Glass Expert Analyzes Drinking Glass Failure

The glass experts at Read Consulting were asked to perform a glass failure analysis on a drinking glass that had failed in a restaurant and had injured a customer. The customer had just filled the glass with cold water and was lifting it when it fell apart causing an injury. failure analysis determined that the failure initiated on the interior surface of the thick bottom of the glass. the fracture surfaces had very few markings. Thus, the forces involved were very low. It appears as if  the glass was still hot after removal from the dishwasher and the cold water created tensile stresses when it hit the bottom of the hot glass. The combination of the  stresses from thermal shock and a preexisting flaw on the glass bottom caused the glass failure. Although the manufacturer warns restaurants to allow these glasses to cool after cleaning and before using, the dynamics in a busy restaurant makes this difficult to do. It is also important to note that the glass on the bottom is over 1/2" thick, and it will cool very slowly.Often waiters will place silverware in glasses when either clearing or serving, and   contact of silverware with the glass bottom can cause damage that can later initiate a failure