Glass fallout in windows has the potential to alter the ventilation condition and the behaviour of the fire in a compartment. Therefore, it is of an interest to fire modellers to be able to simulate the behaviour of glass windows in fires. Most research work has dealt with the fracture of glass windows in fires while some work studied the glass fallout behaviour in the general sense. This research investigated the fallout behaviour of 4 mm and 6 mm thick single glazed glass exposed to a radiant heat source. Only ordinary float type glass was studied in this research. The fallout behaviour of glass was quantified in a probabilistic manner based on the fallout results from the experiments. Standard rubber beadings and non-standard beadings made of kaowool fibres were used to glaze the glass samples in this research. A total of 117 experiments were carried out in this research. The radiant heat fluxes which the glass samples were exposed to ranged from 13 kW/m2 to 58 kW/m2 . In some experiments, the temperature at various points on the glass and thermal strains were measured. Radiant heat flux measurements were also taken during the experiments. The time to glass fracture and amount of fallout were recorded in every experiment. The four-point bending test was carried out on 24 glass specimens to determine the fracture strength and modulus of elasticity for the glass panes used in this research. The mean fracture strength and modulus of elasticity were 64 MPa ± 15 MPa and 76.5 ± 4.0 MPa respectively. The simple lumped heat capacity method was used to predict the time to glass fracture in each experiment. Generally, the times to glass fracture recorded in the experiments were within the predicted times to glass fracture in 60% of the experiments. The distribution of temperature differences at fracture was predicted using the fracture criterion suggested by Keski-Rahkonen (1988). The range of predicted temperature differences at glass fracture was compared with the temperature differences obtained from the experiments. The mean temperature difference at glass fracture ranged from 90 °C to 98 °C while the predicted temperature differences were between 55 °C to 129 °C. Generally, the actual temperature differences were within range of predicted temperature differences in 60% of the experiments. The measured thermal strains at glass fracture were between 239 Pstrain to 697 Pstrain. The type of glazing beading was concluded not to have affected the glass fallout behaviour. It was found that a window with a thinner glass pane is more likely to fallout compared with a window with II a thicker glass pane when exposed the same level of heat flux. The fallout behaviour of glass was quantified with an exponential distribution function and a glass fallout prediction model for 4 mm and 6 mm thick glass was produced from the experimental results.