Interpretation ID: nht76-4.40

DATE: 03/10/76

FROM: AUTHOR UNAVAILABLE; R. L. Carter; NHTSA

TO: Monsanto Polymers and Petrochemicals Co.

TITLE: FMVSS INTERPRETATION

TEXT: This is in response to your letter of December 22, 1975, to Mr. Guy Hunter of my staff, concerning our reasons for prohibiting the use of tempered glass in windshields of motor vehicles.

The use of tempered glass in windshields is prohibited for the following reasons:

1. Tempered glass has little, if any, energy absorbing capability while laminated glass has intrinsic deflective characteristics that provide such capability.

2. When tempered glass breaks, it usually either "crazes" or shatters into many small pieces. If crazing occurs, the driver's vision becomes obscured thus not only endangering himself but others as well. If the glass shatters, the driver and other vehicle occupants are showered with glass pellets which could not only result in loss of control of the vehicle but is also likely to cause eye injuries.

3. When cracked, tempered glass has essentially no retentive capability, thus the likelihood of occupant ejection through the windshield opening is greatly increased in crash situations. Laminated glass, on the other hand, possesses significant retentive capability even after initial cracking of the glass laminate on either side of the plastic interlayer.

If I can be of further help, do not hesitate to contact me.

Sincerely,

MONSANTO POLYMERS & PETROCHEMICALS CO.

December 22, 1975

Guy Hunter -- National Highway Traffic Safety Admin.

Dear Guy:

Our Monsanto Europe associates receive, from time to time, inquiries from a variety of industry and independent sources concerning NHTSA's position on the question of tempered vs. laminated HPR windshields. While I am aware of your position in this matter, would you be willing to document your feelings in a letter which I could distribute to our associates.

Should you agree, it would be appreciated if you could define the reasons for which NHTSA would be opposed to permitting tempered windshield use in the American market, and perhaps include an endorsement of the HPR windshield.

Thank you for your assistance.

Kindest regards,

E. Lacey -- Industry Technical Specialist, Laminated Glass