A Visible Improvement
Audibility?
Audible alarms are firmly established as the warning method for fire detection as well as many other type of safety system and yet their effectiveness has always been limited and now appears to be decreasing further due to changes in people's behaviour.
That may sound like a strange statement to come from someone who works for an organisation that provides literally millions of alarm sounders of many different types every year, but it is I think a fair assessment.
Alarm sounders, or Audible Alarm Devices (AADs) in current parlance, have not changed in their basic function since their conception; that is to make a noise to warn of an emergency. This is in contrast with other elements of safety systems, such as detection technology which constantly advances to provide earlier and more accurate analysis of emergency conditions and has benefitted greatly from developments in electronics and software. So why haven’t alarm sounders moved on at the same pace or in the same way? The underlying technology irrefutably has changed and has brought benefits to efficiency and cost, but the basic function remains unchanged. A 50 year old bell would be just as effective as any current sounder. In fact many bells Fulleon still provides are based on designs from the 1970s.
The limiting factor for audible alarms is people, the basic auditory sense is not evolving so the basic technology is locked into providing an acoustic signal covering a small frequency range.
The observation that the effectiveness of audible alarms is diminishing is based on the rapid changes in society and the built environment.
The often casual regard for alarm signals is born out of the sheer number of alarms we endure every day, right from the microwave "ping" to the invariably ignored car alarm and the ever present mobile phone. The difficulty of identifying an important life safety alarm is compounded by the lack of a nationally recognised UK fire alarm signal, so even critical signals can be consigned to the general morass of contemporary noise.
Mobile technology has spawned the "Podestrian" who are estimated to be involved in as many as 10% of minor traffic accidents (Telegraph Oct 2008). The use of music players and mobile phones either masks the noise of approaching traffic or distracts the user to the exclusion of normal safety considerations. While the “Podestrian” is an essentially external manifestation, there are a surprising number of employees using personal music sources to ease the boredom of repetitive jobs and are quite oblivious to their immediate surroundings.
Normal hearing is taken for granted by most of us, but there are estimated to be nearly nine million people who are deaf or hard of hearing of which 700,000 are thought to be severe to profoundly deaf. (RNID 2005). For these people sounders are of little use. In addition, increased concerns over health and safety are encouraging the greater use of ear defenders in the work place and so there is a sizeable contingent of people who work in environments where any alarm sounded is unlikely to be heard over process noise and may also be rendered below a normal hearing threshold even when the noise has stopped because of the hearing protection in use.
Audible alarms are, however, still treated as the most effective alarm method overall; they are cost effective to install and the efficacy of the installed system can be easily assessed with commonly available instruments, but in many situations they do need to be supplemented.
Visual Alarm Devices
To overcome the issues mentioned above communication needs to be broadened to stimulate senses other than hearing alone and in 2010 the focus is falling on visual alarms.
Visual Alarm Devices (VADs) have been used to supplement audible alarms for many years either as separate units or integrated with the alarm sounders themselves. The awareness of the need to complement audible alarms has received more attention in recent years, no doubt driven by observance of the requirements of the Disabilities Discrimination Act (DDA).
As the use of visual alarm devices has grown there has been a consequent increase in the loading placed on alarm circuits and Fulleon has responded by producing more efficient visual alarms and also by developing versions of all of its sounders with integrated visual alarms to reduce the power and ease installation requirements.
The problem that has been faced by both manufacturers and users is that in Europe there has been no standard method for the measurement of visual alarms or any documents to provide guidance on how to use them within a building. The lack of standards has given rise to manufacturers rating their products in a number of ways, most choosing to use joules, the amount of energy discharged in the flash tube, but this has only a tenuous relationship to the amount of the light produced and nothing to do with where the light goes. Now this has not really mattered as the installers and systems designers had little idea of how bright the visual alarms needed to be, so the criteria for choice often boiled down to power consumption. Aware of the need for a more meaningful comparison of light sources, whether xenon flash tube or LED, Fulleon took the decision to rate all visual alarms by light output, based on testing to the American UL standards and were fortunate to be able to call on the facilities of their sister company Cooper Wheelock for the measurements. This aided comparison between Fulleon products, but did little to allow comparison with competitors or with the decision of what to use in any particular application.
As in any market where there is a requirement, such as the DDA, without any related regulation, there has been much confusion and misinformation in fire industry, some arising through the innocence of ignorance and some intended to exploit that ignorance. Many systems installed with the best intentions may well fall far below the standards required.
Salvation
2010 Will see the introduction of two important documents to the UK. The first: EN54-23 2010 Fire detection and fire alarm systems - Part 23: Fire alarm devices - Visual alarm devices, is close to publication, although at the time of writing it is not exactly clear when. This will provide a method of test and classification for VADs, allowing manufacturers to rate their beacons/strobes/VADs in a way that allows the system designer to compare and assess performance and suitability for an application. The second document being prepared is by a joint task group from BRE/LPC and the FIA and is targeted for publication as LPS 1652 Code of Practice for Visual Alarm Devices used for Fire Warning, later this year. This document will directly complement EN54-23 and provide guidance on how to use the test data to give effective results in typical situations.
EN54-23 is a parallel to EN54-3 for audible alarms, but differs in that VADs are classified into one of three categories by their intended application. Two of the categories for “Wall” mounted or “Ceiling” mounted products have specific targets for light distribution patterns, whereas the third category “Open” allows the manufacturer freedom to specify particular characteristics which fall outside of the other two categories.
The area of coverage determined by the testing is based on the distance at which the “required illumination” is achieved, which is 0.4lumens/m2 on a surface perpendicular to the direction of the light emitted from the VAD.
The Wall and Ceiling classes will require different light dispersion characteristics, the Wall format requiring the manufacturer to state a mounting height on a wall, minimum 2.4m and the width of a square room over which the VAD will provide coverage. So the data on the beacon could read W-2.4-6, ie mounted at a height of 2.4m the VAD will cover a room 6m square. The VAD will therefore be required to cover a volume; below its mounting height. Any light going upward will be wasted as far as this categorisation is concerned.
Similarly the Ceiling format will be assessed on the diameter of its coverage volume when mounted at a height of 3, 6 or 9m. The VAD in this case needs to radiate more or less equally all around.
The Open class will both allow existing designs to be measured, even if not optimised for wall or Ceiling mounting, or permit a manufacturer to design dispersion characteristics specifically for certain applications, maybe to suit corridors or where mounting heights fall outside those prescribed by the standard.
LPS1652 aims to provide guidance on how the data generated by EN54-23 can be used to plan a system and also fills in many of the considerations absent from the information provided regarding visual alarms in the fire industries bible: BS 5839-1:2002+A2:2008 Fire detection and fire alarm systems for buildings. Code of practice for system design, installation, commissioning and maintenance. A key element of the work that has gone into LPS1652 is the assessment of how effective VADs are in practical situations and how the basic data from EN54-24 can be adjusted to suit variations in viewing conditions within a building. This takes into account both direct and indirect viewing of the light from a visual alarm as well as the effects of ambient light levels in the locality.An outcome of these two documents is that VADs used with fire systems are likely to need higher light outputs than are currently employed to meet the requirements of the DDA. Low power devices whether xenon or LED based are likely to be effective only in smaller spaces similar to toilet cubicles; larger areas will require higher output devices with consequently higher power requirements
Undoubtedly this will affect the present generation of visual alarms whether and will particularly test the ingenuity of the engineers working on the next iterations of addressable products.
Future considerations
It should be remembered that VADs are only one solution to supplementing audible alarms and that they too have many limitations on their effectiveness which will require more careful planning than for an audible system.
Increased costs to both manufacturers and installers brought by the new standard will encourage the investigation of other alarm methods such as portable tactile devices, mobile phones and so on.
Despite its shortcomings and the changing behaviour of the public there appears to be little on the horizon to displace the audible alarm from its place as the staple for alarm systems. Voice alarm is commonly used to improve information and understanding, but does not help where a sounder is inaudible or masked by other activities. The way forward appears to be more integration between different techniques and may require solutions tailored more specifically to individuals and locations.
For further information, please contact Cooper Fulleon on: info@fulleon.co.uk
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