Fire Alarm Design to Avoid Costly Mistakes

As a third-party reviewer and an engineer of life safety systems, I’ve seen many fire alarm designs that fail to address a project’s needs. To address a project’s needs, a fire alarm system must perform the following operations:

1. Detect abnormal conditions,
2. Notify occupants of abnormal conditions,
3. Transmit fire alarm signals, and
4. Control occupant facilities (shutdown appropriate devices, release magnetic door holders, initiate elevator recall, etc.).

Retaining a quality Fire Protection Engineer (FPE) is important to ensure each operation is properly addressed. An over engineered system is costly to the client, while an under engineered system endangers occupant safety and provides a false sense of security. In the State of New Hampshire, a quality engineer will design a fire alarm system in accordance with the State of New Hampshire Building Code (RSA 155-A). Specifically, the International Building Code (IBC-2009). A quality engineer will also design a fire alarm system to comply with the New Hampshire State Fire Code (Saf-C 6000). Including, but not limited to, the National Fire Alarm and Signaling Code (NFPA 72-2013) and the Life Safety Code (NFPA 101-2015).

To detect abnormal conditions, codes require fire alarm systems to use manual pull stations and monitor automatic sprinklers, where provided. Smoke and/or heat detectors are required to protect select entities, such as elevators and fire alarm control units, but are rarely required to provide complete coverage. Occupancies that require additional detectors include: day-cares, health care facilities, hotels/dormitories, apartment buildings and residential board and care facilities. In all cases, it’s rare to require complete coverage and thus costlier for the client to design as such. However, it’s good engineering practice to provide complete coverage in buildings not equipped with sprinklers. Without automatic detection, a fire may grow to considerable size before personnel are notified.

To properly notify occupants of abnormal conditions, the building’s height, area and occupancy must be evaluated to determine if the system is required to have voice evacuation (audio notification through speakers). It’s costly to replace horns with speakers once horns have been quoted or installed. Local Authorities Having Jurisdiction (AHJ) will notice this mistake which cost thousands of dollars to fix.

Historically, digital dialers (traditional phone lines) have been the prevalent technology for fire alarm signal transmission. However, recently adopted codes affect the transmission of fire alarm signals. Per NFPA 72-2013, a fire alarm system employing a digital dialer must use a secondary means of signal transmission, such as a wireless cellular transmitter or a radio box. However, these devices are permitted to transmit signals without the aid of other technologies. A quality engineer will evaluate each individual project to determine the best method of signal transmission. It would be a mistake to implement the same technology for every project as installation cost vary with each method at each site. A quality engineer will also consider the cost of monitoring.

To control occupant facilities, a building must be evaluated for its systems as well as its occupants. Lately, codes have focused on the detection of carbon monoxide (CO). However, little focus has been given to the shutdown of fossil fuel burning devices. Generally, CO detection is required in new occupancies (other than certain existing health care facilities) in which occupants might be asleep or otherwise have decreased capability of self-preservation and where vehicles, combustion equipment, or appliances are present. A quality engineer will consider the shutdown of fossil fuel burning devices upon CO detection; this is appropriate in almost all scenarios. Without automatic shutdown, occupant safety is endangered while the cause of excess CO is investigated.

In closing, the retaining of a quality FPE, to produce or review fire alarm design documentation, is important to ensure a system is appropriate for a project. A quality FPE will avoid costly mistakes by neither over or under engineering a fire alarm system.

Written by: Mark R. Richards, PE

Leave a Reply