Performance of type X gypsum board on timber to non‐standard fire exposure

Summary Timber buildings are becoming increasingly sought after for their aesthetic and environmental appeal. Commonly, timber elements are encapsulated using multi‐layered fire rated gypsum board in order to prevent the timber from contributing additional fuel load to the fire or to be approved by authorities. In recent studies performed in the last 5 years where non‐standard fire exposures have been utilised, there have been concerns as to whether encapsulation successfully can improve the fire performance of the assembly due to board fall off or heat penetration between layers in the full duration of a non‐standard fire scenario (which includes cooling phases and burn out). There has been a dearth of attention in understanding the underlying mechanisms to these documented behaviours. To address this research gap, a two‐stage research program studying multi‐layered and fire‐rated gypsum clad stand‐alone columns was undertaken by the authors in both a field and controlled laboratory study. These experiments were conducted with the purpose of understanding timber column multi‐layered encapsulation performance in non‐standard fires that include a natural cooling phase. In the field study, a stand‐alone timber column within a large, open farm structure was encapsulated in three layers fire rated gypsum board. The fire was spot‐ignited and allowed to burn until the building and the column collapsed. That experiment provided evidence that the fire rated gypsum board was not sufficient to protect this timber column, as the temperature increases under the layers of gypsum board were equivalent to the temperature increases on the exterior of the column. The second stage of the research involved four, encapsulated timber columns with localised non‐standard fires (methanol pool fires exposing one face only) in controlled laboratory conditions. These tests used novel narrow‐band spectrum illumination to document the underlying breakdown of the gypsum board with non‐standard fire exposure and cooling phases. Results of these experiments imply that timber elements can be adequately protected from fire exposure providing that the screw spacing is strictly adhered to and redundant layers are utilised. The article concludes with a listing of priority research areas that will advance knowledge of the performance of gypsum boards on timber in fire.