It is known from practice that nearly all the metals, under certain conditions, are capable of burning in atmospheric air. Steel and aluminium in large structural thickness, on the basis of their behaviour in fire, are clearly evaluated as non-combustible. However, the dusts of aluminium, iron in fine distribution and metal cottons from thin metal fibres can easily be ignited and thus burn intensively. The alkali metals (lithium, sodium, potassium), the alkaline-earth metals (calcium, magnesium, zinc), zirconium, hafnium, titanium, etc. ignite extremely easily in the form of a powder, filings or thin bands. Some metals have such a high sensitivity that they are stored separately from air, in inert gas atmospheres or under a liquid that is neutral for the metals.
The combustible metals and those that are conditioned to burn produce extremely violent burning reactions that are high-speed oxidation processes releasing considerably higher quantities of heat than observed from the burning of combustible and flammable liquids. The burning of metal dust in the case of settled powder, following the preliminary phase of glowing-ignition, might grow to rapid burning. With stirred-up dusts and clouds of dusts that might result, severe explosions can occur. The burning activity and affinity for oxygen of some metals (such as magnesium) are so high that after being ignited they will continue to burn in certain media (e.g., nitrogen, carbon dioxide, steam atmosphere) that are used for extinguishing fires derived from combustible solid materials and liquids. Extinguishing metal fires presents a special task for fire-fighters. The choice of the proper extinguishing agent and the process in which it is applied are of great importance.
Fires of metals may be controlled with very early detection, the rapid and appropriate action of fire-fighters using the most effective method and, if possible, removal of metals and any other combustible materials from the zone of burning or at least a reduction of their quantities.
Special attention should be given to the protection against radiation when radioactive metals (plutonium, uranium) burn. Preventive measures have to be taken to avoid the penetration of toxic decomposition products into living organisms. For example, alkali metals, because of their ability to react violently with water may be extinguished with dry fire-extinguishing powders only. Burning of magnesium cannot be extinguished with water, carbon dioxide, halons or nitrogen with good success, and more important, if these agents are used in fire-fighting, the hazardous situation will become even more severe. The only agents that can be applied successfully are the noble gases or in some cases boron trifluoride.