What type of detectors are often installed in shelters to detect smoke?

Photoelectric smoke detectors and ionization smoke detectors are commonly installed in shelters for smoke detection because they each utilize different technologies to identify the presence of smoke, thereby providing comprehensive coverage against different fire scenarios.

Photoelectric smoke detectors work by directing a light beam into a sensing chamber; when smoke enters that chamber, it scatters the light, triggering the alarm. This type is particularly effective for detecting slow-smoldering fires that produce a lot of smoke without flames.

On the other hand, ionization smoke detectors use a small amount of radioactive material to ionize the air in a sensing chamber. When smoke enters the chamber, it disrupts the ion flow, causing the alarm to sound. This type is more responsive to fast, flaming fires that produce little smoke initially.

By using both types of detectors in shelter environments, the risk of undetected fires can be minimized, enhancing the safety of the residents and staff. Other options listed do not primarily focus on smoke detection; for example, heat detectors respond to elevated temperatures rather than smoke, and manual pull stations require direct human action to activate the alarm system. Thus, the combination of photoelectric and ionization detectors provides crucial early warning in the event of a fire.