts a separate test of the seat cushion and seat back with those components mounted on the pedestal used in its trucks. In that test, Mack subjects those components to 20 times the weight of the seat back, seat cushion and pedestal applied at the center of gravity of the entire seat system (seat back, seat cushion, and pedestal).

In responding to Mack, NHTSA said that a manufacturer can separately test the seat in the manner followed by Mack. Thus, a manufacturer can conduct one test of the upper section of the seat by applying 20 times the weight of those components to the upper section and then separately test the seat, as anchored to the vehicle floor, by applying 20 times the weight of the entire seat, including the pedestal, at the center of gravity of the entire seat.

In your sixth and final question, you asked whether the tether belt would have to meet the seat belt assembly requirements of Standard No. 209. S3 of Standard No. 209 defines, in part, a seat belt assembly as "any strap, webbing, or similar device designed to secure a person in a motor vehicle to mitigate the results of any accident. . . ." Since your tether belt is not designed to restrain an occupant, it would not be required to meet the requirements of Standard No. 209.

If you have any further questions, please let me know.

Sincerely, Erika Z. Jones Chief Counsel

DET-85-258

December 19, 1985

Mr. Frank Berndt Chief Counsel National Highway Traffic Safety Administration 400 Seventh Street, S.W. Washington, D.C. 20590

Dear Mr. Berndt:

Subject: Test Procedures for Seat Belt With Tether Belt

Regarding the compliance with the requirements of FMVSS 207 and 210, we would request you to answer the following questions and provide necessary information on a seat belt with tether belt, which is used on an airsuspension truck seat. Please see Fig. 1 on the next page for the outline of the system.

1. We think that (1) the securing on the floor end or the tether belt, (2) the tether belt itself, and (3) the area where the seat belt and tether belt are together secured to the seat constitute the seat belt anchorage as defined in FMVSS 270 S3. Is this correct?

2. Since the seat belt is secured to the seat together with the tether belt, we think FMVSS 207 S4.2(c) is applicable. Is this understanding correct?

3. If your answer to the question 2 above is yes, there seems to be no necessity for testing the system separately to FMVSS 210 S4.2 if the system meets the requirements or FMVSS 207 S4.2(c). Is this correct?

4. If your answer to the question 2 above is yes, is the use of the struts mentioned in FMVSS 207 S5.1.1 permitted in testing the system? Then, how is the center of gravity or the seat determined? Is it the center or gravity or the entire system including the seat stand which incorporates the suspension and slide mechanisms?

5. If the center of gravity is to be determined as in para. 4 above, this center exists inside the suspension mechanism as shown in Fig. 2, and thus the crossmember for the struts cannot be installed.

Is there any established regulation or procedure which specifies what load is to be applied where? If no, please advise what action we are to take.

6. It is our understanding that the tether belt is to meet the requirements or FMVSS 209 as linked to the seat belt. Is this understanding correct?

Thank you for your cooperation.

Sincerely yours,

Koji Tokunaga Manager, Engineering

jj