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Types and operation of smoke detectors




When designing a fire detection system should provide for a set of equipment which is able to detect and report the presence inside of a building elements such as smoke, flames and high temperatures.

These electronic devices detect the presence of fire based on physical phenomena associated with the development of the fire itself and must therefore be placed according to very precise rules, better indicated in the Uni 9795, where you can find the standard indications related to positioning of the sensors and devices.

There are various types of detectors, which are classified into three main categories:



heat detectors and temperature, that is, those sensitive to rising temperature in the environment;

Flame detectors, which are sensitive to the radiation emitted by the flames of a fire;

smoke detectors, those sensitive to particles of the products of combustion and/or pyrolysis suspended in the atmosphere, which are gathering, forming layers of smoke in the environment.

The smoke detectors are classified by their principle of operation. These are typically point and their placement in a space varies depending on the model and the range of individual items.

In particular their position must be such that smoke sources present in the environment to be monitored do not give rise to false alarms.

In fact, the detector must not be installed where they may be directly invested by aerosol products from some processes or products placed by air conditioning units, air flow ventilation.

In addition, the number of detectors must be determined so that the values are not exceeded (max) of floor area guarded by each sensor depending on the plant surface (S) and inclination (α) of the premises guarded.

The legislation establishes rules for the installation and maintenance of fire detection systems; of course the choice of detector is crucial for the protection of people and environments, because even a few seconds of delay in raising the alarm can be fatal.

Smoke and gas detectors: how they work and how to choose them



Smoke and gas detector is a device that checks for harmful gas to humans within enclosed spaces such as kitchens or service environments inside a House.

The set consists of a container filled with a readily gas and two components: one that acts as an anode and one that acts as the cathode.

The sensor is activated when this device detects the presence of a poisonous gas that triggers the alarm mechanism emits sound and light signals.

Gas detectors for professional and domestic use semi-open, detecting the presence of sulphur dioxide, carbon dioxide and methane gas and often provide for the automatic closing of the gas supply valve.

Must be installed by a trained technician, operation should be checked regularly and must be replaced after a maximum of 4-5 years.

In addition, the detectors can be easily connected to a domotic system or intrusion. Important is to position the detector away from any ventilation devices fixed to the ceiling, as the air that comes out of any gas disperses, distorting or even preventing detection.

If the floor is oblique or are there any canals or ravines, the detector shall be placed on the lower or profound, because those are the places where the gas will tend to accumulate.

Ionization smoke detectors



Ionization chamber smoke detectors are used in those places where you are not:

air humidity higher than 95%
development of vapours and gases
significant air currents
high concentrations of dusts

In fact, these systems are very sensitive in detecting fires with very slow combustion of materials with smoke and flue gases typical of paper, wood, rubber, plastics etc, especially when stacked.

The detector consists of two plates and charges from a radioactive source; the particles between the two plates ionize the air.

The normal condition, so in the absence of smoke, requires the presence of positive and negative charges.
They will be attracted to two plates in such a way as to form a small ionization current.

In case of fire, the molecules of smoke entering the room, neutralize these ions causing a lowering of the current. This variation is revealed by an electronic circuit that sends the signal to activate the alarm.

A company specialized in the production of such devices even in the industry is the Edwards Signaling.

Photoelectric smoke detectors



Smoke detectors in retroreflective sensor base their operation on the principle of darkening of the infrared beam, the device, caused by the presence of fumes.

They are particularly suitable for the protection of buildings with wide open spaces, such as cinemas, the atres, supermarkets, shopping centers, warehouses and hallways but also apartments and villas on several levels.

The transmitter sends a beam of infrared light at a high-efficiency reflector, which refers to the receiver. The analysis of the received signal determines the alarm condition.

The alignment of the detector is made easier by using a pointing device.

Inside a house or an apartment the device shall be placed in each environment, so as to guarantee maximum control condition.

A popular model, which generally must be applied to the ceiling, is that Vesta proposed by companies SD3. Very similar in form to traditional devices to the ionization, but differences in technology.
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