FIRE ALARM SYSTEMS
WHY HAVE A FIRE ALARM SYSTEM?
The answer to this question depends on the premises in question and the legal requirements. In large high-rise buildings, such systems are essential to warn all occupants that a fire or emergency situation exists and the system is used to control evacuation in an orderly way. Large sites with a retained fire brigade may require the system to call the brigade and direct them to the area of risk. The property may have considerable intrinsic value and the insurers either require a fire detection system or may incentivise its use.
The building may be unoccupied for periods where equipment is still powered and the owner wishes to ensure that if anything goes wrong fire fighters are called to the scene in a timely manner.
Fire alarm systems are often used for other purposes as well as fire detection and alarm, such as bomb alert signalling, monitoring systems for high risk equipment or places, emergency call systems and even class change systems for schools.
Sometimes fire detection and alarm systems are used to compensate for structural fire protection shortcomings or to give special cover for items of high value. Whatever the reason, an automatic fire detection and alarm system generally provides a network of manual callpoints, fire sensors and alarm warning devices over the area covered. It is, in effect, the eyes and mouth of the building to constantly monitor the building and warn if a fire breaks out, or is suspected. In the same way we do if we see flames or smell burning.SYSTEM DESIGN
In order to undertake the process of designing a fire system for a building it is necessary to have a sound understanding of the relevant design standards, the legal framework surrounding building safety legislation and a sound working knowledge of product application theory. The importance of consultation with all relevant parties cannot be overstressed, neither can the importance of specialist advice in relevant areas. The following system design process is intended to give a reasonable overview of all the areas of knowledge required for the successful design of a fire alarm system.
OVERVIEW OF CERTELEC'S DESIGN PROCESS
The following describes a typical fire alarm system design process, after each item a section number is provided which relates to the area within the design guide where further information can be found.
Understand the reasons for installing the fire alarm system in the specific property
- Conduct a risk assessment to help determine requirements
- Consult with all interested parties
- Decide on the relevant design standard
- Establish if third party approval is required - for equipment and/or installation.
- Decide on the type of alarm technology to be used
- Decide on the appropriate protection category and extent of coverage where relevant- Plan the zoning of the building
- Select and position relevant system components
- Select the appropriate detectors for each area
- Position the detectors
- Select suitable callpoints and position at appropriate locations
- Agree on the means of summoning the fire authority
- Plan the alarm signalling arrangements (sounders, beacons, pagers etc)
- Select a suitable panel (suitably sized and rated with adequate standby autonomy)
- Review the design such as to - minimise the potential for false alarms
If a fire detection or alarm system is required then it is necessary to establish the specification for the system. In the UK BS5839-1:2002 is normally the appropriate standard for commercial and industrial premises. BS5839-6 relates to residential premises and other standards such as HTM 82 for hospitals relate to specific building types.
5.1 LIFE SAFETY
Category M systems are manual systems and rely on the occupants of the building discovering the fire and acting to warn others by operating the system. Such systems form the basic requirement for places of employment with no sleeping risk. Manual cover should be included in all Life Safety systems except L5 systems where it may or may not be provided. In addition to manual means of triggering an alarm, L category systems will also normally have an element of coverage using automatic fire detection such as smoke or heat detectors. The precise classification depends on the nature of the area(s) provided with automatic protection Category 5 systems are the ‘custom’ category and relate to some special requirement that cannot be covered by any other category. Where such systems are specified careful reference much be made to the objective of the cover. Category 4 systems cover escape routes and circulation areas only. Detectors might be sited in other areas of the building, but the objective is to protect the escape route. Category 3 systems provide more extensive cover than category 4. The objective is to warn the occupants of the building early enough to ensure that all are able to exit the building before escape routes become impassable. Category 2 systems relate to automatic fire protection in defined areas of the building as well as satisfying the requirements of category 3. The wider cover would relate to parts of the building considered to have a high level of risk. With category 1 systems, the whole of a building is covered apart from minor exceptions. 5.2 PROPERTY PROTECTION
Category 2 systems provide fire detection in specified parts of the building where there is either high risk or where business disruption must be minimised. The system is installed throughout the building - the objective being to call the fire brigade as early as possible to ensure that any damage caused by fire is minimised. Small low risk areas can be excepted, such as toilets and cupboards less than 1m².