This article is a continuation of the Fire Safety Design stage 1, and continues with Fire Design stage 4. Read more about the second stage(siting of manual call points) and the third stage(select automatic detectors) in Fire Safety Design.
All manual call points, whatever the system, should be RED in colour and comply toBS EN 54-11Type A, and should be located as follows:
- Onall storey existsandall exitsto open air irrespective whether they are designated fire exits;
- So that nobody has to travel more than45 metresto reach one except if the exit routes are undefined, in which casethe direct line distance should not exceed 30 metres;
- The above distances need to bereducedto 25 and 16 metres respectively, if there are persons with limited mobility or there is a likelihood of rapid fire development;
- Onescape routes and exitsto the open air, so that no one has to travel more than 45 metres on a defined route and 30 metres on an undefined route;
- In all areas withpotential high fire risk, such as kitchens, etc;
- Wherephased evacuation is planned, call points will need siting on all exits from a particular zone;
- 1.4 metres + or – 200mm above the floor;
- Call pointsfitted with protective hinged covers for whatever reason should be listed as a Variation;
In is very important to:
- Havean adequate number ofdetectorsto fully cover the area requiring protection;
- Selectthe correct type of detectorto match the potential fire type;
- Tosite the detectorsto give the best chance of detecting the fire quickly;
- To take into accountthe potential threat of false alarms.
We would strongly recommend that the designer reads Section 2&3 ofBS 5389-1:2002, for further advice on the selection and siting ofautomatic detectors.
Optical detectorsare generally used for detecting slow smouldering fires while ionisation detectors are better suited to free burning high energy fires.
How to avoid false alarms
Within the standard, a strong case is made to avoid false alarms. There are some areas where the placement of automatic smoke detectors should be avoided.
Irrespective of the type of smoke detector, the areas to be avoided are steamy, dusty or smoky enviroments such as kitchens, showers or bathrooms.
Other areas where care should be taken when using optical detectos are: enviroments with large amounts of dust, areas where steam occurs or where there are likely to be infestations of small insects such as grain thrip flies.
Other forms of detectors – some advices
- Fixed temperature heat detectors
The fixed temperature heat detectors can be used in areas where smoke detectors are unsuitable; however, they are not advisable for use in corridors or where production of smoke may be a threat to people’s escape;
- Rate of rise heat detectors
Rate of rise heat detectors, which have a combined fixed temperature and rate of rise sensing element, may offer improved reaction times. However, they should not be used within kitchens or where there is likely to be a rapid fluctuation in temperature, like the loading bays, boiler rooms, lantern lights, etc.
- Duct detectors
This device incorporates anoptical smoke detectorwhich samples the air extracted from the duct via a sampling tube. While this may appear to be an ideal solution for a wide range of applications, it is strongly recommended that before its use, you consult a professional design team for further information. Air velocity and dilution of the air will greatly affect the expected sensitivity of such a device;
- Beam detectors
Unlike a point type detector, beam detectors provide detection over a much greater area as well as being suitable for siting at much higher mounting heights. Generally, one beam detector can protect an area of up to 100m in length with a width dependant on the roof construction(flat or apex).
Ideal for use in shopping malls, warehousing, aircraft hangers or buildings with high atria.
These are the 2nd and 3rd stages ofour recommendation of fire design/fire safety design(seestage 1). To be continued with the next steps.