Fire Alarm Initiating Devices Can Be Lifesavers
Fire alarm systems are basically used in four different ways: to detect fires, respond to the manual activation of a fire alarm device, monitor signals from other fire-related systems and alert the building occupants to evacuate the building, and to alert off-site authorities so they may respond to the situation.
Although technology continues to lead to more advanced and accurate devices, the basic product categories and proven best practices continue to form the basis of proper fire alarm/life-safety system design, installation and service. The following material serves as an introduction for those relatively new to the discipline and as a refresher for experienced fire system technicians.
It All Begins With NFPA 72
NFPA 72, the National Fire Alarm Code, covers the installation requirements for fire alarm systems. This book covers everything from mounting heights and spacing of devices for installers to system operational requirements for manufacturers.
Chapter 5 of NFPA 72 covers spacing and location requirements for all types of initiating devices that can be connected to a fire alarm control panel (FACP). It covers general requirements for all types of smoke and heat detectors, including reductions for ceiling height and nonsmooth ceilings. It covers the location and spacing of pull stations, and it covers the requirements for fire sprinkler monitoring devices. More on this at the conclusion of this article.
Signal Initiating Devices Include Manual, Automatic Signaling
Signal initiating devices on a fire alarm system generate signals (alarm or supervisory) to be processed by the fire alarm control unit. These devices may generate signals by manual activation, automatically when they detect heat or smoke, or when triggered by another system or device when it goes into off-normal condition. The type of signal sent to the control, and the response of the control, depends on the device itself and how the zone is programmed to respond.
Pull Stations Available in Single or Dual-Action Configurations
Manual fire alarm boxes, more commonly known as pull stations, are manually activated by a person who wishes to initiate a fire alarm. Depending on the configuration of the system, activation of the device immediately causes a general alarm throughout the building, or signals only in a specified area to alert authorities to investigate further (presignal systems). General alarm applications are considerably more popular, as presignal systems require special circumstances and AHJ (authority having jurisdiction) approval.
Pull stations may be either single or dual action depending on the number of physical actions required for activation. A single action pull station only requires a single physical action to activate it. This action is typically pulling a lever. A dual action requires two physical actions to activate it. The actions may be pushing in a door, breaking glass or lifting a cover to gain access to the second device to activate the alarm.
NFPA 72 requires pull stations to be mounted so that the operable part of the station (actuator) is between 3 1/2 and 4 1/2 feet off the floor. Mounting at this height allows easy access by a standing person or a handicapped individual in a wheelchair.
NFPA 72 also requires pull stations to be located throughout the protected area in places where they are easily accessible and along the normal path of exit from an area. At least one pull station must be provided on each floor and at least one must be located within 5 feet of each exit door on a floor. Sets of exit doors wider than 40 feet require a pull station on each side. Additional units must also be provided within 200 feet horizontal travel distance on the floor.
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