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Slop-over and boil-over

Hazard Knowledge

A ‘slop-over’ is where thermal expansion or surface boiling of product causes burning fuel to flow over the side of its container.

A ‘boil-over’ (also known as a steam explosion) can occur in prolonged tank fires containing petroleum mixtures with a wide range of boiling points, such as petroleum crude oil and certain fuel oils.

As the lighter, more volatile fractions of the mixture burn off, the heated heavier residues start to displace, moving a heat wave downwards through the tank.

Petroleum crude oil, heated to several hundred degrees centigrade, will eventually reach a water layer at the base of the tank that will suddenly boil and turn to steam. This sudden eruption ejects the whole of the tank contents and produces a dangerous shower of burning liquid, radiated over the immediate area.

these hazards are well known within the petrochemical industry, such hazards may be encountered in a variety of situations involving flammable liquids that are on fire within containers.