Interpretation ID: nht76-5.2
DATE: 08/31/76
FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA
TO: Volvo of America Corporation
COPYEE: ALLIED CHEMICAL CORP.; U.S. TESTING CO., INC.
TITLE: FMVSS INTERPRETATION
TEXT: This is in response to your April 6, 1976, request for interpretations regarding certain sections of Safety Standard No. 209, Seat Belt Assemblies, when applied to the continuous loop seat belt assemblies provided on current Volvo vehicles.
Paragraphs S4.4(b)(1) and (2) specify performance requirements for components in the pelvic restraint and upper torso restraint portions of a belt system, tested separately and in combination. You ask for verification of your interpretation that the requirements for separate testing of pelvic and upper torso portions are inapplicable to a continuous loop seat belt, on the basis that this type system "can never in real life be subjected to forces only in the pelvic restraint." Your letter includes an illustration of your test apparatus for determining compliance with paragraph S4.4(b), and you request verification that your procedure is correct.
Section S5.3(b) of the standard sets forth the test methods that would be used in a determination of whether a Type 2 seat belt assembly conforms to the requirements of S4.4(b). Paragraph S4.4(b)(1) specifies that the pelvic restraint shall withstand a force of not less than 2,500 pounds, and S4.4(b)(2) specifies that the upper torso restraint shall withstand a force of not less than 1,500 pounds. The Volvo continuous loop belt systems are subject to these requirements. A recent NHTSA interpretation letter to Toyo Kojyo (copy enclosed) on the same subject sets forth the responsibilities of the manufacturer in cases where the specified test procedures may not be entirely suitable to a new safety component design. In testing continuous loop belt systems for compliance with S4.4(b)(1) and (2), the agency has interpreted S5.3(b) to necessitate the use of a clamp in the same fashion as suggested by Toyo Kojyo to ensure that the force is applied to the appropriate portion of belt webbing and hardware. It must be understood, of course, that the NHTSA cannot approve a manufacturers's test procedure as the basis of due care in advance of the actual events that underlie certification. It is impossible for the agency to foresee whether the various aspects of a particular test procedure will be conducted in a proper fashion, based solely on a written description of that test procedure.
In the second part of your letter you asked whether the buckle crush requirements of paragraph S4.3(d)(3) of Standard No. 209, when tested in accordance with the procedures specified in S5.2(d)(3), are applicable to Volvo seat belt buckles and, if so, whether Volvo's interpretation as to how the test should be conducted is correct.
It is true that the buckle requirements were originally included in the standard to guard against possible damage to the buckle caused by the steering wheel in a crash situation. Since the issuance of the standard, new seat belt assembly designs have been developed in which the belt buckle is located between the front seats. As you pointed out in your letter, these buckles are not likely to be contacted by the steering wheel in a crash situation.
In view of the significant design changes that have occurred, the agency has reconsidered its 1972 interpretation to United States Testing Company on this subject. Because it is unlikely that any of these buckles would be damaged by compressive forces in a crash, we have determined that the requirements are inappropriate. Therefore, we conclude that the existing S4.3(d)(3) buckle requirements are not applicable to buckles that are located between bucket seats and attached to the console or to the end of a rigid cable or bar.
SINCERELY,
April 6, 1976
Frank Berndt, Acting Chief Counsel National Highway Traffic Safety Administration
Re: Interpretation of FMVSS 209 Demonstration Procedures
FMVSS 209 - Seat Belt Assemblies, specifies in detail performance requirements which must be met by automotive seat belt assemblies. The manner in which conformance with these requirements is to be demonstrated is outlined in S5 of FMVSS 209. Both the performance requirements and the demonstration procedures reflect the design characteristics of those types of seat belt assemblies commonly in use when the standard was written. We have experienced difficulty in applying these requirements to the single loop type seat belt assembly employed on current Volvo vehicles.
Attached are a discussion of section S4.4(b) and a discussion of sections S4.3(d)(3) and S5.2(d)(3) of FMVSS 209 outlining our interpretation of how the requirements of FMVSS 209 apply to single loop type seat belt assemblies. Also attached are illustrations of the Volvo single loop seat belt assembly. Your verification that our interpretation of FMVSS 209, as stated in the attached discussions, is consistent with the requirements of FMVSS 209 would be appreciated.
Any questions on this matter may be addressed to the undersigned. Thank you for your prompt consideration of this request.
VOLVO OF AMERICA CORPORATION Product Engineering and Development
Donald J. Gobeille, Jr. Product Safety Engineer
Request for Interpretation FMVSS 209 S4.3(d)(3) and S5.2(d)(3)
S5.2(d)(3) specifies that a seat belt buckle shall be subjected to a compressive force of 400 pounds applied ". . . anywhere on a test line that is coincident with the centerline of the belt extended through the buckle . . ." (alternative 1) or ". . . on any line that extends over the center of the release mechanism and intersects the extended centerline of the belt at an angle of 60 degrees . . ." (alternative 2). The requirements which shall be met, when tested in this manner, are found in S4.3(d)(3).
The intent of these requirements is expressed in Docket 69-23, Notices 1 and 2, published on March 17, 1970 (35 F.R. 4641) and on March 10, 1971 (36 F.R. 4607), respectively, where it is stated that the test will tend to eliminate buckle designs which are prone to accidental damage, or which release during the initial phase of the accident.
For a design where the buckle is rigidly mounted on the floor between the front seats (see attached description), its location protects it from accidental damage and from release during the initial phase of an accident. It is our interpretation that if the buckle crush requirements are at all applicable to buckles of this design and location, they shall be tested in accordance with alternative 1 above and the force shall be applied as indicated on the attached description. The basis for this interpretation is that the only damage which may occur results from compression if the seats are displaced as a result of a side impact, where the protective effect of a belt in any case can be discussed.
Therefore we request you to:
(1) state if the buckle crush requirements of S4.3(d)(3), when tested in accordance with S5.2(d)(3), are applicable to the described type of buckles, and
(2) if so, if our interpretation as to how this test shall be conducted is correct.
Request for Interpretation FMVSS 209 S4.4(b)
S4.4(b) specifies requirements for Type 2 seat belt assemblies. S4.4(b)(1) and (2) specify requirements for components in the pelvic restraint and in the upper torso restraint, respectively. Then S4.4(b)(3) specifies requirements for components which are common to pelvic and upper torso restraints.
A Type 2 seat belt assembly which is designed as a continuous loop seat belt with a sliding locking tongue, can never in real life be subjected to forces only in the pelvic restraint. Therefore we interpret S4.4(b)(1) and (2) as not directly applicable to such a design of seat belts. Only S4.4(b)(3) should apply, which indirectly covers the same aspect of performance. The maximum elongation requirements of S4.4(b)(4) and (5) can be met by limiting the double-roller block travel to 10 inches when the 6000 pounds force is applied.
The breaking strength requirement of S4.4(b)(6) for a webbing cut of the pelvic restraint should be applicable to any webbing cut in a continuous loop seat belt.
In accordance with our interpretation, a continuous loop seat belt assembly should be tested as indicated in the following figure:
As can be seen from this figure, the test set up includes all attachment hardware, and the positions of the components simulate as close as possible their actual positions in a vehicle.
We request that you confirm our interpretation as stated above.
(Graphics omitted) Part of drawing No 1290538
(Graphics omitted)