Rod Nash, P.E.
Vice President of Engineering
Collins Industries, Inc.
15 Compound Drive
Hutchinson, KS 67502-4349
Dear Mr. Nash:
This responds to your request for an interpretation of Federal Motor Vehicle Safety Standard (FMVSS) No. 222, School Bus Passenger Seating and Crash Protection.You ask how the standard applies to school bus seats that are adjoining, yet have individual sized backs for each passenger" and "unique cushions for each student."You enclosed copies of product literature from Freedman Seating Company that indicates that each seat is 17 inches wide, and that two seats together are 35 inches.
You first ask about the test procedure in S5.1.3, Seat performance forward. S5.1.3 specifies that school bus passenger seats must deflect in a specified manner when force is applied through a loading bar that is centered behind the seat back. The loading bar is described in S6.5 of FMVSS No. 222. S6.5 specifies, "the length of the loading bar is 102 mm less than the width of the seat back in each test. "
You ask whether the "width of the seat back" as stated in S6.5 refers to the width of one seat back or the width of both seat backs together. Our answer is that in this situation the two seats would be considered as a single "seat" for the purposes of FMVSS No. 222. Our answer is consistent with an August 16, 2004, interpretation letter to American Suzuki Motor Corporation, on FMVSS No. 214, Side Impact Protection. In the letter to Suzuki, we noted that the term "bench seats" is not defined in FMVSS No. 214 and stated:"However, seats are commonly considered bench seats when their separate sections are side-by-side, as shown in your photographs, even when they are separately adjustable. "
Therefore, the width of the seat back used in the determination of the length of the loading bar would be the overall width of both seat backs together. The seat back width would be measured on a horizontal plane 406 mm above the seating reference point across both seat backs and the loading bar would be 102 mm shorter than this measurement.
Your second question asks about the correct method of determining the necessary projected surface area of the seat back under S5.1.2 of FMVSS No. 222. S5.1.2 states:
Seat back height and surface area. Each school bus passenger seat shall be equipped with a seat back that, in the front projected view, has a front surface area above the horizontal plane that passes through the seating reference point, and below the horizontal plane 508 mm above the seating reference point, of not less than 90 percent of the seat bench width in millimeters multiplied by 508.
Although your letter asks about "the correct place to determine seat back width," in fact the requirement for projected surface area is based on seat bench width. Thus, the required projected surface area is calculated by multiplying 508 times the seat bench width, which in this case encompasses both adjoining seats, and then multiplying by 0.9. In your example, the seat bench width is 889 mm (35 inches). The projected area is calculated excluding the V-shaped notch area in the back seat in the same manner that the area of the radius of the corners of conventional seat backs is removed (reference TP-222-03).
I hope this information is helpful. If you have any further questions, please feel free to contact Dorothy Nakama of my staff at this address or by telephone at (202) 366-2992.