Interpretation ID: aiam3716
NSK Representative Office
5400 S. State Street
Ann Arbor
MI 48104;
Dear Mr. Doi: This responds to your letter asking whether a continuous loop seat bel system with a tension reliever ('window-shade device') on the upper torso section of the belt must have a one-way locking tongue.; Continuous seat belt systems are permissible under Safety Standard No 208 if certain conditions are met. Paragraph S7.1.1 of that standard requires adjustment of the lap belt portion of Type 2 belts 'by means of an emergency locking or automatic-locking retractor' and adjustment in most cases of the upper torso portion 'by means of an emergency-locking retractor.' The language permits single retractor, continuous loop systems if the single retractor does 'automatically adjust' the tension of the lap belt portion to prevent excessive slack. Because of the danger of submarining due to a slack lap belt, the agency has restricted the acceptability of continuous loop systems under S7.1.1 in two areas.; First, to conform to the requirements, the buckle of the assembly mus be designed by the manufacturer with a sufficiently low level of friction to qualify the lap portion as automatically adjusting. This means that when the belt is buckled by the vehicle occupant, the retractor must be capable of cinching the lap belt tightly around the occupant's pelvic area (regardless of where the buckle tongue is located along the belt webbing when the belt is fastened). The friction in the buckle tongue cannot be so high that the occupant must manually pull the belt webbing through the tongue to tighten the lap belt. Based on our viewing of your proposed belt system (presented by your representative in a May 25th meeting), it is our opinion that your system does not have a sufficiently low level of friction that it would automatically adjust the lap belt portion. It is impossible for us to judge how this system would perform when installed in a vehicle, however, since the angle of the buckle tongue at the time of fastening does affect its friction level. It is the manufacturer's responsibility to determine whether or not its belt design complies with the standard. The agency does not offer advance approval of any motor vehicle or piece of motor vehicle equipment. Further, the agency does not make determinations of compliance of a vehicle or item of equipment prior to the manufacturer's certification of that vehicle or equipment.; The second restriction in regard to continuous loop systems concern the use of manual and automatic tension relieving devices on the upper torso portion of the continuous loop. In past letters of interpretation, the agency has limited the use of tension relieving devices to the upper torso section of seat belts that have an individually adjustable lap belt. A system does not have an individually adjustable lap belt if slack which is introduced into the continuous loop by a 'window shade' device or 'comfort clip' is directly transferred to the lap belt. Thus, in answer to your specific question, yes, a continuous loop seat belt system with a tension reliever on the upper torso portion of the belt should have a one-way locking tongue or some other method of preventing slack from returning to the lap belt. The high friction in the buckle tongue of your belt design would likely prevent the return of belt slack to the lap belt. However, as pointed out above, this high friction would also likely prevent the lap belt from adjusting automatically. Granted, these are somewhat conflicting concerns and they do present a tremendous design challenge. However, the agency believes these are necessary requirements if manufacturers include tension-relieving devices in their continuous loop systems.; I hope this clarification will be of help to you in your design plans. Sincerely, Frank Berndt, Chief Counsel