Interpretation ID: aiam4968
Inc. 2798 S. Fish Hatchery Rd. Madison
Wisconsin 53711-5398;
"Dear Mr. Kubehl: This responds to your letter of February 4, 1992 concerning the requirements of Federal motor vehicle safety standard No. 209, Seat belt assemblies. You asked for verification of your understanding of the requirements of two sections of Standard No. 209. Your discussion of these two sections and our response follows. In 209-S.4.4a(1), it is clearly stated that a loop force of 5000 pounds is required to produce a force of 2500 pounds on each structural component. However, part 209-S4.4b(4) seems to be a bit ambiguous. It states: 'The length of the pelvic restraint between anchorages shall not increase more than 20 inches or 50 centimeters when subjected to a force of 2500 pounds'. My interpretation of this statement is that one must employ a loop force of 5000 pounds to achieve 2500 pounds of force on each component, as specified in S4.4a(1). I am concerned that one could misinterpret the above statement as requiring a 2500 pound loop force, rather than the intended value of 5000 pounds. Your statements indicate a common misunderstanding of the requirements of S4.4 of Standard No. 209. A seat belt assembly would not be subject to the requirements of S4.4(a) and to the requirements of S4.4(b). If the seat belt assembly is a Type 1 seat belt assembly, defined in S3 as 'a lap belt for pelvic restraint,' the assembly is subject to the requirements of S4.4(a). Section S4.4(a)(1) requires a Type 1 seat belt assembly loop to withstand a force of 5,000 pounds. Section S4.4(a)(2) states that the length of the assembly between the anchorages shall not increase more than 14 inches or 36 centimeters when the load required in S4.4(a)(1) is applied. If the seat belt assembly is a Type 2 seat belt assembly, defined in S3 as 'a combination of pelvic and upper torso restraints,' the assembly is subject to the requirements of S4.4(b). Section S4.4(b)(1) requires the pelvic portion of a Type 2 seat belt assembly to withstand a force of 2,500 pounds. Section 4.4(b)(4) states that the length of the pelvic portion of the assembly shall not increase more than 20 inches or 50 centimeters when the load required in S4.4(b)(1) is applied. Part 209-S5.3a, which addresses the performance of the belt assembly, refers to Figure 5 and requires a tensile force of 2500 pounds. It goes on to say that this force is equivalent to a 5000 pound force being applied to an assembly loop. Figure five is referred to several times throughout the passage, each reference requiring a specific force. Again, because the relationship of the tensile force to assembly loop force is not explicitly stated, we are concerned that one may mistake the tensile force to be the total loop force applied. The test procedure to determine compliance with the requirements of S4.4 of Standard No. 209 is found in S5.3 of that standard. The test procedure for seat belt assemblies subject to the requirements of S4.4(a) (a pelvic restraint) is found in S5.3(a). As you have correctly stated, a force of 2,500 pounds is applied to each component of the pelvic restraint, or a force of 5,000 pounds to the entire loop. The test procedure for seat belt assemblies subject to the requirements of S4.4(b) (a combined pelvic and upper torso restraint) is found in S5.3(b). The pelvic portion of such a seat belt assembly is tested by applying a total force of 2,500 pounds to the entire loop. I hope you find this information helpful. If you have any other questions, please contact Mary Versailles of my staff at this address or by phone at (202) 366-2992. Sincerely, Paul Jackson Rice Chief Counsel ";