Interpretation ID: 77-3.11

TYPE: INTERPRETATION-NHTSA

DATE: 06/27/77

FROM: AUTHOR UNAVAILABLE; J. J. Levin, Jr.; NHTSA

TO: American Seating Company

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your March 24, 1977, letter asking for an interpretation of the requirements for knee contact area in Standard No. 222, School Bus Passenger Seating and Crash Protection, which state that, when impacted, "the resisting force of the impacted material shall not exceed 600 pounds and the contact area on the knee form surface shall not be less than 3 square inches." You ask whether this requirement can be interpreted as meaning that, when impacted, the resisting force of the impacted material shall not exceed 200 pounds per square inch rather than 600 pounds over 3 square inches.

The 600 pound maximum force and the 3 square inch minimum contact area are two distinct requirements. The first specifies an upper bound on the load that will be applied to the upper leg while the latter specifies a lower bound on the knee area over which an impact load must be distributed. To combine the two requirements, as you suggest, tends to relax the contact area requirement for a load which is less than 600 pounds. Such an interpretation would not ensure the level of safety the agency demands for knee contact area. The suggested combination of the two requirements may not provide an adequate distribution of forces over the knee. Accordingly, the agency declines to accept the suggested interpretation of the standard.

SINCERELY,

March 24, 1977

National Highway Traffic Safety Administration

Att: Chief Counsel, Frank A. Berndt

Reference is made to Federal Standard 222, paragraph S5.3.2.2, "When any part on the rear surface of that part of a seat back or restraining barrier within any zone specified S5.3.2.1 is impacted from any direction at 16 feet per second by the knee form specified in S6.7, the resisting force of the impacted material shall not exceed 600 pounds and the contact area on the knee form surface shall not be less than 3 square inches".

We request an interpretation of the requirement for the knee form contact area. The knee recess area of the seat back is the most vulnerable part of the seat not only to vandalism but to hard use by the passenger. This is the area where feet are placed on the back and soles of shoes scuff and damage softer material. Also objects such as briefcases and lunchboxes add to the damage in this area. In fact, in city and inter-city buses this area is normally protected by heavy plastic or stainless steel panels. In the endeavor to provide a more practical surface than the soft vinyl we have been successful in adopting a thin plastic back panel. However, in some areas of the seat back, the resisting force, at 16 feet per second, is only 300 pounds and proportionately the contact area caused by the knee form is about 2 - 2 1/2 square inches.

We question whether the 3 square inches applies to the resisting force of the 600 pound magnitude or if it must extend to the lesser force. If we consider the distribution of the 600 pound force over the 3 square inch area, we are applying 200 pounds per square inch. When we measure the distribution of forces in this manner we meet the 200 pound maximum per square inch.

Under separate cover we are sending you copies of the actual contact areas indicated by the paint imprint. Because your interpretation will have a direct bearing on the construction of the seat as well as performance and economy of maintenance, we would appreciate a response at your earliest convenience.

Chester J. Barecki Vice President - Sales Engineering Transportation Products Division

[Attachments Omitted]

CC: T. HOYT; E. HENEVELD; J. OTT; T. CAMP