Smoke detectors include the following types:

• A. Ionization
• B. Light scattering photoelectric
• C. Light obscuration
• D. All of the above

Answer: (D)

Smoke detectors rely on different sensing methods to detect smoke. Ionization detectors use a small radioactive source to ionize air; when smoke enters the chamber, it disrupts the ion flow and triggers the alarm. They tend to respond quickly to flaming fires. Photoelectric detectors use light; in the light-scattering type, smoke particles scatter the beam and redirect light to a sensor, which is especially good at detecting the larger smoke particles produced by smoldering fires. Light obscuration detectors send a beam of light to a sensor and detect the smoke by the beam being blocked or reduced, signaling an alarm. Each type covers different fire characteristics, and many detectors use more than one principle or are designed as dual-sensor units. Because all three approaches exist, the best choice is that all of the above.