Interpretation ID: nht94-7.7

DATE: April 1, 1994

FROM: John Womack -- Acting Chief Counsel, NHTSA

TO: Jane L. Dawson -- Specifications Engineer, Thomas Built Buses, Inc.

TITLE: None

ATTACHMT: Attached to letter dated 11/22/93 from Jane L. Dawson to Walter Myers

TEXT:

This responds to your letter to Walter Myers of this office in which you posed two questions regarding Federal Motor Vehicle Safety Standards (FMVSS) 217, Bus Window Retention and Release.

Your first question related to the definition of "daylight opening" found in the final rule amending FMVSS 217, dated November 2, 1992, (57 FR 49413) (hereinafter Final Rule). Specifically, you asked "(w)hat constitutes an obstruction and how close to the door does an object have to be in order to be considered an obstruction?"

The term "daylight opening" is defined in the Final Rule as "the maximum unobstructed opening of an emergency exit when viewed from a direction perpendicular to the plane of the opening." An obstruction in this context would include any obstacle or object that would block, obscure or interfere with, in any way, access to that exit when opened. In determining the "maximum unobstructed opening of an emergency exit," we would subtract, from the total area of the opening, the area of any portions of the opening that cannot be used for exit purposes as a result of the obstruction. The area measurements would be taken when viewed from a direction perpendicular to the plane of the opening. I have enclosed a copy of a March 24, 1994 letter to Mr. Bob Carver of Wayne Wheeled Vehicles which provides an example of how the amount of area to be credited was determined for a specific design.

You should be aware that the agency published a notice of proposed rulemaking to amend Standard No. 217 on December 1, 1993, (58 FR 63321). The notice proposed two alternate means for determining the maximum amount of area that will be credited for all types of emergency exits on school buses. The agency is currently reviewing the comments received in response to this notice. I am enclosing a copy of this notice.

In your second question you referred to the current provisions of S5.2.3.1(b), FMVSS 217, which provides that a left-side emergency door must be located in the rear half of the bus passenger compartment. You then asked whether that requirement was changed in the Final Rule. The answer is yes.

Section S5.2.3.1 of FMVSS 217, as amended in the Final Rule, provides manufacturers two options for the provision of school bus emergency exits, S5.2.3.1(a) (Option A) and S5.2.3.1(b) (Option B). Option A requires a rear emergency door. If additional emergency exit area is required, the first additional emergency exit must be a left side door located as near as practicable to the midpoint of the passenger compartment. Option B requires a left-side emergency door and a pushout rear window, but does not designate a specific location for them. Thus, the amended standard does not specify a location for a left-side emergency door installed for Option B, the equivalent of current S5.3.3.2(b).

I hope this information will be of assistance to you. Should you have any further questions or seek additional information, please feel free to contact Walter myers of my staff at this address or at (202) 366-2992.