Fire Alarm Systems

fire alarm

What is it?
A fire alarm system uses devices like smoke, heat, and carbon monoxide detectors to sense a fire and alert area occupants of danger. Alarm alerts are provided through audio appliances such as speakers and horns while visual alerts are made with bright flashing strobe lights.

How does it work?
Conventional fire alarm systems use dedicated circuits (called “zones”) to group a number of devices together. A signal from any one of the devices in a zone is representative of the entire zone. For example: In a two-story building all of the detectors on the first floor are grouped together as Zone 1. When Zone 1 goes into alarm all you really know is that there is an alarm on the first floor. It could be in a lobby, break room, or hallway. A conventional system will only identify signals by zone and not by particular device.

Addressable fire alarm systems are intelligent. Each device can be programmed into the system with a unique address and given a description. For example; D012345 Smoke Detector 1st Floor Lobby. This makes it very easy to identify exactly where a device signal originates. Addressable fire alarm control panels can also be linked together in a network. The unification of fire alarm systems across a multi-building or campus environment can simplify the administration and maintenance of large scale systems.

Devices & Functions

  • Fire Alarm Control Panel
    The control panel receives signals from the fire alarm initiating devices (smoke detectors, heat detectors, pull stations) located throughout the building and communicates to the Central Monitoring Station. If an initiating device goes into alarm the panel will send power to the notification appliances to evacuate the building.
  • Voice Evacuation
    Fire alarm voice evacuation systems use pre-recorded voice messages to notify occupants of a fire and evacuate the building. Example: “Attention Please, Attention Please, the fire alarm in this building has been activated. Cease operations and proceed to the nearest fire exit and leave the building. Do not use elevators.”
  • Mass Notification
    Mass notification systems are similar to voice evacuation but deliver announcements for non-fire types of emergencies. For some dangers, the best course of action is to remain in place. The mass notification system will give instructions specific to the type of emergency announced. Common types of emergencies announced through mass notification are hurricane, flash flood, and terrorist alerts.
  • Annunciator
    Annunciators are located in key areas of a building and connect directly back to the fire alarm control panel. Their purpose is to provide fire alarm system information and status quickly without a search through the building to find the control panel location. Annunciators are usually located at the main entrance of a building for emergency responders to quickly determine where the fire is.

Initiating Devices

Smoke Detectors

  • Ionization
    Ion smoke detectors are very sensitive to particulates in the air and may false alarm in dusty environments. But, because of their extra sensitivity, they are better at early flame detection. The fire sensing technology in ion smoke detectors uses radioactive matter to charge the air inside the unit. When smoke enters the detector it disrupts the charged air and activates an alarm. Note: System Sensor a global manufacturer of fire alarm devices discontinued their ion detector production in April 2015 citing low customer need.
  • Photoelectric
    Photo smoke detectors use a beam of light housed in a chamber. As smoke fills the chamber it scatters the light and forces it to diffuse onto a sensor located adjacent to the beam. When the light hits the sensor an alarm is activated.
  • Aspirated
    Aspirated Smoke Detectors collect air through plastic tubing or pipes and sense smoke base on the number of particulates in the sampled air. ASD’s are very accurate and sensitive. They can detect smoke before is visible to the naked eye.
  • Beam Detector
    Beam detectors project a beam of light to a reflective point and sense the level of interference that is caused by smoke or dust particles in the air. They are useful to cover wide open areas that would be difficult or expensive to protect with traditional detection methods. A couple of common places where beam detectors are used are skylights and warehouses.

Heat Detectors

  • Fixed Temperature
    Obviously, heat detectors detect heat, but there are some subtle differences in how some of the various types function. The fixed temp type will signal an alarm when a predefined temperature is reached. The temperature rating of the heat detector is selected based on where and how the heat detector will be used. Common fixed temp ratings are 135° and 200°F.
  • Rate-of-Rise
    Rather than alarm at a given temperature, rate-of-rise types monitor the environment of a sharp increase in temp over a short period of time. Temperature increases of 12° to 15°F in under one minute will activate the detector.
  • Carbon Monoxide Detectors
    Unlike carbon dioxide, which is vital to life on earth, carbon monoxide kills an average of 170 Americans every year, even more if you count automotive related incidents. These detectors operate similar to a rate-of-rise heat detector. The device will alarm if a defined level of gas becomes present in the environment within a specified period of time.
  • Multi- Criteria Detectors
    These detectors offer an excellent way to reduce the number of devices in an overall system design by combining multiple types of detection metrics in one device.
  • Pull Station
    Pull stations are used to manually activate a fire alarm system. They are usually wall mounted near an entry or exit locations throughout a building. The intent is to provide an easy way for people evacuating the building to activate the fire alarm system if it has not already been set off.

Notification Appliances

  • Strobe
    A strobe is a visual notification device. It is nothing more than a bright flashing light. The visual cue is intended to gain the attention of building occupants and make them aware that there is an active alarm and immediate attention is required. Strobes are especially effective for the elderly and people that suffer from hearing loss.
  • Horn; Horn Strobe
    Horns are a very effective method of notification. When the fire alarm system goes into alarm the horns will sound to notify occupants and initiate an evacuation. Some horns have strobes built in that can increase their notification capability and reduce the overall footprint of the fire alarm system design.
  • Speaker; Speaker Strobe
    Speakers are used as part of a voice evacuation or mass notification system. Speakers allow for audio messages to be sent out over the system similar to a public address. Prerecorded audio messages provide can deliver calm and authoritative instructions during many different types of emergencies. Speakers can also have strobes built in to expand their notification capability for the hearing impaired.
  • Chime; Chime Strobe
    Chimes are similar to horns in that they provide an audible tone to notify occupants of an alarm event. However, the purpose of chimes is to notify the attending staff of an event and not the occupants of the entire building. This difference in which occupants to notify is specific to the building and occupancy type and the design is always determined by a qualified fire alarm or electrical engineer. The chime is simply the notification technology that enables the fire alarm system to function as specified. Chimes can also be coupled with strobes for enhanced notification.
  • Remote Power Supply
    Notification device circuits require power to flash strobes, sound horns and play messages through speakers. This power is delivered to the device similar to an amplifier powering a speaker. The fire alarm control panel will normally have the capability to drive at least one notification circuit. If the circuit is full or the panel does not have notification capability a remote power supply is required. These remote power supplies provide dedicated power to the notification devices. They can be located next to the fire alarm control panel or strategically placed throughout the building to reduce cable installation costs.

Device Monitoring and Control

  • Monitor Module
    Monitor modules create a point of contact for the fire alarm system to monitor auxiliary type systems such as HVAC units, fire smoke dampers, 120V circuits, elevator status, stairwell pressure, and just about anything that needs to be interfaced with the fire alarm system. These modules will allow the fire alarm panel to indicate the device status of the monitored equipment on the panel display and report the status to the Central Station monitoring service.
  • Relay Module
    Relay modules provide a set of contacts and allow the fire alarm panel to switch them on command. The output provided by a relay module is a voltage free dry-contact. The power to energize the interfaced device is fed from a different source through the relay. In an alarm event, the relay will cut or send power to the auxiliary device or system.
  • Control Module
    Control modules distribute and supervise power for notification appliance circuits (NAC’s). When the fire alarm panel enters an alarm state the control module reverses the polarity of the distributed power. The diodes in each notification device (i.e. horn, speaker, or chime) then allow the power through to the electronic sounder and the audible alarm is generated.

Special Note: Please, do not attempt to design, install, or service fire alarm systems unless you are a trained professional. Fire alarm systems are highly regulated by national standards committees and government entities at every level. If you are interested in learning more about becoming a certified fire alarm professional visit: The National Fire Protection AssociationNational Institute for Certification in Engineering Technologies.

Question: Did this post help you find the answer to a fire alarm question? If so I’d like to hear from you in the comments section below.