Manual fire alarm activation
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A fire alarm pull station is an active fire protection device, usually wall-mounted, that, when activated, initiates an alarm on a fire alarm system. In its simplest form, the user activates the alarm by pulling the handle down, which completes a circuit and locks the handle in the activated position, sending an alarm to the fire alarm control panel. Fire alarm pull station are often reset using a key, which allows the handle to go back up to its normal position, however, this will not reset the fire alarm. Single pull systems are simpler, but run a higher risk of accidental pulls.
Coded pull stations
In the past, pull stations controlled the entire system. These coded pull stations were much bigger than modern pulls and had a code wheel in them. This was a gear mechanism that was wound up when the station was pulled (and, unlike modern pull stations, the handle did not stay down). The gears would turn a small wheel with a specific number of teeth, which determined the coding. The teeth would push up on a contact, which would open and close a circuit, pulsing the code to the bells or horns. This code was used by building security to determine where the alarm was originating from. Example: a pull station in the fourth floor elevator lobby of an office building has a code of 5-3-1. When the station is pulled, the security officers in the building look up 5-3-1 in a master list of codes. After finding the location of the pull, they check to see if there is a real fire. If there is, they evacuate the building and call the fire department.
System tests could be conducted in one of two ways: In a coded pull station, there is either a test hole on the front (which is usually activated with an allen wrench) or a test switch on the inside. Turning the switch one way causes the notification appliances to sound continuously (or in the case of single-stroke bells, ding once). Turning it the other way and then activating the pull allows a silent test to be done in which the station's mechanical parts are checked to ensure proper function. Once pulled, the station would do at least four rounds of code before resetting itself. Coded pulls were used in new fire alarm systems until roughly the 1960s. Up until the late 1980s and early 1990s, panels were made with an extra zone to accommodate any existing coded pull stations. Nowadays, coded pull stations are very rare and almost never seen in working fire alarm systems.
Modern pull stations
Many modern fire alarm pull stations are single action and only require the user to pull down the handle. Other fire alarm pull stations are dual-action, and as such require the user to perform a second task before pulling down, such as lifting up or pushing in a panel on the station (the Fire-Lite BG-10/BG-12, Simplex 2099-9756/4099-9003 and the Cerberus Pyrotronics (Siemens) MS-501 are examples of this design), or shattering a glass panel with an attatched hammer (the Simplex 4251-30/4099-9002 are examples of this). Perhaps the most recognizable pull station is the T-bar style pull. The style is so named because the handle is shaped like the letter "T". This style was first manufactured by Simplex, and is now manufactured by many other companies.
Resetting a fire alarm pull station after it has been operated normally requires building personnel or emergency responders to open the station using a key, which often is either a hex key or a more traditional key. Opening the station normally causes the handle to go back to its original position, allowing the alarm to be reset from the fire alarm control panel after the station has been closed.
In areas where false calls are a problem, pull stations may be covered with a clear plastic cover that sounds a loud tamper alarm when removed, creating focus on the fire alarm. If this is not a sufficient deterrent, the pull handle may be loaded with ink, powder, or gel dye which can be used to help identify who pulled the alarm.
Manual call points
In Europe, a manual call point, usually referred to as an MCP within the fire protection industry, and as a "break glass" in the UK, is used to allow building occupants to signal that a fire or other emergency exists within the building. They are usually connected to a central fire alarm panel which is in turn connected to an alarm system in the building, and often to a local fire brigade dispatcher as well. The first MCP (as we know it) arrived in Europe in 1972 and was invented by KAC. [1]
MCP's would historically be printed with FIRE as a title above a glass element, where the element would be glass which would be covered with plastic. This element design would be the old British Standard. The new European Standard EN54 says that the title should be the House Flame symbol, and the glass would appear differently. The glass will still be covered with plastic on the printed side.
Previously, the old British standard did not allow hinged covers and plastic resettable elements. Plastic elements must have the same printing as the EN54 glass.
See also
