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Guide to beam detection for fire alarm systems

What are reflective beam detectors?

Reflective beam detectors are devices that project an infa-red light which is then returned via a reflector plate, this provides a sensing path across the protected space. When enough smoke obscures this infra-red beam, the returning signal strength will be reduced and will result in a fire condition being generated.

This sensing path can be up to 160m, in the case of the Fire Beam Xtra from The Fire Beam company, meaning large areas can be protected with minimal installation of devices compared with standard point detection. For instance a warehouse measuring 150m in length by 15m in width would only require a single beam. For the same area 30 optical point detectors would be needed.

When is beam detection suitable?

Reflective beam detectors can technically be used for any areas where a standard optical smoke detector would be specified. This being said they provide the most benefit in the following scenarios;

  • High ceilings – the maximum height standard point detectors can be cited is 10m whereas beam detectors can operate up to 40m.
  • Large open areas – many buildings have large open areas such as warehouses, hotels and leisure centres. Due to the size of these areas they are likely to require a significant number of optical detectors. Beam detectors however can protect extended lengths (160m in the case of the Fire Beam Xtra) meaning this solution can save time & money.
  • Installation limitations – there may be certain installations where it is impossible to get to the areas where optical detectors would be mounted such as swimming pools and cathedrals. In these situations beam detection may be best suited as they are located on the perimeter of the area with the beam emitted through the detection area.


The following are some consideration which should be kept in mind when considering the feasibility of reflective beam detectors;

  • Field of view – whilst the beam itself has a very small diameter, suitable distance around this beam is still required. In the case of the Fire Beam Xtra a 50cm radius from centre of the beam is the minimum distance needed.
  • Access to beam head & reflective plate – during the routine maintenance and testing of beams, access to both the beam head and reflective plate will be needed. Access to the reflector is required for both testing & cleaning whilst access to the beam head is required for cleaning only. As beams can be cited upto 40m high, special access equipment is often required for the installation and it being required again for this maintenance is sometimes overlooked.

Beam detection calculator

The following calculator will show you how many beam detectors will be required to protect an area. This calculator should be used as a guide and the final calculations will always be subject to a final fire alarm design.