FDNY CoF Cleaning and Testing Smoke Detectors (F-78) Practice Test

The photoelectric detector operates based on the principle of light interruption. It contains a light source and a light sensor positioned at an angle to each other. Under normal conditions, the light emitted by the source does not reach the sensor. However, when smoke enters the detection chamber, it scatters the light towards the sensor, triggering the alarm. This mechanism makes photoelectric detectors particularly effective at sensing smoldering fires, which produce more smoke than flaming fires.

In contrast, the ionization detector uses ionized air to detect smoke. It contains a small amount of radioactive material that ionizes the air and allows current to flow between two electrodes. When smoke enters, it disrupts this ionized air, altering the current flow and triggering the alarm. This mechanism is sensitive to fast-flaming fires.

The projected beam detector utilizes a beam of light projected across an area, where interruption of this beam due to smoke or obscuration will activate the alarm. Although it also relies on light, its functioning differs from that of a photoelectric detector, which is typically more enclosed and operates on scattered light.

A heat detector does not rely on light at all; it senses changes in temperature to detect fires, making it distinct from any type of smoke detector and unrelated to