Initiating Devices Flashcards

A photoelectric smoke detector is most effective at detecting which type of fire?

Answer: A slow, smoldering fire that produces a large amount of smoke.

Photoelectric smoke detectors operate using a light source and a sensor. When smoke particles enter the chamber, they scatter the light beam, causing it to hit the sensor and trigger the alarm. This technology is particularly effective at detecting the larger smoke particles produced by slow, smoldering fires.

In a commercial building, what is the primary function of a duct smoke detector?

Answer: To shut down the HVAC system and prevent the spread of smoke throughout the building.

Duct smoke detectors are installed in HVAC ductwork to detect the presence of smoke. Their main purpose is to prevent the circulation of smoke from a fire in one area of a building to other areas through the ventilation system. Upon detecting smoke, they send a signal to the fire alarm control panel, which then typically shuts down the HVAC fans and closes dampers.

Which of the following is a requirement for the installation of manual fire alarm pull stations according to NFPA 72?

Answer: They must be located within 5 feet (60 inches) of the entrance to each exit.

NFPA 72, the National Fire Alarm and Signaling Code, requires that manual fire alarm boxes (pull stations) be located within 5 feet (60 inches) of the entrance to each exit. The operable part should be between 42 and 48 inches from the floor, and they are required to be red in color.

A rate-of-rise heat detector is designed to activate when:

Answer: The temperature increases by a specified number of degrees per minute.

Rate-of-rise (ROR) heat detectors are triggered by a rapid increase in temperature over a short period, typically around 12-15°F (6.7-8.3°C) per minute. This allows them to signal an alarm before the temperature reaches a high fixed point, providing earlier warning for fast-developing fires.

In a dusty industrial environment, such as a woodworking shop, which type of automatic initiating device would be most appropriate to minimize nuisance alarms?

Answer: Heat detector

Heat detectors are the most suitable choice for dusty environments where smoke detectors are prone to false alarms caused by airborne particles. Heat detectors respond to the thermal energy of a fire and are unaffected by dust, making them more reliable in such locations.

An ionization smoke detector is generally more responsive than a photoelectric detector to:

Answer: Fast, flaming fires with small, invisible combustion particles.

Ionization smoke detectors contain a small amount of radioactive material that ionizes the air between two charged plates, creating a current. When small, invisible particles of combustion from a fast-flaming fire enter the chamber, they disrupt this current, triggering the alarm. They are generally more sensitive to these types of fires than photoelectric detectors.