Manual fire alarm activation is typically achieved through the use of a pull station (USA & Canada) or call point (Europe, Australia, and Asia), which then sounds the evacuation alarm for the relevant building or zone. Manual fire alarm activation requires human intervention, as distinct from automatic fire alarm activation such as that provided through the use of heat detectors and smoke detectors. It is, however, possible for call points/pull stations to be used in conjunction with automatic detection as part of an overall fire detection and alarm system. Systems in completed buildings tend to be wired in and to include a control panel. Systems for use during construction can also be wireless or mechanical, however it is recommended by the Structural Timber Association in the UK that for timber-framed constructions, interconnecting wireless systems be used.
Video Manual fire alarm activation
Fire alarm pull station
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. After operation, most fire alarm pull stations must be restored to the ready position using a special tool or key in order for the panel to be reset. Primitive manual stations, requiring only a single action or hand motion to activate, can be subject to unwanted activation by jarring or accidental contact. Early strategies to cope with this problem included requiring the operator to break a pane of glass to release an internal spring-operated mechanism. Manual pull stations that require two hand motions, such as lift up and pull down, or push in and pull down, have since replaced the break-glass and single-action models in many modern installations.
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. They had 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. For example, consider a pull station in the fourth floor elevator lobby of an office building with a code of 5-3-1. When the station was pulled, the security officers in the building would look up 5-3-1 in a master list of codes. After finding the location of the pull, they would check to see if there is a real fire. If there was, they would 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 (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 typically used in new fire alarm systems until roughly the 1950s, and then occasionally into the 1970s. Until the early 1990s, some 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 to sound the alarm. 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 or shattering a glass panel with an attached hammer. Perhaps the most recognizable pull station is the T-bar pull, so named because the handle is shaped like the letter "T". This style is manufactured by many companies including simplex global fire control and many more.
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 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 some places, particularly at college dormitories and schools, students set off fire alarms as a prank or simply because they want to (out of anger or curiosity). These false alarms can convey a risk to apathy among occupants if they occur repeatedly, causing them to dismiss the importance of alarms or ignore them completely. In areas where false alarms are a recurring problem, pull stations may be covered with a clear plastic 'Stopper' cover that will cause people to notice the person by sounding an alarm when tinkered with or opened, creating focus on the fire alarm. Because of these and other issues, setting off a fire alarm when there is no fire or other emergency is illegal in many jurisdictions.
Maps Manual fire alarm activation
Manual call points
In Europe, Australia, New Zealand, and Asia, pull stations are generally not used; instead a manual call point is used, which is usually referred to as an MCP, call point or Fire Point within the fire protection industry and as a "transmitter" in Japan. They are 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 modern MCP arrived in Europe in 1972 and was developed by KAC.
Manual call points are used to initiate an alarm signal, and operate by means of a simple button press or when glass is broken revealing a button. They can form part of a manual alarm system or an automatic alarm system. There will be an indicator on the monitoring unit for visual indication to locate the call point easily, and there should be a visual identifier of the unit which triggered the alarm, typically a mechanical flag which operates on a latch and must be manually reset, e.g. by a key.
Previously, the old British standard did not allow hinged covers and plastic resettable elements. Plastic elements must have the same printing as the EN 54 glass.
Temporary MCPs
It is becoming increasingly common in the UK and Europe for wireless MCPs to be used in temporary environments such as construction sites. These typically provide the same level of protection as a standard wired fire alarm installation, but can be moved around as needed in the changing environment of a building under construction without the need for specialist electrician installation. They often combine call point functionality with sounder and strobe functions for ease of installation.
Such systems typically operate a similar structure to a standard wired fire alarm network, in that Manual Call Points may be mixed with automatic fire detection in the form of heat detection and smoke detection (often specially designed to be dust resistant, due to the increased likelihood of dust on a construction site) and can be connected to a monitoring base station unit. This unit provides visual identification of the triggering unit in any alarm, and should also be able to monitor radio signal strength (which may change as the build progresses) and battery life.
Due to their use for life inherent purposes, radio receivers used in such systems should be of Category 1 standard.
European Standard
Fire detection and alarm products placed on the market within the European Union must, in accordance with Regulation (EU) No 305/2011, conform to the European harmonised technical standard EN 54 Fire Detection and Fire Alarm Systems.
EN 54 part 11 is the section of the mandatory standard relating to manual call points.
European Committee for Standardization (CEN, French: Comité Européen de Normalisation) is responsible for the development and maintenance of the standard, as part of its remit for developing harmonisedEuropean standards for free movement of goods in the European Union countries.
The EN 54 certification of each device has to be issued annually, and for products of this nature must be issued by a notified body in accordance with the stringent testing procedures outlined within the standard.
If an EN 54 certificate is over one year old, it has expired and it is not a valid certificate. Manufacturers can not sell or install the device with expired certification in any country of the European Union.
See also
- Fire safety
References
External links
- Video demonstrating a coded pull station made by Simplex.
Source of the article : Wikipedia
0 Comments