Increasing Your Fire Alarm Literacy

Increasing Your Fire Alarm Literacy


Part six in a series that examines a vital link in the fire protection system.

Fire alarm system functions revolve around the technical requirements of NFPA 72A, Local Protective Signaling Systems. The key word is local: The local system can be manual, automatic, or a combination of the two. However, because of the special or hazardous nature of some occupancies, most building codes direct that fire alarm systems provide more than simply local annunciation. They require local protective systems to be connected to alarm monitoring services distant from the protected premises.

In the following discussion I use the terms public fire department and authority having jurisdiction. In some cases these two agencies are the same, but not always. The public fire department provides field response to the alarm signal, whatever kind it may be. The authority having jurisdiction is the agency charged with code interpretation and enforcement of installations and maintenance of fire alarm systems.


Engineering Standard NFPA 71, Installation, Maintenance, and Use of Central Station Signaling Systems, describes how signals from an NFPA 72A system are transmitted to a distant monitoring point. This arrangement is the most common method of monitoring fire alarm systems off premises. This monitoring point is not always in the same city as the protected premises—it can be several states away. Wire lines connect the premises and the central station.

Central stations hire personnel to be in attendance at all times in a monitoring office. Their job is to supervise the condition of the fire alarm circuits and to receive alarms. Received alarm signals are passed along to the public fire department by a telephone call or by a radio link. The alarm is not transmitted automatically from the central station to the fire department. Most fire departments have a special phone line dedicated to receiving calls from central stations. The phone line’s number usually is not published and is known only to central station operators. In a quality monitoring facility, the operators know the difference between the various types of signals and how to process them.

Central stations are designed and located in a high-quality structure so that the equipment, circuits, and employees are protected against fire, storms, earthquakes, and other natural disasters. There are very strict standards for the station’s building, power supplies, and equipment. Central stations are operated by companies that do not have a financial or operational interest in the protected premises.

Central stations receive three types of signals from a premises: alarm, supervisory, and trouble. The actions expected of a quality central station on receipt of these signals are as follows:

Alarm signal. On receipt of an alarm signal, the central station

  • Immediately notifies the public fire department communication center.
  • Dispatches a runner or a technician to the scene of the alarm (normally the response time for this person is 45 to 60 minutes).
  • Notifies the subscriber by telephone or other predetermined method.
  • Notifies any other parties that the authority having jurisdiction may require.

Supervisory signal. When a supervisory signal is received from a fire suppression system such as an automatic sprinkler system, halon system, or dry chemical system, the central station:

  • Calls the person designated by the subscriber to look after problems of this type —such as a watchman or private security agency who responds to the premises.
  • Notifies a runner or maintenance person to investigate the cause of the signal. If the cause of the signal appears to be restored, the runner or maintenance person might be recalled. Typical response time for this service is 45 to 60 minutes.
  • Notifies the public fire department if the department so wishes. Normally there is no statutory requirement for the fire department to respond to supervisory signals. This is a policy matter determined by the local public fire department.
  • Notifies the authority having jurisdiction if this supervisory signal results from some kind of failure that causes the suppression system to be out of service for a period of more
  • than eight hours.
  • Notifies the authority having jurisdiction of the restoration and the nature of the failure when the suppression system is restored to service.
  • Trouble signal. On receipt of a trouble signal from a fire protection system such as a fire alarm or suppression system, the central station
  • Calls the facility immediately by telephone to see if the nature of the difficulty can be determined.
  • Dispatches or finds contract services to arrive at the trouble site within four hours to begin maintenance, if required.
  • Notifies the subscriber in writing that a trouble signal was received and notifies the authority having jurisdiction about the nature of the signal (if it so wishes), provided the failure time exceeds eight hours.


Engineering Standard NFPA 72D, Proprietary Protective Signaling Systems, establishes standards for a fire alarm monitoring station when it serves properties under the same ownership as the monitoring station. The protected premises may be located in a complex such as a large industrial site or the buildings may be located in various parts of a community. The important point is that each building is tied into a monitoring service owned by the same company that owns or operates the monitored sites.

Consider a large industrial complex covering 50 acres. All or many of the buildings in the complex have sprinkler systems. These systems transmit to a proprietary station located usually at a main security office in the complex. Trained operators are on duty at all times. When an alarm, supervisory, or trouble signal is received, the operator notifies the proper parties. In the case of an alarm signal, the public fire department is notified by telephone or radio link. Notification is by personal contact, not automatic means.

Proprietary stations are very much like central stations in function. The monitoring site is in a separate fireresistive building or special room. The personnel in this office are dedicated to monitoring fire and security devices only. They should not be dedicated to performing services different than those associated with taking care of a monitoring station.

Proprietary stations also receive alarm, supervisory, and trouble signals. Following are the actions taken on receipt of each alarm.

Alarm signal. On receipt of an alarm signal, proprietary station personnel

  • Notify the public fire department.
  • Notify the plant fire brigade.
  • Dispatch a runner to the alarm location (under normal conditions, the response time for the runner does not exceed 45 to 60 minutes).
  • Make sure the tripped system is restored to normal operating condition as soon as the reason for the trip is discovered.

Supervisory signal. On receipt of a supervisory signal, proprietary station personnel

  • Dispatch a runner or mainte-
  • nance person to discover the reason for the signal (the normal time for the runner to respond is approximately 45 to 60 minutes).
  • Notify the fire department of the supervising signal, if required.
  • Notify the authority having jurisdiction that the system is partially or wholly out of service if the period of impairment exceeds eight hours, if required.
  • Notify the authority having jurisdiction in writing regarding the nature of the supervisory signal and the restoration of service if the system has been out of service for more than eight hours, if required.
  • Trouble signals. On receipt of a trouble signal, proprietary system personnel
  • Notify a designated supervisory person that there is an indication of some kind of system failure.
  • Send a runner or maintenance
  • person to the building to investigate the nature of the trouble.
  • Notify the authority having jurisdiction that a trouble condition has been experienced if it exists for more than four hours, when required.
  • Notify the authority having jurisdiction in writing regarding the nature of the trouble, when it happened, and when the trouble was repaired when the fire alarm equipment has been out of service for eight hours or more, when required.


Engineering Standard NFPA 72C, Remote Station Protective Signaling Systems, describes the features and operation of a remote station. Remote stations are more like central than proprietary stations in that they have no financial or operational interest in the protected sites. Fire departments that directly receive fire alarm signals are usually classified as remote stations. Of course, when a fire department dispatch office acts as a remote station there is no need to retransmit

the signal except to fire stations using regular fire department dispatch procedures. However, many fire departments are withdrawing from this service.

Where fire department communication centers do not provide remote station monitoring, the authority having jurisdiction usually determines remote station technical requirements within the jurisdiction.

Police department communication centers are common locations for remote station facilities. In smaller communities, the village or town fire station often acts as a remote station facility. It is rare that nongovernmental agencies provide remote station service.

The following actions take place when alarm, supervisory, or trouble signals are received at the remote station facility:

Alarm signal. When a fire alarm signal is received at a remote station facility, retransmission of the alarm signal shall be by

  • A voice circuit dedicated to communications between the remote station and fire dispatch. This circuit does not wind its way through any telephone switching center but rather is stretched directly between the remote station and fire dispatch.
  • Automatic transmission of coded signals between the remote station and fire dispatch on a dedicated line.
  • A one-way telephone at the remote station facility. The telephone circuit is for outgoing calls only to fire dispatch through commercial telephone switching facilities.
  • A private radio communications channel between the remote station and fire dispatch. Usually this circuit is set up and authorized by the public fire department.

Supervisory and trouble signals. On receipt of a supervisory alarm, personnel on duty notify either an owner of the property or some person designated by the owner. The remote station does not notify the fire department or the authority having jurisdiction; it is not directly responsible for dispatch of any person to the scene for any reason.


Engineering Standard NFPA 72B, Auxiliary Protective Signaling Systems, defines the requirements for fire alarm notification systems. Alone these systems are unable to notify the public fire department, but when they are connected into a public fire alarm notification system they call the public fire department on the trip of an initiating device.

An example of a public fire alarm notification system is the familiar street corner fire alarm pull box. Whether these systems exist in your community depends on where you live. Older central cities in the northeast part of the United States still have many of these systems in place. Fire departments at one time funded fire alarm line maintenance crews, but budget problems forced many of them to abandon this practice. Street boxes in some communities changed from wire lines to radio communications. Regardless of the method of transmitting the alarm signal from the “street corner” to the dispatch office, the system is considered a public fire service alarm system.

In its simplest form, an auxiliary protective signaling system consists of a local fire alarm detection and signaling system serving a building or complex. The fire alarm control panel has a feature called the city connection. This city connection is attached to the public fire alarm system at the street with wires. When the local fire alarm system operates, it also operates the public fire alarm system, almost as if it were a simple street corner box placed at the address of the building or complex.

An example is a public school property. Say the property contains two buildings, connected into a single fire alarm panel in the main building. When any alarm initiating device activates, the local alarm sounds, the city connection operates an electromechanical relay, and an alarm signal is placed on the public fire alarm system. The dispatch office reads the coded signal received at the dispatched office and dispatches the appropriate fire apparatus. This connection, which looks to the fire alarm system like a street corner pull box, is called a master box by some fire departments. A master box can be activated at the street or by the premises’ remote features.

The following actions occur when a auxiliary signaling system operates:

Alarm signal. When an initiating device activates at the protected premises, an alarm signal is imposed on the municipal or public fire department fire alarm signal. The public system is configured to recognize that the alarm signal is from an auxiliary fire alarm system. On receipt of the alarm signal, the fire dispatch office transmits the alarm directly to the appropriate fire stations.

Supervisory ancl trouble signals. Auxiliary protective signaling systems do not normally transmit supervisory or trouble signals for the premises’ fire alarm system. These signals are annunciated by audible and visible devices at the premises only.

Fire alarm systems are considered by many fire service personnel to be nuisances at best. Fire service officials often talk halfheartedly among themselves and to the public about what fire alarm systems can do for fire prevention and life safety without understanding how fire alarm systems fit together. The difference between a local alarm and a remotely annunciated alarm is often a mystery to them, and it should not be.

Training officers, battalion-level officers, and company officers should work with company personnel toward a better understanding of fire alarm systems. Don’t make fire alarm systems any more complicated than they already are. Take your time, look carefully at how the parts fit together, and then use this knowledge to understand what the fire alarm system is trying to say to you when you approach the fire alarm control panel.

Increasing Your Fire Alarm Literacy


Increasing Your Fire Alarm Literacy


Part five in a series that examines a vital link in the fire protection system.

The signaling system is the part of a fire alarm system that alerts occupants when an alarm initiating device detects an emergency condition. Signaling devices are either visible or audible.


The most common visible fire alarm signaling device is a flashing red light. All too often fire service personnel improperly refer to visible devices as “strobes.” Strobes are actually one type of visible annunciator.

The visible device is selected according to the application. Flashing lights are used in factories and office buildings. Strobe lights often are used in occupancies that serve the disabled. Where flashing lights are used for attention-getting purposes such as advertisements, strobe lights must be used for emergency warning; otherwise, the flashing lights will compete with the fire alarm signaling lights and confuse occupants. The high-intensity, short-duration strobe works well to attract occupants’ attention in emergencies.


Audible devices emit sounds to notify occupants of an emergency. The sound output of audible devices is measured in decibels (dB). There are more types of audible devices than there are visible devices. Following are examples of audible devices.

Bells. These are the most common audible devices and are available in different sizes. Most common occupancies—business, storage, and mercantile-use bells to notify occupants. The bell’s diameter is a good indication of its sound power output.

Horns/klaxons. Industrial locations usually use horns or klaxons. They work well in high ambient noise settings because of their unique raucous signal. The noise output level is loud enough that occupants can hear and identify the signal over ambient noise in a factory or other industrial location.

Chimes. These are used in occupancies to notify staff that an emergency exists without instilling panic in other occupants. Nursing homes and hospitals frequently use chimes.


The sound level required in one occupancy usually is not the same for other occupancies. You can determine whether the sound level is adequate by using a decibel meter—an electronic instrument that measures sound intensity.

Each assembly, business, storage, mercantile, and residential occupancy has a typical day-to-day noise level. This level is called the occupancy’s ambient noise level. Nationally accepted engineering standards suggest that fire alarm signals be approximately 15 dB louder than an occupancy’s ambient noise level.

The measurement of sound intensity taken with a decibel meter can help determine if the signaling device is sufficient for the occupancy.Common visible and audible signaling devices.

Fire alarm installers or inspection personnel who are familiar with the operation of decibel meters measure the ambient noise level in a room by placing the decibel meter in an agreed-on location approximately five feet above the floor. They obtain a reading that includes inside mechanical noises as well as outside noises that filter in.

When the fire alarm system activates, signaling devices should increase the meter reading at least 15 dB. If the reading does not increase sufficiently, the inspection team and the designer may select another location in the room. If this location does not provide a sufficient signal level, the authority having jurisdiction usually requires additional signaling devices.


Recent legislation on the federal and state levels has focused on providing adequate annunciation to people with disabilities. However, much of the design criteria is vague. For instance, it is not yet technically clear what light intensities and durations will attract the attention of a person with a hearing disability.

It is easier to attract the attention of people with vision loss because of sound’s ability to more readily travel around corners and through opaque objects such as walls. Strobe lights have a unique but limited ability to warn people with hearing disabilities because of their high instantaneous intensity and short flash duration.


Alarm initiating devices require special circuits to ensure that signaling zone wiring does not unknow ingly fail before a fire incident requires the zone to perform. If the circuit fails before the fire incident, the detection devices are useless when a fire does occur.

Signaling circuits are similarly protected with trouble monitoring features. If a wire breaks or one side of the signaling circuit touches the ground, a trouble signal indicates on the fire alarm control panel. Wiring failure in any signaling circuit in a fire alarm system causes a yellow trouble light to appear and an audible signal to sound at the control panel.


In occupancies such as large assemblies, movie theaters, and churches, it is common to alert the occupants using an emergency voice alarm or voice evacuation system. The speakers and audio amplifiers associated with this system differ from regular public address systems: They have special circuits that “watch over” the integrity of the speakers, speaker wires, and circuits inside the audio amplifier driving the speakers. Emergency power supplies the amplifiers and speakers so that instructions can be given to the occupants even when the building’s regular electrical service is disrupted.

The fire alarm system.Typical voice evacuation and voice command apparatus, often found in high-rise settings.

Operator’s Console

Master Program Keyboard –

Information Printout

Firefighter’s Telephone (Master)

One-way Voice Communications Microphone

Pre-recorded Safety Announcement Tape

Automatic voice annunciation. Fire companies occasionally may encounter an alarm system with prerecorded evacuation alarm messages. On operation of an alarm initiating device, the fire alarm control panel electronically commands the tape to start playing. The taped message instructs the occupants of the building.

Manual voice annunciation. With manual voice annunciation, a responsible person located in a protected room notifies the occupants. An annunciation panel monitors all of the building’s fire alarm initiating devices. This protected room is constantly manned when the building is occupied.

During building familiarization tours, fire companies study building layouts and identify notification zones. The companies also note how the voice communication system works. The special room and equipment allow the incident commander to instruct occupants to move toward one exit or another or not to move at all. For example, the incident commander can identify by name or number operational stair towers for firefighters and evacuation stair towers for occupants. The system also is used to calm occupants who otherwise might tend to panic. Incident commanders can use manual voice communication systems to guide firefighters throughout the building and to inform them of incident progress.


Since emergency voice alarm and communications systems are true fire alarm signaling systems, they must include circuit failure monitoring for the wiring and other critical circuits. This feature is called trouble monitoring and operates on the same principle as the monitoring of initiating and signaling circuits.

An emergency voice alarm system audio amplifier differs from a regular public address audio amplifier in that some of its more critical parts are monitored for trouble. If critical amplifier parts fail while not being used, an audible and visible alarm activates in the control room.