Examination of the Thermal Conditions of a Wood Floor Assembly above a Compartment Fire

Examination of the Thermal Conditions of a Wood Floor Assembly above a Compartment Fire  

Four real-scale experiments were conducted by NIST 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 15.5 ft x 15.5 ft x 8 ft 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. 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. 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 1100 ºF. 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.

 

Test 1 - Examination of the Thermal Conditions of a Wood Floor Assembly above a Compartment Fire

The floor system installed for this experiment was laminate flooring over OSB with composite wood I-joists spaced 24 inches apart. Video views from top left: Side A, BST thermal imager showing upper level floor, aSi thermal imager showing upper level floor, Clock, video showing upper level floor, VOx thermal imager showing upper level floor, CD corner, thermal imager view of lower level interior, video view of lower level interior.

Ignition starts at 0 seconds. The first gypsum board is removed at 10 minutes, 10 seconds. The second gypsum board is removed from the doorway at 15 minutes, 35 seconds. Flashover occurs in the lower level at 17 minutes, 45 seconds. Flames come out of the lower level door at 18 minutes, 5 seconds. Thermal imagers are removed at 23 minutes, 25 seconds. The floor collapses at 24 minutes and 30 seconds. Extinguishment begins at 24 minutes, 50 seconds.

Test 2 - Examination of the Thermal Conditions of a Wood Floor Assembly above a Compartment Fire

The floor cover examined was a carpet surfaced floor with composite wood I-joists spaced 406 mm (16 in) apart.
Ignition starts at 0 seconds. The first gypsum board is removed at 600 seconds. The second gypsum board is removed at 1025 seconds. Localized flashover occurs at 1040 seconds. Thermal imagers are removed at 1090 seconds. Complete flashover occurs at 1110 seconds. The floor collapses at 1675 seconds. Extinguishment begins at 1695 seconds.

Test 3 - Examination of the Thermal Conditions of a Wood Floor Assembly above a Compartment Fire

The floor examined was a carpet surfaced floor with solid wood joists spaced 406 mm (16 in) apart.
Ignition starts at 0 seconds. The first gypsum board is removed at 600 seconds. The second gypsum board is removed at 930 seconds. Localized flashover occurs at 930 seconds. Complete flashover occurs at 965 seconds. Thermal imagers are removed at 1200 seconds. The floor collapses at 1485 seconds. Extinguishment begins at 1505 seconds.

Test 4 - Examination of the Thermal Conditions of a Wood Floor Assembly above a Compartment Fire

The floor cover examined was a carpet surfaced floor with composite wood I-joists spaced 406 mm (16 in) apart.
Ignition starts at 0 seconds. The first gypsum board is removed at 600 seconds. The second gypsum board is removed at 1025 seconds. Localized flashover occurs at 1040 seconds. Thermal imagers are removed at 1090 seconds. Complete flashover occurs at 1110 seconds. The floor collapses at 1675 seconds. Extinguishment begins at 1695 seconds.