How does an ionization smoke detector function?

An ionization smoke detector functions by using a small amount of radioactive material along with charged plates to detect smoke particles. The radioactive material, typically americium-241, ionizes the air in the detection chamber, which creates a flow of ions between two charged plates. When smoke enters the chamber, it disrupts this flow of ions. Specifically, smoke particles attach to the ions, reducing the number of ions available to carry the electric current between the plates. This change in current triggers the alarm, indicating the presence of smoke and, potentially, a fire.

This technology is particularly effective in detecting fast-flaming fires, such as those fueled by paper, wood, or fabric, because it responds quickly to the small particles produced during combustion. Understanding the operational principles of ionization smoke detectors helps fire investigators appreciate their strengths and limitations in fire detection scenarios.