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What are the various types of Fire Alarm initiating devices?

Fire alarm systems protect businesses, schools and hospitals from fires, as well as multi-family homes. Fire alarm systems are complex networks of interconnected components. Each component plays a unique role in fire protection.

The fire alarm initiating apparatus is the most prominent component of these systems and probably the one that you are most familiar with.

The Fire Alarm Initiating Devices are?

In a fire alarm system, the initiating devices are those which detect possible fires and activate an alarm. These devices are the system’s triggers, and they are the most prominent aspect of the fire alarm system.

The alarm system’s control panel connects initiating devices via 4-way or 2-way circuits. The control panel constantly monitors them. The board detects an initiating device and activates it. It sounds the alarm and sends out an emergency call.

Fire alarm initiating devices can include smoke detectors and sprinkler water flow switches.

Types of Fire Alarm Initiating Devices

There are two types of initiating devices.

  • Automatic initiating devices:

    User can trigger these devices automatically when the conditions are right. These devices include:

  1. Smoke detectors
  2. Water flow switches for fire sprinklers
  3. Heat detectors

There are two types of automatic initiating devices: spot type and linear type.

Spot types are detectors that only focus on the area they are installed in, while linear type devices have a wider detection area that communicates with a single control unit. Spot types include the standard ionization smoke detector and the light-obscuration, photoelectric smoke detector. (Learn more about these two types below).

Spot types are more affordable, but installers have must connect each one to the fire alarm system individually.  They should also install additional devices to cover the area adequately. Linear types, though more costly, require only one hook-up to the fire alarm system and cover a larger area.

  • Manual initiating devices:

    These devices must be/can be manually activated by someone when they see a fire alarm. This refers to a manual pull station.

The conditions that activate one of these devices (smoke or heat or manual adjustment) trigger the alarm state. At this point, the fire alarm system sends out audible and visible alarms to alert building occupants about the hazard.

How do Initiating Devices Work?

Many fire alarm systems will include multiple types of initiating devices. Each device’s role and trigger requirements are unique. Each device must be installed individually and connected to the circuitry of the fire alarm system.

These devices can be connected once they are installed. They will then operate in the same way as normal to detect fires and alert the system.

We are briefing some explanations about how each type of initiating device works:

  • Smoke detectors:

    These devices are fast-reacting, highly effective fire alarm initiators that can quickly respond to a fire alarm system before it has had a chance for a fire to develop fully. Because fires produce smoke early in the development of fires, well before the heat sets off water sprinklers and heat detectors.

There’s two types of smoke detectors, ionization or photoelectric.

Ionization smoke detectors measure airflow current using ionized water held in a sensing chamber. The wind is reduced when smoke enters the room. The sensor activates when the current drops sufficiently.

Photoelectric smoke detectors can detect smoke using one of two methods: light or photoelectric.

Light-scattering is one method. This involves placing a light source (and a sensor) inside the detector in such a manner that the sensor cannot detect light under normal conditions. Smoke can cause the detector to reflect or scatter light. The sensor is activated when there is enough light.

Light obscuration is another photoelectric method. In case, the light source and the detecting sensor are often two separate components. The light beam is projected onto the sensor and it will remain inactive as long as it receives the light. The detector will activate if smoke from a fireplace fills the air and blocks the light beam.

  • Sprinkler Water Flow switches:

    A sprinkler water flow switch, which is located inside a fire sprinkler system, detects water flowing through its pipes.

Stagnant water can build up in pipes if a sprinkler system is not activated. When a fire-induced temperature activates a fire sprinkler, water flows through the sprinkler and out of the open fire sprayer. This is when the sprinkler water flow switch detects the change in the water activity and alerts the fire alarm control panel that a sprinkler system has been activated.

  • Heat Detectors:

    Heat detectors are the oldest type of automatic initiating device.Sometime they are slowest to respond to a fire and are therefore the most reliable. There are two types: the fixed temperature and rate-of-rise.

Preset, fixed-rate heat detectors will turn on when the temperature in the room reaches a specific temperature. It can take time for a fire to grow so there might be some delay between activating the first device and the fire actually starting.

However, the rate-of-rise heat sensor activates when the temperature in the area around it rises more than 15 degrees per minute. In response to the rapid temperature rise, the chamber’s air expands and presses against the contacts of the chamber. This triggers activation.

Although rate-of-rise heat sensors are more effective at detecting fires than others, they still need a fire to activate. This is why they should not be relied on alone.

  • Manual Pull Stations:

    Often seen in movies as a way to escape awkward situations, manual pull stations allow people to activate the fire alarm in an emergency.

Single- or dual-action pull stations can be used. Single-action stations require only one physical act to pull a lever. This activates the alarm. Dual-action stations require two actions to activate the alarm. For example, you must first break the glass cabinet that contains the lever or lift a cover to reach the lever.

Most systems send a signal to the control panel when the lever is pulled. A general alarm is then sounded throughout all buildings, alerting everyone to evacuate.

Although each fire alarm initiating device is activated according to different conditions, their overall function within a fire alarm network is the same: to activate in response to a fire and signal the fire alarm control panel that it is in alarm mode.

Choosing the Right Fire Alarm Initiating Devices for Your System

There are many types and styles of initiating devices. The ones that I have listed here do not represent all. There are many other types and customizations available.

A different set of conditions activates each device so it is important to know that not all alarm systems should rely only on one. Sprinkler water flow switches or heat detectors are great at protecting buildings by notifying the system about a fire. However, they don’t activate quickly enough to protect people inside the building. To create a fire alarm system that is truly life-saving, smoke detectors are necessary.

Your facility’s unique circumstances, materials, layout, staffing, residents, and staff can all influence which type of fire alarm initiating device is most effective and where it should be placed. If you are getting ready to build, or if your current fire protection system needs updating or maintenance, don’t wait – Click for a more-info best guideline for the Fire alarm system.


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