NFPA National Fire Alarm and Signaling Code (NFPA 72) Practice Exam 2025 - Free NFPA 72 Practice Questions and Study Guide

Photoelectric light-scattering smoke detectors function by utilizing a light source, often a laser or LED, which emits a beam of light into a sensing chamber. When smoke particles enter this chamber, they interact with the light. The particles reflect and scatter the light towards the sensor, which is designed to detect this scattered light. This increase in light detected by the sensor indicates the presence of smoke, triggering the alarm.

The mechanism relies heavily on the properties of smoke particles, particularly their ability to scatter light. The strength of the signal received by the sensor correlates with the concentration of smoke in the air. As the density of smoke increases, more light is scattered, leading to a stronger signal and a higher likelihood of alarm activation. This method is reliable and effective for smoke detection, particularly in scenarios where smoldering fires are present since these types of fires produce larger smoke particles that scatter light more efficiently.

The other choices do not accurately describe the basic operation of photoelectric smoke detectors. For instance, the absorption of light does not directly lead to detection by these devices, and while heat may be a byproduct of combustion, it is not utilized in detecting smoke through this technology. Additionally, sound waves are not a factor in the detection process of photo