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Foam is a highly efficient agent consisting of water, foam concentrate and air. A constant percentage of foam concentrate is steadily added to the water stream by inductors. The water foam mixture produced in this way is converted into foam in foam generators. The degree of foaming depends on the capacity of the foam generator, the foam concentrate and on the rate of induction. A wet, heavy fire fighting foam is obtained by adding very low percentage of air to the water/foam mixture. A higher percentage of air makes the foam drier and lighter.

In general foams are classified as follows:-

Type Expansion Ratio
Low expansion foam 1:4 to 1:20
Medium expansion foam 1:21 to 1:200
High expansion foam 1:201 to 1:1000

The decision as to which of the three types of foam should be used for fire fighting depends on several criteria. The fact that the fire is quickly covered with a sufficiently high, dense layer of foam is of decisive importance for successful extinguishing.

Low Expansion Foam

Generally used at an expansion ratio of 1:5 to 1:7, ensuring very rapid spreading of the foam. The foam floats on liquids and adheres to inclined and vertical surfaces. Low expansion foam is mainly used against burning liquids e.g. gasoline, benzene, carbon disulphides, oils and lacquers, solvents etc. Due to its high specific weight, large throwing ranges can be achieved, as may be required on tankships, tank farms and as a result of aircraft crashes.

Medium Expansion Foam

Generally used with a form expansion ratio of 1:40 to 1:150 and is especially suitable for fighting fires close to the ground for example in storerooms for inflammable liquids, in lock systems (in the event of tanker leakage’s ), and in lacquer and paint factories etc. When applied in these cases medium expansion foam is extremely fluid, insensitive to heat, and stable enough to withstand effects of light wind. When medium expansion foam is applied in the lower expansion ratio ranges, throwing ranges of up to 12 metres can be attained which is often of great importance for effective extinguishing.

High Expansion Foam

High expansion foam is extremely ‘dry’ and therefore very light. Depending on the type of foam generator, foam expansion ratios of up to 1:1000 can be achieved. Some kinds of foam generators produce more than one thousand cubic metres per minute, so that even large rooms can be foamed to the roof within minutes. The main field of application of high expansion foam is also the flooding of rooms affected or endangered by fire. Above all, production halls and storage rooms can be effectively protected in this way.

Inside air high expansion foam system

In combination with a high expansion foam generator a special foam concentrate for the protection of storage spaces is used. This is a synthetic foam forming agent, to which stabilisers have been added, whose most important property is that in the case of acidic smoke and combustion gases being drawn in to the generator, an extremely stable extinguishing foam is produced. The agent has been hygienically approved, is biodegradable and can be used with fresh, salt, brackish and industrial water.

Nitrogen Foam System

Nitrogen foam systems are generally used for applications where conventional foam systems may prove inadequate. As a consequence, no specific design standards exist. In practice the design criteria applicable to medium and high expansion foam systems are used, modified were necessary to take account of the nature of the hazard and the characteristics of nitrogen foam systems. The system offers a means of flooding a hazard volume with nitrogen filled foam bubbles to provide protection against fire or build up of flammable gases.

Premix Foam System

When a guaranteed pressurized water supply is not available, Universal Fire have developed a “Premix Foam System” as shown below. In this system the water and foam concentrate are mixed at the correct proportions and contained within a pressure vessel – premix foam tank. Propulsion for the foam solution is provided by an inert gas (argon or nitrogen) cylinder through a pressure regulator. This system is completely “stand alone” in that it requires no other power, other than a 24 VDC 1 amp to initiate discharge or manual operation. As environmentally friendly inert gasses are used, this system is suited for enclosed risks.