The LWF Blog

Fire Safety Engineering for Design – Fire Detection & Alarm Systems – Part 144

August 7, 2023 10:34 am

LWF’s Fire Safety Engineering blog series is written for Architects, building designers and others in the construction industry to highlight and promote discussion on all topics around fire engineering. In part 143, LWF began to take a look at fire alarm systems for domestic dwellings and gave an overview of the grades and categories of system for domestic application. In part 144, we touch on the NFPA 72 guidance for fire alarm systems in private dwellings, as well as examining the types of fire detection systems.

The type of grade and category of system installed in a new private dwelling will be based on the relevant codes and standards, any local regulations in place, the size of the building and its usage. The nature of the occupancy will also be relevant, whether it is to be owner-occupied, students in halls of residence or short-let tenancies.

Whatever grade and category is chosen for a building, it should be acceptable to all stakeholders.

NFPA 72 contains recommendations in chapter 11 relating to the use of fire alarm systems in residential builds. The levels of detection are similar to those laid out in BS 5839-6, but are more prescriptive and categorised into building types rather than into grades and categories. The selection of a system under NFPA 72 is therefore more straightforward.

Types of fire detection systems

All fire detection systems have the same principle to detect a fire in common. A fire or product of combustion causes a disturbance in the steady-state signal within the detector. The differences between product types relate to what products the devices are designed to detect and the way the signal is processed by the fire alarm control and indicating equipment (CIE).

The majority of fire detection systems fall into two over-arching categories:

• Conventional monitored systems
• Addressable systems (including analogue addressable)

Conventional monitored systems use a basic method of detecting fire. The detectors on the system are either smoke or heat sensitive and are wired in radial circuits from the control panel. A resistor or semiconductor is placed at the end of each circuit and this creates a known resistance across the circuit, providing a steady-state reference.

In part 145 of LWF’s series on fire engineering, we will continue to talk about conventional monitored fire detection systems before moving on to cover addressable systems (including analogue addressable). In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.

Lawrence Webster Forrest has been working with their clients since 1986 to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact the LWF office on 0800 410 1130.

While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.