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Fire alarms have a very important role in buildings, since they warn occupants when a fire is detected. Modern fire alarm systems can also alert the local fire department, ensuring a quick response. They can also be configured notify building managers who are away from the building, and other key personnel.
When building systems malfunction, they normally cause disruption for occupants. For example, an HVAC issue can make indoor temperatures uncomfortable. However, when fire protection measures fail, human lives and property are at stake. For this reason, there is zero tolerance for failure when designing and installing a fire alarm system. Proper maintenance is also important to ensure ongoing protection.
Depending on the type of building and local building codes, some fire protection measures may be optional. However, building owners should consider fire alarms even when they are not required in a specific project, due to the protection they offer.
Even if a building is never affected by fire in its entire service life, fire alarms and other protection measures bring several benefits. For example, insurance companies may offer better plans and lower premiums when a building is well protected against fire. In buildings with commercial spaces for rent, reliable fire protection can help convince tenants to sign a contract.
Fire Alarm Design: Meeting Standards and Building Codes
Since fire alarms have a critical function in buildings, they are subject to stringent design standards. While this increases the complexity and installation cost of fire alarm systems, it is necessary to ensure they will always work properly.
The industry standard for fire alarms is the NFPA 72 National Fire Alarm and Signaling Code, and there are also design requirements in the NFPA 101 Life Safety Code. These standards were developed by the National Fire Protection Association, which also provides design requirements for sprinkler systems (NFPA 13), and other fire protection measures and building systems.
- NFPA 72 covers all requirements of fire alarm systems: design, testing, maintenance, operation and minimum performance requirements.
- On the other hand, NFPA 101 covers more general requirements, such as the occupancy groups where fire alarms should be used.
- Since fire alarm systems have many electrical components, they must also meet the requirements of the NFPA 70 National Electrical Code. Any electrical installation that does not follow code creates a fire hazard, and this includes fire alarm systems.
Local governments use NFPA standards as reference when establishing the fire protection requirements in their building codes. Building owners with properties in many cities must be aware that there are code differences. Working with a qualified engineering firm is important to make sure that local requirements are met.
In addition to meeting NFPA standards, fire alarm systems must also use components that are listed by Underwriters Laboratories (UL) or a similar certification laboratory. If the connections and devices of a fire alarm system create a fire risk themselves, they defeat their own purpose.
When new fire protection codes are published, existing fire alarm systems do not always require an upgrade. However, if a specific feature is considered critical, it may be required retroactively for existing fire alarm systems. Fire protection engineers recommend getting a flexible design that is easy to upgrade if needed.
The following recommendations can improve the reliability of fire alarm systems in the long run:
- The design should consider future component failures, and simplify their replacement.
- Specifying the right equipment, considering situational and environmental conditions.
- Using listed enclosures (UL or equivalent) to protect components when needed.
- Working with reliable manufacturers who have local presence, to ensure the availability of replacements when needed.
In New York City, retroactive fire protection requirements are mandated with Local Laws. An example is Local Law 26 of 2004, which many fire sprinklers mandatory for many buildings.
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Information technologies have made fire alarms more reliable. Older fire alarm systems can only monitor general zones, while newer installations have addressable components. For example, older installations only indicate the zone where a fire occurs, while modern systems can identify the exact fire or smoke sensor that activated the fire alarm.
Existing fire alarm systems can be upgraded without a complete replacement. Normally, they only need additional wiring and communication features. The circuit boards on older control panels will likely need a replacement to use addressable components.
In the NFPA 72 standard, addressable circuits are designated as signaling line circuits (SLC). Some equipment suppliers produce SLCs that support dozens of devices. However, fire protection engineers don’t recommend using SLCs at full capacity, leaving space for additions or modifications. Having too many devices on the same circuit is not recommended either, since a fault can disable all of them simultaneously.
Signaling line circuits are classified into Class A and Class B, based on how they are wired:
- Class A circuits use 4 wires, providing a redundant connection for all devices. If one of the wires is damaged or disconnected, the fire alarm can continue operating.
- Class B circuits only use 2 wires, and all devices depend on a single connection. The circuit cannot operate properly if one of the wires is damaged or disconnected.
Thanks to their redundancy, Class A circuits offer better protection than Class B circuits. Wiring and installation costs are increased with Class A circuits, but in return the fire alarm system becomes more reliable.
Oversizing SLCs is not recommended by fire protection engineers. Larger wires increase the capacitance of an SLC, causing signal distortion and slower communication. On the other hand, the notification appliance circuits (NAC) that power horns and other indicating appliances can be oversized with no problem.
Fire alarms can also be designed as part of an emergency communication system (ECS). Unlike a conventional fire alarm system, which only detects fire, an ECS notifies emergency conditions of many types (including fire).
