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Alarm Systems
Buildings may also be equipped with detection systems that will transmit an alarm. Some detectors are designed to respond to smoke, and others to heat. In many jurisdictions, detection systems are required in public buildings, apartment houses, and sometimes even in private homes. Two major types of smoke detectors are available. One is an ionization device that contains a small radioactive source for ionizing the air molecules between a pair of electrodes, permitting a very small current to flow between the pair. If smoke particles from a fire enter this space, they reduce the flow of current by adhering to the ionized molecules. The drop in current sets off a buzzer or other alarm. The second type of smoke detector uses a photoelectric cell. In some of these detectors, smoke that enters obscures a steady beam of light; in others, the smoke scatters a light ray from a diode so that the cell can detect it. In either case the change sets off an alarm. The alarm may sound locally, or it may be designed to alert a central station with notification to the fire department. Photoelectric detectors are slower than ionization detectors, and sometimes both principles are combined. Both types can be run by batteries or by building current. TEXT 2
Portable Fire Extinguishers Portable fire extinguishers are an item of firefighting equipment containing a fire extinguishing medium. Portable fire extinguishers are perhaps the most commonly used fire extinguishing devices. They are economical and effective first aid fire-control system if they are used quickly and efficiently. They are generally small and light in weight and can be carried by hand. These extinguishers are known as hand extinguishers. Larger models of certain types, known as transportable fire extinguishers, may be mounted on a simple two-wheel chassis which is moved by hand to the fire. Their advantages are their simplicity in operation and design. Their disadvantages are that they must be operated manually and their effectiveness depends on the training of the person using them. Portable fire extinguishers may be classified according to the extinguishing agent they contain and according to their method of operation. Portable fire extinguishers can be divided into five categories according to the extinguishing agent they contain: 1. Water type extinguishers. 2. Foam type extinguishers. 3. Dry powder type extinguishers. 4. Halogenated hydrocarbon type extinguishers. 5. Carbon dioxide type extinguishers. They are also divided into categories according to their method of operation. Extinguishers are normally operated by the use of gas and air pressure in the upper part of the container which forces extinguishing medium out through a nozzle. In the older type of extinguishers, such as the soda-acid, the gas pressure is produced chemically by the reaction of an acid and alkali. In the chemical foam extinguishers the mixture of two compounds produces carbon dioxide gas and foam. Other types of extinguishers use a cartridge containing an inert gas (normally carbon dioxide) under pressure. In other types, however, the pressure riser agent (air or inert gas) is stored with the extinguishing medium in the body of the extinguishers, and so the body of the extinguisher is permanently pressurized. A fire extinguisher consists of several basic components. The first is a container with extinguishing agent. The size of the container determines the amount of extinguishing agent that can be stored and in this way determines the size of fire an extinguisher can handle. In the small, first-aid, water fire extinguishers, a propellant must be provided. Usually this is carbon dioxide, which is either generated when needed or stored in a cartridge. When a foaming agent is used in such an extinguisher, the foam is rendered still more effective by the inert gas that fills the bubbles.
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