The LWF Blog

Fire Engineering Design and Risk Assessment – Types of Fire Alarm Detector – Part 15

September 8, 2016 9:33 am

In our recent blog series for Architects and those involved in building planning, we have been looking at the different types of fire alarm detector used for specialist applications. In our last blog we looked at in what circumstances Aspirating Systems might be used and today we will talk about Flame Detectors and Gas Combustion Detectors and how they might be used.

 

Flame detectors are not generally in widespread use, but are more likely to be found in circumstances where particular assets are to be protected. Flame detection is more important in areas where very flammable materials or liquids may be in use or in storage near high value items. For this reason, aircraft hangars would be a prime example of a situation in which flame detectors might be used.

 

There are two types of flame detector – ultraviolet, which looks to detect ultraviolet radiation within flames and infrared, which is activated by the flickering of infrared radiation from flames.

 

As these detectors cannot detect smoke, they are sometimes used in conjunction with other types of detector such as heat and smoke.

Their use in a new and purpose designed fire alarm system would be unlikely these days as flame detectors are commonly replaced largely by video detection.

 

Gas Combustion Detectors are designed to detect specific gases which are produced during combustion. They are commonly known as Carbon Monoxide Detectors although the detectors which would be installed as a part of an alarm system differ from the standalone units which are purchased by consumers for use in their homes.

 

Gas Combustion Detectors are designed specifically to detect fires where a lack of heat or oxygen can restrict fire development and cause it to smoulder.

While they are very effective at detecting the particular kind of fire described, there are limitations which must be borne in mind.

 

Because Carbon Monoxide diffuses within a building and so can travel some significant distance, it can be that a detector not in the immediate area may be triggered, which means it could be hard to pinpoint the origin of the fire.

 

A Carbon Monoxide detector may not respond to a fire which has a good oxygen supply and is therefore burning with a high level of smoke, as it is only designed to pick up on the gases.

 

Within the detector unit, the sensor itself has a finite life and therefore would need checking and replacing at regular intervals. This means that maintenance can be a little onerous. There are longer life options available which use infrared detection but these can be too expensive for many purposes.

 

If Carbon Monoxide detection is necessary as a part of a fire alarm system, serious consideration should be given to combining these detectors with others which can detect smoke and heat in order to provide a more comprehensive protection.

 

In the next blog, we will give an overview of video smoke detection before looking at how and where detectors should be sited. 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 for over 25 years to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact Peter Gyere on 020 8668 8663.