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When water comes into contact with hot bitumen, a powerful reaction occurs. This is because when water is heated to the temperature of the bitumen, it vaporises and expands.
The risk of these kinds of accidents, known as boil-over, is particularly high if hot bitumen is loaded into a tanker that previously transported emulsion or another product with a high water content. Other risk factors are if the tank has not been used for a long time, as condensation can easily form, or if it has been left standing open. In just a few seconds, 10 litres of water can expand to form 20,000 litres of steam. When the pressurised steam passes through the liquid bitumen, a hot foam is formed that is forced out through the manhole or, if the tank is closed, causes an explosion.
In other words, it is extremely important that the driver always makes sure that the tank is free of water or aqueous products before loading.
To raise the safety awareness regarding boil-over, Eurobitume has produced a practical manual in four steps. You can find it here: