Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition.
Fire is hot because the conversion of the weak double bond in molecular oxygen, O2, to the stronger bonds in the combustion products carbon dioxide and water releases energy (418 kJ per 32 g of O2); the bond energies of the fuel play only a minor role here. At a certain point in the combustion reaction, called the ignition point, flames are produced. The flame is the visible portion of the fire. Flames consist primarily of carbon dioxide, water vapor, oxygen and nitrogen. If hot enough, the gases may become ionized to produce plasma. Depending on the substances alight, and any impurities outside, the color of the flame and the fire's intensity will be different.
An outdoor wood fire
The ignition and extinguishing of a pile of wood shavings
The fire maps show the locations of actively burning fires around the world on a monthly basis, based on observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite. The colors are based on a count of the number (not size) of fires observed within a 1,000-square-kilometer area. White pixels show the high end of the count—as many as 100 fires in a 1,000-square-kilometer area per day. Yellow pixels show as many as 10 fires, orange shows as many as 5 fires, and red areas as few as 1 fire per day.
A structure fire is a fire involving the structural components of various types of residential, commercial or industrial buildings, such as barn fires. Residential buildings range from single-family detached homes and townhouses to apartments and tower blocks, or various commercial buildings ranging from offices to shopping malls. This is in contrast to "room and contents" fires, chimney fires, vehicle fires, wildfires or other outdoor fires.
Structure fires typically have a similar response from the fire department that include engines, ladder trucks, rescue squads, chief officers, and an EMS unit, each of which will have specific initial assignments. The actual response and assignments will vary between fire departments.
It is not unusual for some fire departments to have a pre-determined mobilization plan for when a fire incident is reported in certain structures in their area. This plan may include mobilizing the nearest aerial firefighting vehicle to a tower block, or a foam-carrying vehicle to structures known to contain certain hazardous chemicals.
A burned house