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Interpretation ID: 571.209 -- Inflatable Seat Belt Assembly -- Autoliv -- 16-003634 -- 05.22.2017

Mr. David Prentkowski
Autoliv North America
1320 Pacific Drive
Auburn Hills, MI 48326

Dear Mr. Prentkowski:

This responds to your letter concerning the application of Federal Motor Vehicle Safety Standard (FMVSS) No. 209, Seat Belt Assemblies, to an inflatable seat belt assembly your company is developing. You ask which strength test applies to a structural sew pattern that connects the assemblys conventional webbing to its inflatable portion. Specifically, you ask us to confirm your tentative conclusion that the sew pattern is subject to the assembly performance requirements contained in S4.4(b)(2). As explained below, S4.4(b)(2) applies to the sew pattern, but it is not the only applicable strength requirement. The sew pattern, along with the rest of the restraint, must also meet the webbing breaking strength requirement in S4.2(b). What follows is our analysis of your question based on the facts you provided.

Description of Your Product

From the description in your letter and a follow-up phone conversation with Daniel Koblenz of my staff on January 19, 2017, we understand your product to be a Type 2 seat belt assembly with a continuous pelvic and upper torso restraint. The restraint is constructed from a segment of conventional webbing that is connected by a sew pattern to an inflatable portion. The unsewn end of the restraints conventional webbing is connected to a retractor mechanism that can be pillar-mounted or parcel shelf-mounted, and the unsewn end of the restraints inflatable portion is connected to an anchor that includes a gas generator that fills the inflatable portion in certain crash modes. While your product is in use, the sew pattern is typically located behind the occupants shoulder between the occupant and the retractor mechanism.

Requirements

FMVSS No. 209 contains two breaking strength requirements that Type 2 seat belt assemblies must meet: one for the entire seat belt assembly and one specifically for the webbing. As to seat belt assemblies, S4.4(b) states, in relevant part: Type 2 seat belt assembly. Except as provided in S4.5, the components of a Type 2 seat belt assembly including webbing, straps, buckles, adjustment and attachment hardware, and retractors shall comply with the following requirements when tested by the procedure specified in S5.3(b): (2) The structural components in the upper torso restraint shall withstand a force of not less than 6,672 N.

As to webbing, S4.2(b) states, in relevant part: The webbing in a seat belt assembly shall have not less than the following breaking strength when tested by the procedures specified in S5.1(b): . . .Type 2 seat belt assembly. . . 17,793 N for webbing in upper torso restraint. Please note that, under FMVSS No, 209 S4.1(i), all straps that are used in a seat belt assembly to sustain restraint forces must meet the webbing requirements of S4.2. FMVSS No. 209 S3 defines a strap as a narrow nonwoven material used in a seat belt assembly in place of webbing.

These two breaking strength requirements are both applicable, which means that an assemblys upper torso webbing (or a strap subject to webbing requirements) is subject to both S4.4(b)(2) and S4.2(b). However, because the breaking strength requirement for the upper torso webbing (17,793 N) is greater than the breaking strength requirement for the upper torso assembly components (6,672 N), the question of whether webbing (or a strap subject to webbing requirements) complies with FMVSS No. 209s breaking strength requirements effectively turns on whether it meets the webbing-specific requirements of S4.2(b).

Discussion

 

a. The sew pattern is integrated into the upper torso restraint and cannot be tested in isolation. Before discussing which breaking strength requirement applies to the sew pattern, it is necessary to clarify what the sew pattern is. In your letter, you mistakenly discuss the sew pattern as though it is a discrete component with its own compliance requirements that are severable from the requirements that apply to the two restraint segments that the sew pattern connects. While past interpretations have considered hardware components as discrete components, the sew pattern is inherently different than a hardware component.

The sew pattern is not a discrete component; it is a manufacturing material that is integrated into and made a part of the upper torso restraint. For this reason, we have determined that the entire upper torso restraintincluding the sew pattern, conventional webbing and inflatable segmentsshould be treated as a single integrated component for the purpose of determining whether it is subject to the breaking strength tests in S4.4 and S4.2.

b. The upper torso restraint is a structural component that is subject to S4.4(b)(2). In your letter, you state (and we agree) that the sew patternand by extension, the upper torso restraint that it holds togetheris structural. You believe that, because the upper torso restraint is a structural component, it must meet the assembly performance requirement in S4.4(b)(2). We agree that S4.4(b)(2) applies. We do, however, wish to note that this letter supersedes a 1973 letter to Takata Kojyo Co., which determined that S4.4(b)(3) was the relevant requirement.[1]

c. The upper torso restraint is also a strap that is subject to S4.2(b). We have determined that the upper torso restraint falls within the definition of strap. Accordingly, the upper torso restraint, including its subcomponents, must meet the breaking strength requirements of S4.2(b).

Our conclusion that the entire upper torso restraint is a strap is rooted in both the definition of strap and our previous interpretations of that definition. As noted earlier, FMVSS No. 209 defines a strap as a narrow nonwoven material used in a seat belt assembly in place of webbing.[2] We interpret the term nonwoven material here to include any restraint material that is not purely constructed out of webbing (i.e., woven) material. This means that a restraint constructed from both woven and nonwoven materials and that is used in place of webbing is considered a strap. Accordingly, we determined in a 2010 letter to Mr. Kazuo Higuchi that the inflatable portion of an inflatable seat belt assembly that was constructed from an inflatable bladder encased in woven fabric fell within the definition of strap.[3]

Consistent with our determination in the Higuchi letter, we have concluded here that the upper torso restraint of your seat belt assembly fits within the definition of strap. Like the inflatable segment in the Higuchi letter, the upper torso restraint in your seat belt assembly is constructed from a combination of woven material (the conventional webbing) and nonwoven material (the inflatable portion and the sew pattern), and is used in a seat belt assembly in place of webbing. Therefore, the entire upper torso restraintincluding the conventional webbing, inflatable portion, and sew patternis a strap.

Because the upper torso restraint is a strap, it is subject to S4.1(i), which states that [a] strap used in a seat belt assembly to sustain restraint forces shall comply with the requirements for webbing in S4.2. As noted above, S4.2(b) requires that webbing in the upper torso portion of a seat belt assembly withstand a force of at least 17,793 N. Therefore, to comply with FMVSS No. 209, your seat belt assembly must be able to withstand a force of at least 17,793 N when tested in the manner prescribed by S4.2. Please note that, as stated in the Higuchi letter, NHTSA will not disassemble the restraint when testing it.

 

 

Other Issues

Please be aware that, as a strap the upper torso restraint must meet all of the S4.2 requirements for webbing, not just those for strength and abrasion. We felt it necessary to clarify this point given your statement: [W]e understand that both the webbing and inflatable seat belt portions of the system would need to meet the strength and abrasion resistance requirements as specified in FMVSS 209. FMVSS No. 209 S4.1(i) requires that straps comply with the requirements for webbing in S4.2. There are a number of requirements in S4.2 in addition to strength and abrasion resistance.

 

If you have any questions, please contact Daniel Koblenz of my staff at (202) 366-2992.

 

Sincerely,

 

 

Stephen P. Wood

Acting Chief Counsel

NCC0200:Dkoblenz:3/2/17:revised 4/20/17:62992(cyb 5/3/17)

Reprinted with edits 5/3/17 and 5/22/17

S:\INTERP\209\571.209 -- Inflatable Seat Belt Assembly -- Autoliv -- 16-003634 -- 05.22.2017.docx
Greenbooks FMVSS No. 209, Redbooks, NRM, NEF

 

[1] The April 9, 1973 letter to Takata Kojyo Co. is NHTSAs sole prior interpretation directly discussing the breaking strength requirements for restraint sew patterns (available at https://isearch.nhtsa.gov/gm/73/nht73-6.15.html). Takata Kojyo had asked about a structural sew pattern in an upper torso restraint that connected two conventional webbing segments of different widths.  In NHTSAs response, the agency concluded that the entire restraint, including both webbing segments and the sew pattern, should be considered a single component, but also that the restraint was a common pelvic and upper torso restraint which must meet [the requirements of S4.4(b)(3)] regardless of whether sewing or other means is used to make the belt assembly. We believe that NHTSAs analysis in the Takata Kojyo letter incorrectly interpreted the word common in S4.4(b)(3) to refer to components that are physically part of both the upper torso and pelvic restraints, such as a continuous loop restraint. We believe that common in S4.4(b)(3) instead refers to the load that a given component experiences in a crash scenario.  If a component experiences only upper torso (or pelvic) crash loads, it is considered to be part of the upper torso (or pelvic) restraint, respectively, for purposes of S4.4(b).  Conversely, if the component experiences both upper torso and pelvic crash loads, it is considered to be common.  Because the upper torso portion of a restraint only experiences upper torso loads, we do not consider it to be a common component under S4.4(b)(3) even if it is part of a continuous loop restraint. 

[2] S3. Note also that webbing is defined in S3 as a narrow fabric woven with continuous filling yarns and finished selvages.

[3] See letter to Kazuo Higuchi (May 7, 2010), available at https://isearch.nhtsa.gov/files/08_004614%20209.htm. See also TK Holdings, Inc. Interpretation Request (July 8, 2009), available at https://www.regulations.gov/document?D=NHTSA-2010-0067-0002 (explaining that the inflatable portion of the subject inflatable seat belt assembly is constructed of some woven material, some coated fabric and some knit material).