When is EWIS required in an Australian building?

EWIS is required under NCC 2025 E4D9 in any building with an effective height over 25 metres, Class 9a health-care buildings over 1,000 m² or 2 storeys, Class 3 aged-care or school residential buildings over 2 storeys, Class 9b theatres over 1,000 m² or 2 storeys, and Class 9b schools over 3 storeys.

What is the difference between EWIS and an occupant warning system (OWS)?

EWIS has multiple evacuation zones with staged evacuation and a warden intercom system. An OWS has a single amplifier and one zone that activates the entire building at once. EWIS is required for buildings triggering NCC E4D9; smaller buildings may use an OWS.

What sound level do EWIS speakers need to produce?

Under AS 1670.4, EWIS speakers must produce at least 10 dB above ambient noise, with a minimum of 65 dBA and a maximum of 105 dBA. Speech intelligibility must be at least 0.5 STI where ambient noise is below 85 dBA.

What are the EWIS alert and evacuate tones?

The alert tone is a slow repeating beep that tells occupants to prepare to evacuate. The evacuate tone is a rising whoop that tells occupants to leave the building. The system must switch from alert to evacuate within 10 minutes of fire detection.

What standard governs EWIS design in Australia?

AS 1670.4:2024 governs the design, installation and commissioning of emergency warning and intercom systems in Australian buildings. The NCC 2025 calls up this standard through clause E4D9.

Emergency Warning and Intercommunication Systems (EWIS)

Section 1

What You Need to Know

EWIS (Emergency Warning and Intercommunication Systems) tells people in a building that there is a fire and guides them out safely. The NCC (National Construction Code) requires EWIS in tall buildings over 25 metres and in certain health-care, aged-care, and school buildings. AS 1670.4 sets the rules for how the system works. If the system fails at commissioning, you will not get an occupation certificate.

Section 2

The Rules

Buildings with an effective height over 25 metres must have EWIS (NCC 2025, E4D9)
Class 9a health-care buildings need EWIS if the floor area exceeds 1,000 m² or the building has more than 2 storeys (NCC 2025, E4D9)
Class 3 aged-care or school residential buildings need EWIS if they have more than 2 storeys (NCC 2025, E4D9)
Class 9b theatres and public halls need EWIS if the floor area exceeds 1,000 m² or the building has more than 2 storeys (NCC 2025, E4D9)
Class 9b schools need EWIS if the building has more than 3 storeys (NCC 2025, E4D9)
Speakers must produce at least 10 dB above ambient noise, with a minimum of 65 dBA and a maximum of 105 dBA (AS 1670.4)
Speech intelligibility must be at least 0.5 STI where ambient noise is below 85 dBA (AS 1670.4)

Section 3

What This Means in Practice

Take a 10-storey office tower at 35 metres tall. It exceeds the 25-metre threshold, so it needs a full EWIS. The system has speakers on every floor, warden intercom phones (WIPs) in every evacuation zone, and a master emergency control panel (MECP) in the fire control room. The MECP sits next to the fire indicator panel (FIP) so the fire brigade can control both from one spot.

The EWIS runs a staged evacuation. When fire is detected, the alert tone (a slow beep) sounds on the fire floor. Wardens check the situation and report back using the WIP phones. Within 10 minutes, the system must switch to the evacuate tone (a rising whoop) and cascade through adjacent floors. This stops everyone rushing the stairs at once.

Speakers run on 100V line circuits and need careful placement. Every spot in the building must hear the alarm at 10 dB above background noise. In a busy food court at 70 dBA ambient, speakers need to hit 80 dBA. In a quiet office at 45 dBA, the 65 dBA minimum still applies. The fire engineer sets the zones, but the building services engineer sizes the amplifiers, routes the speaker cables, and coordinates ceiling locations with the architect.

Section 4

Key Design Decisions

1

EWIS vs. Occupant Warning System (OWS)

If your building is under 25 metres and does not fall into the E4D9 building classes, a simpler OWS may be enough. An OWS has one amplifier and one zone. EWIS has multiple zones with staged evacuation and an intercom system.

Trade-off: EWIS typically costs significantly more than an OWS due to multiple amplifier channels, zoned wiring, and intercom hardware. But it is the only compliant option if E4D9 applies. Getting this wrong means redesign and delay.

2

Speaker Type: Ceiling vs. Surface Mount

Use ceiling-mount speakers in standard office and retail areas with accessible ceilings. Use surface-mount horn speakers in car parks, plant rooms, and areas with concrete slab ceilings where there is no ceiling void.

Trade-off: Ceiling speakers blend into the fit-out. Surface-mount speakers are visible but reach further in open spaces. Pick early so the architect can plan the ceiling grid.

3

Zone Layout and Staged Evacuation Sequence

Align EWIS zones with the building's fire compartments and the emergency plan. Each zone needs its own amplifier channel, speaker circuit, and at least one WIP phone. The fire engineer defines the zones; the building services engineer wires them.

Trade-off: More zones give finer control over evacuation staging but add amplifier channels, wiring, and cost. A typical office tower runs one zone per floor.

4

Speech Intelligibility vs. Background Noise

AS 1670.4 requires 0.5 STI in areas below 85 dBA ambient. High-reverb spaces like atriums and car parks are hard to get right. You may need directional speakers or extra units to hit 0.5 STI.

Trade-off: Extra speakers and acoustic modelling add cost for each problem zone. Failing the STI test at commissioning means rework under program pressure.

Section 5

Who Needs to Know What

Section 6

References

AS 1670.4:2024, Fire detection, warning, control and intercom systems — Part 4: Sound systems and intercom systems for emergency purposes
National Construction Code 2022, Volume One, Part E4 — Visibility in an emergency, exit signs and warning systems (E4D9)
AS 1670.1:2024, Fire detection, warning, control and intercom systems — Part 1: System design, installation and commissioning
AS 1851-2012, Routine service of fire protection systems and equipment
ISO 8201, Acoustics - Audible emergency evacuation signal
AS ISO 7240.24, Fire detection and alarm systems - Part 24: Sound system loudspeaker requirements

Emergency Warning and Intercommunication Systems (EWIS)

What You Need to Know

The Rules

What This Means in Practice

Key Design Decisions

EWIS vs. Occupant Warning System (OWS)

Speaker Type: Ceiling vs. Surface Mount

Zone Layout and Staged Evacuation Sequence

Speech Intelligibility vs. Background Noise

Who Needs to Know What

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References

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