Fire Alarm Detectors (2)

Combined Smoke and Heat Detectors

Combine smoke and heat detector shall comprise of two chambers. One chamber containing the photoelectric smoke detector and the other shall contain the heat detector. The smoke detector shall utilize a horizontal optical bench construction which houses the detector and the optical sensor.

The detector shall be arranged for radial detection of forward scattered light. The heat detector operates at fixed temperature set at 57 ^oC, 71 ^oC or 99 ^oC to trigger the alarm. The setting  depends on the application and as specified in the project documentation. The detector shall be fully operational after initiation of an alarm without any maintenance.

Duct Smoke Detector

                Duct smoke detectors shall be provided in the main return air duct adjacent to each air handling unit (AHU). They have to be of the duct mounted type and initiate alarm in case of a developing fire. These  provide with two sampling tubes. The first, an inlet tube for intake of air from the duct to the sensor assembly. Duct smoke detectors should be interlocked with the air handling unit motor and  volt free contact shall also be provided to raise an alarm on the main fire alarm panel. Installation of duct mounted detectors shall be approved by the air-conditioning section.

Beam Detectors

                Beam detectors provide a cost effective method of covering wide open plan areas, however care should be taken that activities in the space do not obstruct the beam and that the building structure is such that the beam does not ‘move’ or false operation may result. If optical beam detectors are mounted within 600mm of the ceiling level, they should be positioned such that no point in a protected space is more than 7.5m from the nearest part of the optical beam. Should the beam detector be mounted more than 600mm below ceiling level then spacing should be altered to 12.5% of the height of the beam detector above the highest likely seat of any fire.

                Other than the part of the beam within 500mm of the beam’s transmitter or receiver, if any other section of a beam which runs closer than 500mm to any wall partition or other obstruction to the flow of hot gasses, that section of the beam should be discounted from providing protection. Where optical beam detectors are mounted in the apex of pitched roofs then the same enhanced spacing can be applied as for point smoke detectors (see above). The area covered by a single optical beam detector should not exceed that of a single detection zone.

Infrared flame detectors

The infrared flame detectors is capable of detecting infrared radiation produced by flaming fires involving carbonaceous materials. The infrared flame detectors must be approved and listed by the Loss Prevention Council Board and manufactured under the appropriate category by the Underwriters Laboratories, Inc (UL), and should be bear the “UL” label. The infrared flame detector detects a fuel fire of 0.1 m² area from a distance of 30 m for the following fuels.

a.       Petrol

b.      N-Heptanes

c.       Kerosene

d.      Diesel Oil

e.       Alcohol

f.       Ethylene glycol

The infrared flame detectors employ narrow band filters that block unwanted radiation such as that emanating from the sun or tungsten filament lamps. The infrared flame detectors is designed to be sensitive to modulation of the received radiation in a small range of frequencies corresponding to the flicker flames. The infrared flame detectors is designed to have high resistance to contamination and corrosion. The electronic assembly of the infrared flame detectors will be encapsulated in high resistivity epoxy resin. The infrared flame detectors  includes RFI screening and feed through connecting components to minimize the effect of radiated and conducted electrical interference.