Molten metal splash commonly occurs during a spillage or in the case of molten aluminium, when uncontrolled moisture or wet materials are introduced causing metal to violently explode throwing dangerous molten metal into the air.
The melting point of a substance is the temperature at which it changes state from solid to liquid at atmospheric pressure: at the melting point, the solid and liquid phases exist in equilibrium. A substance's melting point depends on pressure and is usually specified at standard pressure in reference materials. The melting point is also referred to as liquefaction point, solidus or liquidus.
Many companies such as aluminium and steel manufacturers, foundries and other industrial metal-working operations face the challenge of protecting their employees from the hazards associated with molten metal splash. This responsibility carries serious legal consequences when companies fail to provide and use personal protective equipment in proper repair and flame resistant clothing designed specifically for the type of molten metal hazard that is present.
Foundry workers, fabricators and welders are the most commonly injured in a molten metal splash hazard. However, any worker or employee who passes near a point at which metal is heated to a molten state may suffer an injury from a molten metal splash.
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Secondary protective clothing in the hot metal industry is defined as ‘protective clothing for continuous wear during work activities in designated workplace locations in which intermittent exposure to molten substance splash, radiant heat and flame source are possible’.
The essence of secondary protective clothing in this industry rests in two critical factors:
The textile must be flame resistant so that it will not ignite and continue to burn when the heat source is removed.
In the specific instance of exposure to molten metal the textile must demonstrate the ability to shed molten metal from its surface without sticking.
Molten aluminium is typically handled at 700°C to 788°C (1300°F to 1450°F) to avoid premature solidification. Contact with molten aluminium can cause severe burns and create a serious fire hazard. Mixing water or other contaminants with molten aluminium can cause explosions, which are more frequent in the aluminium scrap remelting process due to moisture and contamination being prevalent in scrap. These explosions range widely in violence and can result in injury or death as well as destruction of equipment and plant facilities.
Prior to the collapse of the Twin Towers at the World Trade Centre, powerful explosions were heard within the buildings. The explosions were later attributed to large amounts of molten aluminium being mixed with water and other contaminants. Expert opinion believes that when the airplanes entered the towers and lodged presumably near the centre of the buildings, the airplane hulls became trapped inside an insulating layer of building debris. The opinion further believes that the hulls, rather than the buildings, absorbed most of the heat from the burning jet fuel. The intense heat melted the aluminium in the hulls, which then flowed downward through the building gaps and stairways. It is believed the molten aluminium reacted with water from the sprinkler systems on the floors below and other contaminants, such as plasterboard and rust, resulting in violent explosions. The force generated by these explosions is the likely reason why the towers collapsed and why so quickly. To date this opinion remains unproven due to the non-release of any remaining World Trade Centre debris for further testing.
The aluminium industry has reported more than 250 aluminium/water explosions since 1980. Alcoa Aluminium carried out an experiment under controlled conditions, in which 20 kilograms of aluminium smelt was allowed to react with 20 kilograms of water, to which some rust was added. The explosion destroyed the entire laboratory and left a crater 30 metres in diameter.
This video (1:23) demonstrates how a thermal explosion can occur when water contacts molten aluminium.