Dr Zzeus Q&A: How do i decide the best detector and which are bad for false alarm activations?

Dr Zzeus Q&A: How do i decide the best detector and which are bad for false alarm activations?

In this regular column, ‘Dr Zzeus’ Tom Brookes, MD of Zzeus training and chairman of the FSA, will answer your questions related to fire safety compliance. This month’s involves the selection of detectors…

Q. I’ve had a few issues with fire detectors giving false alarms, and when I’ve spoken to the manufacturers, they’ve said either it’s the wrong type of detector for the smoke or area. Most designs we receive from the architect just state smoke detectors or heat detectors. Is there an easy way of deciding the best detector and which are bad for false alarm activations?

BS 5839 1:2017 is the latest version of the standard and Section 3: Limitation of false alarms and unwanted fire alarm signals, delves deeply into the main causes of false alarms and how to limit them – I strongly recommend reading this section thoroughly. The fire alarm and detection sector is under extreme pressure to cut false alarms from current levels to as few as possible. Also, within the standard is Annex E, which takes you through selecting types of detectors for certain areas and which are better and worse for detection and false alarms. In Annex E, there are two tables that I have simplified for this article and colour-coded.

Firstly, look at Table 2 (below, left) and decide on the type of fire phenomenon, then look at the detectors that are green. The bright green is the fastest acting, while reds will be very slow-acting to the fire type. The next step is to refer to Table 3 (below, right) and think of the area and what false alarm phenomenon may occur in that area. Now follow the line across to which detectors are highlighted green and compare with the fastest-acting detectors.

  • TABLE 1
  • TABLE 2

If we use detection for a hotel bedroom with ensuite shower as an example, it’s very likely to have “smouldering furnishings”, so by referring to Table 2 we can see the green detectors are optical, CO2, multi-sensor detection optical/heat/ and multi-sensor detection optical/heat/CO2. We can now choose any of these to detect the fire.

Now consider what the causes of false alarms in a hotel room may be – steam, aerosols like deodorant and hairspray – and refer to Table 3 to see which items are very good green detectors for BOTH these types of issues. The CO2, Heat and Flame detectors are identified in this case. Now compare the two sets of detectors from your two tables and the best detector for detection and fewer false alarms would be the CO2.

Do you have a question you’d like answered? Email your queries to: Tom@Zzeus.org.uk

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