 | Fire! What fire?
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| 15 Dec 2009
Kevin Cooper, northern regional sales manager for Gent by Honeywell and author of Gent's latest CPD course, 'Fire! What Fire?' looks at the particular issue of sounder positioning and compliance with BS 5839 Part 1: 2002
Getting a building delivered on time and on budget can cause a major headache for those working on it. These days every minute over deadline costs money, which is why signing off a fire alarm system at the commissioning stage is vital.
Taking the time and trouble to get every detail correct at design stage is crucial in order that when it comes to signing a project off it is a painless process, making life easier for everyone involved.
With fire professionals facing the increasing burden of regulation, the industry has had to raise its game and comply with national standards such as BS5839- 1:2002. This UK code of practice focuses on the fire detection system design, installation and maintenance responsibilities during the life of the system.
At Gent by Honeywell we have been working with the Construction CPD Certificate Service, to deliver a series of seminars in key subject areas affecting the fire industry.
This latest course completes the jigsaw providing guidance for designers on the choice, use and most effective placement of sounders in buildings. This ensures the requirements of BS 5839 Part 1: 2002 are met with regard to adequate provision of audible warning in the event of a fire being detected.
The standard is totally prescriptive when it comes to the audibility levels required in order that a building can be certified compliant. However, the issue facing installers is the lack of guidance in terms of their placement and spacing, unlike automatic fire detectors and manual call points.
In a nutshell, a designer and installer's basic task is to provide recognisable, audible and visual signals at a level that is sufficient to help with the safe evacuation of a building. But audibility is often found to be too low at the commissioning stage.
At the outset, a system designer has to take many factors into consideration including false alarm management, Disability Discrimination Act 1996 (DDA) compliance and plant isolations to name a few.
When considering the fire alarm system evacuation strategy the designer in conjunction with other interested parties such as the End User, Fire and Rescue Services, Building Control and insurers has to take into account the method of evacuating a building. The decisions made will be dictated by the building use, complexity and consequences of evacuating the building, such as loss of revenue and costs to restart production.
The choice of sounder type will be dependant on whether the building is open to the public, in which case, consideration may be given to using voice messaging in the form of a voice evacuation and public address system (PA/VA) or sounders or sensor sounders having voice messages embedded in the devices.
In a hospital where a two-stage system is required – evacuation of area of fire and alert adjacent areas – consideration must be given to systems where the sounders can be fully synchronised and ideally using sounders that can produce two distinct sounder tones or messages.
In most buildings the choice of sounders employed will be down to simple building layout and ease of application.
In addition to the type of sounders to be installed the designer also needs to consider whether all personnel in a building need to be alerted at the same time and modern systems can be programmed to:
• Delayed Sounder Operation – Employed to give staff time to investigate a real incident or a false alarm, often used in schools due to malicious system activation.
• Staff Alarms – Used where it is only necessary to alert trained personnel in a building and fire alarm sounders may not be used but devices such as pagers are employed or coded messages via a PA/VA system. Examples of this use are hospital wards and Aged Persons Homes where staff need to be aware of an alarm but patients do not need to be disturbed unless they have to be evacuated.
• Phased Evacuation – Employed in buildings where attempting to evacuate all personnel or public would be dangerous and escape routes not able to cope, for example, high rise buildings, shopping centres and airport terminal buildings.
As mentioned, BS 5839-1: 2002 is very clear on audibility levels. Generally audibility levels should be 65dBa or 5dBa above ambient noise and in terms of sleeping accommodation it should be 75dBa at the bedhead, but in no circumstance should a sounder exceed 120dBA. Designers must also avoid mixing tones such as bells and sounders.
Designers should consider the ambient background sound levels that will be present in a building once in use. I would advise any designer to conduct a site survey and measure ambient noise levels, such as plant rooms and general office areas, which can be as high as 65dBa, for example.
Other obstacles to take into consideration are doors; sounders are often placed in corridors but you will lose 30dBA through a fire door and 20dBA through a normal door.
There are simple mathematical calculations detailed in the Gent by Honeywell 'Fire! What Fire?' CPD that can predict a sound pressure level at a point between two sounders and through a door, going some way to ensure compliance.
But it's not always just about getting the noise levels right, there are times where a designer needs to supplement sounders with visual indication, such as concert arenas, or compliance with the DDA or simply where sounders are not safe, such as operating theatres.
Again, these must comply with the British Standards and have a flash rate of 30 to 100 per minute and a preferred colour is red.
Finally, when it comes to the commissioning stage and conducting the tests and for some reason the audibility levels have not been met – don't panic. Before installing additional sounders some simple checks can be made to avoid further costs and disruption. Is the sounder set to the highest setting or is the sounder tone set to the correct position?
The Gent by Honeywell 'Fire! What Fire?' CPD course has been written to provide anyone involved in the design, installation, commissioning and maintenance of a fire detection system with some simple hints, tips, guidelines and mathematical calculations to ensure that the system has a chance of meeting the requirements of the British Standard once it has been installed.
The CPD is open to anyone involved in provision of compliant fire detection and alarm systems. We believe that as we are all dealing with life saving technology it is vital that as an industry we are delivering the same high standards.
Kevin's Cooper's top five tips:
1. Don't mix sounders and bells
2. Every time you double the distance from a sounder you lose 6dBa
3. You lose 30dBa every time sound has to travel through a fire door
4. Sleeping accommodation should have a sounder in every bedroom to ensure you achieve 75dBa at the bedhead.
5. If the audibility levels have not been met – don't panic! There is likely to be a simple explanation, such as the sounders are not at the highest setting
For more information, please go to: www.gent.co.uk
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