Fire alarm systems keep buildings and building occupants safe from fires. While it is easy to oversimplify them, fire alarm systems are complex networks of many connected devices and components, all working together to detect and alert at the presence of fire.
Fire alarm initiating devices include manual pull-down boxes, ceiling sprinklers, and more.
Fire alarm initiating devices detect signs of a fire and activate an alarm. These components are the system’s triggers and the most visible part of the fire alarm system. Initiating devices include smoke detectors, sprinkler water flow switches, and manual pull stations.
2- or 4-way circuits connect initiating devices to the fire alarm system’s control panel. The control panel goes into an alarm state when activation by an initiating device occurs. This sounds like the alarm in the building. Some panels automatically send out a call for emergency services. You can also get 24/7 alarm monitoring for added protection.
There are two types of fire alarm initiating devices: manual and automatic.
Manual initiating devices are manual pull-down stations that can only be activated by hand. You are probably familiar with these devices. Most commercial buildings, including retail stores, event centers, sports arenas, and offices, have them. Manual pull-down stations are required by state and local law. NFPA 72, the fire alarm standard, even has codes pertaining to where in the building these levers must be located.
Automatic initiating devices trigger automatically in the presence of fire. These devices include smoke detectors, fire sprinklers, and heat detectors. There are two distinct operating types among automatic devices: spot and linear.
Spot-type devices detect smoke and fire in the immediate area. The smoke alarm in your home —which you’ve probably accidentally set off in your kitchen at some point—is a spot-type detector, as are most residential smoke detectors. This is why when you burn dinner, only the smoke detector nearest the kitchen goes off, while others farther away do not trigger.
On the other hand, linear-type devices can detect smoke over a wide range of space and transmit the alarm signal to a central control panel. Expect to find these in larger commercial buildings—because a single detector covers more area, and fewer total devices are needed. Additionally, the control panel can pinpoint the location of the alarm, making it easier to establish where the emergency (or false alarm) is taking place.
How do initiating devices work?
Each fire alarm device plays an important role in triggering an alarm, and they each have unique requirements for doing so. Let’s go through each device separately to describe how they work.
Manual Pull Stations: Manual pull stations allow people inside a building to initiate a fire alarm in the case of an emergency. There are two types of pull stations: single action or dual action. In single-action stations, individuals can activate the alarm with one downward pull on the lever. Much like two-factor authentication for online applications, dual-action stations require two actions to set off the alarm. This means an individual must break a glass cabinet containing the pull station or lift a plastic cover out of the way.
When the lever gets pulled in most systems, the control panel emits an alarm throughout the entire building.
Sprinkler Water Flow Switches: A fire sprinkler system emits water from overhead to stop fires. The fire sprinkler water flow switch is a device inside the fire sprinkler that detects the flow of water through the system’s pipes.
High heat, not smoke, trigger a fire sprinkler. Most fire sprinkler heads come equipped with a glycerin-filled glass bulb. As the glycerin heats up due to the heat from a fire below, it expands, shatters the glass bulb, and triggers the sprinkler head. The fire sprinkler switch senses this flow of water and transmits a signal to the fire alarm control panel, which sets off a general alarm.
Note that fire sprinkler systems are not included with the installation of some fire alarm systems. You may have to hire a fire sprinkler specialist. Speak with your fire alarm system installer for more information.
Smoke Detectors: There are two types of smoke detectors: ionized and photoelectric.
In general, ionized smoke detectors are more responsive to flaming fires. These detectors contain a small amount of radioactive material held between two electrically charged plates. An ion current flows between the two plates. When smoke reaches the detector’s chamber, it stops iron’s flow causing the alarm to activate.
Photoelectric smoke detectors are more responsive to smoldering fires. These detectors aim at a non-visible light away from the detector. When smoke fills the chamber, the light reflects back onto the detector and triggers an alarm.
Heat Detectors: Heat detectors work by measuring temperature rise. Though accurate, there may be a relatively long delay between when the fire starts and when the heat detector triggers an alarm. There are two types of heat detectors: rate of rising and fixed temperature.
Rate-of-rise heat detectors activate when temperatures rise significantly in a short time, such as 15 degrees in one minute. As the temperature rises, the air inside the detector expands, causing the alarm to go off.
Fixed temperature detectors activate when the room reaches a pre-specified temperature. Unfortunately, a fire can take a while to heat up a room or building. This is especially true in large, open spaces.
Rate-of-rise and fixed temperature detectors have specific applications and are not used as often as traditional smoke detectors.
Though each initiating device operates independently, all of these components can be integrated into one fire alarm system. Each device is the same: initiate an alarm in the presence of smoke or fire.
Work with a professional fire alarm system installer to determine the best fire alarm devices for your home or business; and ensure your system meets code.
Fire alarm systems are critical to the safety of homes, businesses, and the people inside them. As you can see, they aren’t just plug-and-play type devices—each component is complex, working independently to detect smoke or fire.
These systems and devices require professional installation to ensure they work properly and meet code. Don’t know who to call or what makes for a great fire alarm installer? Read through our guide on what you should know before buying a fire alarm system. In it, we discuss the types of questions you should ask and what kind of questions you should expect to get from fire alarm installation companies.
At Bay Alarm, our expert fire alarm installers are ready to help. Whether you need a fire alarm system for your home, business, or a newly constructed building, we’re here to help! Don’t leave the protection of life and property to chance—give us a call today for more information and schedule a system consultation.