Characteristics of Some Specific Metals

Aluminium is a light metal with good electrical conductivity. In its usual forms it does not present a problem in most fires. However, its melting point of 660° С (1220° F) is low enough to cause the collapse of unprotected aluminium structrucal members. Aluminium dust is a severe explosion hazard. Aluminium does not ignite spontaneously.

Iron and steel. Iron and steel are not considered combustible. In the larger forms, such as structural steel, they do not burn in ordinary fires. However, steel dust may be ignited, and iron dust is a fire and explosion hazard when exposed to heat or flame. Iron melts at 1535° C, and ordinary structural steel at 1430° С.

Magnesium. Magnesium is a brilliant white soft metal. It is used as a base metal in light alloys for strength. Its melting point is 648,8° C. Dust or flakes of magnesium are easily ignited, but in solid form it must be heated above its melting point before it will burn. It burns fiercely with a brilliant white light. When heated, it reacts violently with water and all moisture.

Titanium. Titanium is a strong white metal, lighter than steel, that melts at 2000° С. It is mixed with steel in alloys to give high working temperatures. It is easily ignited in smaller forms (titanium dust is very explosive), though larger pieces offer little fire hazard. Titanium is not considered to be toxic.

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Metals

Nearly all the metals will burn in air under certain conditions. Some oxidize rapidly in the presence of air or moisture, generating sufficient heat to reach their ignition temperatures. Others oxidize so slowly that heat generated during oxidation is dissipated before they become hot enough to ignite.

Certain metals, titanium, sodium, potassium, calcium, zinc, lithium, hafnium uranium zirconium, thorium, and plutonium, are referred to as combustible metals because of the ease of ignition of thin sections, fine particles or molten metal. However, the same metals in massive solid form are comparatively difficult to ignite.

Some metals, such as aluminium, iron and steel, that are not normally thought of as combustible may ignite and burn when in finely divided form. Particle size, shape, quantity, and alloy are important factors to be considered when evaluating metal combustibility. Dust clouds of most metals in air are explosive. Alloys, consisting of different metals or metallic compounds combined in varying proportions, may differ widely in combustibility from their constituent elements. Metals tend to be most reactive when in finely divided form.

Hot or burning metals may react violently upon contact with other materials. A few metals, such as uranium, thorium and plutonium emit ionizing radiation that can complicate firefighting and introduce a contamination problem. The toxicity of certain metals is also an important factor in fire protection.

Temperatures in burning metals are generally much higher than temperatures in burning flammable liquids. Some hot metals can continue burning in nitrogen, carbon dioxide, or steam atmospheres in which ordinary combustibles or flammable liq­uids are incapable of burning.

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