Initiating Devices Flashcards

Which type of smoke detector uses a small amount of radioactive material to ionize air and detect combustion particles?

Answer: Ionization detector

Ionization detectors use a small radioactive source (typically Americium-241) to ionize air between two charged plates; combustion particles disrupt the ion current and trigger an alarm.

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

Answer: Slow smoldering fires that produce large smoke particles

Photoelectric detectors use a light-scattering principle that responds most effectively to large smoke particles generated by slow, smoldering fires.

What is the maximum spacing between smoke detectors on a smooth, flat ceiling as specified by NFPA 72?

Answer: 50 feet

NFPA 72 establishes a default maximum spacing of 30 feet (900 sq ft area) between smoke detectors on smooth, flat ceilings, but allows up to 50 feet in some listing conditions.

A projected beam smoke detector consists of which two primary components?

Answer: Transmitter and receiver

A projected beam detector uses a transmitter that emits an infrared or laser beam and a receiver that measures beam obscuration caused by smoke.

Where are duct smoke detectors required to be installed according to NFPA 72 and NFPA 90A?

Answer: In HVAC ducts to detect smoke and shut down air handling units

Duct smoke detectors are installed in HVAC supply and return air ducts primarily to detect smoke and initiate shutdown of the air handling unit to prevent smoke circulation.

Which condition would cause a spot-type smoke detector to generate a nuisance alarm?

Answer: Steam or high humidity near the detector

Steam and high humidity can cause water vapor condensation in the sensing chamber, mimicking smoke particles and triggering a false (nuisance) alarm.

An aspirating smoke detection (ASD) system draws air samples through a pipe network to a central detection unit. What is a primary advantage of this design?

Answer: Ability to detect extremely low concentrations of smoke at very early stages

ASD systems actively sample air and can detect very low concentrations of smoke particles, providing early warning long before a conventional spot detector would respond.