An automatic fire alarm system is designed to detect the unwanted presence of fire by monitoring environmental changesassociated with combustion. In general, a fire alarm system is classified as either automatically actuated, manually actuated, or both. Automatic fire alarm systems are intended to notify the building occupants to evacuate in the event of a fire or other emergency, report the event to an off-premises location in order to summon emergency services, and to prepare the structure and associated systems to control the spread of fire and smoke. Kerberos represents BOSCH Fire Alarm Systems and configurations in the Lao PDR.
- Fire alarm control panel: This component, the hub of the system, monitors inputs and system integrity, controls outputs and relays information.
- Primary Power supply: Commonly the non-switched 120 or 240 Volt Alternating Current source supplied from a commercial power utility. In non-residential applications, a branch circuit is dedicated to the fire alarm system and its constituents. “Dedicated branch circuits” should not be confused with “Individual branch circuits” which supply energy to a single appliance.
- Secondary (backup) Power supplies: This component, commonly consisting of sealed lead-acid storage batteries or other emergency sources including generators, is used to supply energy in the event of a primary power failure.
- Initiating Devices: This component acts as an input to the fire alarm control unit and are either manually or automatically actuated. Examples would be devices like pull stations or smoke detectors.
- Notification appliances: This component uses energy supplied from the fire alarm system or other stored energy source, to inform the proximate persons of the need to take action, usually to evacuate. This is done by means of a flashing light, strobe light, electromechanical horn, speaker, or a combination of these devices.
- Building Safety Interfaces: This interface allows the fire alarm system to control aspects of the built environment and to prepare the building for fire, and to control the spread of smoke fumes and fire by influencing air movement, lighting, process control, human transport and exit.
- Manually actuated devices; Break glass stations, Buttons and manual fire alarm activation, are constructed to be readily located (near the exits), identified, and operated.
- Automatically actuated devices can take many forms intended to respond to any number of detectable physical changes associated with fire: convected thermal energy; heat detector, products of combustion; smoke detector, radiant energy; flame detector, combustion gasses; fire gas detector, and release of extinguishing agents; water-flow detector. The newest innovations can use cameras and computer algorithms to analyze the visible effects of fire and movement in applications inappropriate for or hostile to other detection methods.
- Audible, visible, tactile, textual or even olfactory stimuli (odorizer) to alert the occupants. Evacuation signals may consist of audible or visible appliances with a distinct audible tone or speakers to deliver live or pre-recorded instructions to the occupants.
- In the United States, fire alarm evacuation signals generally consist of a standardized temporal code 3 audible tone, with visual notification in all public and common use areas. Emergency signals are intended to be distinct and understandable to avoid confusion with other signals.
Other methods include:
Audible textual appliances, which are employed as part of a fire alarm system that includes Emergency Voice Alarm Communications (EVAC) capabilities. High reliability speakers are used to notify the occupants of the need for action in connection with a fire or other emergency. These speakers are employed in large facilities where general undirected evacuation is considered impracticable or undesirable. The signals from the speakers are used to direct the occupant’s response. The system may be controlled from one or more locations within the building known as Fire Wardens Stations, or from a single location designated as the building Fire Command Center. Speakers are automatically actuated by the fire alarm system in a fire event, and following a pre-alert tone, selected groups of speakers may transmit one or more prerecorded messages directing the occupants to safety. These messages may be repeated in one or more languages. Trained personnel activating and speaking into a dedicated microphone can suppress the replay of automated messages in order to initiate or relay real time voice instructions.
Emergency Voice Alarm Communication Systems
- Some Fire Alarm Systems utilize Emergency Voice Alarm Communication Systems (EVACS) to provide pre-recorded and manual voice messaging to building occupants. Voice Alarm systems are typically used in high-rise buildings, arenas and other large “defend-in-place” occupancies such as Hospitals and Detention facilities where total evacuation is difficult to achieve.
- Voice-based systems provide response personnel with the ability to conduct orderly evacuation and notify building occupants of changing event circumstances.
- In high rise buildings, different evacuation messages may be played to each floor, depending on the location of the fire. The floor the fire is on along with ones above it may be told to evacuate while floors much lower may simply be asked to stand by
An important consideration when designing fire alarms is that of individual zones. Specifically:
- A single zone should not exceed 2,000m² in floor space.
- Where addressable systems are in place, two faults should not remove protection from an area greater than 10,000m².
- A building may be viewed as a single zone if the floor space is less than 300m².
- Where the floor space exceeds 300m² then all zones should be restricted to a single floor level.
- Stairwells, lift shafts or other vertical shafts (non stop risers) within a single fire compartment should be considered as one or more separate zones.
- The maximum distance traveled within a zone to locate the fire should not exceed 60m.