ASD – Rising to the Most Demanding Challenges
Everybody knows that fire always has the potential to be a real threat to both life and property. It is therefore vital to know that personnel and property are reliably and efficiently protected from its outbreak wherever possible. However, should the unthinkable happen and the circumstances come about for combustion to occur, the very least that we would all want is the assurance that we receive the earliest and most reliable detection possible.
It is generally accepted that aspirating smoke detection (ASD) is one of the technologies that provides the earliest detection of the incipient stages of combustion. Aspirating smoke detection systems – also widely known as air sampling detection systems – can detect smoke before it is even visible to the human eye.
The systems generally consist of a network of independent pipes with one or more sampling apertures that actively draw air into a highly sensitive smoke-sensing chamber. There, the sampled air is precisely and accurately analysed by a scattered-light detector for smoke particles. If smoke particles beyond a pre-set threshold are detected, the system triggers an immediate alarm. In that way, a timely warning is given, along with the opportunity to fully investigate the cause of the alarm. The most appropriate response can then be initiated to stop the fire gaining a hold and so prevent injury, damage and disruption to business.
Aspirating systems can be up to a thousand times more sensitive than a standard point detection system. By combining this level of sensitivity with an environmental learning capability, it is possible for such a system to provide and maintain the optimum operating level and keep unwanted or false alarms to an absolute minimum – without external input. Aspirating systems also usually have the capability to monitor their own integrity and, in the event of the system’s ability to detect smoke being compromised for any reason, an alert is raised. Conventional point detection usually comprises passive devices that are simply constantly monitored. The systems have no ability to determine whether any occurring smoke will actually reach the detectors.
An Alternative with So Many Applications
Aspirating smoke detection is no longer a new technology, having been tried and proven in many different applications. Nor is it simply an alternative option to standard point detection, which is generally more than suitable for most standard applications where cost and basic compliance to regulations are often the main selection criteria.
Aspirating detection is still very widely used within IT and telecommunications environments – the arena for which it was originally developed – protecting highly ventilated areas such as data centres, information technology and computer centres, telecommunication facilities, laboratory and research centres, electronic measuring rooms, transformer rooms and clean rooms.
In these mission-critical facilities, high power loads and minor deficiencies in the electrical equipment can lead to short circuits or dangerous overheating. However the dilution of any resulting smoke and any redirection of it by the vigorous airflow would most likely prevent any signals of combustion from reaching conventional detectors in adequate time or in sufficient quantities to trigger an alarm. In the event of a substantial fire breaking out, the potential loss in either a data centre or server room might not be just the important or irreplaceable data they hold, but also the significant revenue for its safe storage along with the IT company’s reputation.
Release of Gaseous Extinguishants
In these IT areas, such as electrical control rooms, substations, computer, server and telecommunication rooms, wherever gaseous extinguishing systems are employed, codes of practice now call for two levels of detection before the release of extinguishants. This “coincidence” or “double-knock” protection as it is known, can utilise two independent detection systems, designed for one to confirm the other (double-knock).
High Power and Heavy Ventilation
However, it is not just IT environments that are heavily ventilated these days. Many buildings today are served by close-control air conditioning systems that operate with high-velocity airflows. These strong currents can effectively prevent any smoke generated in the first stages of a fire from reaching conventional detectors. This is particularly true of the incipient stages of combustion when “cool” smoke lacks the thermal lift to rise to the ceiling, where smoke detectors are traditionally sited.
Installers of aspirating systems can overcome these problems by siting the sampling apertures of the pipework within the airflow produced by the air-conditioning units – usually with most effect in front of the intake grill or duct for expelled air. In this way the quickest and most certain of responses is generally assured.
Detection Under Difficult Conditions
Aspirating smoke detection systems are ultra-sensitive, quiet and unobtrusive – qualities that make them suited for a multitude of applications and there are now many other applications, environments and conditions where today’s prevailing considerations make aspirating detection a more viable and effective option than standard point detection. As well as affording the earliest warning, aspirating detection systems are also particularly suited wherever environmentally challenging conditions prevail, limiting the effectiveness of standard detectors.
There are applications where conditions are extremely hot or cold, wet or dusty. There are places with unusual or hard-to-access areas like intermediate ceilings, raised floors, cable ducts, distribution cabinets and display cases. Unlike traditional point detection systems, the detection units of aspirating systems do not need to be situated in the protected area. Only the sampling pipes are located within the area, continuously extracting air and carrying it to the detection chamber for analysis. This makes aspirating systems ideal for use in applications traditionally difficult to protect with conventional detectors such as textile drying areas, tobacco plants, cold stores and food preparation areas.
The ability of most systems to filter out dust particles completely enables them to perform highly effectively in even the dustiest locations while still keeping unwanted alarms to a minimum. This means they can even be installed for use in recycling facilities, paper and flour mills, coal conveyors, wood recyclers, cable tunnels and textile areas.
Even Greater Reliability
Providing the earliest warning in harsh environments coupled with absolute reliability, however, is still a real challenge, but there are now available aspirating smoke detectors that can distinguish between smoke and dust – even in the most demanding application areas.
In the past, even for aspirating systems, differentiating between airborne particles of smoke, dust and steam has led to the generation of too many unwanted alarms. Now, new models of aspirating detector combine optical dual-wavelength technology with patented detection chamber technology. The new optical technology utilises light of two differing wavelengths. This enables the detection of the smaller airborne particles produced in the earliest stages of overheating or open flame. By determining the exact size and concentration of the actual airborne particles, the detectors are able to distinguish between smoke, dust and steam. As a result of this analysis, they are able to detect smoke in the very early stages of combustion reliably – with a high immunity to other deceptive phenomena. Such early, accurate and reliable detection – that is largely immune to external interference – can eliminate the downtime and resulting costs of unwanted or false alarms caused by steam, dust and other misleading airborne conditions of hostile environments.
Some of the new models can provide up to three modes of operation, such as: ‘ultrasensitive’, ‘auto-discrimination’ and ‘robust’. Depending on the application, it is possible to choose between ten different parameter sets. To make sure the extinguishing is triggered at a higher obscuration level, a separate parameter set is available for this purpose. The new detectors are easy to install and their integration into existing systems is also possible in order to ensure full transparency of both display and operation. Integration makes it possible to configure the detectors, perform maintenance work and handle alarm and fault management on the system’s control panel, thereby optimising control and lowering overall costs.
Protecting High Spaces
In large spaces, such as lobbies, atria, high-rack warehouses, distribution centres, industrial production areas, airports and hangars, ceiling heights in excess of 12 meters can make the use of conventional detectors totally ineffective. Stratification – the term used when smoke sits in a layer well below the ceiling – occurs when smoke does not have sufficient thermal buoyancy to reach the ceiling where detectors would ordinarily be situated.
Beam detectors are sometimes used in this kind of scenario in place of ceiling-mounted detectors, but they are inherently low in sensitivity and also prone to false alarms caused by building movement, airborne activity and high-level operation of equipment such as cranes or forklifts interrupting the beams. Maintenance of ceiling-mounted detectors at these kinds of heights is also fraught with difficulties.
Maintenance is, of course, vital for any detection system to carry on operating in optimum condition. In the case of conventional point detectors, the high number of devices covering any area or the inaccessibility of their positioning can create all kinds of practical difficulties. In some instances, such as public buildings, areas or even the whole buildings often need to be closed for maintenance to be safely undertaken. The positioning of the detection chambers of aspirating systems being away from the protected area, means that access is often much easier. This is particularly true of high ceilings, but under floor voids, escalators and other inaccessible areas that can also benefit from the easier maintenance of aspirating systems.
Dependable yet Unobtrusive
There are those places too where an aesthetically appealing fire protection solution is desired or where high detection sensitivity is needed for the protection of cultural assets. In historical buildings, museums, galleries, theatres, cinemas, artefact collections and archive rooms, the items and assets housed there are often irreplaceable.
Sometimes, in historically important buildings with ornate interiors such as cathedrals and palaces or places of aesthetically sensitive architecture, the systems put in place must also respect the historic significance and visual and aesthetic appeal of the settings, which are often complex and unique. In prisons and correction centres, systems need to be as unobtrusive as possible or concealed for a much different reason. In these cases, the less visible the systems are the better, in order to avoid the wanton vandalism of detectors which is often a recurring problem in penal institutions.
By using capillary tubes to carry the air to be sampled to the system’s pipe work, aspirating detection systems can be barely visible to even the most enquiring eyes. The capillary tubes can be flush terminated or easily hidden within features such as light fittings on the ceiling because the sampling tubes are so small.
Aspirating smoke detection originally developed for use in the IT industry to provide the earliest possible and most reliable detection in highly ventilated environments, has since been implemented with great success in a diverse range of applications – from heritage buildings and retail complexes to flour mills and metro stations. Its ability to detect combustion in its very earliest stages means that it can be used with efficient and timely extinguishing systems to prevent fires rather than simply detect them. Its high detection reliability and its immunity to deceptive phenomena make it the ideal choice in many difficult and challenging environments. The practicalities it brings for maintenance and unobtrusive detection makes it the preferred option to standard point detection and other systems in so many more.
For further information, go to www.siemens.com