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[ Specialised Fire Detection Systems ]
Air Sampling / HSSD (High Sensitivity Smoke Detection)
An air-sampling smoke detector is capable of detecting microscopic particles of smoke. Most air-sampling detectors are aspirating smoke detectors, which work by actively drawing air through a network of small-bore pipes laid out above or below a ceiling in parallel runs covering a protected area. Small holes drilled into each pipe form a matrix of holes (sampling points), providing an even distribution across the pipe network. Air samples are drawn past a sensitive optical device, often a solid-state laser, tuned to detect the extremely small particles of combustion. Air-sampling detectors may be used to trigger an automatic fire response, such as a gaseous fire suppression system, in high-value or mission-critical areas, such as archives or computer server rooms.
Most air-sampling smoke detection systems are capable of a higher sensitivity than point type smoke detectors and provide multiple levels of alarm threshold, such as Alert, Action, Fire 1 and Fire 2. Thresholds may be set at levels across a wide range of smoke levels. This provides earlier notification of a developing fire than spot type smoke detection, allowing manual intervention or activation of automatic suppression systems before a fire has developed beyond the smouldering stage, thereby increasing the time available for evacuation and minimizing fire damage.
Beam Detectors
Beam detection has become commonplace within large open warehouses. Beam Detectors are cost effective when compared with using point detection and suitable for heights way above the operating limits of conventional smoke detection.
It all sounds too good to be true however, there are important factors to consider when selecting and installing beam detectors.
The operational range of a standard beam detector is 100M with coverage up to 15m Wide. Immediately we can see that covering 1500m2 with one pair of beam detectors is quite impressive. This also means that the beam must be connected to its own zone on a conventional fire alarm panel or its own software zone on an analogue addressable control panel. In the case of the latter a short circuit isolator will also be required as no zone can exceed 2000m2 under BS5839 part One:1988.
The next consideration must be sunlight. Certain manufacturers have produced "Solar Blind" beam detectors with the use of I.R. filters whereas others will be affected by sunlight pouring through roof lights into the beams I.R. receiver. In this case false alarms will often result at set times of the day and of course with seasonal fluctuation, low winter sun being a prime example.
Beam detectors spanning 100m are prone to movement. Steel framed buildings move. This is a normal occurrence, but when trying to hit a target approximately 100mm x 100mm from 100m away even a few degrees of movement can cause problems. Correct initial alignment is critical as is a solid & secure fixing to structural steel or brickwork. In many cases bracing and special brackets may be required.
Maintenance is also critical. Detector lenses become coated with dust and alignment will be affected by building movement over time. You should always re-align and clean all beam detector lenses once per annum to ensure reliability and performance.
Duct Probe
The presence of smoke in a ventilation duct is detected by sampling the airflow through the duct via two sampling tubes. A detector and base are mounted within the sampling chamber, which is located on the external skin of the duct, with sample and exhaust probes passing into the duct in an area of low turbulence. The unit requires an analogue optical detector and base and is supplied with full fixing instructions.
Gas Detection Systems
The most common method employed to continuously monitor for leakage of hazardous gases is to place a number of sensors at the places where any leaks are most likely to occur.
These are often then connected electrically to a multi-channel controller located some distance away in a safe, gas free area with display and alarm facilities, event recording devices etc.
‘How many detectors do I need?’ and ‘where should I locate them?’ are two of the most often asked questions about gas detection systems, and probably two of the most difficult to answer. Unlike other types of safety related detectors, such as smoke detectors, the location and quantity of detectors required in different applications is not clearly defined.
The placement of detectors should be determined following the advice of experts having specialist knowledge of gas dispersion, experts having knowledge of the process plant system and equipment involved safety and engineering personnel.
Detectors should be mounted where the gas is most likely to be present.
Intrinsically Safe Fire Detection Equipment
Intrinsically safe fire detection equipment is defined as "equipment and wiring which is incapable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific hazardous atmosphere mixture in its most easily ignited concentration".
This basically means that intrinsically safe equipment and wiring operates using electrical and thermal energy below the level that would be required to spark an explosion in a hazardous area such as an oil refinery.
Linear Heat Detection Cable
Linear Heat Detection (LHD) is a versatile and economical fire detection product. Designed for use in a wide variety of fire and heat detection applications, LHD cable is particularly suited for harsh environmental conditions, where maintenance access is in a physical or hazardous area, and/or where there is a requirement to cost-effectively install fire detection in close proximity to the hazard.
Linear Heat Detection cable is a combination of advanced polymer and digital technologies that can detect heat conditions anywhere along the length of the cable. The cable is comprised of two tri-metallic conductors individually insulated with a heat sensitive polymer outer-layer, and engineered to break down at specific fixed temperatures. This allows the twisted conductors to make contact and initiate a fire alarm condition at the control panel, without any calibration for changes in the ambient temperature. Nor is it required that a specific length be heated in order to initiate a fire alarm, adding to the versatility of this unique product.
For further flexibility, Linear Heat Detection cable can be utilized with fire alarm control panels by utilizing either addressable monitor modules on an intelligent system, or by connecting the cable directly to the detection circuit of a conventional fire detection and control panel. In addition, the distance locating option allows the control panel to identify and display the exact location, in feet or meters from the fire panel, where the heat source interacted with the linear heat detection. That's a tremendous amount of valuable information in a small, easy to install and maintain fire detection package!
• Easy installation and maintenance
• Minimal false alarms
• Provides hazard coverage at every point on the cable for maximum protection
• Compatible with intelligent and conventional detection and fire alarm panels
• Available in a variety of lengths, cable coatings and alarm temperatures for maximum flexibility.
Ultra-violet / Infrared (UV/IR) Flame Detector
Ultra-violet/Infrared (UV/IR) flame detector delivers high performance security with functions and features that set it apart. The flame detection reacts to both UV and IR flame radiation delivering accurate and reliable fire monitoring, yet is immune to arc welding, hot body radiation, lightning or sunlight. Two spectrums of radiation must be recognized and confirmed by precisely tuned sensors for the UV/IR to initiate a fire condition, greatly reducing false alarms while providing critical safety performance to your site and personnel.
Enclosed in a rugged, explosion-proof housing, the UV/IR flame detectors is capable of stand-alone operation or can be connected to a variety of control devices to create a dependable fire monitoring system. The user can define sensitivity and time delay settings and the built-in testing routines ensure continuous operation.
The UV/IR Flame Detector has a extra wide field of view - up to 120 degrees.
Flame detectors come in many sizes and variations but generally fall into three groups.
Infra-red Flame Detectors
Infra-Red (IR) Flame Detectors respond to flaming fires emitting light in the infrared area of the spectrum (modulating at 5 to 30 cycles per second). I.R. Flame Detectors can respond to a fire condition in typically less than 50 milliseconds and are designed to detect hydrocarbon fires whilst ignoring potential false alarm hazards such as arc welding, nuclear radiation and x-rays.
The sensor usually incorporates a delayed response, selectable in the range 3-30 seconds, to minimise responses to non-fire sources of radiation. In this way alarms are only generated by a sustained, flickering sources of I.R. radiation - e.g. fire.
The sensitivity of Infrared Flame Detectors is affected by the distance of the device from the fire source such that, if a distance is doubled the fire has to be four times as large to be detected. The trigger delay is therefore adjusted to suit the installation conditions shorter delays for lower mounting, longer delays for higher mounting.
Ultra Violet Flame Detectors
UV Flame Detectors are extremely fast and capable of detecting flaming fires emitting light in the ultra violet area of the spectrum. Typically, UV Flame Detectors can respond to a fire in less than 10 milliseconds and are used in high hazard applications such as petrochemical plants, munitions factories and other areas where flammable or explosive liquids or solids are handled or stored.
Ultra Violet Flame Detectors can be used in explosive atmospheres and some are capable of being directed at specific hazards.
Models can have angular fields of view ranging from 90 to 180 degrees. Sensitivity is usually factory set for the application.
UV Flame Detectors should not be used around arc welding, as they will respond to the UV light given off by the welding process.
Ultra Violet - Infra-red Flame Detectors
UV-IR Flame Detectors respond to flaming fires emitting light in both the ultra violet and the infrared area of the spectrum.
UV-IR Flame Detectors require both the UV and the IR sensors to alarm simultaneously thereby making them highly resistant to common sources of false alarms such as welding, x-rays, lightning, artificial lighting and interrupted hot body radiation.
High Risk Areas
For high-risk areas, a detector may be set with a low delay threshold for greater sensitivity and shields used to eliminate possible causes of false alarms.
Some detectors designed for very fast response do not have the 'flicker' discrimination feature but instead have two sensors with different spectral responses in order to distinguish an actual fire from other sources of IR radiation.
Wireless Detection
A wire-free fire system utilises sophisticated secure, radio communications to interconnect the sensors with the controllers.
Wire-Free Benefits
- Sensors can be fitted in less than 10 minutes;
- The fabric of the building is protected and undamaged;
- Disruptive installation works are kept to a minimum;
- Eliminates costly fire-rated cable;
- The systems can be easily moved or upgraded as building use changes.
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