The LWF Blog

Fire Safety Engineering for Design – Fire Detection & Alarm Systems – Part 152

October 2, 2023 10:58 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 151, LWF started to talk about the available types of fire alarm, starting with ionisation chamber smoke detectors. In part 152, we continue from that point.

Combined or multi-sensor heat and smoke detectors

A combined or multi-sensor heat and smoke detector may be used as part of a fire alarm system to gain the benefit of having both heat and smoke detection.

Commonly, the smoke detection element is of the optical method type and the heat detection is through a flat-response heat detector.

Modern multi-sensor detectors can provide detection for various signals including heat, smoke and combustion gases.

Point-type heat detectors

A point-type heat detector is designed to send a signal to trigger an alarm when the temperature surrounding a pre-determined spot reaches a pre-determined level.

Some detectors of this type may also include a rate of rise element designed to track a rapid rise in temperature before triggering the alarm.

While changes in temperature can be a useful way of detecting a fire, point-type heat detectors tend to be less sensitive than other detectors and so are probably best used where smoke detectors are deemed unsuitable due to particulate matter on a normal basis, (i.e. a smoke detector may trigger false alarms due to the environment in which the detector is sited).

Linear heat detectors

Linear heat detection relies on a specially-designed cable, which is able to detect changes in temperature along its length. There are two main types:

A simple metallic cable involving two steel cores twisted together, each cable insulated with a temperature-sensitive polymer. Once any section of the cable is heated to a pre-determined temperature, the polymer melts and the two wires touch, triggering an alarm at the control equipment.

Fibre optic linear heat detection is a more sophisticated option because it continually monitors the temperature along its length at intervals of around 1 metre. The results are obtainable at the control equipment and allow the system to be monitored and tweaked to allow for unusual temperature events which are not related to fire.

In part 153 of LWF’s series on fire engineering, we will continue exploring the types of smoke and heat detectors for fire alarms with beam detectors. 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.