The Effect of Thermal Tempering Processes on the Sharpness and Injury Potential of Pint Glasses

Glass drinkware is widely used in the UK. However, glasses are sometimes used as impulsive weapons in incidents related to alcohol consumption, particularly with imperial pint glasses (~568 ml). In order to reduce the potential for injury with such glasses, glass manufacturers adapted thermal tempering processes to produce tempered (also referred to as toughened) pint glasses. Tempered glass is known for its dense fracture properties and is considered to be a safer alternative to non-tempered (annealed) glass. Tempered pint glasses are now widely used throughout the UK. However, there is no standard which regulates the quality of tempered drinking glasses. This lack of standardisation has been identified as a cause for varying effectiveness of using tempered drinking glasses to reduce injury potential. This thesis aimed to examine the injury potential of pint glasses and to provide a foundation for a future standard for tempered drinking glasses. The work included: examination of the fracture properties of annealed and tempered drinking glasses; replication and analysis of physical attacks with pint glasses; and assessments into the sharpness of various glass fragments as an indicator of injury potential. The base region of tempered pint glasses was found to fracture extensively, limiting certain methods of glass attacks. Fragments from the near-rim region were found to vary significantly in size between glasses due to lower wall thicknesses and residual stress. Replications of glassing attacks indicated high forces are involved with such attacks, although the damage severity is lessened with tempered glasses. Sharpness assessments revealed little significant change in fragment sharpness due to tempering. This suggests that changes in injury potential are more likely due to practical considerations such as reduced fragment size, rather than a change in inherent sharpness properties.