How to Test Emergency PA System Compliance

Regulatory Background

Emergency voice communication systems (EVCS), voice alarm systems (VAS), and emergency PA systems must meet speech intelligibility requirements specified in building codes and fire safety standards. IEC 60268-16 defines the STIPA measurement method. BS 5839-8 requires minimum STI of 0.50 for voice alarm systems. EN 54-16 specifies requirements for voice alarm control and indicating equipment. NFPA 72 references intelligibility testing for mass notification systems. Building authorities require documented STI measurements as part of commissioning and periodic recertification, typically every 1-3 years.

Compliance Requirements

Standard	Minimum STI	Application
BS 5839-8	0.50	Voice alarm systems (UK)
EN 54-16	0.50	Voice alarm control (EU)
NFPA 72	0.50 (0.70 preferred)	Mass notification (US)
AS 1670.4	0.50	Fire detection (Australia)

Measurement Procedure

1. Open SonaVyx STI measurement tool and select STIPA mode.
2. Connect the STIPA test signal to the emergency PA input (replacing the normal announcement source).
3. Set the system to emergency mode at the designated emergency SPL level.
4. Measure STIPA at the worst-case listener positions: farthest from speakers, reverberant areas, high-noise areas, under obstructions.
5. Record the STI value at each position along with the position description.
6. Measure background noise (LAeq) at each position with the PA system silent.
7. Measure ambient SPL at each position with the PA playing the STIPA signal.
8. Document the signal-to-noise ratio (SPL minus background noise) at each position.

Interpretation

Every measured position must meet the minimum STI requirement for the applicable standard. A single position below the threshold constitutes a compliance failure. STI of 0.50 corresponds to "Fair" intelligibility, which means most common words and simple sentences are understood. For life safety applications, aim for STI above 0.55 to provide margin. The signal-to-noise ratio should be at least 10dB at every position for reliable intelligibility. If STI is below 0.50 at any position, identify whether the dominant factor is reverberation (high RT60), background noise (high NC), coverage (low SPL), or frequency response (band-limited system).

Solutions

For coverage gaps: add speakers to cover positions where direct sound level is insufficient. Emergency PA systems should provide uniform coverage at every occupied position, unlike entertainment systems that can accept some variation. For reverberation: in corridors and stairwells, add absorption to reduce RT60 below 1.5 seconds in the 500Hz to 4kHz range. For background noise: coordinate with building management to assess HVAC noise during emergency mode, since emergency may require higher ventilation. For frequency response: ensure speakers reproduce 500Hz to 4kHz adequately and apply equalization to emphasize the 2-4kHz consonant region. Replace band-limited horn speakers with full-range models where intelligibility is insufficient.

Documentation

Create a measurement report documenting each test position, the STI value, background noise level, and signal level. Include a floor plan showing measurement positions with color-coded pass/fail indicators. SonaVyx report generator creates this documentation automatically. Submit the report to the building authority or fire safety officer as part of commissioning certification. Schedule annual remeasurement to maintain compliance.

Measure emergency PA compliance with SonaVyx STI