Detector types and design principles

We will explain the detection types and design principles in this chapter. Before the detector types, if we investigate necessary issues to fire effects and detector selection;

Fire Effects

Result of combustion, smoke, heat and flame are occurred. Detectors are produced to detect one or more than one of them.

Fire effects formation priority can be changed according to combustible material types. For example; if wood or cotton are fired, firstly smoke would be occurred then heat increases and last inflammation is occurred. Because of this, flammable material types and effects should be determined. Also, ceiling height, airing system effects, environment conditions and fault alarm possibility are important things to make decision detector type.

Optical smoke detector

Optical smoke detector features and performance criterion are specified in EN 54-7 Standard. Primarily selected optical smoke detector should have this standard. Optical smoke detector selection is done according to conditions in CEN/ 54-14 Standard 6.4 and 6.4.2 chapter. Detectors are mounted apart from area that doesn't need to protection. Area that doesn't need to protection is specified in CEN/ 54-14 Standard A.5.3.8 chapter. Optical smoke detector mounting place is determined according to conditions in CEN/ 54-14 Standard 6.5, 6.5.2 and A.6.4 chapter. In order to prevent fault alarm, selection and location are done according to CEN/ 54-14 Standard Annex B.2. Optical smoke detector utilizes the light scatter sensing principle. It has an infrared light source, which emits signals and a photo-diode, which senses the scattering light with the effect of smoke entering the chamber.

Optical smoke detector is used for the normally without dust and dirty rooms, hall, saloons etc. which have wooden and textile derivative materials. Optical smoke detector is mostly preferred at the present times.

Fire detectors protection radius is shown in Table A. Ceiling shouldn't be exceed 11 m. In order to smoke detector detects properly, ceiling height shouldn't be exceed 11 m as shown in table A. But, mounting, installation, maintenance and test difficulties are occurred higher than 6-7 m.

 

Distance of between two detectors should be 7, 5 m. between detector and wall should be 5, 3 m.

Ionization smoke detector

Ionization smoke detector features and performance criterion are specified in EN 54-7 Standard. Primarily selected optical smoke detector should have this standard. Ionization smoke detector has same detector selection and place criterion principle with optical smoke detector.

Ionization smoke detector consists the cell which allows to smoke entry. In this cell, there is continuously radioactive radiation. Smoke that is entered to cell cause to reference current and voltage values and smoke detector realized that changing.

Ionization smoke detector can detect deodorant, cooking smells. It can be cause to fault detection. Also, when a smoke detector being contaminated, detector cannot be cleaned completely and in this process calibration is changed. Because of this, ionization smoke detectors are not preferred.

Beam type smoke detector

Beam type smoke detector features and performance criterion are specified in EN 54-7 Standard. Primarily selected optical smoke detector should have this standard. Beam type smoke detector selection is done according to CEN/ 54-14 Standard 6.4 and 6.4.2 section. Beam type smoke detector mounting place is determined according to CEN/ 54-14 Standard 6.5, 6.5.2 and A.6.4 sections. In order to prevent fault alarm selection and mounting place are determined according to CEN/ 54-14 Standard Annex. B.2 section.

• Beam type smoke detector consists of 2 parts as a receiver and transmitter. Transmitter send continuously a signal to receiver. Beam detectors works on the principle of blocking light. The place of installation of receiver and the transmitter should see each other.

It gives fault signal or fire alarm depends on the user choice if there is material (Usually freight and goods in storage) between receiver and transmitter.

Designed with surface mounting technologies for smoke detection in warehouse, malls, museum, place with high ceiling, factories, hangars etc.

Should be mounted as facing each other max. 100 m distance. Receiver and transmitter horizontally protect 7.5 m in both sides.

 

Heat detectors

Ionization smoke detector features and performance criterion are specified in EN 54-5 Standard. Primarily selected optical smoke detector should have this standard. Heat detector selection is done according to CEN/ 54-14 Standard 6.4 and 6.4.2 section. Heat detectors mounting place is determined according to CEN/ 54-14 Standard 6.5, 6.5.2 and A.6.4 sections. In order to prevent fault alarms, selection and mounting base is determined according to CEN/ 54-14 Standard Annex B.3 section.

According to standard 60°C environment temperature is threshold. Also, if environment temperature increasing exceeds 30°C, this is detected as fire alarm. As shown as follows, If fixed heat is exceed the 60°C and temperature increasing exceed 30°C both of this cases, combined heat detectors are used generally

 

Heat detector is suitable for areas that have dust, vapor, smoke particles (kitchen, car park, laundry, ironing room, dusty factories etc.) and where has sudden temperature increasing possibility.

Heat detector covers a 5m radius circle area. To avoid "blind points" among coverage areas, detectors' coverage areas should be overlapping as shown in the figure below. Thus, every detector covers a square of 7.1m x 7.1m, equaling to 50 m2. Distance between detector and wall should be in 3, 55 m, between two detectors should be in 7, 1 m.

 

Smoke and heat detector (multisensor detector)

Multi sensor detector features and performance criterion are specified in EN 54-5 and EN 54-7 standard. Primarily selected multi sensor detector should have this standard. Multi sensor detector selection is done according to CEN/ 54-14 standard 6.4 and 6.4.2 sections. Multi sensor mounting place is determined according to CEN/ 54-14 Standard 6.5, 6.5.2 and A.6.4 section. In order to prevent fault alarms, selection and mounting is done according to CEN/ 54-14 Standard Annex B.2, B3 and B5 article.

Multi sensor detectors are suitable for place where the fire effects can be different as heat or smoke. For example; wood, sheet, industrial companies.

Flame detector

Multi sensor detector features and performance criterion are specified in EN 54-10 standard. Primarily selected multi sensor detector should have this standard. Flame detector selection is done according to CEN/ 54-14 Standard 6.4 and 6.4.2 sections. Mounting place selected is done according to CEN/ 54-14 Standard 6.5, 6.5.2 and A.6.4 sections. In order to prevent fault alarms, selection and location are done according to CEN/ 54-14 Standard Annex B.4 article.

Smoke detectors can't detect effect of the clean-burning liquid. If the fire is expected from this materials and there are no other type materials definitely flame detector should be used. But detection should be supported with heat detectors because flame detector detects with viewing principle. 0, 1 m2 Liquid-fuel and flammable gas fire are detected in 10 sec. at distances in below table. Because of this, location is done according to detection distance.

 

Air sampling detector

Air sampling detector features and performance criterion are specified in EN 54-20 standard. Primarily selected air sampling detector should have this standard. Air sampling smoke detector selection is done according to CEN/ 54-14 Standard 6.4.2 and 14.2 sections. It contains air sampling, analysis device, pipe and equipment as shown in below figure.

 

Air sampling smoke detector is used in areas that need faster and true detection.

As result, before the detectors are selected flammable materials should be determined for each place then compatible detectors (smoke/heat/multisensor/air sampling) should be selected.

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