A Study of Calcination of Gypsum Wallboard

Christopher L. Mealy
Daniel T. Gottuk
Hughes Associates, Inc.

Presented at International Symposium on Fire Investigation, 2012


The prevalence of gypsum wallboard in fire scenes makes it a potentially valuable source of information to fire investigators when assessing a fire scene. The exposure of gypsum wallboard to heat from a fire can result in calcination, which in turn can theoretically be correlated to the total heat exposure to that area. Therefore, if properly characterized, a calcination depth profile of a given enclosure could provide fire investigators with a detailed history of the total heat exposure to the walls and ceiling of the space. This history, when combined with other findings, could provide valuable insight as to where the area of origin was located or how the fire developed. The approach taken in this work incorporated small- and full-scale testing to accomplish several goals: 1) develop an objective method for measuring the calcination depth of gypsum wallboard, 2) assess the utility of the calcination depth surveys in full-scale fires, and 3) characterize the impact of suppression water on calcination depth measurements. In this work a probing pressure of 0.86 kg/mm2  (1175 psi) was identified as providing accurate calcination depth measurements. The benefit of calcination depth surveys in full-scale enclosure fire scenarios was realized primarily for cases where visual patterns were not obvious. The application of water to calcined GWB was found to alter the measured depth of calcination by an average 18 percent, when collected 24 hours after heating/water application and less than five percent after 30 days. This data suggests that if measurements are to be collected in areas that have been wetted by suppression activities for any extended period of time, it would be advisable to delay measurements until the water has been removed.

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