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Interpretation ID: 003059 bts

    Mr. Joe Masci
    Pollak Switch Products Division
    300 Dan Road
    Canton, MA 02021

    Dear Mr. Masci:

    This responds to your May 2, 2003, faxed letter and your telephone conversations with Mr. Otto Matheke of my staff concerning the application of Federal Motor Vehicle Safety Standard (FMVSS) No. 209, Seat belt assemblies, to a seat belt tension sensor (BTS). You stated that the BTS is used in conjunction with a passenger weight classification system to prevent misclassification of children seated in child safety seats. Your letter asked several questions as to how a seat belt assembly using a seat belt tension sensor would be tested for compliance with Federal standards. Each of your questions is addressed below.

    1. General Applicability of FMVSS No. 209.

    You asked if the BTS would be considered part of the seat belt assembly under FMVSS No. 209, or if it would be considered an anchorage under FMVSS No. 210, Seat belt assembly anchorages, which is a vehicle standard. S3 of FMVSS No. 210 defines a seat belt anchorage as:

    [A]ny component, other than the webbing or straps, involved in transferring seat belt loads to the vehicle structure, including, but not limited to, the attachment hardware, seat frames, seat pedestals, the vehicle structure itself, and any part of the vehicle whose failure causes separation of the belt from the vehicle structure.

    Accordingly, FMVSS No. 210 applies to fixed attachment points on the vehicle structure and the associated hardware. FMVSS No. 209 applies to seat belt assemblies, defined as:

    [A]ny strap, webbing, or similar device designed to secure a person in a motor vehicle in order to mitigate the results of any accident, including all necessary buckles and other fasteners, and all hardware designed for installing such seat belt assembly in a motor vehicle. (S3 of FMVSS No. 209)

    In your phone conversation, you stated that the BTS is sold to manufacturers of seat belt assemblies and may be placed in a variety of positions on the assembly. As a component of the seat belt assembly, the BTS would be subject to the requirements of FMVSS No. 209. However, because the BTS may be incorporated into a seat belt system in a variety of ways, we are unable to determine whether the BTS could ever be considered a seat belt anchorage under FMVSS No. 210.

    2. FMVSS No. 209 Strength requirements

    In your letter you included a diagram properly identifying the components of a Type 2 seat belt assembly and asked for verification of the strength requirements for each labeled component. The strength requirements for FMVSS No. 209 are contained in: S4.2, webbing; S4.3, hardware; and S4.4, assembly performance.

    Under S4.2(b), webbing in the pelvic restraint portion of a Type 2 seat belt assembly must have a breaking strength of not less than 22,241 N (5,000 pounds). The upper torso portion of a Type 2 seat belt assembly must have a minimum breaking strength of 17,793 N (4,000 pounds). The testing procedure for both portions of webbing is contained in S5.1(b).

    S4.3(c) requires that attachment hardware bolts used to secure the pelvic restraint of a seat belt assembly must be able to withstand a force of at least 40,034 N (9,000 pounds) when testing in accordance with S5.2(c)(1). Other attachment hardware designed to receive the ends of two seat belt assemblies shall withstand a tensile force of at least 26,689 N (6,000 pounds) when tested under S5.2(c)(2).

    S4.4 sets forth the strength requirements of a Type 2 seat belt assembly in subsection (b). Under S4.4(b)(1), each structural component in the pelvic restraint must withstand a force of not less than 11,120 N (2,500 pounds). This includes the BTS, if it is located along the pelvic portion of the pelvic restraint. S4.4(b)(2) requires that each structural component in the upper torso restraint portion of the seat belt assembly be able to withstand a force of not less than 6,672 N (1,500 pounds). This includes a torso guide loop and retractor if the design permits only upper torso restraint forces on the restraint. Under S4.4(b)(3), any structural component that is common to both the pelvic and upper torso restraints must withstand a force of not less than 13,345 N (3,000 pounds). This would include any buckle or portion of the BTS that would be subject to forces from both the pelvic and upper torso restraints. The seat belt assembly performance for a Type 2 seat belt assembly is tested by the procedure specified in S5.3(b).

    3. Procedure for Testing Assembly Performance

    In your letter you asked what would be the proper method of attaching and orienting an assembly with a BTS under the test procedures in S5.3. Under S5.3, each end of the pelvic or torso portion of the belt assembly is attached to an anchorage bar to form a loop over rollers on a testing machine. (See FMVSS No. 209 Figure 5, enclosed.) The anchor points are such that the webbing is parallel in two sides of the loop. The attaching bolts are either aligned with or at an angle of 45 or 90 degrees to the webbing, whichever results in an angle nearest to 90 degrees between webbing and attachment hardware.

    You stated that you believe the appropriate testing method for an assembly with the "BTS installed between the fixed anchor on the pelvic-only side of the belt and the belt webbing" would be to utilize the procedure in S5.3(a)(2) for a "nonthreaded anchorage." Such a determination would be governed by the specific application of the belt assembly and not by the presence of a BTS. S5.3(a)(2) declares that testing will be performed in accordance with the installation instructions provided with belts designated for use in specific models of vehicles. In such an instance, the anchorages of the vehicle-specific assembly would be installed for testing so as to produce the maximum angle in use indicated by the installation instructions. From your letter and phone conversations, the BTS is sold to seat belt assembly manufacturers for eventual use in a variety of vehicle models. As such, the "nonthreaded anchorage" procedure would only be appropriate in those instances where the BTS is incorporated into a seat belt assembly that is designed for a specific vehicle and is accompanied by instructions for installation specific to that vehicle.

    For the assembly you specified, compliance testing would require the attaching bolts to be set according to the general set-up procedure. The attaching bolts would be positioned under S5.3(a)(2) such that the angle between the webbing and the attachment hardware is as close to 90 degrees as possible.

    4. Minimum Force Requirements for Assembly Performance

    In your letter you asked if the force minimums listed for the Type 2 belt component strength requirements apply to each component individually or to the test loop as a whole. The answer is that these force requirements apply to the components and not to the test loop. Under S4.4(b) of FMVSS No. 209, for a Type 2 belt, the structural components in the pelvic restraint must withstand a force of not less than 11,120 N (2,500 pounds), the structural components in the upper torso restraint must withstand a force of not less than 6,672 N (1,500 pounds), and structural components that are common to the pelvic and upper torso restraints must withstand a force of not less than 13,345 N (3,000 pounds). The test procedure for Type 2 belt assembly components requires a tensile force equal to that of the appropriate minimum be applied to the components (S5.3(b)). Therefore, in compliance testing of the pelvic restraint portion of a Type 2 seat belt assembly, a force of 22,240 N (5,000 pounds) would be applied to the test loop. The application of the 22,240 N (5,000 pounds) would be required so that the components would experience a tensile force of 11,120 N (2,500 pounds); the minimum required.

    We note that in a letter to Mr. Douglas Kubehl, dated March 16, 1992, we took the position that under S4.4(b) and the corresponding procedure in S5.3(b), the minimum force requirement would be applied to the test loop. However, we have reconsidered that interpretation and conclude that it was incorrect. The previous interpretation would result in Type 2 seat belt assembly components being tested to much lower force requirements than components in a Type 1 seat belt assembly. However, it is our understanding that all manufacturers of Type 2 seat belt assemblies have built and tested their products in a manner consistent with this revised interpretation, so this revision will not cause any seat belt assemblies (or the vehicles in which they are installed) to become noncompliant. To the extent a manufacturer has relied upon our previous interpretation, we will only pursue an enforcement action for noncompliance with the standard prospectively.

    5. Manual Belts Subject to the Requirements of FMVSS No. 208

    In your letter, you ask if you are correct in understanding that the strength requirements of S4.4 do not apply if the requirements of S5.1 of FMVSS No. 208 are met instead. Your understanding is correct. Under S4.6 of FMVSS No. 209, manual seat belt assemblies subject to the requirements of S5.1 of FMVSS No. 208, Occupant crash protection, would not be required to meet the requirements of S4.2(a)-(f) and S4.4 of FMVSS No. 209. [1] This includes the FMVSS No. 209 strength requirements for seat belt assembly components.

    You further ask, "how frequently do vehicle manufacturers opt for the 208 test option over the static component strength tests in 209?" A seat belt assembly subject to FMVSS No. 209 must comply with that standard, and be certified by its manufacturer as conforming to that standard. We do not collect or maintain data on how vehicle manufacturers certify with respect to their seat belt assemblies, although NHTSA may examine a manufacturer's certification in connection with any prospective or pending enforcement action. As such, we do not know with what frequency manufacturers opt for the FMVSS No. 208 compliance option.

    I hope you find this information helpful. If you have any further questions, please contact Mr. Chris Calamita of my staff at (202) 366-2992.


    Jacqueline Glassman
    Chief Counsel


    [1] Excepted from this provision are seat belts that are subject to S4.1.2.1(c)(2) of FMVSS No. 208, which cross references FMVSS No. 209. S4.1.2.1(c)(2) does not apply to vehicles manufactured on or after September 1, 1986.