Interpretation ID: 1984-2.43

TYPE: INTERPRETATION-NHTSA

DATE: 08/03/84

FROM: AUTHOR UNAVAILABLE; Frank Berndt; NHTSA

TO: Transport Canada

TITLE: FMVSS INTERPRETATION

TEXT:

Mr. G.N. Farr, P. Eng. Transport Canada Standards and Regulations Division, Road Safety and Motor Vehicle Regulation Ottawa, Ontario K1A 0N5 CANADA

Dear Mr. Farr:

This responds to your request for an interpretation of the requirements of Standard No. 222, School bus passenger seating and crash protection (49 CFR S571.222). First, I would like to apologize for the delay in responding to your letter. You specifically asked for an interpretation of section S5.1.3.4 of Standard No. 222, which section requires the seat back to absorb 4,000W inch-pounds of energy. This energy is applied to the seat by a loading bar moving forward. When calculating the energy absorbed by the seat, the force transmitted back through the loading bar after the forward pressure is released is subtracted from the energy which was transmitted through the loading bar when it was moving forward. You asked at what point the forward movement of the loading bar is stopped in order to permit the seat back to rebound with a resultant energy absorption by the seat back of 4,000W inch-pounds. You noted that the rebound characteristics of the seat being tested would have to be known in advance to calculate the point at which the forward movement of the loading bar should be stopped.

This point was explained in the preamble to the notice of proposed rulemaking which preceded the adoption of Standard No. 222 (40 FR 17855; April 23, 1975) (copy enclosed). An earlier proposal had specified a requirement that, "The energy necessary to deflect the seat back 14 inches shall be not less than 4,000W inch-pounds". This agency decided that this language created needless confusion, by inaccurately combining two different requirements. Accordingly, the requirements were set forth in two separate sections. Section S5.1.3(b) now specifies that seat back deflection shall not exceed 14 inches. This requirement is related to the requirement in section S5.1.3.4 that the seat back absorb 4,000W inch-pounds.

When conducting the compliance testing for section S5.1.3.4, the agency deflects the seat back as far as it will go, and then releases the seat back. If the seat back absorbs 4,000W inch-pounds of energy or more when tested according to the procedures set forth in S5.1.3.4, it is deemed to pass the test. If the seat back does not absorb 4,000W inch-pounds during the test, the seat back has failed the test. I think your question arose from your impression that the testing must be continued until the seat back has absorbed exactly 4,000W inch-pounds of energy. This agency tests only to see if the seat back absorbs 4,000W inch-pounds or more.

Should you need any further information on this subject, please feel free to contact me.

Sincerely,

Frank Berndt Chief Counsel

Enclosure

Ottawa, Ontario, K1A 0N5, January 9, 1984.

Office of Chief Counsel, National Highway Traffic Safety Administration, 400 Seventh Street, S.W., Washington, D.C., 20590, U.S.A.

Dear Sir:

On November 22, 1983 we wrote to request a copy of any legal interpretations which have been made to clause S5.1.3.4 of FMVSS 222. A copy of the letter is attached.

We would appreciate it if you could review this item and respond at your earliest convenience.

Yours very truly,

G.N. Farr, P. Eng., Standards and Regulations, Road Safety and Motor Vehicle Regulation.

Attach.

Ottawa, Ontario, K1A 0N5, November 22, 1983.

Office of Chief Counsel, National Highway Traffic Safety Administration, 400 Seventh Street, S.W., Washington, D.C., 20590, U.S.A.

Dear Sir:

This is a request to be provided with a copy of any legal interpretation which has been made to clause S5.1.3.4 of FMVSS 222. The interpretation would involve the method used to determine the amount of energy absorbed in deflecting the seat back (or retaining barrier). S5.1.3.4 of FMVSS 222 requires that an additional force be applied until 4000W inch-pounds of energy has been absorbed by the seat back. The force-deflection curve used to calculate the energy consists of both the forward and rearward travel of the loading bar pivot point. The question regarding clarification is, at what point do you stop the forward movement of the loading bar, in order to permit the seat back to rebound, with a resultant energy absorption of 4000 W inch-pounds? The rebound characteristics of the seat back would have to be known in advance in order to determine this point.

If a legal interpretation of this point has been made in the past, we would appreciate receiving a copy of same.

Yours very truly,

G.N. Farr P. Eng., Standards and Regulations, Road Safety and Motor Vehicle Regulations