Fire Alarms- How Do They Work?

We are currently divided about the mechanical workings of fire alarms and are looking for some information.

Please observe this fire alarm. . You will notice the glass bar on the bottom is missing.

If we pulled this alarm, would it work? Or does the glass bar somehow complete a circuit, thus creating the alarm when broken- which would mean that it is currently non-operational without this bar?

The glass bar is there to show responding firefighters which alarm was pulled.
(In the event there was no fire, of course).

Oh, and the particular alarm that had its glass broken, usually has to be re-set by building maintenence. They put a new piece of glass in. Some of these alarms swing down on a hinge when the glass is broken, and it has to be held in the closed position when inserting new glass.

:dubious: Wouldn’t the presence of the red handle in the downward position accomplish the same thing? It seems a bit redundant to me.

Without said glass bar, is it still operational?

Yes. Pulling the handle down activates the alarm. The little glass, as explained, only indicates that that particular alarm had been pulled. If the alarm handle springs back, which many do, then it’s not redundant to have that glass there. In the schools in which I’ve worked over the years, false alarms were occasionally pulled. The only way the firemen knew which one was pulled was by the absence of said glass bar. (The old story that schools sprinkled on the handles some special powder that could be noticed by ultraviolet lights JUST to catch the prankster, was a canard. It may have been effective, however, in the same way that dummy cameras are.) xo, C.

FYI-the object pictured isn’t a fire alarm, it’s a manual pull station, one of a number of initiating devices connected to a control panel. While the rod break style still exists, latching pull stations are more popular given that they require nothing other than a special wrench for reset. Beyond that, addressable alarm systems pinpoint the initiating device via a serial number entered at the time of system activation.

the fire alarm manual pull station in the picture is manufactured by the edwards company. the glass rod is a tamper indicator, nothing more. in order to reset this type of pull station, you need a small screwdriver. there is a scew slot on the top. a slight turn counter clockwise will allow the entire ffront of the pull station to swing down. on the silver back plane, there will be a toggle switch. if the station has been tripped, the switch will be up. push the switch to the down position. while the manual pull station is open, you can pull a small silver colored tab in, and on the front of the pull station slide in a new glass rod. once this is complete, simply swing the front of the pull station back up and snap it into place. this will allow you to reset the fire alarm panel.

jftr: i am a state licensed fire alarm technician and work for a company that installs edwards equipment.