04/09/2022
Safe tech announces its services in the field of supplying and installing fire alarm systems for private and public entities with all efficiency and professionalism through specialized engineers with long experience in this field and in cooperation with many manufacturers of these devices.
A complete explanation of the fire alarm system
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1- Fire alarm system:
- Purpose of fire alarm and detection systems
• The main purpose of these systems is to quickly respond to the fire and then convert this early response into an audio and visual signal to alert an individual or group of individuals in the building, place, relief or fire center that there is a fire in its early stages.
2- Stages of fire:
Most fires go through four distinct stages:
PRELMINARY STAGE
• SMOKING STAGE
• FLAME STAGE
• HEAT STAGE
A- Primary stage:
This stage is devoid of watching smoke or flame even feeling heat, but what happens in this stage is the generation of a quantity of combustion particles as a result of the chemical analysis process. Time may not exceed a few minutes and ionization detectors respond to this stage.
B - the smoke phase:
As the fire continues to develop, the amount of combustion particles increases to the extent that it can be seen with the naked eye, which is called in this case (smoke), but until this stage no flame or heat is observed, and photoelectric detectors respond to this stage.
c- Flame stage:
With the development and growth of the fire more and more, it reaches the point of ignition and the appearance of the flame, and at this stage the smoke rises and the sensation of heat increases, and the infrared detectors respond to this stage.
C- Heat stage:
In this stage a large amount of heat, flames, smoke and toxic gases are formed. This stage is characterized by its very rapid development, which does not take more than a few seconds. In addition, the transition of the flame phase and its transformation into a heat phase usually takes place very quickly, and heat detectors respond to this stage.
3- Alarm systems:
Alarm systems:
Fire alarm systems detect and control fire and are divided into two systems:
A- Conventional System:
It is the system that relies on the fact that a group of detectors connected to each other on a specific area gives a warning on this area through which the security man moves in this area and discovers the location of the fire.
B- Addressable System:
It is the system that depends on the group of detectors connected to each other in the area taking the numbers and names of the places where the detector is located, so that when a fire appears on the control panel, the detector number, the name of the area and the time of the fire appear
1- Control panel for fire systems:
It controls the system, feeds it with the necessary efforts, and monitors its work, as the alarm reaches it from the detectors, and it operates the bells, sirens and indicator lights.
An audible and a light alarm is given when a fire occurs, with an indication of the area of its occurrence.
It operates on the electric current (220 volts 50 Hz) and is equipped with backup batteries that operate automatically in the event of a power outage, and it has a charging device that charges the batteries when the current returns.
Equipped with the ability to self-test and give an audible warning signal in the event of a failure in the panel or in any part of the system components, or in the event of a power outage or disconnection of the batteries.
Supplied with a switch to give a general warning to evacuate the site.
Equipped with a set of "rebels" to stop the air-conditioners and disconnect the power
1- Combustion products reagents:
• Combustion products detectors include a group of devices called Fire Detection. The operating system of these detectors is designed to work when they detect one of the four main products of combustion, which are:
Ionized Gas Detectors (Invisible Combustion Products)
Smoke Detectors (Visible Combustion Products) - Photocell.
heat detectors.
Optical detectors.
A - ionized gas detectors
• The phenomenon of fire is what happens from the ionization of particles when they undergo combustion, and these particles are out of balance in the electrons, which makes them tend to take electrons from other particles, and detectors of ionized gases use this phenomenon in operating this type of detectors.
• In the detector there is a sensor room with a small opening for the entry of air in the room or the place to be protected. Next to the chamber opening from the inside, there is a small amount of a radioactive substance that ionizes the air of the detector room. Inside the detector there are also two electrodes (two electrodes), one of which is positively charged and the other negative. The negative plate is located closer to the source of the radioactive substance, and the ionized particles work by the action of the substance. The radioactive element releases an electron that goes to the positive plate, which causes a current to flow between the two plates continuously.
• When a fire occurs and the ionized fire products enter the detector room, and since they are out of balance (i.e. they need electrons), they work to capture the electrons passing between the two plates (which work on the flow of current), which leads to stopping the flowing current and issuing an alarm
A - smoke detectors (visible combustion products)) photocell)
• Smoke detectors are manufactured using a photoelectric cell connected to a specific light source. This cell is a flat disk that converts light into an electric current. This cell is used in two ways to detect smoke:
• The first: using the beam.
• The second: depending on the resistance and scattering of the ray.
• The beam method is adopted by shining a light beam through the area to be protected until it reaches inside the photovoltaic cell. And since this cell works to convert this beam into an electric current permanently (as long as the beam is on it) and this current is used to keep the circuit switch open, and when smoke intercepts the path of the light beam, the electric current stops, which leads to closing the circuit and issuing an alarm
A- Heat detectors:
• The abundant heat produced by combustion, which is detected by specific devices using the three primary principles of thermophysics:
First, heat expands materials.
Second: heat works to melt materials.
Third: The electrothermal properties of hot metal can be detected.
Thus, there are three groups of devices that use these principles in detecting fire, which are:
constant temperature.
temperature rise rate.
A mixture of constant temperature/rate of temperature rise.
1- Constant temperature:
The first type: double-metal constant temperature, in which two metals or two alloys are used, and each metal or alloy has a different coefficient of expansion from the other when heated. More quickly, which leads to the arc of the chip towards the side of the metal with a lower coefficient of expansion, then the amount of arc and the difference in expansion between the two metals at a specific temperature is calculated.
After knowing the amount of metal arc and the difference in expansion, the double chip is placed inside the (detector) chamber in such a way that the electrical conductors are locked when a certain amount of arc is reached and an alarm is triggered
The second type: This type is based on the principle that most metals melt when exposed to heat. Moreover, the melting point of most metals is very specific, meaning that the melting point of the solid material does not change, and soft metal alloys (with a low melting point) are used for this purpose after they are Modify the components of the alloy until a specified melting point is achieved, after which the alarm will sound.
• The third type: This type depends on the expansion of solvents by heat, where the solvent expands and begins to ev***rate when exposed to heat, which leads to an increase in the v***r pressure. The solvent is placed inside a breakable glass bottle designed to shatter at a certain pressure and the v***r pressure of the solvent at which the glass is broken is calibrated At the same moment, it also records the temperature at which the pressure led to the smashing of the glass, so that the specific temperature for breaking the glass can be determined. This bottle is then placed inside the detector to separate the two conductors, and when the glass is broken, the conductors close the circuit and an alarm is sent.
It can rely to a large extent on constant temperature detectors, but the disadvantage is that their sensitivity is very low, and most of these types of detectors must be replaced after sensing a fire.
1-Rate Of Rise Detectors
The idea of running a constant temperature detector
Rise rate detectors depend on the expansion properties of heat and the main exception is the thermoelectric rise rate detector.
Most height rate detectors use a small air-filled chamber whose bottom is made of a thin, flexible metal membrane. They are known as thermal rise rate detectors. When the air expands inside the room, the membrane is forced outward, and when the membrane is pushed to a predetermined level, it forces a set of electrical conductors to open or lock The circuit and this change in current serves to send a signal to the alarm panel.
The first type is called “Spot Detectors.” These detectors look like a hemisphere and are distinguished by their copper color. It must be taken into account that if they are painted in any color other than the factory color, they must be replaced immediately, as the coating of any detector affects its ability to sense and detect heat. .
The second type uses a tube extending over the area to be protected, and the space inside the tube works as a room, and the tube is connected to a working vessel with a flexible membrane that works with the same idea as the previous membrane.
There are also many other types that work on the same foundations and rules mentioned above
Optical Detectors:
• Photodetectors are also called flame detectors, and there are two main types of photodetectors:
infrared detector
The first: reveals the light in the ultraviolet spectrum.
The second: reveals the light in the infrared spectrum.
Alarms provide several other services in addition to their original function, which can be summarized as follows:
• Turning off ventilation or heating and air conditioning systems to control smoke.
• Lock fire doors.
• Return elevators to the ground floor automatically.
• - Turn on the extinguishing system.
• Inform the fire station.
All this is available to us at safetech company.
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