Speech Intelligibility Testing for Emergency Warning Systems

Australian Standard 1851-2012

AS1851 Table 6.4.3.3

Five-Yearly Service Requirements for Emergency Warning Systems

Carry out speech intelligibility testing in all areas of the building where required to meet the requirements of the approved design of the system and property

Measure and record sound pressure levels from at minimum one reference point for each amplifier and ensure that each recorded measurement is consistent with the required sound pressure level.

Measure and record the impedance of each loudspeaker circuit and that that it has not changed by more than 15% from the last test or exceeded the rated output.

Clause E4D9

National Construction Code (NCC)

Emergency Warning & Intercom Systems

An emergency warning and intercom system complying, where applicable, with AS 1670.4 must be installed—

in a building with an effective height of more than 25 m; and
in a Class 3 building having a rise in storeys of more than 2 and used as—
1. the residential part of a primary or secondary school; or
2. accommodation for the aged, children or people with a disability; and
in a Class 3 building used as a residential care building, except that the system—
1. must be arranged to provide a warning for occupants; and
2. in areas used by the residents, may have its alarm adjusted in volume and content to minimise trauma consistent with the type and condition of residents; and
in a Class 9a building having a floor area of more than 1000 m² or a rise in storeys of more than 2, and the system—
1. must be arranged to provide a warning for occupants; and
2. in a ward area, may have its alarm adjusted in volume and content to minimise trauma consistent with the type and condition of patients; and
in a Class 9b building—
1. used as a school and having a rise in storeys of more than 3; or
2. used as a theatre, public hall, or the like, having a floor area more than 1000 m² or a rise in storeys of more than 2.

What is Speech Intelligibility

In Australia, ensuring that emergency warning systems (EWS) are clear and understandable is critical for occupant safety in buildings during emergencies. The Australian Standard AS1851-2012, which governs the routine service of fire protection systems and equipment, outlines specific requirements for maintaining these systems, including speech intelligibility testing for emergency warning systems. This article explains the importance of speech intelligibility testing and the five-yearly requirements under AS1851-2012.

Speech intelligibility refers to how clearly spoken messages from an emergency warning system can be understood by building occupants. In high-stress situations like fires or evacuations, clear communication can mean the difference between a safe exit and confusion. Poor acoustics, background noise, or faulty equipment can degrade message clarity, putting lives at risk. AS1851-2012 ensures systems are tested regularly to maintain their effectiveness.

Testing Requirements

Under AS1851-2012, emergency warning systems must undergo routine maintenance, with more comprehensive checks required every five years. For speech intelligibility, the standard emphasizes verifying that messages remain clear and audible across all designated areas. The five-yearly requirements include:

Speech Intelligibility Assessment: Testing to confirm that spoken messages meet the minimum intelligibility criteria, typically using objective measures like the Speech Transmission Index (STI). The system must achieve an STI score of at least 0.5 in areas where ambient noise is below 85dB(A), ensuring “fair” or better intelligibility for most listeners.

System Performance Verification: Checking the entire emergency warning system, including amplifiers, loudspeakers, microphones, and wiring, to ensure they function correctly and deliver clear audio. This involves inspecting for wear, damage, or degradation that could affect sound quality.

Coverage and Audibility Checks: Confirming that sound levels are adequate (not less than 65dB and not exceeding 105dB) and that speakers are positioned to cover all evacuation zones effectively, accounting for building acoustics and potential reverberation issues.

Documentation and Reporting: Maintaining detailed records of test results, including STI measurements and any corrective actions taken. These records serve as evidence of compliance and allow for comparison with future tests to monitor system performance over time.

How It’s Done

Speech intelligibility testing typically involves specialized equipment, such as a VOXBOX to generate a standardized test signal (like the STIPA signal) and a VOX analyzer to measure intelligibility at various points in the building. Two technicians are often required: one to operate the signal source near the system’s microphone and another to take measurements throughout the facility. Tests are quick, with each measurement taking about 18 seconds, and results are logged for compliance records.

Why It Matters

Adhering to AS1851-2012’s five-yearly testing ensures that emergency warning systems remain reliable and effective. Non-compliance can lead to fines, legal liabilities, or, worse, failure to protect occupants during an emergency. Building owners and facility managers must work with qualified fire safety technicians to schedule and document these tests.