Does My Building Need Aspirating Smoke Detection (VESDA)?
Most buildings are well served by ordinary smoke detectors, the familiar point detectors fixed to the ceiling that respond when smoke reaches them, and for an office, a shop or a block of flats they are exactly the right tool. There are buildings, though, where those detectors struggle, either because the space is too large and too high for smoke to reach a ceiling detector in any useful time, or because the environment is too harsh, too dusty or too cold for conventional equipment to work reliably, or because visible detectors simply cannot be tolerated in a historic interior. For those buildings, aspirating smoke detection, often known by the brand name VESDA after its best-known manufacturer, is frequently the answer, and the purpose of this article is to help you work out whether your building is one of them.
What aspirating smoke detection actually is
Where a conventional detector waits for smoke to drift up to it, an aspirating system goes looking for the smoke instead. A pump continuously draws air from the protected space through a network of slim pipes fitted with small sampling holes, and delivers that air to a single, very sensitive detector mounted somewhere accessible, so the sensing element sits remote from the area it is watching rather than on the ceiling above it. The detector itself is far more sensitive than a standard point detector, often cited as around a hundred times more so, which means it can pick up the minute quantities of smoke given off in the very earliest stages of a fire, frequently long before there would be any visible sign. For a building owner, the practical value of that early warning is the time it buys, time to investigate, to shut down a process, or to act before a small problem becomes a serious one.
Where it earns its place
The clearest case is the large, high-roofed building, and for our part of the world that most often means a warehouse or distribution centre, where the roof may be many metres above the floor and powerful ventilation keeps the air moving. In that setting smoke dilutes and disperses before it ever reaches a ceiling-mounted detector, so a point detector may respond slowly or not at all, whereas an aspirating system with sampling points distributed through the space, and at more than one level where the building is very tall, overcomes that dilution and gives a dependable early warning. The large logistics and warehouse sites across Greater Manchester and Merseyside are exactly the kind of premises where this comes up.
Heritage and historic buildings are the second common case, because the pipework can be concealed and the sampling points made almost invisible, which allows effective detection to be installed in a church, a listed hall or a museum without the visual intrusion of detectors and conduit across a protected ceiling, a consideration we deal with regularly in places of worship. The third case is the harsh or sensitive environment, which covers cold stores and freezer warehouses where ordinary detectors ice up, dusty or dirty manufacturing areas where they clog, premises with a high risk of vandalism where exposed detectors would be damaged, and the server rooms, comms rooms and battery or UPS rooms found in many commercial premises, where the value of the equipment and the cost of downtime justify catching a fault at the smouldering stage.
- High ceilings or large open volumes, such as warehouses, atria and production halls.
- Strong or constant airflow that would dilute smoke before it reached a ceiling detector.
- A historic or sensitive interior where visible detectors and cabling are unacceptable.
- Cold, dusty, dirty or otherwise harsh conditions that defeat ordinary detectors.
- Critical rooms, such as server, comms and battery rooms, where very early warning protects against costly downtime.
- Areas at high risk of vandalism or mechanical damage.
How it compares with ordinary detectors
It is worth being clear that aspirating detection is not simply a better version of a point detector that every building should aspire to, and in the great majority of premises a well-designed conventional system is entirely appropriate and considerably cheaper to install and maintain. The case for aspirating detection rests on the specific conditions described above, where height, airflow, environment or appearance defeat the alternatives, and there is a related technology, the optical beam detector, that is sometimes used in large spaces for similar reasons, though aspirating systems tend to be preferred where access for maintenance is awkward, where clutter or building movement would interrupt a beam, or where the air is simply too diluted for a beam to perform. The right comparison is therefore not which system is best in the abstract, but which system suits the building in front of you, and that is a judgement the fire risk assessment is there to inform.
Sensitivity classes, in plain English
If you look into aspirating detection you will quickly meet the idea of sensitivity classes, and it is worth understanding at a high level even though the detail is a matter for the system designer. The relevant standard, BS EN 54-20, sets out three classes, running from Class C, which is broadly equivalent to a standard point detector and can be used in its place, through Class B for situations with moderate smoke dilution such as higher ceilings or moving air, to Class A, the highest sensitivity, used where dilution is severe or where the earliest possible warning is needed to protect business-critical or high-value contents. One useful point to hold on to is that the class describes the sensitivity achieved at each individual sampling hole rather than the raw sensitivity of the detector unit, which is why the design of the pipe network matters as much as the choice of detector.
What to keep in mind with aspirating systems
An aspirating system is a piece of working machinery drawing the building's air through itself day and night, so it needs proper maintenance, and while the detectors tolerate a degree of dirt, heavy contamination can eventually obstruct the sampling pipework and degrade performance, which makes a sensible cleaning and servicing regime part of owning one. Where a system has been extended with additional gas sensors for specialist applications, those sensors have a finite life and need replacing when exhausted, which is a maintenance cost worth knowing about in advance. On the positive side, aspirating systems are relatively tolerant of false alarms compared with some other technologies, which is part of their appeal in busy operational settings. As with any fire detection, the system should be designed, installed and maintained by a firm with third-party certification under a recognised scheme such as BAFE SP203 or an LPCB listing, and the information about how the system works should be captured in the building's fire safety records so that its role is understood by whoever manages the premises.
How the decision actually gets made
No regulation tells you, in so many words, to install aspirating smoke detection, and the question of what detection a building needs is answered by its fire risk assessment, which weighs the nature of the building, the way it is used, the value and importance of what it contains, and the speed of warning required, and from that determines the detection strategy. Our role is to carry out that assessment and tell you what the building genuinely requires, whether that is a conventional system that does the job perfectly well or aspirating detection for a space where nothing else will, and because we do not sell or install detection equipment, that recommendation is made on the merits of your building rather than with a product to shift. From there you can appoint a certificated installer to design and fit the system, with a clear assessment behind the specification.
Not sure what fire detection your building needs?
Fletcher Risk carries out fire risk assessments for warehouses, heritage buildings, commercial premises and industrial sites across the North West, North Wales and the West Midlands. We will assess your building and advise plainly on the detection it needs, from conventional systems to aspirating smoke detection, independently of any installer or manufacturer. If we can help, please get in touch.
We cover Cheshire West, Cheshire East, Merseyside, Greater Manchester, Lancashire, Flintshire & Wrexham, the North Wales Coast, Gwynedd, Shropshire and Staffordshire.
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