S95 Fire Alarm System Operation 2 — Questions and Answers
Question 1: During a fire alarm signal, the control unit begins a pre-signal delay before notifying occupants. What is the primary purpose of this delay?
- To allow time for automatic suppression systems to activate first
- To permit trained personnel to investigate and confirm the alarm before general evacuation (Correct answer)
- To give the fire department time to arrive on scene before occupants react
- To reset the initiating device if it was triggered accidentally
Correct answer: To permit trained personnel to investigate and confirm the alarm before general evacuation
A pre-signal (or presignal) delay allows designated staff to investigate the alarm source before general notification, reducing unnecessary evacuations.
Question 2: A smoke detector in a corridor repeatedly goes into alarm during early morning hours with no visible smoke present. The MOST likely cause is:
- Faulty wiring in the initiating device circuit
- High humidity or condensation affecting the detector chamber (Correct answer)
- The detector is programmed for nighttime sensitivity mode
- Electromagnetic interference from HVAC startup
Correct answer: High humidity or condensation affecting the detector chamber
High humidity or condensation can cause ionization and photoelectric detectors to alarm nuisance-free by mimicking smoke particle density in the sensing chamber.
Question 3: According to NFPA 72, a single station smoke alarm differs from a system smoke detector primarily because it:
- Uses a different sensing principle that is more accurate
- Contains its own integral notification appliance and is self-contained (Correct answer)
- Must be connected to a supervising station to be code-compliant
- Is only permitted in residential occupancies of less than 500 sq ft
Correct answer: Contains its own integral notification appliance and is self-contained
A single station alarm integrates the detector and notification appliance in one unit, operating independently without a central control panel.
Question 4: A fire alarm control unit (FACU) is in the 'silenced' condition. Which of the following statements is TRUE?
- The alarm signal has been acknowledged and all initiating devices have reset
- Audible notification has been silenced but visual indicators and alarm condition remain active (Correct answer)
- The system has been placed in a full reset and is ready for normal operation
- Remote supervising station notification has been suspended until manual reset
Correct answer: Audible notification has been silenced but visual indicators and alarm condition remain active
Silencing only quiets audible appliances; the FACU remains in alarm condition with visual indicators active until the system is fully reset.
Question 5: Which component in a fire alarm system is responsible for converting a detected condition into an electrical signal sent to the control unit?
- Notification appliance
- Initiating device (Correct answer)
- Signal line circuit
- Annunciator panel
Correct answer: Initiating device
Initiating devices such as smoke detectors, heat detectors, and manual pull stations sense a condition and send a signal to the FACU.
Question 6: A fire alarm system supervisory signal is generated when:
- A smoke detector enters alarm state
- A sprinkler system valve is found in a partially closed position (Correct answer)
- The control unit battery voltage drops below acceptable levels
- A manual pull station is activated by a building occupant
Correct answer: A sprinkler system valve is found in a partially closed position
Supervisory signals indicate an off-normal condition in a fire protection system, such as a closed or partially closed sprinkler control valve.
Question 7: In a fire alarm system, Class B wiring differs from Class A wiring primarily in that Class B:
- Uses fiber optic cable instead of copper conductors
- Does not provide continuity of operation when a single open fault occurs (Correct answer)
- Requires end-of-line devices at each initiating device
- Is only approved for use with addressable control panels
Correct answer: Does not provide continuity of operation when a single open fault occurs
Class B circuits will lose communication to devices beyond a single open fault, whereas Class A circuits use a loop that maintains operation despite one open.
S95 Fire Alarm System Operation 2
During a fire alarm signal, the control unit begins a pre-signal delay before notifying occupants.
What is the primary purpose of this delay?