Beam-type detectors are the standard solution for high and large volumes because they can scan hundreds of square meters with a single device. However, their installation is not an assembly job, but a geometry task: what the device detects is not smoke, but the weakening of light coming from the opposite point — and that point must remain in the same location throughout the year.
Where is it used
The area of beam-type detectors consists of volumes where point detectors are either insufficient or maintenance is impossible:
- High-bay warehouses and logistics centers. Wide spans, high ceilings, continuously moving loads.
- Production halls and hangars. Volumes where ceiling height carries the risk of smoke dilution in point detection.
- Sports halls, indoor swimming pools, exhibition and display areas. Ceiling access is only possible via platform or scaffolding.
- Historic structures, mosques, museums, churches. Structures where routing devices and cables to the ceiling creates problems both aesthetically and from a protection standpoint; beam pairs can be concealed flush with the wall.
- Atriums and high gallery voids. Smoke layer monitoring in inter-floor openings.
Two types: opposed and reflective
| Opposed (transmitter + receiver) | Reflective (single unit + prism) | |
|---|---|---|
| Wiring | Power and signal required at both ends | Power and signal required only at one end; passive prism at opposite end |
| Range | Generally suitable for longer spans. | Effective range is shorter because the beam travels both ways. |
| Installation | Two points are aligned. | Aligned from a single point; installation is rapid. |
| Typical preference | Industrial volumes with very wide spans. | Historic structures with difficult cabling and medium spans. |
In reflective type, attention must be paid to keeping the prism clean and stable; dust on the prism surface consumes the device's own dirt compensation over time.
Placement rules
Beam-type detectors are evaluated within EN 54-12 scope; placement is performed according to design rules applicable to the premises (EN 54-14 and BYKHY). Four measurements are determinative in the field:
Distance of beam from ceiling
If the beam is placed immediately below the ceiling, smoke reaches the beam late due to stagnant hot air layer on the ceiling surface; if placed too low, it remains below the smoke layer. For this reason, the beam is maintained at a specific distance from the ceiling. In cases where the roof is pitched, an additional beam may be required in the ridge area, because smoke accumulates first at the highest point.
Distance between beams and from wall
Each beam protects a strip of specific width on either side. Therefore, the distance between adjacent beams and the distance of the beam from the wall are calculated together — the strip adjacent to the wall is maintained at half the width of the strip between two beams. As ceiling height increases, these distances are re-evaluated according to design rules.
Range
Each product has approved minimum and maximum operating span. Minimum range is as important as maximum range: a long-range device used at short span may receive the signal too strongly and fail to distinguish minor attenuations. For short distances, the attenuating filter provided by the manufacturer is used.
Obstruction corridor
A specific volume along and around the beam line must be permanently kept clear. In a warehouse, this means the shelf height is fixed in the design; subsequently raised shelves will cause the system to generate false alarms from day one. When this constraint is not discussed with the architecture and operations teams beforehand, the area is disabled after the system goes live.
Structural movement: the most overlooked issue
In beam systems, the majority of faults encountered in the field are not device faults; they are building movement. Steel roofs expand and contract with seasonal temperature variation, timber trusses move as they absorb moisture, and reinforced concrete structures continue to settle when new. A millimeter of angular misalignment is enough for the beam to miss the receiver over a long span.
For this reason, in wide spans, devices with automatic alignment compensation are preferred; these devices interpret slow signal changes as soiling or misalignment and readjust themselves, while interpreting sudden changes as smoke. The choice of mounting surface is equally important for this reason: the device is mounted, as far as possible, to a rigid surface connected to the main load-bearing structure of the building; thin sheet panels, suspended ceilings, or vibrating machine platforms are not suitable.
False alarm and fault causes
| Symptom | Possible cause | What is done |
|---|---|---|
| Sudden alarm, brief duration | Forklift mast, crane, suspended material blocks beam | Beam corridor is reviewed; if necessary, beam is raised or route is shifted |
| Gradually increasing soiling warning | Lens or prism has become dusty | Cleaning during periodic maintenance; interval is shortened in dusty environments |
| Seasonal signal loss | Roof expansion, structural shift | Realignment; if recurring, use automatic alignment device or more rigid mounting |
| Fault at specific times | Direct sunlight or strong lighting entering the receiver | Route modification or shading; optical bandpass selectivity of the device is checked |
| Alarm in humid conditions | Steam or condensation attenuates the beam | Route is separated from steam source; if necessary, technology is switched to heat-based detection |
Multi-beam detection in open and very large areas
There are two situations where classical single-beam devices struggle: lightweight steel structures with significant structural movement and very large open volumes where a single line is insufficient. In these cases, devices that transmit multiple beams at different angles and evaluate them using imaging methods on the receiver side are used. Their advantage is the ability to distinguish an object temporarily blocking the beam from genuine smoke — in volumes with moving equipment, they significantly reduce false alarms.
Maintenance
In beam systems, annual maintenance does not consist merely of alarm testing. Tasks to be performed: lens and prism cleaning, alignment signal level reading and comparison with initial commissioning value, checking how much of the dirt compensation margin has been consumed, alarm threshold verification with approved test filter, and physical traversal of the beam corridor to identify any new obstructions. The last item is most frequently omitted and most often causes faults in warehouse operations.
Periodic maintenance of beam-type detectors is part of detection system maintenance . For introductory information on the subject, you can refer to our beam detector article .
Project and product
For opposed and reflective beam-type detectors, automatic alignment models and accessories, you can refer to the beam detector product group , and for layout and range calculations suitable for your volume, you can contact usA zone monitoring module connects an entire conventional detector line to the addressable loop. Critical areas are renewed with addressable devices while secondary zones continue to operate with their existing wiring. This provides significant cost advantage in capacity upgrade and renovation projects.
Frequently Asked Questions
What is a beam detector and how does it work?
It is a linear smoke detector based on the principle of infrared light emitted from one point reaching the receiver on the opposite side or being reflected from a prism back to its own receiver. When smoke enters the beam path, part of the light is absorbed and scattered; the device measures this attenuation and triggers an alarm.
What is the maximum distance a beam detector can work?
It varies by product and each device has an approved minimum and maximum span range. The minimum range is as important as the maximum range; when a device is used at a shorter distance than planned, the attenuator filter specified by the manufacturer must be used.
What should be the distance between beam detectors?
Each beam protects a strip of defined width on both sides; the distance between adjacent beams and the distance to the wall are calculated accordingly, and the strip on the wall side is maintained at half the width of the strip between the two beams. The values are determined according to ceiling height and design rules, and must be calculated during the design phase.
Why is a beam detector giving false alarms?
The most common cause is physical obstruction of the beam path: forklift mast, crane, subsequently raised shelf or suspended material. Other causes include lens and prism fouling, alignment deviation due to roof expansion, direct sunlight reaching the receiver and steam. The solution is not to reduce sensitivity but to eliminate the cause.
Should a warehouse use a beam detector or a point detector?
In warehouses with high ceilings and large spans, beam type detectors both reduce the stratification problem and facilitate maintenance access. Comparison should be made not on the basis of device quantity but on the basis of covered area and maintenance access; in a space where the ceiling cannot be reached, periodic maintenance of a large number of point detectors becomes impractical.