Interpretation ID: aiam4917
Engineering Services Blue Bird Body Company P.O. Box 937 Fort Valley
GA 31030;
"Dear Mr. Turner: This responds to your letter of August 19, 1991 requesting an interpretation of section S5.3.2 of Standard No. 217, Bus Window Retention and Release. That section specifies two force application options for release mechanisms of emergency exits, low force application and high force application. Your letter was sent in connection with an investigation by NHTSA's Office of Enforcement of a possible noncompliance of a 1990 Blue Bird bus with that standard, and you sent a sample bus window to assist in understanding your letter. You requested confirmation of your understanding that the requirements of section S5.3.2, 'with regard to motion, apply to the application forces and not the release mechanisms being activated by the forces.' You also requested confirmation of your 'understanding of the principles of mechanics, as applicable to FMVSS 217 requirements, that straight linear forces can cause rotary motion to occur and can be used to manually operate a rotary mechanism.' You asked these questions to support your contention that the release mechanism of the 1990 Blue Bird bus window can be operated by a force that is straight, perpendicular to the undisturbed exit surface, and that the high force application option is therefore available for that window. The issues raised by your letter are addressed below. Section S5.3.2 specifies that certain emergency exits 'shall allow manual release of the exit by a single occupant using force applications each of which conforms, at the option of the manufacturer, either to (a) or (b).' Subparagraphs (a) and (b) set forth requirements for the two application force options, low force and high force. The specified requirements cover location, type of motion, and magnitude. The type of motion specified in (a) for low force application is 'rotary or straight', the type of motion specified in (b) for high force application is 'straight, perpendicular to the undisturbed exit surface.' We agree that the requirements in (a) and (b) concerning type of motion refer to the force applications that would be made by a single occupant and not to the release mechanisms that are activated by such force applications. While we do not disagree with your contention that it is possible for straight linear forces to cause rotary motion to occur, we do not believe, based on our examination of your sample bus window, that the force application that must be made by a single occupant to release the window would be 'straight, perpendicular to the undisturbed exit surface.' We interpret the term 'type of motion,' as used in (a) and (b), to refer to the entire motion of a force application that would be made by a single occupant in releasing an exit. In order to operate the release mechanism on the Blue Bird bus, it appears that a single occupant must lift the release handle upward as well as pulling it outward. Given the upward part of the motion, it would not be 'perpendicular to the undisturbed exit surface.' Therefore, the high force application option is not available for such a design, and it must meet the low force application requirements. I hope you find this information helpful. If you have further questions, please contact Mary Versailles of my staff at this address or by telephone at (202) 366-2992. Sincerely, Paul Jackson Rice Chief Counsel";