Which smoke detector type contains a small amount of radioactive material and functions by sensing a decrease in conductance of the air when smoke…

Ionization smoke detectors utilize a small amount of a radioactive isotope, typically Americium-241, to create a constant flow of ionized air particles between two electrodes within a sensing chamber. This flow establishes a small, measurable electrical current. When smoke particles from a fire enter the chamber, they attach to the ions, neutralizing them. This action disrupts the current flow, effectively decreasing the electrical conductance of the air. The detector's circuitry senses this drop in current and triggers the alarm. This technology is particularly sensitive to the small particles produced by fast-flaming fires.

A. Photoelectric: This type operates on the principle of light scattering or obscuration caused by smoke particles, and does not use radioactive material.

B. Cloud chamber air sampling: This high-sensitivity method works by causing moisture to condense on smoke particles to form a visible cloud, not by ionization.

C. Light scattering: This is the operational principle behind a type of photoelectric detector, not a distinct detector category that uses radioactive material.

1. SFPE. (2016). SFPE Handbook of Fire Protection Engineering (5th ed.). Springer. Section 4, Chapter 1, "Detection of Fires and Special Hazards," pp. 1298-1299. (Describes the operating principle of ionization detectors, stating they "contain a small radioactive source that ionizes the air in a sensing chamber.")

2. NFPA 72®, National Fire Alarm and Signaling Code®, 2022 Edition. Annex A, Section A.17.7.1.3, "Ionization Smoke Detection." (Explains that ionization smoke detection is based on a change in conductance of the air caused by smoke particles.)

3. Cote, A. E. (Ed.). (2008). Fire Protection Handbook (20th ed., Vol. 1). National Fire Protection Association. Section 14, Chapter 1, "Detection Devices and Systems," p. 14-12. (Details how ionization detectors work by using a radioactive source to ionize air and how smoke particles reduce this ionization, triggering an alarm.)