Interpretation ID: nht74-3.14

DATE: 06/11/74

FROM: AUTHOR UNAVAILABLE; Richard B. Dyson; NHTSA

TO: The Adams & Westlake Company

TITLE: FMVSS INTERPRETATION

TEXT: This is in reply to your letter of April 16, 1974, concerning an interpretation of the requirements of Motor Vehicle Safety Standard No. 217, "Bus Window Retention and Release" (49 CFR 571.217). You appear to ask whether bus windows containing tempered glass must meet the release requirements of paragraph S5.3.2 after (as well as before) the retention test required by S5.1 when the glass breaks during the retention test. You state that tempered glass, once broken, is easily removed from the entire lite by touch, implying that when this is the case there is no longer a need for any release mechanism to be further tested.

Paragraph S5.3.2 requires the release mechanism to meet specified requirements both before and after the window retention test of S5.1 irrespective of the glazing material used in the lite. Consequently, release mechanisms for windows of tempered glass must conform to the requirements even though the glass may be broken during the retention test

While your argument that the requirement seems unnecessary when tempered glass is used is not without some basis, it is also quite likely, in our view, that bus passengers in a crash may be ignorant of the quality of tempered glass to which you refer and thus still attempt to operate the emergency exit using its release mechanism.

Yours truly,

April 16, 1974 Larry Schneider Office of Chief Consul National Highway Traffic Safety Administration

In regards to Motor Vehicle Safety Standard No. 217, "Bus Window Retention and Release", please refer to S5.3.2 which states:

"When tested under the conditions of S6. both before and after, the window retention test required by S5.1, each emergency exit 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)"

In the design of our particular application, we use a single sliding lite in a vehicle less than 10,000 lbs. GVWR and have opted to meet the low force application described in (a). See attached drawing DM-8991-2.

Our question centers on the above quote from the specification particularly when tempered glass is used. We foresee no difficulty in meeting the release test before the retention test but does the tempered glass, once broken, qualify as an uncostructed opening due to the ease of removal of any glass that might remain in the opening. Tempered glass as you are probably well aware, once stressed to the point of breakage, crumbles into small cubes over the entire lite and may be easily removed by touch.

Your earliest reply will be appreciated.

Ronald J. Hansing Project Engineer

Attachment cc: H. C. Gildnor

C. M. Miller

R. Prey

E. V. Gordon

July 10, 1974

Office of Chief Consul National Highway Traffic Safety Administration

ATTN: Richard Dyson

Please find enclosed drawing DK-1553 which should have been sent with letter dated July 3, 1974.

Ronald J. Hansing Project Engineer

RJH:cpp Enclosure