FST Fire Alarm Systems 4 — Questions and Answers
Question 1: What condition causes a 'common cause' failure concern when all detectors on a single initiating device circuit share the same pathway?
- Overloaded panel capacity
- A single fault disabling all devices on that circuit (Correct answer)
- Excessive detector spacing
- Incompatible device manufacturers
Correct answer: A single fault disabling all devices on that circuit
A common cause failure occurs when one event (such as wire damage) can disable multiple devices simultaneously, undermining system reliability.
Question 2: Per NFPA 72, voice evacuation messages in high-rise buildings must be intelligible at what minimum speech transmission index (STI) or equivalent metric?
- 0.35
- 0.45
- 0.50 (Correct answer)
- 0.65
Correct answer: 0.50
NFPA 72 requires emergency voice/alarm communications to achieve an STI of at least 0.45 (or CIS 0.50 equivalent) to ensure intelligible instructions during emergencies.
Question 3: A rate-of-rise heat detector will activate when:
- Temperature exceeds 135°F regardless of rise rate
- Temperature rises more than 12–15°F per minute (Correct answer)
- Smoke particles enter the sensing chamber
- Flame radiation is detected
Correct answer: Temperature rises more than 12–15°F per minute
Rate-of-rise heat detectors trigger when temperature increases faster than approximately 12–15°F per minute, indicating a rapidly developing fire.
Question 4: Which initiating device is MOST appropriate for a parking garage where vehicle exhaust could cause nuisance alarms from smoke detectors?
- Ionization smoke detector
- Photoelectric smoke detector
- Linear heat detector (Correct answer)
- Carbon monoxide detector
Correct answer: Linear heat detector
Linear heat detectors respond only to heat, making them immune to exhaust fumes and appropriate for environments where smoke detectors would generate nuisance alarms.
Question 5: Under NFPA 72, a fire alarm system at a protected premises must be inspected and tested at what minimum frequency?
- Monthly
- Quarterly
- Semi-annually
- Annually (Correct answer)
Correct answer: Annually
NFPA 72 requires a minimum annual inspection and test of fire alarm systems, though some components (batteries, supervisory devices) require more frequent testing.
Question 6: What is the purpose of a 'positive alarm sequence' (PAS) feature in a fire alarm system?
- Ensures alarms cannot be silenced without a code
- Provides a delay allowing trained personnel to investigate before general evacuation (Correct answer)
- Automatically notifies the fire department
- Sequences evacuation floor by floor
Correct answer: Provides a delay allowing trained personnel to investigate before general evacuation
Positive alarm sequence allows up to 3 minutes for an initial investigation and 3 more minutes for acknowledgment before triggering full evacuation, reducing false alarm dispatches.
Question 7: In a fire alarm system, the term 'trouble signal' specifically indicates:
- An active fire condition
- A fault that could impair system operation (Correct answer)
- A supervisory off-normal condition
- A system in alarm reset mode
Correct answer: A fault that could impair system operation
A trouble signal indicates a fault condition — such as an open circuit, low battery, or ground fault — that could prevent the system from functioning properly.
FST Fire Alarm Systems 4
What condition causes a 'common cause' failure concern when all detectors on a single initiating device circuit share the same pathway?