How do ionization and photoelectric smoke detectors differ in their response to fires?

• A. Ionization detectors respond quickly to flaming fires with smaller smoke particles; photoelectric detectors respond to smoldering fires with larger smoke particles.
• B. Photoelectric detectors respond to flaming fires with smaller smoke particles; ionization detectors respond to smoldering fires.
• C. Both types respond equally to all fire types.
• D. Ionization detectors rely on heat rather than smoke.

Answer: (C)

Ionization and photoelectric smoke detectors work differently, which is why they don’t respond the same way to every fire. An ionization detector uses a small amount of radioactive material to create a steady current between two plates. Smoke particles entering that chamber disrupt the current, triggering the alarm. This mechanism tends to react fastest to flaming fires, which produce a lot of small smoke particles that reach the sensor quickly.

A photoelectric detector uses a light source and a sensor. Smoke particles scatter the light into the sensor, setting off the alarm. This setup is more responsive to smoldering fires, which generate larger smoke particles that remain suspended and scatter more light.

So, while both detectors can detect both types of fires, one is generally quicker for flaming fires and the other for smoldering fires. Note that heat detectors are a different type and respond to heat rather than smoke. For comprehensive protection, some systems use both types or dual-sensor units.