The area of post-flashover fire investigation using the degradation or calcination of gypsum plasterboard has attracted interest in many countries. Many fire investigators often see the results of the calcination of gypsum plasterboard that can be particularly useful tool as an indicator of fire origin and fire severity. This thesis examines the depth of calcination of gypsum plasterboard under simulated fire exposure conditions and develops a practical method of assessing the calcination. Past methods were found only concerned about the relative calcination depths hence the actual calcination measurements are of little importance and measurements taken often depend on the testing personnel. For this purpose, constant force probe was developed to give a better representation of the actual calcination depth and consistent measurement due to its constant penetrating force into the fire damaged plasterboard. The relative changes; increasing or decreasing in calcination depth measurements at different local positions after the room burnout can be used to predict the likely fire origin and fire development scenarios. Bench scale cone calorimeter tests were carried out to expose gypsum plasterboards to different heat fluxes for varying exposure time, establishing the depth of calcination.

A method of predicting the time when the fire has been put out and the calcination depth for complete burnout of a compartment has been established. This is based on a correlation between the calcination depth and fire severity obtained from the experimental data and the radiant exposure area correlation concept. Further validation is required to ensure the method is reliable by conducting full scale compartment tests. The full scale compartment tests would also provide the use of calcination depth of gypsum plasterboard in real fires as an indicator of fire severity.