Safety glass for vehicle windscreens

 GT V02 1961 186-191

For just over twenty-jive years it has been a compulsory requirement in Great Britain that any glass fitted as a windscreen to a road vehicle must be of a type known as safety glass. For this purpose safety glass is defined by B.S. 857 as 'a glass which, if fractured, gives fragments which are less liable to cause severe cuts than those of ordinary glass'. Two types of glass, laminated and toughened, are recognized as complying with this requirement. The characteristics of laminated and toughened windscreens are described with particular reference to their strength, the patterns they produce on fracture, and to the character of the edges of the fragments of glass. The problem of the visibility through toughened glass after
fracture is considered in detail. Causes of shattering of toughened glass windscreens of vehicles on the road are discussed as is also the desirability of drivers being made aware of what to expect when this type of windscreen shatters. Examples of the screen being shattered while the car is travelling at high speed are given and comments are made on the special screens which contain barrier zones giving a clear view to the driver after shattering of the main portion of the windscreen. Based on investigations, by the Road Research Laboratory, of road accidents an analysis of the incidence of head and facial injuries is given for the two types of safety glass. It is suggested that there is a strong case for the use of toughened glass for windscreens in spite of the disadvantage of some loss of vision on shattering.

R. D. Lister
Road Research Laboratory, Department of Scientific and Industrial Research