Introduction:
The fireman needs to be familiar with the equipment, fittings installed, to protect the buildings by means other than the use of water and also with the media used in these installations.
The installations described include those which use foam, carbon-dioxide, vaporizing liquids and dry powder.
2.Foam Installations (LX) :
(A) Pump operated mechanical foam installation:
This type comprises a foam concentrate tank outside the area to be protected, the capacity being dependent on the area involved. The tank has a water supply and an inductor fitted on it.
The water control valve is opened until required amount of water is flowing into the tank. The "venture effect" created in the inductor draws the resultant mixture of foam concentrate and water from the tank through the non-return valve. The foam solution is then delivered to foam generators within the protected area, where foam in formed and conveyed to the spreaders or pourers.
(B) Self Contained pressurized type:
This system comprises a water storage tank and a foam concentrate storage tank, the capacity of each dependent on the area to be protected. One or more carbon dioxide cylinders are fitted to expel the water from the storage tank. An inductor unit is fitted adjacent to the tanks and two pipes are laid from the unit to the foam concentrate tanks; the high pressure side leads to the top of the tank and the low pressure side to the internal siphon tube. When carbon dioxide is released from the cylinders, it expels the water from the storage tank through the inductor, the right amount of concentrate being drawn from the concentrate tank into the water stream. The foam solution is then delivered to the generators in the protected area where foam is formed and conveyed to the spreaders and pourers.
(C) Pre-mixed Foam Installation:
A pre-mixed foam installation comprised of a cylindrical storage tank, designed for a maximum working pressure of about 10 bars, which is filled with a foam solution (i.e, foam concentrate and water). The capacity of the tank is determined by the quantity and depth of foam coverage required. The tank is fitted with an inlet connection from carbon dioxide gas cylinders of appropriate, having a disc-closure valve and a lever operated piercing head. The rate of discharge of carbon dioxide gas in the event of fire is controlled so that a continuous pressure will be maintained within the storage tank, giving constant rate of flow foam.
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(D) High Expansion Foam Installation (HX) :
High expansion foam, as used in fixed installations, is a mass of uniform bubbles, each about 10mm in diameter, having an expansion ratio of approximately 1000 volumes of foam for each volume of solution. One of its principal attributes, therefore, is the ability to produce a large amount of foam from a small amount of water, with a consequent reduction in water damage.
In addition to the actual production of foam, high expansion foam installations incorporate devices which automatically close fire resisting doors and open roof vents. The installations are electrically operated by relay from an automatic fire detector operating on the rate-of-rise of temperature principle.
If any one detector locates a fire, the installation actuates and the following sequence of events is set in motion:
i)Alarms sound in the affected area.
ii)A valve opens allowing water to pass to the generator.
iii) The fan motor(if fitted) is started.
iv) Water gathers in an accumulator, producing pneumatic pressure which opens protecting doors on the generator, open doors covering duct openings in the affected area and sets in motion mechanism for closing fire resisting doors.
Reference:
Reference should be made to the Indian Standard Specification (I.S. 12835 (Part-I): 1989 reaffirmed June 2000) code of practice for design and installation of fixed fire extinguishing systems part-1.
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