Interpretation ID: nht73-6.1

DATE: 10/16/73

FROM: AUTHOR UNAVAILABLE; Robert L. Carter; NHTSA

TO: Twin Coach Highway Products Incorporated

TITLE: FMVSS INTERPRETATION

TEXT: Thank you for your letter of August 22, 1973, concerning the requirements of Federal Motor Vehicle Safety Standard No. 217, Bus Window Retention and Release.

Following are answers to your four questions:

1. In a phone conversation with Richard Dyson on September 26 you explained that the window mechanism in question (which you mentioned you are no longer using) requires the release of both mechanisms before the window releases -- that is, before the window will no longer conform to the retention requirements in paragraph s5.1, s5.1.1, and s5.1.2 of the standard. In this case, only one of the force applications necessary to operate both mechanisms need differ by 90 degrees to 180 degrees from the direction of the original push-out motion of the emergency exit.

2. You are correct that the post in front of the window is not an obstruction so long as it permits passage of the ellipscid. However, when a post cuts a window opening into two segments as shown in your enclosed sketch, only the segment that passes the ellipscid, not the entire window opening, may count toward the measurement of total area specified in paragraph s5.2.

3. Although Figure 30 shows only the boundaries for high and low force access regions when the bus is upright (and when an obstacle is between the occupant and the unit), these same dimensions are these that are to be applied when the bus is overturned on either side, with the side on which the

bus is resting being considered as the floor. The transposition of these dimensions is illustrated to some extent in Figure 3D.

Whether or not both rear windows must be made into emergency exits rests solely on whether both windows are necessary for the bus to meet the unobstructed opening requirements, and the emergency exit release requirements of s5.3 and s5.5 when the bus is upright and overturned on either side.

4. The cut-off date for windows which do not comply with the standard is that of the date of manufacture of the bus in which the window is installed. All buses manufactured on or after September 1, 1973, must comply with the requirements of Standard No. 217.

If I can be of further assistance, please do not hesitate to ask.