Interpretation ID: nht79-2.37

DATE: 03/22/79

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Blue Bird Body Company

TITLE: FMVSS INTERPRETATION

TEXT:

March 22, 1979 NOA-30

Mr. W. G. Milby Manager, Engineering Services Blue Bird Body Company P.O. Box 937 Fort Valley, Georgia 31030

Dear Mr. Milby:

This responds to your November 29, 1978, letter asking several questions about test procedures conducted in accordance with Standard No. 222, School Bus Passenger Seating and Crash Protection. Your questions concern the impact and contact area test requirements of the standard.

First, you suggest that the head and knee impact tests should be conducted with only one impact allowed per seat back. The standard states in S5.3.1: "A surface area that has been contacted pursuant to an impact test need not meet further requirements contained in S5.3." You apparently interpret "surface area" to mean an entire seat back.

The purpose of the above-cited sentence in S5.3.1 is to assure manufacturers that the agency will not hit the test seat in the identical spot twice during compliance testing. However, it is permissible for several tests to be run on a seat as long as the test device does not impact the same specific area previously contacted by the device in an earlier test. This test method is appropriate because it approximates accident conditions. A seat is likely to be impacted more than once in an accident when the seat immediately behind it is occupied by three passengers. Accordingly, the agency will continue to run multiple tests on a seat back but will never impact the same "surface area" more than once.

In your second question, you suggest that a test sequence is appropriate for contact area testing. The agency disagrees. The agency agrees that the head form and knee form impact tests are different tests for the reasons outlined in your letter. However, nothing in those reasons compels the agency to conclude that a test sequence would be appropriate for contact area testing. In an accident, the impact of children on a seat back may or may not be sequential in nature.

Therefore, the existing test method, which permits the agency to sequence tests in any manner, closely reflects actual accident experiences. Accordingly, the agency will not adopt a specific sequence in its test procedures.

Sincerely,

Frank Berndt Acting Chief Counsel

November 29, 1978

Mr. Joseph J. Levin Chief Counsel National Highway Traffic Safety Administration Washington, D.C. 20590

SUBJECT: FMVSS 222

Dear Mr. Levin:

The purpose of this letter is to seek an interpretation regarding the sequence of testing required by FMVSS 222.

The testing sequence is important because many of the tests required by the subject standard have an interactive effect.

It is obvious that bus seats are an expendable item in a collision. This is attested to by the destructive nature of the requirements of the subject standard.

The head and knee impact requirements of the subject standard are both destructive in nature, and both have interactive effects not only with respect to each other, but also with respect to subsequent impacts within the head requirements or subsequent impacts within the knee requirements.

Because of the interactive effect of these requirements, not only on the immediate contact area, but also the surrounding area, it is not appropriate to conclude that a non compliance exists based on multiple impacts on any given seat. We believe this issue is addressed by S 5.3.1 which states "...a surface area which has been contacted pursuant to an impact test need not meet further requirements contained in S 5.3". It is further addressed by S 5.3.2.2. This section states "When any point ... is impacted...". (Emphasis added). We interpret this singular language to indicate that for compliance test purposes, only one point should be impacted on any given seat. We therefore seek your confirmation of this interpretation.

It should be noted here, as a practical matter, that multiple impacts on a particular seat are appropriate so long as the resulting data do not indicate a non compliance. This is so because multiple impacts on a particular seat constitute a worst case approach; if the seat passes under these circumstances, then it can be assumed it passes if only one impact per seat is made. However, if an indicated non compliance is encountered, it must be verified by impacting a virgin seat in the same location.

The second issue relating to testing sequence is the 3 in2 contact area requirement vs. the HIC and Force Distribution requirements with the head and maximum force requirements with the knee. We interpret the contact area requirements to be distinctly different tests for both the head and the knee for two reasons:

1. S 5.3.1.2 and S 5.3.1.3 require different velocities for the two tests, and

2. S 6.8 requires that the head form, knee form and contactable surfaces must be clean and dry during impact testing.

We therefore seek your confirmation of this interpretation also.

The importance of these issues was raised recently during compliance testing now being conducted by NHTSA at Mobility Systems laboratories. We urge you to resolve these issues by interpretation prior to the issuance of the FMVSS 222 compliance test report on the Blue Bird All American bus currently at Mobility Systems.

Thank you for your prompt reply.

Very truly yours,

W. G. Milby Manager, Engineering Services

sw