Interpretation ID: 1983-3.15

TYPE: INTERPRETATION-NHTSA

DATE: 10/27/83

FROM: AUTHOR UNAVAILABLE; Frank Berndt; NHTSA

TO: State Purchasing and General Services Commission; Texas

TITLE: FMVSS INTERPRETATION

TEXT:

Mr. Troy C. Martin Specifications Chief State Purchasing and General Services Commission Lyndon Baines Johnson State Office Building P.O. Box 13047 Capitol Station Austin, Texas 78711-3047

Dear Mr. Martin:

This responds to your letter to Mr. Kratzke of my staff seeking an interpretation of Standard No. 222, School Bus Passenger Seating and Crash Protection (49 CFR S 571.222). You indicated that you have been informed that section S5.1.2 of that standard requires that 90 percent of the total projected area of the seat backs on school buses must lie between a horizontal plane passing through the seating reference point and a parallel horizontal plane 20 inches above the seating reference point, and that this requirement appeared to be a geometric impossibility. The information you received about the requirements of section S5.1.2 is erroneous.

Section S5.1.2 does not specify any requirements for the total projected area of the seat back. It simply mandates that the projected area of the seat back between the two planes you described be at least 90 percent of the width of the seat multiplied by 20. This requirement is very simple to satisfy geometrically by using a rectangle. If the seat back were rectangular, the area between the two planes would be 100 percent of the width of the seat multiplied by 20. The agency allows the width of the seat back to be multiplied by 90 percent so as to permit the use of seat backs which taper up at the top, but which still provide an adequate level of safety protection for the occupants.

The reason for specifying a requirement for the amount of area a seat back must have between these two planes is to ensure that "compartmentalization" is not compromised. Compartmentalization is the term for protecting the occupants in the event of a crash by confining them within an area of sturdy, well-padded seats. If the seat back in front of a school bus occupant occupied less than 90 percent of the area between the two planes (the area that occupant is most likely to contact in case of a crash), the padded area to cushion the blow of that occupant might not be sufficient.

If you have any further questions or need further information on this subject, please feel free to contact Steve Kratzke at this address and at (202) 426-2992.

Sincerely,

Frank Berndt Chief Counsel

August 11, 1983

Mr. Steve Kratzke, Attorney Office of Chief Counsel National Highway Traffic Safety Administration 400 7th Street SW, Room 5219 Washington, DC 20590

Dear Mr. Kratzke:

As you requested during our recent telephone conversation, I am asking for an interpretation of Paragraph S5.1.2. of Federal Motor Vehicle Safety Standard No. 222, "School Bus Seating and Crash Protection." I understand that the value

90% X Seat Width X 20

to be the projected area in square inches of the seat back (in a vertical plane) that lies between two horizontal planes, one going through the seating reference point (SRP), and the other through a point 20 inches above the SRP.

I have been informed by one of the engineers at a school bus body plant that 90% of the total projected area of the seat back must lie within these two planes. It appears to me that this is a geometric impossibility!

Your consideration of this request would be appreciated.

Sincerely yours,

Troy C. Martin Specifications Chief

TCM/dh