Early warning system

Aspirating smoke detection (ASD) systems have been available for over 20 years now. Originally targeted at the detection of smoke in high airflow environments, the advantages of such systems are now widely understood and the technology is being applied in a greater range of applications than ever before. According to a recent survey by I&I Proplan, ASD now accounts for 7% of the European market for non-domestic fire detectors. This continues to grow as people realise the benefits of ASD and the low total cost of ownership that it offers in many environments.

The application of ASD saw a step rise in growth with the introduction of laser-based detectors in the late 1990s. “This technology offers an unrivalled range of sensitivity (from 0·005% obscuration/m to 20% obscuration/m) and as such initiated a significant increase in the diversity of ASD applications – into places such as cold stores, warehouses, manufacturing facilities, power stations, cable tunnels, atria and so on,” explains Peter Massingberd-Mundy of Vision Systems’ VESDA arm.

That accelerated growth is now set to move up a notch with the availability of VESDA’s high sensitivity LaserFocus detector, claims Massingberd-Mundy. “This detector is specifically targeted at applications when the need for a top quality, high sensitivity ASD system has existed but the perceived high installation costs have prohibited their use,” he says.

Massingberd-Mundy cites seven market drivers he considers encompass the reasons ASD solutions are specified:

• to provide earliest possible detection to enable business continuity;
• to allow extra time for safe evacuation;
• to avoid unnecessary suppression release;
• in environments where smoke is difficult to detect eg open spaces;
• in areas with challenging environmental conditions eg dirty locations, cold stores;
• in buildings where aesthetics and concealed detection are important;
• in locations where maintenance access is limited

Blickling Hall’s trust

The National Trust’s Blickling Hall in Norfolk is one recent example of how the LaserFocus’ ASD technology is bringing benefits to smaller spaces than was traditionally possible. It has proved invaluable to achieve concealed detection in some of Blickling Hall’s rooms.

Built in the early 17th century and one of England’s great Jacobean houses, Blickling Hall is famed for its spectacular long gallery, library and collections of furniture, pictures and tapestries, which are priceless and irreplaceable.

The National Trust installed an ASD system ten years ago; this ‘point a box’ system was specified simply on grounds of cost. Unfortunately it proved unreliable and, in association with Defensor Fire Detection Systems, the National Trust has chosen to deploy a more reliable, high sensitivity ASD system. “This is specifically designed as aspirating smoke detection as opposed to being an adaptation of conventional technology,” explains Massingberd-Mundy.

There are seven areas currently protected, including the long gallery (see photo, over), and some innovative thinking has seen the existing pipework utilised to minimise disruption during the conversion to VESDA technology. The detectors’ relay outputs are linked to the main fire alarm system using standard interfaces to the detection loop.

“The main driver for using ASD in this area is the concealed detection it offers, but consideration is also being given to exploiting the detectors’ ability to generate an early warning,” says Massingberd-Mundy. This is particularly relevant in public areas where early warning of an incident would allow on-site staff to investigate and perhaps intervene to prevent a minor incident escalating to cause damage or a disruptive and unnecessary evacuation of the building. As such the system would be classified as a ‘Class C’ (normal) sensitivity system under the EN 54-20 standard (see box, below) with perhaps a requirement to provide a ‘Class B’ (enhanced) pre-alarm warning signal.

As a Class C system, the solution in most rooms is ‘prescriptive’, whereby the positioning of the sampling holes is in accordance with the spacing needs for conventional point detectors specified in BS 5839-1. Ultimate performance of such a solution is reliant on approval by the Loss Prevention Certification Board (LPCB) of the detector. Type testing must demonstrate that it meets the minimum performance requirements of CEA4022, where one sampling hole has equivalence to a point detector.

In one area the sample point spacing does not fully comply with BS 5839-1, so a National Trust performance test is specified using a smoke generator and oil-filled electric radiator – a test method that provides some thermal lift to a benign smoke aerosol ie a smoke that has been approved for use in historic buildings. “This is a good example of performance-based testing, a technique that is gaining wider acceptance as risk-based fire engineering approaches are becoming more common under the new Fire Safety Order,” says Massingberd-Mundy.

Another interesting aspect of this project is that all rooms have at least two sampling points. As such, the cumulative effect (whereby smoke entering more than one hole results in an earlier response to diffused smoke than is possible with conventional point detection systems) means that the resulting system is guaranteed to be well within the minimum requirements of a Class C sensitivity system, therefore risk of damage due to fire is minimised.

EMC squared

For the EMC chamber at the LPCB in Garston, Hertfordshire, LaserFOCUS was specified to protect its semi-anechoic RF chamber – a business critical asset valued in excess of £400 000. The chamber is in use over 90% of the time, therefore it is critical to provide a reliable fire protection system as loss or non-availability of the facility has serious business implications.

A clear requirement for this project was an ASD system approved by LPCB and installed by an LPS1014 company, Hall and Kay. “LaserFocus proved to be the ideal solution for the protection of a facility deemed to be a high value, medium/high-risk environment, because there is a small probability that the high fire load of carbon impregnated foam cones may start to smoulder when overheated,” says Massingberd-Mundy.

The key driver in this application is the need for early detection of any fire threats. As such, a Class A (high sensitivity) system was provided, which was required to respond to the 1 m hot wire test (from BS 6266) and the BFPSA Code of Practice. Prior to commissioning, the unit was left running for several weeks having completed a two-week autolearn period that set the alarm threshold automatically at 0·082% obscuration/m. During the hot wire test the peak smoke reading was observed as 0·18% obscuration/m. Even though this occurred about one minute after the end of the formal test, it was deemed to be sufficient as the application is in still air. This result and decision were clearly noted on the commissioning documents and agreed by all parties.

Such case studies provide good illustrations of how the use of ASD systems is being extended to smaller areas. “Unfortunately there are many situations where such precautions have not been taken and the consequential losses have been substantial,” claims Massingberd-Mundy. In a world where the focus is on reducing risk, such developments are showing themselves to be very valuable assets.