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Peter Massingberd-Mundy, technical product manager, Vision Systems, indicates the drivers that have lead to aspirating smoke detectors being specified for small areas and explores
four examples of such applications.
The benefits of aspirating smoke detection (ASD) systems are widely understood and the technology is being applied in a greater range of applications than before. According to the I&I Proplan survey, ASD now accounts for 7% of the European market for non domestic fire detectors and this continues to grow as people realise the many benefits of ASD and the low total cost of ownership that they offer in many environments.
One major contribution to the continued growth of the ASD market is the availability of the new and affordable, high sensitivity, VESDA LaserFOCUS detector which was launched in October 2004. This detector is specifically targeted at applications when the need for a top quality, high sensitivity ASD has existed but the perceived high installation costs have prohibited their use.
This article reviews the seven market drivers that are widely considered to encompass the reasons why ASD solutions are specified and installed. Four specific projects are then presented illustrating how the VESDA LaserFOCUS has been able to satisfy these drivers in a number of smaller area applications. Throughout the article reference is made to the proposed new EN54-20 standard. This proposed standard is for the type approval of Aspirating Smoke Detectors and it is due to be published early in 2006. The standard introduces three sensitivity classes for ASD; A = Very High Sensitivity, B = Enhanced Sensitivity and C = Normal Sensitivity. It is a standard that will help specifiers and users of ASD systems clearly differentiate the capabilities of the various ASD systems on the market.
ASD systems have been available for more than 20 years. Originally targeted at the detection of smoke in high airflow environments, the application of ASD saw a step rise in growth with the introduction of the VESDA LaserPLUS in 1998. This laser-based detector offers an unrivalled range of sensitivity (from 0.005% obsuration/m to 20% obscuration/m) and as such initiated a significant increase in the diversity of ASD applications – into places such as cold stores, warehouse, manufacturing facilities, power stations, cable tunnels, atria and so on. The following seven market drivers usefully summarises all the possible applications and are just as applicable to small areas as they are to the more traditional large areas protected by the VESDA LaserPLUS.
High sensitivity ASD systems are used:
– 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 (e.g. open spaces, high air flows and high ceilings)
– In applications with challenging environmental conditions (e.g. dirty locations, colds stores and wash-down areas)
– In buildings where aesthetics and concealed detection are important
– In locations where maintenance access is limited.
The following four projects illustrate the further market expansion into smaller areas that the VESDA LaserFOCUS has inspired.
Small telephone exchange
At a small telephone exchange in South Cambridge, two LaserFOCUS detectors are being introduced by ADT Fire and Security plc to protect a small area previously protected by conventional point detectors. One LaserFOCUS provides the active sampling and protection of the room space, Air Handling Unit (AHU) return grill and the Pressure Relief Vent (PRV), whilst the second provides a reference signal to offset any possible influence from external environments.
Such a referencing arrangement is common in early warning applications where fresh air is used for cooling of IT and telecom equipment. Essentially it reduces the risk of false alarms which may be caused by externally generated smoke or pollution entering the protected area and triggering an early warning alarm. This is achieved by analysing the incoming air using a ‘reference detector’ and combining this information in the alarm decision algorithms for the active detector sampling from the protected area.
The active system has been modelled using the VESDA pipe modelling programme Aspire2 and the 3D representation is shown in the figure. This modelling capability enables the flow though and sensitivity of each hole on the VESDA detector to be acutely predicted. Most importantly the total flow through the detector is predicted as 21.7 litres per minute (lpm) and during commissioning this can be verified on the live flow reading provide by the LaserFOCUS.
The small telephone exchange is contained within a single small room measuring approximately 20m x 7m and was previously deemed ‘too small’ to justify protection using VESDA. However, the VLF-250, which is capable of covering up to 250m2, is ideally suited to such a small area and is therefore being used in the refurbishment and upgrade of the exchange.
The primary reason for using ASD in this particular environment is for the earliest possible detection of a fire and to ensure the Exchange’s business continuity. As such, the system is required to meet the one metre Hot Wire test (as specified in BS6266 and the BFPSA code of practice). This is would be defined as a ‘Class A’ ASD system under the new definition of EN54-20.
Blickling Hall
Recently installed into The National Trust’s magnificent Blickling Hall, in Norfolk, the LaserFOCUS ASD technology has proved invaluable to achieve concealed detection in some of its rooms.
The National Trust had already installed an ASD some 10 years ago. The original system, a PIAB (point a box) ASD system was specified simply on grounds of cost. Unfortunately it has proven unreliable and, in association with Defensor Fire Detection Systems Ltd, the National Trust has chosen to take up the opportunity presented by VESDA LaserFOCUS and deploy a more reliable, high sensitivity ASD system, which is specifically designed as an Aspirating Smoke Detection as opposed to being an adaptation of conventional technology.
There are seven areas currently protected, including the long gallery , and some innovative thinking has been used to utilise the existing pipework 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. 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 a damaging incident or at best resulting in a disruptive and unnecessary evacuation of the building.
As such the system would be classified as a ‘Class C’, normal sensitivity system under the new EN54-20 standard 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 a ‘prescriptive solution’, whereby the positioning of the sampling holes is in accordance with the spacing requirements for conventional point detectors specified in BS5839-1 (the British Standard code of practice for fire detection and alarm systems). Ultimate performance of such a prescriptive solution is reliant on the ‘Type test’ LPCB approval of the detector which demonstrates that it meets the minimum performance requirements of CEA4022 (where one hole has equivalence to a point detector). However, in one of the areas the sample point spacing is not in full compliance to BS5839-1 so a National Trust performance test is specified using a smoke generator and oil filled electric radiator – a test method which provides some thermal lift to a ‘benign’ smoke aerosol (i.e. a smoke that has been approved for use in historic buildings). This is a good example of performance based testing, a technique which is gaining wider acceptance as risk based fire engineering approaches are becoming more common under the new Fire Safety Order.
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 ‘normal’ sensitivity system and therefore risk of damage due to fire is minimised.
Norfolk County Hall
The main telephone room at Norfolk County Hall, measuring approximately 8 metres by 6.5 metres has an FM200 automatic extinguishing system installed by Defensor Fire Detection Systems Ltd . This is because it has been identified as a critical room for communications – both within in the building and to external premises and personnel.
It has been recognised that a VESDA Aspirating system (in addition to the co-incidence conventional system used to trigger the FM200) is an essential part of the protection strategy – providing early warning and the potential to avoid an expensive and disruptive release of the FM200 for a minor incident where another measure would have sufficed.
In such an integrated environment, the first warning of a potential fire threat is provided by an alert relay of the VESDA LaserFOCUS, which is interfaced to a local sounder.
If early intervention at this alert stage proves to be ineffective, the fire relay on the LaserFOCUS is interfaced to shut down the air conditioning and signal to the main County Hall analogue addressable fire alarm system via a loop interface unit. This then allows the co-incident point detectors to operate in a still air environment and releases the FM200 (if there is sufficient smoke present to trigger the release).
The main driver for using the VESDA in this application is clearly to avoid unnecessary suppression release and using EN54-20 terminology would be a Class A ‘high sensitivity’ system designed to provide the earliest possible warning of a fire event.
Interestingly, in similar applications a VESDA may be interfaced to provide one of the detector inputs for the co-incident gas release. In this case a Class C ‘normal sensitivity’ response would be more appropriate which could be provided by a third alarm relay (available on a LaserPLUS and shortly on a LaserFOCUS with a relay card). In this case the arrangement would be to use the Alert to provide local early warning, Action to shutdown the Air conditioning and Fire2 to interface to the extinguishing panel.
Whilst the specific sequence of events depends on the particular application, building, availability of personnel and operational/occupancy procedures, the flexibility of the VESDA ASD detectors ensures that they can be successfully integrated into any response strategy.
EMC Chamber – LPCB Garston
For the EMC Chamber at Garston’s LPCB/BRE in Hertfordshire, LaserFOCUS was specified to protect its semi-anechoic RF chamber. As a ‘business critical’ asset valued at in excess of GB pound 400,000, LaserFOCUS has provided the perfect early warning solution. The Chamber is in use more than 90% of the time, therefore it is critical to provide a reliable fire protection system as loss or non-availablity of the facility has serious business implications.
A clear requirement for this project was a ASD system approved by LPCB and designed, installed and commissioned by an LPS1014 certified company; Hall and Kay Fire Engineering were selected to do this. The newly approved LaserFOCUS proved to be the preferred solution for the protection of a facility deemed to be high value medium/high risk environment. Specifically there is a small probability that the high fire load of carbon inpregnated foam cones may start to smoulder when overheated due to unusually high levels of RF energy. Plastic pipes and fittings plus lead throughs were used to bring capillary sampling points through the chamber ceiling. This was to avoid interference with the EMC characteristics of the chamber.
So the key drivers in this application is the need for early detector of any fire threats. As such a Class A ‘high sensitivity’ system was provided which was required to respond to the 1m hot wire test (from BS6266 and the BFPSA Code of Practice).
Prior to commissioning, the unit was left running for several weeks having completed a two week Autolearn period which set the alarm threshold automatically at 0.082%obscuration/m. During the hot wires test (see photos 1 and 2) the peak smoke reading was observed to be 0.18%obscuration/m and, even though this occurred about one minute after the end of the formal test, it was deemed to be sufficient on account of the application being in still air.
This result and decision were clearly noted on the commissoning documents and agreed with all parties concerned.
Conclusion
These four case studies provide some good illustrations of how the VESDA LaserFOCUS is being used to satisfy the drivers for applying ASD in smaller areas.