TK Holdings, Inc.
888 16th Street, NW, Suite 800
Washington, DC 20006
Dear Mr. Higuchi:
This letter is in response to your request for an interpretation of the abrasion resistance requirements of Federal Motor Vehicle Safety Standard (FMVSS) No. 209, Seat Belt Assemblies, as they relate to an inflatable seat belt your company is developing. You request confirmation of your interpretation that since the inflatable portion of your seat belt assembly never contacts any hardware in the system, it need not meet the abrasion resistance test requirements for that portion of the seat belt assembly. Based on the information supplied to this agency and for the reasons explained below, it is our opinion that the inflatable portion of the seat belt assembly must meet the abrasion requirements of S4.2(d) of the standard after being subjected to abrasion as specified in S5.1(d) but not S5.3(c) of the standard.
By way of background, the National Highway Traffic Safety Administration (NHTSA) does not provide approvals of motor vehicles or motor vehicle equipment. Under the National Traffic and Motor Vehicle Safety Act, now codified as 49 U.S.C. Chapter 301, it is the responsibility of the manufacturer to ensure that its vehicles and equipment comply with applicable requirements. Title 49 U.S.C. Chapter 301 authorizes NHTSA to develop and enforce FMVSSs applicable to new motor vehicles and new items of motor vehicle equipment, which require minimum levels of safety performance for motor vehicles. FMVSS No. 209 prescribes requirements for seat belt assemblies.
In your letter, you described an upper torso restraint that is intended to inflate in crashes above a specified severity. You stated that this inflatable seat belt assembly deploys in conjunction with a vehicle’s air bags and is intended for use in the front outboard seating positions of motor vehicles. Your letter stated that the inflatable portion of the upper torso restraint has a section of the assembly that crosses the upper torso consisting of an inflatable bladder enclosed in an internal fabric tube that is encased in an external fabric cover. In your letter you explained that, when deployed, one side of the external fabric cover tears open, allowing the internal bladder to inflate. Your letter further stated that upon inflation, the length of this section of the assembly is reduced with results similar to the pretensioning function of a conventional torso belt.
The abrasion resistance requirements of FMVSS No. 209 are specified in S4.2(d), which reads as follows:
d) Resistance to abrasion. The webbing of a seat belt assembly, after being subjected to abrasion as specified in S5.1(d) or S5.3(c), shall have a breaking strength of not less than 75 percent of the breaking strength listed in S4.2(b) for that type of belt assembly.
S5.1(d) specifies a “hex-bar abrasion test,” in which the webbing is repeatedly passed over a hexagon bar. S5.3(c) specifies a test in which the webbing is abraded by repeatedly passing it through the assembly buckle or manual adjustment device. NHTSA added the latter test in 1971 because it was concerned that the hex-bar abrasion test does not adequately simulate the type of webbing abrasion caused by some buckles. The agency noted that the standard as amended retained the hex-bar test, but supplemented it with an additional abrasion requirement. See 36 Fed. Reg. 4607 (March 10, 1971).
In your letter, you argue that since the inflatable portion of the seat belt assembly never contacts any hardware in the system, it would serve no purpose to demonstrate compliance with S4.2(d) for that portion of the assembly. You ask that we interpret the standard not to require such compliance.
We decline to provide such an interpretation. We recognize, however, that the S5.3(c) test may not be appropriate for the type of design you describe. As noted above, the agency specifically added that test requirement because of concern about the type of abrasion caused by some buckles, and in that test, the webbing is abraded by repeatedly passing it through the assembly buckle or manual adjustment device. The inflatable portion of the seat belt assembly you described in your letter never goes through assembly hardware, and it appears unlikely that it would fit through the assembly hardware. Given these considerations, we would not apply the S5.3(c) test but would apply the S5.1(d) hex-bar abrasion test. The standard does not provide an exclusion for the type of design you describe, and there does not appear to be any reason why the S5.1(d) test could not be conducted for such a design.
In your letter, you suggest, as an alternative interpretation, that the inflatable portion of your seat belt assembly falls outside the definitions of “webbing” and “strap,” and therefore this portion of the assembly need not demonstrate compliance with any of the requirements for webbing in S4.2 (which straps must also meet). We also disagree with this suggested interpretation. Even if the inflatable portion of the seat belt assembly does not fit within the definition of “webbing,” we believe the definition of “strap” is sufficiently broad to include the product.
You ask that if we do not agree with your suggested interpretations that we provide additional information as to how the provisions of S4.2(d) would be applied, and how the portion of the inflatable belt assembly would be selected for evaluation. As discussed earlier, we would not apply the S5.3(c) test but would apply the S5.1(d) hex-bar abrasion test. Moreover, we would conduct that test without disassembling the inflatable portion of the seat belt assembly.
We note that in preparing this interpretation, we have considered a number of issues related to FMVSS No. 209 and testing of inflatable seat belts, including issues specific to the inflatable seat belt design you described. It should not be considered as precedent for how we would address requests for interpretation with any differing facts.
If you have any further questions, please do not hesitate to contact Sarah Alves of my staff at (202) 366-2992.
O. Kevin Vincent