Fire Alarm Systems 101

Many technicians new to the fire/life safety field perform fire alarm system installations. For these technicians, the code and the equipment they intend to install look ominous.

Let’s assume a technician must install a new system in accordance with someone else’s design. To start, every technician must invest in a copy of NFPA 72 2016, National Fire Alarm and Signaling Code. The code contains the nuts-and-bolts requirements that a technician needs to complete a code-compliant fire alarm system installation.

For the next step, let’s apply the code to a hypothetical structure: a five-story hotel with residential, assembly and retail components. The design documents include engineering specifications and drawings of the proposed system. We need to look at the drawings for the locations and number of devices and appliances that will make up the system. We also need to look to the specifications for the requirements, which determine any specific products the designer has chosen.

The building will have manual fire alarm stations at each exit on each level of the four-story residential portion. We will need to install additional manual fire alarm stations at each exit of the first-level stores (mercantile occupancy). The one assembly portion of the building, designed to hold 400 occupants, will have a manual fire alarm station at each of its exits.

The assembly space can be divided into three equal spaces with exits at the front and back of each portion. Each portion will have a manual fire alarm station at each of its exits.

An automatic sprinkler system will protect the building. The waterflow switch and associated supervisory devices in the basement must connect to the fire alarm system. In addition, the owner has requested smoke detectors spaced throughout the residential floors, hallways, stores and assembly space. Furthermore, the specifications require each hotel room to have a system-connected smoke detector with a sounder base. The building fire alarm system connects to a supervising station using radio and by a digital alarm communicator transmitter.

That gives us a good idea about the building, so the technician must research the devices to be installed. Chapter 17 provides installation requirements for all initiating devices, such as manual fire alarm boxes, smoke detectors, sprinkler waterflow switches and sprinkler gate valve supervisory switches. The code specifies the following for manual fire alarm pull stations:

  • They must be mounted securely (a back box is needed—required by other codes).

  • They must be mounted on a background of contrasting color.

  • They must be mounted at a height so that someone can reach the operable part of the device at not less than 42 inches nor more than 48 inches from the finished floor.

  • They must be installed to remain conspicuous, unobstructed and accessible.

  • They must be red.

  • They must be located within 5 feet of each exit doorway on each floor.

  • They must be located so that the travel distance to the nearest manual fire alarm box will not exceed 200 feet, measured horizontally on the same floor.

Improperly installed and maintained smoke detectors can cause nuisance alarms, so technicians must ensure the detectors are placed in the correct environments or locations. Technicians must read all code requirements that relate to smoke detector installation.

The basic requirements for smoke detector installation on smooth, level, unobstructed ceilings that do not exceed 10–12 feet high include the following:

  • Where detectors are installed but not operational during construction, they must be protected from construction debris, dust, dirt and damage in accordance with the manufacturer’s recommendations.

  • Spot-type smoke detectors must be located on the ceiling or, if on a side wall, between the ceiling and 12 inches down from the ceiling to the top of the detector.

Generally, the plans will show the smoke detector layout. But when the plans do not, technicians must follow these code requirements:

  • The distance between smoke detectors must not exceed a nominal spacing of 30 feet, and there must be detectors within a distance of one-half the nominal spacing, measured at right angles from all walls or partitions extending upward to within the top 15 percent of the ceiling height.

  • All points on the ceiling must have a detector within a distance equal to or less than 0.7 times the nominal 30-foot spacing (0.7S).

When ceilings do not meet the definition for smooth, level and unobstructed, the code has specific requirements to address all types of ceilings and ceiling heights.

Once technicians have understood the installation requirements, they need to review the code requirements for the notification appliances in Chapter 18. All audible notification appliances must provide the appropriate sound level throughout a building to ensure the occupants can hear them. Two modes of alarm signaling exist: public mode and private mode. While a hospital might call for the private mode, our example requires public mode.

For public mode signaling, audible notification appliances must have a sound level of at least 15 decibels (dBA) above the average ambient sound level or 5 dBA above the maximum sound level having a duration of at least 60 seconds, whichever has the greater value, measured 5 feet above the floor in the area served by the system.

Hopefully, the system’s designer has included enough horns in the public spaces to meet this requirement. During the system acceptance test, most authorities having jurisdiction will want the sound level measured using a calibrated sound level meter. If the technician thinks the design will not meet the code criteria, he or she should promptly submit a request for information. The design calls for the use of sounder bases in each hotel bedroom, which will help to ensure the system will meet the required sound levels in those rooms.

Bedroom notification appliances must use a 520-hertz signal and meet either the sound level requirements mentioned above or 75 dBA measured at the pillow level, whichever has the greater value.

While the designer has the primary responsibility to ensure the system uses the correct notification appliances to meet the required sound level parameters, the installer needs to know what the code requires. The designer also has the responsibility for the layout of the visible appliances. However, the installer should know the following installation requirements apply:

  • Wall-mounted appliances must be mounted so that the entire lens is not less than 80 inches and not greater than 96 inches above the finished floor.

  • Where low ceiling heights do not permit wall mounting at a minimum of 80 inches, wall-mounted visible appliances must be mounted within 6 inches of the ceiling. The room size covered by a strobe of a given value shall be reduced by twice the difference between the minimum mounting height of 80 inches and the actual lower mounting height.

Generally speaking, visible appliances manufactured and listed for mounting on the wall may not be installed on the ceiling unless the particular visible appliance has received a specific UL listing for this purpose.

Chapters 12 and 23 provide the requirements for circuits that connect the initiating devices and notification appliances to the fire alarm system control unit. Three types of circuits are recognized: initiating device circuits, signaling line circuits and notification appliance circuits.

Installers need to review the requirements for each of these circuits and the specifications to find out which circuit class the designer has specified. To this point, the installer will have installed the system backbone with all circuits brought to the fire alarm control unit. The installer will need training on the specific system manufacturer to ensure proper control unit installation.

Although we have covered a lot of the code requirements for this installation, we obviously have not covered them all. Every installer must read the entire NFPA 72 2016, National Fire Alarm and Signaling Code. Knowing the basic requirements outlined above should go a long way in making a fire alarm system installation more efficient and effective.

About the Author

Wayne D. Moore

Fire/Life Safety Columnist
Wayne D. Moore, a licensed fire protection engineer, frequent speaker and an expert in the life safety field, is a principal member and past chair of NFPA 72, Chapter 24. Moore is a vice president with JENSEN HUGHES at the Warwick, R.I., office. He c...

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