Interpretation ID: nht74-5.53

DATE: 08/05/74

FROM: AUTHOR UNAVAILABLE; Richard B. Dyson; NHTSA

TO: The Adams & Westlake Company

TITLE: FMVSS INTERPRETATION

TEXT: Dear Mr. Hansing:

This is in reply to your letter of July 3, 1974, regarding Motor Vehicle Safety Standard No. 217. You requested that we reconsider our opinion of June 11, 1974, that a bus emergency release mechanism which you describe must meet the requirements for emergency exit release in S5.3.2 of the standard after as well as before the retention test required by S5.1, when the glass breaks during the retention test.

Paragraph S5.3.2 requires that the release requirements be met both before and after the retention test. We do not find sufficient justification to relax this requirement in the situation you described. First, it is not clear that it is as easy as you represent to eliminate by hand all of the glazing material left in the frame. More importantly, however, we still question whether most persons are sufficiently cognizant of the qualities of tempered glass to attempt to remove the remaining fragments in an emergency situation. Finally, glazing with completely different breakage characteristics may be used to replace the original tempered glass at some time during the life of the bus. For these reasons, our conclusion of June 11 remains the same.

Yours Truly,

July 3, 1974

Office of Chief Counsul

National Highway Traffic Safety Administration

Attention Mr. Richard Dyson

In regard to Motor Vehicle Safety Standard #217, "Bus Window Retention and Release S5.3.2 and our previous correspondence (here enclosed), please reconsider our request for exemption from having operable release mechanisms after the retention test when glazing with tempered glass.

In my letter to you of April 16, 1974 we noted that tempered glass once broken made the operation of any release mechanism unnecessary, as any glass remaining in the opening would be easily removed by touch. We therefore asked for exemption from the requirement that the release mechanism be operable after the retention portion of the test on the basis that the release mechanism would no longer be necessary in the event of glass breakage.

Our design, which is proposed for use on short and mid-range transit busses, uses an extruded aluminum frame which is screwed to the coach body. The glass is glazed directly into the frame; the stationary lite being returned by a rubber extrusion and bedding tape. The sliding glass is also retained directly in the frame and glides horizontally in a pocket weatherstrip. The release lock mechanism is bonded directly to the sliding lite and retains it in a closed position by engaging a groove in the extruded frame rail.

To meet the opening requirement of S5.2.2B of the spec, the release lock mechanism is disengaged and the sliding lite is moved foreward or rearward, depending on which half contains the sliding lite, until the minimum opening width of 20 inches is obtained. See drawing #DK-1553 and test pictures which show the type of window proposed.

This system meets the preliminary release test and the retention test without question, but if the tempered sliding glass shatters during the lotter test most of the glass, often including the release lock mechanism, falls out of the opening. This obviates any further practical need for the release

lock mechanism as the required opening, if not immediately obtained by the breakage of the sliding lite, can be obtained by touching any remaining glass cubes which will cause them to crumble and fall out. In the event that the tempered glass does not break during testing, or more importantly during crash impact, the mechanism would obviously be required to function.

We feel that our system fully meets the intent of the specification in providing unobstructed openings for emergency agress. We respectfully request that you reconsider our request for exemption from the portion of paragraph S5.3.2 which requires that the release lock mechanism remain operable after the retention test when tempered glass is used in this manner and has broken out during that test. Please give this request your earliest consideration as a reply is urgently needed by August 1, 1974.

Ronald J. Hansing Project Engineer

(Graphics omitted)