The increasing use of Aspirating Detection Systems for fire detection in harsh and other environments
31 March 2016
Aspirating Detection Systems (ADS) are increasingly considered an alternative to traditional smoke and heat detection technologies as, in many cases, they have been proven to provide superior fire and smoke detection, greater resistance to false alarms and to be more cost-effective in the long term. This article by Michael Calvert of Protec Fire Detection plc looks at ADS and its many applications.
I’m not sure I can think of another technology that has become such a widespread solution to so many different fire and smoke detection applications so fast, than Aspirating Detection Systems.
These draw air from the protected space via a network of supervised sampling pipes to a wall mounted fire/smoke detector. The aspirating detector employs an inbuilt blower to transport the air through the pipes from the space.
When they were first conceived some 40 or more years ago, the original concept of aspirating detection systems was to provide early warning smoke detection for telecoms, IT and computer suites. These first ‘comms rooms’ contained high-value equipment and, more importantly, held information and data that could not be lost. Point type smoke detectors were simply not sensitive enough given that these rooms would have air conditioning as standard and therefore smoke from an overheat condition would be diluted.
For many years, generally speaking, early-warning fire detection provided around 90% of the applications for aspirating detection systems. However, as a result of the 2000 ‘dot com’ crash, the main aspirating detector manufacturers branched out to provide a wider range of applications. More recently, aspirating detection has become the accepted solution for applications including general and high bay warehousing, cold storage, atriums and ceiling voids, high ceiling spaces such as airport lounges, indoor arenas and theatres.
Power and other utility plants, industrial conveyor systems, very dusty areas and many different harsh environment applications are also now being protected by aspirating detection systems.
So why has this change happened and why are we now installing aspirating detectors in industrial sites as extreme as waste retrieval and recycling plants? There are a number of answers.
Firstly, aspirating detectors have become more tolerant of false alarms from dust. However, some are more tolerant than others. Optical based aspirating detectors have to employ one or even a number of methods to discriminate dust from smoke. Some of these methods are more successful than others, but ultimately the problem is that some smoke and some dust particles are the same particle size, so total discrimination is not possible with optical detectors.
Only Cloud Chamber based aspirating detectors can claim total immunity to false alarms from dust, as the technology used in these detectors identify optically invisible, sub-micron combustion particles. Smoke and dust are not within the detection range of cloud chamber detectors so these can be successfully installed in the most difficult and dusty environments.
Another reason why aspirating detection systems are now employed in so many applications is that they are a more effective solution compared to other technology options. For example, point type smoke detectors should normally be installed to a maximum mounting height of around 10.5m. So what does a designer specify when he has an atrium that is 15m, 20m, 30m or even 40m high?
Optical Beam Smoke Detectors (OBSD) used to be the obvious and pretty much only solution to high ceiling spaces. However, these beam detector installations often suffered from many nuisance problems including building deflection, sunlight/heat shimmers, natural and manmade obstructions and long term cleaning and maintenance issues.
In 2010, the UK Fire Industry Association (?FIA) Aspirating Smoke Detection Working Group began testing to compare Aspirating Detection Systems with Optical Beam Smoke Detectors in high ceiling spaces up to 40m. As a direct result of these independently verified tests, the FIA Code of Practice for the Design, Installation, Commissioning and Maintenance of Aspirating Smoke Detector Systems was revised to allow aspirating detections systems to be installed to a ceiling height of 40m.
Furthermore, as a result of the FIA Code of Practice document change, the same ceiling height limit was introduced into the revision of British Standard 5839 part 1 in 2013. Therefore fire alarm system designers can now specify aspirating detections systems with confidence in atriums and other high ceiling spaces, knowing they have been tested and proven to be a very effective and compliant solution.
Another advantage of ADS is the benefit of the sampling pipe installation, when compared to the normal wired point type smoke/heat detector system. Ceiling voids are a very good example of this. A sampling pipe installation within a ceiling void that is anywhere between say 3m and 10m high, with sampling holes drilled at the location where point type detectors would be required, provides a maintenance free installation in the void space.
The logistics, access and cost of servicing or attending to faulty electrical devices in these spaces can be extensive, whereas holes in sampling pipes require almost no maintenance (or at worst, the cleaning of sampling pipes and sampling holes can be done remotely without access to the void space).
Let’s now consider some applications with difficult environmental conditions. One example is Cold Storage facilities, where the ambient temperature is normally circa -200C. Regional Distribution Centres for supermarket chains have cold stores the size of football pitches and are often between 10m and sometimes 40m high. These huge storage facilities have millions of pounds of stock and serve entire regions of the country with frozen food. A fire in such a storage facility would create huge disruption to the operation of the supermarket. So how best to protect these rooms?
The reality is that very few technologies will actually operate correctly at these temperature extremes, where most electronic components struggle to function. Also, cold stores are considered to have a high risk of fire threat, as the environment is very dry and therefore an ignition source can create a large fire very quickly. And consideration must also be taken for the height of the ceilings and the high airflows that the chiller units generate.
ADS can be made to operate very successfully in these applications. Sampling pipe and sampling holes are not affected by the low temperatures and as long as some common sense engineering is applied to the complete installation, and these systems can be configured to be set at a very high sensitivity as there is almost no background pollution.
Cold stores, food and other process production areas can create environments where condensation and humidity levels are very high. Aspirating detection systems are also effective here with careful thought, planning and engineering.
A gradient in the sampling pipe installation, sampling holes drilled into the side wall of the sampling pipes, and strategically placed condensation traps amongst other techniques can create a fully functional detection system in these very difficult applications. Again, most other technologies will struggle in this environment, or a compromise on detector sensitivity must be made.
In a waste retrieval and recycling plant we must consider many of the points raised above. These include high ceiling spaces, temperature extremes (day, night, winter, summer) in unheated buildings, high condensation and humidity levels, and most relevant of all, very high dust levels 24 hours per day.
Not only must the best aspirating detector be selected (a cloud chamber device, for example) and be resilient in these conditions, but it is just as critical that the sampling pipe installation is engineered to be robust and to operate in these conditions for many years, with the least possible maintenance requirements and costs.
To achieve this, automated pipe purging units are employed, where the complete sampling pipe installation is cleaned using compressed air. This a programmable function of these units, with pipe cleaning carried out monthly, weekly, daily or even hourly as required. In these plants, hourly pipe cleaning may make the difference between long-term safe operation and a decline in performance, with potentially serious consequences.
In conclusion, aspirating detection systems have been considered the best solution to protect cleanrooms and data centres, where the highest detector sensitivities are required, for a long time. But now, they are also becoming a popular solution for a whole range of unstable, difficult and harsh applications where providing a detection system that actually works in all conditions is the prime objective.
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