Interpretation ID: nht94-3.70

TYPE: INTERPRETATION-NHTSA

DATE: July 14, 1994

FROM: John Womack -- Acting Chief Counsel, NHTSA

TO: Eric T. Stewart -- Engineering Manager, Mid Bus Inc.

TITLE: NONE

ATTACHMT: Attached to letter dated 5/26/94 from Eric T. Stewart to NHTSA Office of Chief Counsel (OCC-10049)

TEXT: This responds to your letter of May 26, 1994, asking whether the daylight opening of a door located to the left of the driver's seat can "be used in the calculations of required emergency exit area if it meets the performance requirements of Standard No. 217," Bus Emergency Exits and Window Retention and Release. The vehicle on which the door is installed has a capacity of 48 children or 40 adults and a gross vehicle weight rating (GVWR) of more than 10,000 pounds (4,536 kilograms).

During a June 27, 1994 phone conversation with Mary Versailles of my staff, you explained that you anticipate producing these vehicles as both buses and school buses. Accordingly, I will address the question separately for each of these vehicle types. As explained below, provided that the exit meets all the performance requirements for a side door exit, it may be possible to apply the area of such a door to the emergency exit area requirements for either type of bus.

Non-School Bus

The emergency exit requirements for non-school buses with a GVWR of more than 10,000 pounds are found in S5.2 of Standard No. 217. That section requires non-school buses to have "unobstructed openings for emergency exit which collectively amount, in tot al inches, to at least 67 times the number of designated seating positions on the bus." That section further requires at least 40 percent of the areas for emergency exit to be on each side of the bus and limits the amount that can be credited for each ex it to 536 square inches. If the door otherwise meets the emergency exit performance requirements, nothing in Standard No. 217 would prohibit counting the door as an emergency exit. Therefore, if the 40 percent distribution requirements are met, the

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unobstructed area of a door to the left of a driver on a non-school bus can be credited, up to a maximum credit of 536 square inches.

School Bus

The emergency exit requirements for school buses with a GVWR of more than 10,000 pounds are found in S5.2.3 of Standard No. 217. That section states "(t)he area in square centimeters of the unobstructed openings for emergency exit shall collectively amo unt to at least 432 times the number of designated seating positions in the bus." All school buses are required to have either a rear emergency door exit or a side emergency door exit and a rear push-out emergency window. To determine if additional emer gency exits are required, the area of "daylight opening" of the front service door and those required emergency exits is subtracted from the total area required.

The formulas in S5.2.3 for subtracting the front service door and the required emergency exits refer to the "size of the available front service door opening" (emphasis added). We interpret this language as allowing the subtraction of the "daylight open ing" of a single front service door. The drawings you faxed on July 12, 1994 indicate that the vehicle has a front service door to the right of the driver in addition to the door to the left of the driver. Since the daylight opening of only one front s ervice door can be credited, the daylight opening of the door to the left of the driver cannot be credited as a front service door.

If additional emergency exits are required, they must be added in the following order:

1) Left side emergency exit door near the mid-point of the passenger compartment (if the vehicle has a rear door exit) or right side emergency exit door (if the vehicle has a side door exit and rear push-out window);

2) emergency roof exit;

3) any combination of side emergency exit doors, emergency roof exits, or emergency window exits.

Since the door to the left of the driver is not credited as the front service door, the only opportunity for crediting the area would be under the third level above. The door could not qualify for category (1), above, because a left side emergency door must be located near the mid-point of the passenger compartment.

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I hope you find this information helpful. If you have any other questions, please contact Mary Versailles at this address or by phone at (202) 366-2992.