ESA Certified Alarm Technician Practice Exam

Which type of photoelectric smoke detector uses reflective properties of smoke for detection?

1. Ionization detectors

2. Light scattering detectors

3. Thermal detectors

4. Multi-sensor detectors

The correct answer is: Light scattering detectors

The choice of light scattering detectors is correct because these devices operate on the principle of light scattering caused by the presence of smoke particles in the air. When smoke enters the chamber of a light scattering smoke detector, it disrupts a beam of light emitted by a light source, such as a laser or an LED. The smoke particles scatter the light, and this scattered light is detected by a photosensitive receiver. When the intensity of the scattered light reaches a certain threshold, it triggers the alarm. This method of detection is particularly effective for sensing smoldering fires, as the smoke produced during such fires tends to create the kind of particulate matter that causes significant light scattering. Unlike ionization detectors, which rely on the ionization of air particles, or thermal detectors, which respond to changes in temperature, light scattering detectors specifically engage with the optical properties of smoke. Multi-sensor detectors, while versatile, incorporate different types of sensors, including ionization and photoelectric technologies, making them dependent on mechanisms beyond just light scattering.