Initiation Devices for Fire Alarm Systems, Part 1
Many business owners are grateful for the protection our fire alarm systems provide, but are not exactly sure what sets off the alarms in their buildings. I receive calls from customers asking what’s required for systems, or why certain devices are used instead of others on certain systems.
The easiest way to understand why we chose to use one device over another is to look at how each device operates. In this two-part blog series, I will talk about some of the more common devices that are installed in fire alarm systems.
One of the most common devices used on a fire alarm system is a pull station. A pull station allows a person to manually activate a fire alarm system. With these devices, you actually pull a lever to alarm the system. There are both single and double action pull stations. The difference between these two is the number of actions it takes to set the device into alarm. The single action pull station requires one action to set it into alarm; the double action pull stations require two actions. The double action pull stations help prevent false alarms. Check out the two pull station in the image. One is activated by a lever pull (one action), the other is activated by pushing then pulling the lever (two actions).
Another device commonly used in fire alarm systems is a smoke detector. There are two main types of smoke detectors: ion and photoelectric.
An ion smoke detector alarms when smoke disrupts the flow of ions between two charged plates inside the detector’s chamber. A photoelectric smoke detector alarms when smoke obscures a beam of light inside the sensing chamber. (The images link to documents that explain how each detector functions in a very simple way. They were written with a residential customer in mind, but the function of the detectors is largely similar.)
There are also detectors on the market the combine these two (and other) smoke detection methods into one device. A smoke detector that is growing increasingly popular is a multi-criteria smoke detector. The multi-criteria smoke detector can use up to four different types of detection to report a fire — photoelectric, thermal, infrared, and CO. Using a multi-criteria smoke detector can decrease the number of false alarms.