Практическая работа 47.. Выписать новые слова в тетрадь, прочитать все текст, перевести письменно 1 текст.. Vocabulary. High expansion foam

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Практическая работа 47.

Выписать новые слова в тетрадь, прочитать все текст, перевести письменно 1 текст.

Vocabulary

High expansion foam – высокократная пена

Fire fighting – тушение пожаров

Mine roadway – горная выработка

Jet engine – инертный газ

Inert air – инертный газ

Move around - передвигаться

Foam concentrate – пеноконцентрат

Air bubbles – пузырьки воздуха

Ratio - пропорция

Expand - распространяться

Oxygen - кислород

Flaming combustion – пламенное горение

Convert - превращать

Quenching effect – эффект тушения

Deep-seated – глубоко скрытый

Topped-up - заполненный

High expansion foam

This a relatively new method of fire fighting which was first invented in the 1950's for dealing with fires in mine roadways. Following more research, based on using high-expansion foam from a jet engine, the Americans then developed a smaller version which was easier to move around and could be used more widely. They also used gas instead of inert air which was the component of the original version and although this may seem strange when we normally think that foam needs air to move it around.

High expansion foam actually consists of air and foam concentrate which stabilizes the air bubbles and water. With an air to water ratio of around 1000:1 the air expands about 30% while it’s being heated to the boiling point of water and the water then expands into steam at around 1700 times its original volume. This way the ratio becomes 1300 parts of air and 1700 parts of steam, which allows the oxygen content of the fire to be reduced from the normal 21% to about 9% and additional heat is removed to convert the water into steam.

Research by the Joint fire association has shown that flaming combustion in fires stops when the oxygen content of the fire in the air around them is reduced to between 12-16%. Although there can still be smouldering when there is as little as 7% oxygen in the air. Although high expansion foam will stop flaming combustion effectively, a cooling or quenching effect is needed to ensure that a deep-seated fire has been completely extinguished. Alternatively, the foam may need to be topped-up as it breaks down until the fire is completely extinguished and this can take a long time.

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