What is an Optical Beam Smoke Detector?

The most common type of smoke detector is the optical point detector. It contains an infrared light beam projected across a small sensing chamber inside the device. When smoke enters the sensing chamber through the outer holes in the detector’s body, it affects the infrared beam, triggering the device into alarm. The alarm alerts individuals to a fire.

Optical beam smoke detectors work on a similar principle, but instead, the infrared light beam is projected across the open area of a building. This effectively transforms the entire building into the sensing chamber. The optical beam detects smoke along the entire beam path, helping to detect fire early and prevent further damage.

How does optical beam detection work?

When smoke passes through an invisible infrared beam, the solid particles and liquid droplets in the smoke reflect and scatter the photons of light. As a result, the intensity of the light is reduced on the far side of the smoke cloud. This reduction in intensity, known as obscuration, can be detected and used as a signal to indicate the occurrence of a fire.

The two main types of optical beam smoke detectors are Reflective and End-to-End. Both types consist of a transmitter (a light source) and a receiver (a detector). Reflective detectors are simpler and more cost-effective to install and maintain than End-to-End detectors. They only require electrical cabling on one side of the protected area, and during servicing, there is only one device to clean and maintain. Aligning a Reflective detector is usually easier than End-to-End, as there is only one piece of equipment to adjust at one end of the beam (the reflector is usually not adjustable). On the other hand, End-to-End detectors require adjustment at both ends of the beam. The reflected beam diverges as it passes back across the space from the reflector, and so more space is required by the beam. An End-to-End beam can pass through a narrower gap.

Optical smoke detectors should be installed near the ceiling to take advantage of the natural accumulation and spreading of smoke that occurs in the upper part of a room during a fire. The maximum height of a room that can be protected by a single set of detectors depends on the sensitivity of the detectors and whether or not the ceiling is flat. Taller spaces will require additional detectors installed at lower heights or supplementary detection.