Notification Appliances and Audibility/Visibility
Notification appliances must be audible and visible so occupants perceive the alarm. Know the concepts: sound pressure level (SPL) in decibels (dB), audibility above ambient noise, intelligibility for voice systems, and candela ratings for strobes.
Key rules: audible appliances must produce a sound level above the ambient noise (typically 15 dB above ambient, with a minimum at the occupant's location), and strobes must meet candela ratings based on room size and mounting. Synchronization is required so strobes flash together in the same field of view to avoid seizure risk. Voice evacuation systems require intelligibility, not just loudness.
Traps: assuming louder is always better; forgetting that a strobe's effective coverage depends on mounting height and room dimensions; confusing dB (sound) with candela (light); ignoring that sleeping areas require specific audibility at the pillow.
Rule of thumb: 15 dB above ambient is the classic audibility target, and strobe candela must match the room's listed coverage. When a question asks about a large room, check candela; when it asks about a noisy room, check dB above ambient.
Worked example: A large open warehouse has high ambient noise. The answer must address both raising SPL above ambient and providing adequate strobe coverage for the room dimensions, plus synchronization.