Four real-scale experiments were conducted by the National Institute of Standards and Technology to measure the temperatures above and below a wood floor assembly exposed to fire conditions from below. The objectives of the experiments were: 1) to examine the heat transfer through a wood floor assembly and 2) to examine the ability of a thermal imager to determine the potential severity of the fire beneath the floor assembly and the ability to provide a sense of the structural integrity of the floor assembly in order to provide improved situational awareness. Each experiment was conducted in a wood framed two story structure. Each story consisted of a single compartment with interior dimensions of approximately 4.7 m x 4.8 m x 2.4 m high. The initial fuel in each experiment consisted of six wood pallets and hay in the center of the lower level compartment. Three different floor assemblies were used. Gas temperatures of the upper and lower compartments as well as the surface temperatures of the floor assembly were measured with thermocouples (TCs). Three commercially available thermal imagers (TIs), each with a different type of sensor were used to view and record the thermal conditions of the top of the floor assembly from the open doorway in the upper compartment. Times to collapse of each floor were also noted. Given the insulating effects of the OSB and the floor coverings, the temperature increase or thermal signatures viewed by the TIs were small given the fact that the ceiling temperatures below the OSB were in excess of 600 ºC. These experiments demonstrated that TIs alone cannot be relied upon to determine the structural integrity of a wood floor system. Therefore, it is critical for the fire service to review their practice of size-up and other fire ground tactics needed to enable the location of the fire prior to conducting fire operations inside a building. The United States Fire Administration (USFA) provided support for this project.
Technical Note (NIST TN) - 1709
engineered wood, fire fighters, oriented strand board, real-scale fire experiment, structural, thermal imager, wood