Interpretation ID: nht87-1.95

TYPE: INTERPRETATION-NHTSA

DATE: 06/04/87

FROM: AUTHOR UNAVAILABLE; Erika Z. Jones; NHTSA

TO: Mr. L. T. Mitchell

TITLE: FMVSS INTERPRETATION

TEXT: Mr. L. T. Mitchell, Specification Engineer Thomas Built Buses, L.P. P.O. Box 2450 1408 Courtesy Road High Point, NC 27261

Dear Mr. Mitchell:

This responds to your letter to me regarding the questions you share with the Connecticut Department of Motor Vehicles (DMV) about paragraph @5.1. 2 of Standard No. 222, School Bus Passenger Seating and Crash Protection. I regret the delay in our respons e. As you know, your letter has supplemented by information we received in a letter from Mr. Harry Gough of the DMV. We have also incorporated into your inquiry information you provided on February 26 to Mr. Paliokas of NHTSA's Office of Vehicle Safety C ompliance concerning the dimensions of the seat back in question. I regret the delay in this response.

The first question you ask is whether @5.1.2 applies to the last row "davenport" type seat found in a rear engine school bus. The answer is yes. By its terms, @5.1.2 applies to "each school bus passenger seat" and makes no exception for the rearmost seat . The second question you ask relates to the concerns you and the DMV have about the requirements in @5.1.2 for seat back surface area. Because Connecticut prohibits the top of rear divan seats to be higher than the lower edge of rear emergency windows, th e state wishes to reduce the height of the seat back on a seat located in the last row of the school bus and reduce the width of the seat cushion (to 29 inches) by use of "spacers." You enclosed a diagram of the seating design to illustrate how the propo sal compares with your standard school bus seat and called the new seat "cushion 2" and the area of its seat back "area 2. " The DMV sent us a diagram showing the location of the spacers on cushion 2.

You believe that the DMV's desired seat back design would not comply with Standard No. 222 and ask us whether you have made a correct determination. As explained below, the answer is yes.

Paragraph @5.1.2 of Standard No. 222 regulates the height and surface area of seat backs on school buses. It states:

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 20 inches above the s eating reference point, of not less than 90 percent of the seat bench width in inches multiplied by 20.

In order to ascertain the compliance with @5.1.2 of the seat back in question, the area of the seat back (in the front projected view) between the two horizontal planes referenced in @5.1.2 is calculated. To calculate this, dimensions are needed for the height of the seat back above the seating reference point (SRP) and the width of the seat back. The information you provided to Mr. Paliokas concerned the SRP and seat back height. According to that information and the diagram you enclosed, the seat back for cushion 2 is five inches lower than your standard school bus seat back. Thus, the height above the SRP of the seat back for cushion 2 is approximately 14.25 inches.

As to the width of the seat back, the question arises whether it should be considered to be 29 or 39 inches wide. While the seat back appears to be 39 inches wide in your illustration, the "spacers" located on each end of the seat in front of the seat ba ck reduce the seat width to 29 inches.

The use of the spacers brings up two related issues. First, are they adequate in rendering portions of the bench seat inappropriate for use as seating surface areas? You as the manufacturer must make a good faith determination of their adequacy. We do no t have enough information at this time to answer this question: however, we will assume for the purposes of this discussion that the answer is yes.

Second, assuming that the spacers are adequate in making portions of the bench seat unlikely to be used for seating, should the surface of the seat back behind the spacers be considered part of cushion 2's seat back surface area for purposes of @5. 1.2? We believe the answer to this question is no. Since non-seating areas are not required to be compartmentalized between high seat backs or restraining barriers, we do not consider portions of a seat back behind non-seating positions as part of the seat ba ck surf ace area required by @5.1.2 to be provided for school bus seats. Hence, if the spacers render cushion 2 into a 29 inch seat, we conclude that the width of the corresponding seat back is 29 inches.

Under @5. 1.2, the front surface area of the seat back between the two referenced planes must be not less than 90 percent of the seat bench width in inches multiplied by 20. The required surface area for a seat back of a 29 inch bench seat thus must be a t least 522 square inches. Since the seat back for cushion 2 has a height above the SRP of 14.25 inches and a width of 29 inches, its area is only 413.25 square inches. Therefore, the seat back does not meet @5. 1.2 of Standard No. 222.

In his letter to us, Mr. Gough argues that the proposed design would not violate the purpose of Standard No. 222 since the seat back in question would be located in the rear of the school bus and no person would be sitting or standing behind it. We canno t accept this argument. Paragraph 52 of Standard No. 222 states: "The purpose of this standard is to reduce the number of deaths and the severity of injuries that result from the impact of school bus occupants against structures within the vehicle during crashes and sudden driving maneuvers." In accordance with this intent, Standard No. 222 requires school buses to comply with "compartmentalization" requirements to provide passenger crash protection. To achieve the benefits of compartmentalization, it i s important that passengers be protected and confined in the event of a crash within an area of sturdy, well-padded seats. The seat back area required by @5.1.2 is necessary, therefore, not only to provide protection to passengers seated behind the seat back, but also to ensure that the protective compartment is provided for occupants of the seat.

I hope this letter is helpful. I am sending a copy of this letter to Mr. Gough for his Information. Please contact my office if you or he have further questions.

Sincerely,

Erika Z. Jones Chief Counsel

December 17, 1986

Ms. Erika Z. Jones Office of the Chief Counsel National Highway Traffic Safety Administration U.S. Department of Transportation 400 7th Street SW Washington, D.C. 20590

Ref: FMVSS #222 Section @5.1.2 - Seat Back Height and Surface Area.

Dear Ms. Jones:

One of our customers has requested an interpretation of FMVSS #222 @5.1.2 - "Seat Back Height and Surface Area".

1)Does @5.1.2 apply to the last row "Davenport" type seat that is found in a rear engine school bus?

2) The Davenport seat back width is 90 inches. Each cushion is 39" wide. If the answer to question number 1 is yes, what seat backs surface area may be used to meet the requirements of @5.1.2 for the total cushion width?

The enclosed illustration shows area number 1 and 2 respectively located above cushion number 1 and 2. Thomas Built Buses interprets @5.1.2 to mean that area 1 must meet the area requirement of @5.1.2 for cushion 1. Thus area 2 with its reduce seat back height does not meet @5.1.2 for cushion 2. Is the Thomas interpretation correct?

Thank you for your help in this matter. We are looking forward to your response.

Sincerely,

Thomas Built Buses, L.P.

L. T. MITCHELL, Specification Engineer

LTH/jw

Enclosure

cc: Matt Mathieson Ron Marion Howard Smith, Connecticutt Distributor