Interpretation ID: nht89-2.86

TYPE: INTERPRETATION-NHTSA

DATE: 08/30/89

FROM: STEPHEN P. WOOD -- NHTSA ACTING CHIEF COUNSEL

TO: DAN TREXLER -- SPECIFICATIONS ENGINEER THOMAS BUILT BUSES, INC.

TITLE: NONE

ATTACHMT: LETTER DATED 05/08/89 FROM DAN TREXLER -- THOMAS BUILT BUSES TO ERIKA Z. JONES -- NHTSA; OCC 3560

TEXT: Dear Mr. Trexler:

This is in reply to your letter of May 8, 1989, to the former Chief Counsel of this agency, Erika Jones. You have received requests "to install a master electrical disconnect switch on many buses." When the switch is turned to the "off" position "it ren ders inoperative the warning signals (to the driver) required by FMVSS 105, 121 and 217. It also inactivates the hazard warning flasher required by FMVSS 108." You ask whether installation of the switch would constitute a noncompliance, or a "safety rel ated hazard." if it is accessible to the seated driver, or if remotely located in the battery or engine compartment, without ready access to the driver.

Although you have not explained the purpose of such a device, we understand that a battery disconnect switch of this nature is deemed desirable by many bus owners to prevent drains on the battery when the bus is at rest. When the switch is activated, th e bus cannot be started and driven because electric power is not available. Under this circumstance we do not believe that the switch either creates a noncompliance with any of the standards listed, nor constitutes a safety related defect, regardless of its location. When the bus is in operation the warning systems of the standards are not affected. The possibility of inadvertent activation when the bus is in use does not constitute a defect in performance, construction, components, or materials such as to create a safety related defect. To forestall any possibility of inadvertent activation, however, you may find it preferable to locate the switch away from the driver.

We understand that a purpose of this switch is to reduce the likelihood of fire after accidents in which there has been fuel spillage. In this circumstance, it is likely that the bus would be positioned either in the roadway or adjacent to it. Safety w ould be enhanced if the hazard warning signal power source were separate from the batteries inactivated by the disconnect switch, so that these warning lamps could continue to operate.

Sincerely,