The science behind optical beam detection in large, open spaces – on show at FIREX 2018

Security market analyst

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Hunter Seymour is a security market analyst with expertise in both the fire and security markets.
June 13, 2018

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(Thanks are due to FFE Ltd for technical data and diagrams in support of this article.)

Think of the vast auditorium of London’s landmark Royal Festival Hall (length 50 metres), double it, and that 100 metres span gives you a very clear idea of the remarkable detecting range for large open-volume spaces granted by optical beam smoke detection.

But this impressive interior at the heart of the largest arts centre in Europe can also be visualised as a measure of beam detection’s advantageous scope for a diversity of open-area applications. These include high-ceiling buildings such as atria of large hotels, church naves, mosques, libraries, stadiums, hangers, turbine rooms, convention centres, airports and rail stations, sports and leisure centres, and warehouses and manufacturing plants.

Efficiencies of scale for high-level solutions

Beyond the purely architectural considerations of linear smoke detection and its discreet siting, you’ll find that specifiers recognise the distinct economic advantages of beam detectors in comparison with point-type detectors. Just consider here their relative coverage and the significant advantages achieved by reductions in installation time and detection unit procurement.

In a typical example, the standard width coverage of a beam is 15m, viewed as 7.5m on either side of the beam centre line, and based on a beam covering 100m range, yielding a theoretical maximum area coverage of 1,500 square metres.

However, the geometry of the location may place practical limitations on full attainment of this area. By contrast, a point detector has a coverage radius of 7.5m. Using the example in the diagram, twenty point detectors would be needed to cover the same range in two rows of ten. The time consumed to install the point detectors and the fact that they are limited to a height of 10.5m, compared with the standard max height of 25m for a beam detector (and up to 40m in certain applications) would, therefore, rule out the use of point detectors in large, open spaces.


Exhibiting at FIREX 2018: FFE Fireray One standalone beam detection – one-minute auto-alignment, light cancellation prevents nuisance alarms, building movement tracking and more 

(This year’s FIREX International (19-21 June, ExCel London) sees ‘next generation’ products launched to the market, with innovations in beam detection at the forefront.  Leading fire detection specialists, FFE Ltd, Stand A250, will be displaying their leading-edge Fireray One (inset image) standalone beam detection, for rapid one-person-installation, with One Minute Auto-Alignment™ using its integrated user interface to makes it operative 8 times faster than previous detectors.

It also features protocols for corrective compensation for building movement and optics contamination. Also on display is the Fireray® Range, including the Fireray 5000 motorised reflective, auto aligning infrared optical beam smoke detector that can be installed with up to two detector heads per system.)


1:14 ratio of fewer detection units

In terms of proportionality, this contrast can be best understood by considering that to cover an area of 1,500 square metres would require at least fourteen point-type detectors, benefiting the specifier of beam detection with considerable savings in both installation and maintenance costs. That is, theoretically, individual point detector coverage can be defined as 100 square metres, the radii overlapping to ensure there are no ‘blind spots’. To achieve the 100m range of the illustrated example, therefore, would require twenty point devices, yielding 2,000 square metres coverage.

(Note: the simplified dimensions are merely for example and manufacturers’ installation data should be consulted for all applications. Refer to Clause 22 of British Standard BS 5839-1:2017 for recommendations as to suitability of devices to match applications. Optical beam detectors must also conform to standards such as BS EN 54-12 and UL268. Where point and line-type detectors cannot be used, specialised detectors are also available, namely the Aspirating Detector, e.g. in critical electronic equipment rooms or clean rooms; and the Duct Probe Unit, an option with a comparable sampling principle, primarily specified for detecting the presence of smoke or combustion products in extract ventilation ducting systems.)

Beams in focus: basic principles

For End-to-End optical beam smoke detection, a Transmitter projects an invisible pulsed beam of IR (infrared) light across the protected open space and a Receiver continuously measures the amount of IR light received (IR is the most usual principle). Because the beam is transmitting IR frequencies in only one direction, the reflected signal (‘tuned’ to a pre-set frequency) does not affect the beam when returned to the Transmitter for analysis.

In the absence of smoke, light passes in a straight line (‘Line-of-Sight’) from the Transmitter to the Receiver, which is set to monitor the Transmitter under normal ambient conditions. In a fire, when smoke enters the path of the beam detector, some of the light is absorbed or scattered by the smoke particles, interrupting or partly deflecting the intensity of the received signal, causing an increase in optical obscuration, the percentage of which can be calculated by pre-set values. Depending on the degree of transmitted light blocked by the smoke, a fire is signalled, thus triggering an alarm state.

Complementing the End-to-End type of detection, a Reflective Optical Beam Smoke Detector comprises a multi-tasking transceiver unit incorporating a light Transmitter and Detector on the same device. The light path for the protected space is created by reflecting light emitted by the Transmitter from a Reflector placed opposite, to be converted by the unit into an electrical signal. Any application of this detection mode requires a good ‘Line-of-Sight’ for the beam to successfully align, with the distinct advantage of cabling restricted to only the Detector for ease of maintenance, while the Reflector can be placed in an area whose access may prove demanding in the future.

Although these optical beam solutions apply equally to modern architectural buildings as they do to heritage sites, comparisons of the two techniques can best be appreciated by examining the challenges set by possibly one of the most critical applications for fire protection in large open-volume applications: warehousing and distribution hubs

Warehouses for e-commerce: a critical application

The choice of beam detectors is defined by their function to detect smoke when it is scattered over wide areas, such as those open-volume interiors – transformed by robotics and automation. These are encountered within massive warehousing complexes and distribution hubs reliant on lean (Just-in-Time) supply chains, which are a significant feature of the booming e-commerce economy today.

Yet, for all this sector’s state-of the-art automated efficiencies in the logistics of ‘fulfilment’, it is a fact that fire losses in warehouses astonishingly add up to around 10 percent of the total cost of all fires with average losses exceeding £1,000,000. (In this sector the value of fire-related loss is estimated at £2,250 per square metre, and smoke-related loss at £405 per square metre. Source: BRE.)

The leading UK journal, Warehouse & Logistics News, says, ‘Warehouse fires in the UK monitored in our pages over the last decade point to a pattern of increasingly larger and higher structures with greater volumes of storage intensifying the fire risk, which is compounded by the widespread use of combustible packaging, including expanded plastics, coupled with rising levels of automation and limited compartmentation.’

According to British insurers, the average commercial fire claim over the last decade has risen 165 percent to more than £25,000 per claim; UK businesses lose over £230 million annually from warehouse fires alone, in addition to nearly 1000 jobs. And, whether it’s an insurance scam or a wanton crime, arson accounts for over 25 percent of all warehouse fires.

Large warehouse and distribution centres typically exceed 2,000 square metres and are often in excess of 20,000 square metres, so with such extensive open spaces the choice of beam detection can narrow to the two detection types described: End-to-End and Reflective. The choice is determined by the fire risk assessment and fire safety objectives, guided by these basic criteria.

Selective 10-step specification checklist

1— Choice: Final choice of detection principle is context-dependent for a particular building and centres on three main considerations: the speed of detection/response required; the need to minimise false alarms; and the nature of the fire hazard, when the expected fire is of a specific type (i.e. generative of visible smoke particles or predicted to be otherwise).

2— Alignment: Power is required for both ends of End-to-End beam detection, and both the Transmitter and Receiver need to be durably aligned on to each other, so factors like ‘alignment drift’ due to flex from seasonal building movement, temperature changes or bulk storage pressures need to be foreseen. Essentially, beam detector elements must be mounted on rigid, stable surfaces. Motorised auto-alignment of beams can correct ‘drift’, with alignment maintained once installed. In addition, maintenance and monitoring can be eased considerably for installers by a configuration hub for tailoring beam modes, with the advantages of an event log for traceability.

3— Change of use: Predicted workspace changes that could interrupt the detector path by introducing foreign bodies into the light beam, such as over-height pallet-stacking or a fork lift truck or a ladder, should condition decision-making.

4— Environmental factors: Alignment of Reflective type beams can require at least 0.5 metre clearance down the whole of the beam’s projection and, ideally, applications should keep clear of any reflective surfaces adjacent to the Reflector area – such as windows, glossy walls or, even, cling film on pallets – that could interfere with signals. However, significant advances in light cancellation technology and building movement tracking have been engineered by UK specialists to significantly mitigate these effects to ensure the beam detector performs dependably in a variety of environments.

5— Roof space: Basically, End-to-End beam detectors can operate effectively through narrower ‘gaps’, and are often more suited to more confined areas or those with many obstructions. For spaces where this is not an issue, Reflective systems will usually be more convenient.

6— Standardisation: Optical beam smoke detectors can be specified when it is deemed good practice in terms of integrated safety measures and having consistent maintenance routines standardise on one type of detector for all open-volume areas identified as suitable by a fire risk assessment.

7— Lines-of-Sight: End-to-End beams and Reflective beams have different Lines-of-Sight. A Beam should not be closer to a wall than 500mm. The apex of a roof must always be covered with a beam. While a Beam under a flat roof has a standard ‘side to side’ coverage of 7.5m (giving 15m), under a pitched roof, this distance can be increased by 1 percent for each degree of slope, up to a maximum increase of 25 percent. For a roof angle of 25 degrees, for example, the width coverage would be 9.375m giving a total coverage of 18.75m.

8—Height Constraints/Smoke Stratification: A beam should be no lower than 600mm from the ceiling and no closer than the radius of the manufacturer’s Line-of-Sight guide. However, despite recognition of the possibility of heat (often solar) causing a ‘thermal barrier’ beneath the roof – to thereby create smoke stratification – often such calculations in siting detectors can be misjudged, so supplementary detection may have to be provided at lower levels in anticipation of detecting the stratified layer. This is because such a stratum of heat has the structure of a physical barrier with sufficient density to deflect smoke downwards, away from the sensing paths of detection devices installed. The ‘thermal barrier’ effect can be a direct cause of fire alarm inaction. Optical Beam Smoke Detectors should be used for applications in which smoke stratification is possible.

 

A recent additional approach to defeating the stratification layer by use of beams is to angle them. For example, beams could be angled at 30 degrees up and down across a ceiling. It should be noted that recent research (FIA) indicates that when angled beams are installed they are best deployed in a criss-cross arrangement. This is intended to ensure that the distance to a beam at any height is not excessive, since a smoke plume tends to deepen around the centre where it becomes denser.  Research remains on-going as to the effectiveness of these innovations.

9— 65% cost saving analysis: As a typical example, comparison between optical beam smoke detectors and point-type smoke detectors, for a warehouse of 400 square metres, taking account of cabling installation costs and number of units purchased, yields the following cost-savings:

Total cost fire detection solution using point detection: £5,200

Total cost fire detection solution using beam detection: £1,820

Total saving for using beam solution in this application: £3,380.

Thanks are due to FFE Ltd for technical data and diagrams in support of this article.

This year’s FIREX International (19-21 June, ExCel London) sees ‘next generation’ products launched to the market, with innovations in beam detection at the forefront.  Leading fire detection specialists, FFE Ltd, Stand A250, will be displaying their leading-edge Fireray One standalone beam detection, for rapid one-person-installation, with One Minute Auto-Alignment™ using its integrated user interface to makes it operative 8 times faster than previous detectors.

It also features protocols for corrective compensation for building movement and optics contamination. Also on display is the Fireray® Range, including the Fireray 5000 motorised reflective, auto aligning infrared optical beam smoke detector that can be installed with up to two detector heads per system.

Exhibiting at FIREX 2018: FFE’s Fireray 5000 motorised reflective, auto aligning infrared optical beam smoke detector can be installed with up to two detector heads per system.

Other beam detection technology at FIREX 2018

Hochiki Europe (UK) Ltd, Stand A355, offers the FB-1 addressable beam detector and SPC-ET conventional beam detector; both of which have an auto-align feature and cover a distance of up to 100m. Speak to the Hochiki team to learn more about these beam detectors and their range of beam detector accessories.

Exhibiting at FIREX 2018: SPC-ET conventional beam detector and FB-1 addressable beam detector

Apollo Fire Detectors, Stand A325, is featuring the high-performance Intelligent Auto-Aligning Beam Detector, which combines a transmitter/receiver in the same detector head with an automatic alignment motor, allowing quick and simple installation. The built-in laser provides rapid initial alignment and the detector head will then automatically re-align, compensating for any building movement.

On Stand A380, Polon-Alfa will present a wide range of devices, including their internationally recognised beam Smoke Detector DOP-6001R.

Join the industry at FIREX 2018 as we reflect on a year of hugely significant discussions and see how this is shaping the future of the fire safety industry. Taking place 19-21 June 2018, ExCeL London.

Life safety is a right not a privilege.  Be part of the answer. Register for your free ticket now

The Future of Fire Safety: download the eBook

Is the fire protection industry adapting to the post-Grenfell reality fast enough? At FIREX International 2019, Europe's only dedicated fire safety event, some of the world's leading fire safety experts covered this theme. This eBook covers the key insights from those discussions on the developments shaping the profession, with topics including:

  • Grenfell Inquiry must yield “bedrock change” – and soon
  • After Grenfell: Jonathan O’Neill OBE on how austerity and policy “on the hoof” are hampering progress
  • Hackitt’s Golden Thread: Fire, facilities and building safety
  • Fire safety community has to “get on board” with technological changes

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