The fire condition known as backdraft, also known as smoke explosion, begins to form well into the free burning stage of a fire. It results from a free burning fire consuming nearly all the available oxygen within a confined area. This smoldering, oxygen starved fire will be reduced to glowing embers resembling the coals found in backyard grills, and continues to fill the confined area with flammable, superheated gases. If a sudden supply of fresh air is introduced into the confined area, either by improper or uncoordinated ventilation, there will be a violent ignition of the gases, and may contain the force of a substantial bomb. Smoke that exits the building in puffs or intervals.
Black smoke changes color to a grayish-yellow color, similar to the color of hay.
Confined area of excessively high heat, with little of no visible flames. Black, oily, tar like substance staining the windows. The method preventing the occurrence of a backdraft is careful execution of ventilation tactics. Vertical ventilation should be performed directly, or as near as possible, over the seat of the fire. The products of combustion exiting up through the opening will remove the high heat and flammable gases from the house, without providing a significant amount of oxygen rich air to the fire.