AK Fire Alarm common mistakes
AK Fire Alarm · Understand the traps and how to avoid them.
When calculating battery capacity for a fire alarm control unit, the candidate uses the full standby current plus alarm current for the entire standby period, rather than applying the derating factor and separate standby/alarm current draws.
Candidates often memorize the formula as 'total current × time' and forget that NFPA 72 requires battery capacity to be calculated at 20°C (68°F) with a derating factor (typically 1.2 for sealed lead-acid) and that the alarm current is only applied for the alarm duration (usually 5 or 15 minutes), not the full 24-hour standby.
What to do instead
Practice the standard battery calculation: (Standby current × 24 hours) + (Alarm current × alarm duration) = ampere-hours, then multiply by the derating factor (1.2) and add 20% for aging. Always verify the battery is rated for the calculated capacity at the expected temperature.
When determining spacing of spot-type smoke detectors, the candidate uses the flat ceiling spacing (30 ft) for sloped ceilings without adjusting for the slope or peak.
Candidates often memorize the 30-foot spacing rule from NFPA 72 for flat ceilings and apply it universally, overlooking the requirements for sloped ceilings (e.g., detectors within 3 ft of the peak, increased spacing based on slope).
What to do instead
Review NFPA 72 spacing requirements for sloped ceilings: for slopes greater than 1 in 8, detectors must be located within 3 ft of the peak, and spacing can be increased based on the slope. Use the formula or tables provided in NFPA 72.
When selecting notification appliances, the candidate ignores the required sound pressure level (SPL) of 15 dBA above ambient or 105 dBA, whichever is greater, and fails to account for the attenuation of sound with distance and walls.
Candidates often focus only on the 105 dBA minimum and forget the 15 dBA above ambient rule, or they assume the appliance rating at 10 ft applies directly to the sleeping area without calculating the loss due to distance and barriers.
What to do instead
Remember: public mode requires 15 dBA above ambient or 105 dBA (whichever is greater) measured at 10 ft, and sleeping areas require 75 dBA at the pillow or 15 dBA above ambient. Always calculate the attenuation: sound decreases 6 dB per doubling of distance and additional loss through walls. Use the manufacturer's data to verify coverage.
When classifying a fire alarm system, the candidate confuses the definitions of conventional, addressable, and multiplex systems, or misidentifies the requirements for each (e.g., applying addressable requirements to a conventional system).
Candidates may not have hands-on experience with different system types and rely on textbook definitions without understanding the practical implications, such as the number of initiating device circuits (IDCs) or the ability to identify individual device locations.
What to do instead
Study NFPA 72 Chapter 23 (or the applicable chapter for protected premises systems) and create a comparison chart: conventional systems use IDCs with devices wired in parallel and indicate only the zone; addressable systems use Signaling Line Circuits (SLCs) and can identify each device individually; multiplex systems use a combination. Know the wiring and supervision differences.
When reviewing plans, the candidate overlooks the requirement for a smoke detector in the immediate vicinity of the fire alarm control unit (FACU) and in areas such as elevator lobbies and machine rooms.
Candidates often focus on the general coverage requirements and forget specific location requirements mandated by NFPA 72 and NFPA 101, such as detector placement near the FACU to ensure early warning of a fire that could disable the control unit.
What to do instead
Memorize the specific locations required by NFPA 72: a smoke detector shall be installed in the immediate vicinity of the FACU (within 5 ft) and in each elevator lobby and machine room (if the elevator is used for fire service access). Also, check for detectors in areas with environmental conditions that may affect operation.
When performing inspection and testing, the candidate tests initiating devices but fails to verify the correct operation of supervisory signals (e.g., valve tamper switches, duct detector trouble) and their distinct audible/visual signals.
Candidates may concentrate on alarm testing and neglect supervisory and trouble signals, or they may not understand the difference between supervisory (e.g., off-normal valve position) and trouble (e.g., open circuit) signals.
What to do instead
Review NFPA 72 inspection and testing requirements: test each supervisory device (valve tamper, duct detector, etc.) to ensure it produces the correct supervisory signal (distinct from alarm and trouble) at the FACU. Verify that supervisory signals are annunciated visually and audibly (if required) and that they are properly logged.
When applying the Alaska Fire Code, the candidate assumes it is identical to the International Fire Code (IFC) without checking for state-specific amendments or adopted editions.
Candidates may not be familiar with Alaska's adoption process and may incorrectly apply the IFC or NFPA 1 without considering Alaska's amendments, which can include changes to fire alarm requirements for remote locations, cold weather, or specific occupancies.
What to do instead
Always check the current edition of the Alaska Fire Code (based on the IFC with amendments) and any state-specific regulations. Note that Alaska adopts NFPA 72 and NFPA 101 with certain amendments; review the Alaska Department of Public Safety, Fire Marshal's Office website for the latest adopted codes and amendments.
When designing or reviewing a fire alarm circuit, the candidate fails to verify that the circuit is supervised and that the wiring method is appropriate for the environment (e.g., using non-plenum-rated wire in a plenum).
Candidates may focus on functionality and overlook supervision requirements (Class A vs. Class B) and the need for specific wiring methods (e.g., FPLR, FPLP) as required by NFPA 70 (NEC) Article 760.
What to do instead
Review NFPA 72 Chapter 12 (Circuits and Pathways) and NEC Article 760. Ensure that initiating device circuits and notification appliance circuits are supervised (Class B or Class A) and that wiring in plenums is plenum-rated (FPLP). Verify that the wiring method is suitable for the environment and that the circuit is properly supervised for opens, grounds, and shorts.
When calculating the required number of notification appliances in a room, the candidate uses only the manufacturer's coverage pattern (e.g., 30 ft spacing) without considering the effect of partitions, ceiling height, or the need for visible signals in public areas.
Candidates may rely on simple rules of thumb and forget that walls, partitions, and ceiling height can block sound and light, requiring additional appliances. They may also overlook the requirement for visible notification in public and common areas.
What to do instead
Use the manufacturer's published spacing and coverage data, but adjust for room geometry: for sound, consider 6 dB loss per doubling of distance and additional loss through barriers; for visible signals, ensure that the entire area is within the rated coverage (e.g., 30 ft at 80 cd). Remember that visible signals are required in public areas and common areas per NFPA 101 and NFPA 72.
When determining the required fire alarm system features for a given occupancy, the candidate misapplies the occupancy classification (e.g., treating a business occupancy as an assembly occupancy) and therefore selects the wrong level of protection.
Candidates may not have a strong grasp of NFPA 101 occupancy classifications and how they trigger specific fire alarm requirements (e.g., manual fire alarm boxes, automatic detection, notification). They may also confuse the requirements for new vs. existing occupancies.
What to do instead
Study NFPA 101 Chapter 7 and the occupancy-specific chapters. Create a table of occupancy types (assembly, business, educational, healthcare, etc.) and the corresponding fire alarm requirements (e.g., manual alarm, automatic detection, voice evacuation). Pay attention to thresholds (e.g., occupant load) that trigger requirements. Practice with sample scenarios.