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A fire alarm system is an active fire protection system that automatically (or manually) detects a fire, or the effects of fire, and performs one or more of the following functions: • warns the building occupants via audible (and possibly visual) alerting devices
A fire alarm system will typically include:
If connected to a remote receiving centre it will also include remote signalling equipment.
The protected premises will generally be subdivided into detection “Zones”. The area of a Zone is typically limited to what can readily be searched by a fire fighter in a short period of time.
An indication of the fire’s approximate location will be provided to attending fire fighters on an “index” map of the building. Analogue Addressable Systems are also able to display a text description of the location of the activated detector or manual call point.
The overall design objective of a fire detection and alarm system is to detect fire as early as possible. However it also needs to resist environmental influences and other potential sources of false activation. Once a fire is detected, the actions taken by the system must be consistent with the building’s overall design, its evacuation plan, and the integrated fire protection strategy for the premises.
For all but the simplest of buildings and risks, fire alarm system design is a specialized activity. It should be performed by a competent engineer with experience in fire protection, and who is trade-certified to act in this capacity. The overall fire safety design for a building is usually done in conjunction with the Architect’s design team during the design phase of the building project, and detailed in a “fire report.” The detailed component selection and final equipment layout and configuration/programming for a fire alarm system is typically performed by a certified fire alarm contractor, in accordance with the requirements of the fire report, during the building’s construction and fit-out phases.
The design of building fire alarm systems in New Zealand is almost always required to be in compliance with New Zealand Standard NZS 4512:2010 Fire Detection and Alarm Systems in Buildings. This national standard covers design, installation, extension, modification, commissioning, testing and maintenance. It also sets down minimum levels of trade qualification for those working on fire alarm systems, and requires independent third-party inspection/audit of all new systems, and all significant system alterations and extensions.
NZS 4512:2010 is the only “Acceptable Solution” for fire detection and alarm systems under the NZ Building Code Compliance Documents. Confirmation by an independent third party inspector of full compliance with this standard generally ensures acceptance under the Building Code regime by the Building Consent Authority (local council). Alternative “Engineered Solutions” are permitted, however these require a building-specific Professional Fire Engineer’s design which must undergo a series of professional reviews in order to be accepted by the Building Consent Authority. In general, such engineered solutions are invoked to allow trade-offs between one compliance parameter and another, or to accommodate unusual building features or occupancy.
Extensions of existing systems should be performed with the same attention to design, but must also consider the capabilith of the originally-installed fire alarm system. The Standard has strict rules about the intermixing of system components, so the equipment used for extensions will generally need to have listed compatibility with the existing equipment. NZS 4512:2010 also has requirements for independent third party inspection of significant system extensions (adding zones or changing the control panel).
Fire alarm systems have input devices connected to them to detect fire or smoke. Below is a list of common detection devices found on a fire alarm system:
Multiple Sensor Detectors – recent advances in technology have allowed for multiple detection principles (combinations of: heat, smoke, CO, flame) to be incorporated into one detector. These so-called “multi-sensor detectors” are becoming increasingly common. Their particular attractions are enhanced detection performance combined with better immunity to false activations (nuisance alarms).
The days of fire alarm bells are well and truly gone for new installations, although bells and sirens may still be present in historical systems. For new installations, a specific standard “rising whoop” tone is now mandatory, with an interspersed verbal message (except for very small buildings). The voice message will typically be something like “Evacuate the building using the nearest fire exit”, and provides positive direction to building occupants.
Although point-type sounders are available to produce this standard alerting signal, it is now most common for a central tone and voice generator/amplifier to be located at the fire alarm control panel, with a network of loudspeakers to reproduce the signal around the building.
Alerting device power comes from the fire alarm’s standby battery, and is not reliant on building mains power, which may well fail during an emergency.
The alerting signals through a building must be identical. For modest additions to existing systems, it is permissible to retain the existing sound (siren, bell). Also on large sites where there is a uniform alerting signal, it is permissible for additional (new) systems to retain the same signal (even if it is, say, a bell sound), however a voice message must be provided on the new system.
A EWIS (Emergency Warning and Intercommunication System) is an enhanced system for fire alarm alerting and evacuation control in larger or more complex buildings. Instead of the whole building receiving the (evacuation) alerting signal simultaneously, the premises are instead subdivided into multiple evacuation zones. In response to signals from the fire alarm system, the EWIS system controls a zone-by-zone staged/phased evacuation according to a pre-programmed scheme.
As with “all out” evacuation, the EWIS system generates the standard “rising whoop” evacuation signal and plays a voice message with evacuation instructions. With an EWIS these messages can be customized for various types of installations, and multi-lingual capabilities are usually available. In addition, a preliminary “Alert” tone, with separate verbal message, can be played to zones that have not (yet) reached the evacuation stage. In a high-rise, for example, this would typically mobilise evacuation (floor) wardens.
A EWIS system is also designed to enable either the fire service or a designated building warden to take manual control of the evacuation, including directing Public Address (PA) messages to all or selected evacuation zones.
An (optional) Emergency Intercommunication (warden telephone) system allows building wardens or fire-fighting personnel to communicate with the master evacuation control panel to coordinate evacuation efforts.
The rationale behind audio evacuation systems is, though conventional fire alarm notification devices alert occupants of a building to the presence of an emergency, they do not provide detailed information to the occupants, such as evacuation routes or instructions. Nor do they allow occupants in the greatest danger to have unimpeded access to escape routes.
EWIS systems usually permit multiple messages. For instance, "non fire" messages can be programmed for situations such as a hazardous material spill, gas leaks, security breaches, etc.
They can also be used to provide non-emergency building Public Address facilities.
Historically, the New Zealand Building Code Compliance Documents designated EWIS systems as “Type 8” Voice Evacuation Systems and they were mandated for new buildings primarily in healthcare, high-rise, and large crowd occupancies (cinemas, stadiums, shopping malls). This is no longer the case and such occupancies are now expected to be subject to specific fire engineering design.
Under NZS 4512:2010, EWIS systems are required to comply with AS 2220 part 1: 1989 and to be installed to AS 1670.4: 2004.
The reliability of fire alarm systems is required to be much higher than some other building systems, due to the reliance placed on active fire protection systems for life safety. This is a fundamental consideration underpinning the NZ building Code and the associated Compliance Documents. Designs therefore tend to be conservative, based on risk and experience.
Mains power supplies are expected to fail under fire conditions, so battery back-up is expected. Batteries are known to fail, so are tested almost continuously by the fire alarm system both for continued presence and capacity. Circuits are automatically supervised for fault conditions, producing fault signals in case of failure.
Sometimes wiring circuits are required to be installed with redundant paths.
Because reliability is so important, monthly testing and annual surveying of fire detection and alarm systems by a qualified trade practitioner is mandatory. Fire detection systems are invariably listed on a building’s compliance schedule, and evidence of satisfactory test and survey must be submitted to the Territorial Local Authority before the building’s annual warrant of fitness (for continued occupation) can be issued.
The Compliance Documents for the New Zealand Building Code define several “types” of Fire Alarm systems. These are usually stated in Building Consents and are (very briefly) summarised as follows:
For a fuller description, please consult the NZ Building Code Compliance Documents themselves, available for download here at MBIE website
“Conventional” fire detection and alarm systems are hard-wired to each group of detection devices. The control and indicating equipment is unable to distinguish alarm and fault conditions from individual devices within the group, and the actual alarm decision is made at each device.
“Analogue Addressable” systems provide information about the exact location and status of every device at the control and indicating equipment. Furthermore, the alarm decision is generally made by the control equipment, rather than the detection device itself.
In general, Analogue Addressable systems offer the following distinct advantages:
Overall, these technical advantages increase system performance and reduce unwanted building evacuations and calls to the Fire Service. Although analogue addressable systems can cost a little more initially, this can be recouped in reduced maintenance and false alarm costs, while offering the benefits of superior performance.
Technology is improving all the time; however the false alarm rate from fire detection and alarm systems remains fairly constant – NZ Fire Service figures indicate that more than 90% of such calls are unwanted (“false”) alarms. With more and more systems being installed, the overall demand on Fire Service resources is increasing.
False alarms disrupt – business, staff, and customers. Repeated false alarms lead to complacency, and alarms being ignored. The Fire Service also levies callout charges for systems which repeatedly give unwanted alarms.
Correct detector selection and placement is of utmost importance in reducing false alarms. Other important measures are the control of building work, good building maintenance, regular detection system maintenance, and premises security
Smoke Alarms are primarily used in domestic residential situations. They are different from the Smoke Detectors used in Fire Detection and Alarm Systems because they have a built-in alerting device, and are designed, tested, and manufactured to different standards. The most common examples are the battery-operated units available in many hardware stores.
Early warning of the presence of smoke in a building is critical to life safety. Some fires can grow rapidly making escape very difficult, especially if the occupants are asleep, intoxicated, and/or the escape routes are smoke-logged. The time difference between escaping from a burning building or dying in a fire can often be measured in seconds. Sometimes fires can smoulder for hours, filling the premises with toxic fumes. Without the early warning provided by a smoke alarm, occupants can perish as they sleep without ever waking.
“Type 1” Smoke Alarms are mandatory under the New Zealand Building Code Compliance Documents for new installations in domestic residential situations, including detached dwellings. Stand-alone battery-powered units are the minimum, however for optimal life-safety benefits, or larger dwellings, interconnected units are necessary to provide adequate sounder audibility to wake all occupants. Permanently-wired mains power, with long-life battery backup, is the most reliable configuration.
Because they have none of the inherent self-supervision or maintenance regimes of commercial Fire Detection and Alarm Systems, and they are not listed on a building’s compliance schedule for occupancy warrant of fitness, it is imperative that dwelling owners conduct their own regular maintenance and testing of their smoke alarms.
These procedures include: annual cleaning with a vacuum cleaner (no disassembly), monthly testing with the alarm’s “test” button, and regular battery replacement (interval depends on type – annual for ordinary dry-cell batteries).
A New Zealand Standard NZS 4514:2002 Interconnected Smoke Alarms for Single Household Units exists, however it is not mandatory. Under the current “Type 1” Compliance Document regime, the requirements are contained in section F7/AS1, and installation is required to be to AS 1670.6 and the manufacturer’s instructions.
Commercially-available domestic smoke alarms are usually either ionisation chamber or photoelectric (light scattering) types. Considerable debate has taken place in the media as to which technology gives better performance, especially considering the price difference between the two is minimal (historically, photoelectric was considerably more expensive and drained batteries much faster).
Ionisation smoke alarms respond most readily to the invisible products of combustion typical of fast flaming fires, but have a much slower response to smouldering fires. Escape routes can therefore become more smoke-logged before a warning is given. Ionisation detectors are prone to nuisance alarms from cooking activities, so must be sited well away from kitchens. They also contain a (very small) radioactive source, which in some countries presents environmental issues (not in New Zealand, where, under current legislation, they are permitted to be disposed of in the landfill with normal household rubbish).
Photoelectric smoke alarms respond most readily to visible smoke, so can give a slower response to fast flaming fires with invisible products of combustion. They are also prone to nuisance alarms from steam, so must be sited well away from bathrooms and saunas.
Photoelectric is the preferred smoke alarm technology for life safety in new installations, as it offers the most consistent early detection performance across all the likely fire scenarios in a residential environment.