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In large or unusual spaces, CCTV cameras can be used to analyse the air and provide early warning of fire. Ian Moore of DTEC outlines the technology and uses of video smoke detection.
Video Smoke Detection is a camera based fire detection system, which can be used in areas that traditionally have been challenging for fire safety professionals, such as lofty and voluminous areas. It works by using standard CCTV images which are analysed by image processing software, which looks for the particular ‘pattern’ that smoke produces. This is carried out by programming the software to look for the determined amount of smoke expected over a specified area within the camera’s image. Once smoke has been detected it is able to alert the operator using 16 volt-free contacts, as well as giving a visual representation of the smoke detected on the system’s monitor.
VSD is suited to a variety of applications and other complex commercial applications where conventional smoke detectors may not be effective, either due to air movement, stratification or background contamination. These include historic buildings, power generation halls, warehouses, atria, tunnels, cold stores, aircraft hangars, shopping centres, onshore and offshore petrochemical installations – as VSD detects the smoke at source it is unaffected by the size of such areas. More importantly, it is an early warning detection system which conventional detection may not be able to offer, as smoke has to be able to reach the device before it is activated.
But how does video smoke detection distinguish between smoke and other phenomena such as steam, dust and exhaust fumes? If pollutants which are part of the normal environment are present, the system is engineered to accommodate them by adjusting the smoke detection parameters. During the commissioning period, unwanted alarm phenomena are engineered out and smoke tests are performed on each camera to ensure the system is detecting in all environmental conditions.
As part of both the design survey and commissioning phase, areas of potential false alarms are identified and programming steps taken to eradicate them. A period of on-site ‘soak testing’ will identify any further problems not already evident at initial set up. These can then be engineered-out during the final commissioning stage and, if necessary, throughout the maintenance phase.
Theoretically the system can detect a fire on the moon, but it would need a clear night, a 300-metre smoke plume and a camera with a three-metre lens! In everyday terms, the protected area and appropriate camera and lens are determined when the site survey is carried out. The camera lens and line of sight designate the viewing area and establish the distance between the fire and cameras. As a rough guide to detect a fire, 10% of the monitor height needs to register smoke, though this sensitivity can be increased or decreased by programming the software. As video smoke detection sees smoke at its source, it detects it rapidly. Other advantages are:
– It does not have to wait for the smoke to reach the camera.
– It is less affected by airflow movements.
– It is more accurate about the location of the source.
– It has no problems with stratification of smoke and thermal barriers.
– It has a better structured response to the incident.
– It can reduces danger to by being able to remotely view an incident, obviating the need for direct investigation.
A single camera provides a large area of protection. Additionally, each camera view can be subdivided into zones that can be individually identified to reduce search areas. The cameras can also be placed to overlook areas that cannot be easily accessed for the installation and maintenance of conventional detection systems.
If a large area needs to be protected, VSD can work out cheaper. This is most evident where there are suitable, existing CCTV cameras – many of the installations use a combined security and fire detection system. Providing the existing cameras are of adequate quality and cover the area that is deemed to be at risk, all that is required is the standard analogue video feed from each camera. This can be ‘tapped’ from the back of the multiplexer unit to minimise installation works.
For the system to detect smoke, it must be ‘visible’ to the system. In low light conditions this can be accomplished with relative ease using low light cameras and/or infra-red illumination, depending on the light levels envisaged.
As with a great deal of technology, VSD is constantly being updated. Most of these improvements are software upgrades that can be easily uploaded on a regular basis, so always ensuring the system operates at its optimum. New VSD systems are fitted with a DVR-IP [Digital Video Recorder] allowing operators to record and play back pre and post-alarm incidents, enabling them to have extra information about the cause of the incident. Remote access also allows on-line diagnostics, so maintenance can be performed, again reducing costs and time.
It is fairly simple to integrate a video smoke detection system with a conventional fire detection system, or other building management systems. VSD provides freely programmable, volt-free outputs, so providing compatibility with systems that accept an input. In this instance, each camera can have its own output or a summary output and this is programmed to meet the customer’s requirements. It can also provide fault outputs to the required system for monitoring in the same way.
Video smoke detection installations are present in a variety of applications around the world. .