Interpretation ID: nht73-3.10

DATE: 01/11/73

FROM: AUTHOR UNAVAILABLE; Richard B. Dyson; NHTSA

TO: Nissan Motor Co. Ltd.

TITLE: FMVSR INTERPRETATION

TEXT: This is in reply to your letter of November 21, 1972, concerning the definition of "head impact area" in 49 CFR 571.3(b).

Your question is whether the lower portion of the dashboard depicted in your letter is within the head impact area. Without knowing the interior dimensions of the vehicle, we cannot give you a definite answer. We can, however, describe the circumstances under which the lower part of the dash might be within the head impact area.

Under paragraphs (a) through (c) of the definition, the test device is pivoted forward about specified centers until it contacts the vehicle. These contact points, which together comprise the head impact area, are divided into two groups, those above the lower line of the windshield glass (paragraph (b)), and those below (paragraph (c)). Although the measurement of the head impact area is a continuous process, the separation of the contact points into two groups was accomplished by paragraphs that are not parallel in structure. This has caused some confusion.

The intent of paragraphs (b) and (c) of the definition might have been expressed in a single paragraph, reading as follows:

With the pivot point to "top-of-head" dimension at each value allowed by the device and the interior dimensions of the vehicle, pivot the measuring device from a vertical position forward and downward through

all arcs in vertical planes to 90 degrees each side of the vertical longitudinal plane through the seating reference point, until the head form contacts an interior surface or until it is tangent to a horizontal plane 1 inch above the seating reference point, whichever occurs first.

In our opinion it would be appropriate for you to employ this procedure to determine whether any part of the lower dash pad in your drawing falls within the head impact area. The goal of your evaluation would be to determine whether it is possible for the test device to be pivoted downward so that it contacts the lower pad without first contacting the upper pad. If at a particular point the device contacts the upper pad, and if the device is at its minimum length of 29 inches and its pivot point is on the seating reference point, then the area of the lower pad directly beneath that contact point would not be contactable and would not be a part of the head impact area. If, however, there is a point at which the head form in its downward arc would miss the upper pad and contact the lower pad, the lower pad would at that point be within the head impact area. It is quite possible that some points on the lower pad would be within the head impact area, while others would not.