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Low cost fire alarm circuit. Description. W hen there is a fire breakout in the room the temperature increases. This ultra compact and low cost fire alarm senses fire breakout based on this fact. Transistor BC177 (Q1) is used as the fire sensor here. When the temperature increases the leakage current of this transistor also increases. The circuit is designed so that when there is an increase in the leakage current of Q1, transistor Q2 will get biased. As a result when there is a fire breakout the transistor Q2 will be on. The emitter of Q2 (BC 108) is connected to the base of Q3(AC 128). So when Q2 is ON Q3 will be also ON. The transistor Q3 drives the relay which is used to drive the load ie,light,bell,horn etc as an indication of the fire. The diode D1 is used as a free wheeling diode to protect it from back EMF generated when relay is switched. Low cost fire alarm circuit. admin April - 19 - 2008 85 Comments Description. W hen there is a fire breakout in the room the tempe...

1.7 Different types of fire extinguishers Fire extinguishers are used to put out small fires. They are of different types with each made to deal with a specific class of fire. They are classified according to firefighting material in the equipment.  The following are the most commonly used: Water Extinguishers Usually used to put out fires on burning solid materials. Foam Extinguishers Used to put out fires on burning oils and chemicals. Carbon Dioxide Extinguishers Used to fight fires on burning gases or vapours. Dry Powder Extinguishers Used to deal with fires on burning, flammable liquids and some solids, such as wood and paper. Water and foam are conductors of electricity. Therefore, they should never be used to fight electrical fires unless the supply of electricity is disconnected; carbon dioxide and dry powder extinguishers are recommended Instead. Other Extinguishers Besides the above commercially made fires extinguishers, sand, soil and other covering materials may be used...