Spontaneous failure of a passable laminated glass floor element

It is well-known that thermally toughened safety glass is subjected to a certain risk of spontaneous failure due to nickel sulphide particles included in the material. However, the present contribution focuses on a very uncommon case in which two out of three glass layers of a thermally toughened laminated slab of a passable floor element failed spontaneously.After initial on-site observations, witness interviews and reconstruction of the exact circumstances of the failure, no direct external cause such as hard or soft body impact, and local heating could be found. Consequently, the laminated glass slab was further investigated in the laboratory. During the laboratory analysis, several techniques have been used, such as crack pattern analysis, optical microscopy, and FEG scanning electron microscopy.As a result of the failure analysis, a nickel sulphide particle could be clearly detected. Based on striking similarities, a.o. in the crack pattern, breakage of the underlying glass layer of the laminate could be attributed to nickel sulphide as well.A method to assess the probability of failure of a double NiS failure is proposed. In spite of the design philosophy followed by the designer, in which the probability of this failure mode was not considered to be significant, this failure and risk analysis demonstrated clearly its importance for building practice.

► We analysed a glass laminate of which two of three glass panes broke spontaneously.
► A crack pattern analysis indicated twice a fracture due to an inclusion in the glass.
► A NiS inclusion was undeniably located at one of the crack origins.
► A calculation method for the probability of a double NiS failure is proposed.
► The structural analysis demonstrated that a HST is required to comply with EN1990.