Most small buildings use a single-stage fire alarm: any alarm sounds the evacuation signal everywhere. Larger and more complex buildings often use a two-stage system, which first alerts staff and then evacuates, or a voice system that tells people what to do floor by floor. The choice is set mainly by the building code for your building type, and then by how the building is run.
Single-stage systems
In a single-stage system, any alarm input, whether a detector, pull station or sprinkler flow switch, sounds the alarm signal throughout the building at once. Everyone leaves. It is simple, easy to understand and suitable for most low-rise and small buildings where everyone can get out quickly and there are no staff on hand to investigate.
Two-stage systems
A two-stage system separates the first warning from the order to evacuate. The first stage is an alert signal, which sounds with a distinct pattern so that staff know an alarm device has operated. Trained staff acknowledge it at the panel and go to investigate. If they confirm a fire, or if they do not acknowledge or resolve it within a set time, the system automatically moves to the second stage: the alarm signal, which means evacuate. Some inputs, such as particular pull stations or a key switch, can send the system straight to the alarm signal.
Two-stage systems are used in buildings such as hospitals, care facilities, large office towers and some assembly buildings, where moving everyone at once is difficult or harmful and staff are present at all times. They only work if staff are trained, the response is written into the fire safety plan and practised, and the timing is set as the code and the authority having jurisdiction require. A two-stage system in a building with no one available to respond is worse than a single-stage one.
Voice evacuation systems
A voice system uses speakers instead of horns or bells. It still sounds tones, but it can also play recorded messages and let the fire department or trained staff speak to the building from a central control location. Building codes require voice communication in some building types, such as high buildings, and owners choose it in others because a spoken instruction gets a faster and calmer response than a tone.
The main advantage is control. Different areas can get different messages at the same time. A typical approach in a tall building is to evacuate the fire floor and the floors next to it first, while telling everyone else to stand by. That keeps stairs from filling with people who are not in immediate danger and leaves room for firefighters coming up.
Making messages understandable
A voice system is only useful if people can understand the words. Loudness alone is not enough: a loud message in a hard, echoing space can be unintelligible. Designers aim for speech intelligibility, which depends on speaker spacing, the power tap on each speaker, the acoustics of the room and the background noise.
- More speakers at lower volume usually beats fewer speakers turned up, especially in corridors and rooms with hard surfaces.
- Problem spaces such as atriums, parking garages, gyms and mechanical rooms need individual attention.
- Messages should be short, plain and tested with real occupants. They tell people what is happening and exactly what to do.
- Testing during verification includes checking that messages are audible and understandable in each area, using listening checks and, on some projects, instrument measurements of intelligibility.
Other parts of a voice system
Central control and microphones
Voice systems have a control location, usually near the main entrance where firefighters arrive, with a microphone, zone selection switches and status indicators. Recorded messages run automatically; live announcements override them.
Firefighter communication
Many voice systems include two-way communication for firefighters, such as emergency telephones or jacks at stairs and other locations, so crews inside can talk to the command post.
Survivability
Because the system must keep talking to floors while a fire is burning on another floor, codes set requirements for how the wiring and amplifiers are protected and arranged. A fire on one floor should not silence speakers elsewhere. Designers meet this with routing, protected risers, fire-rated cable and the arrangement of amplifiers.
Non-fire messages
Some owners want to use the same speakers for other emergencies, such as lockdowns or severe weather. This is possible in some systems, but fire alarm functions must always take priority, and the codes and authority having jurisdiction may limit what can share the system. Plan it at design time rather than adding it later.
Common mistakes
- Fire safety plan out of step with the panel. The plan says staff have a certain time to investigate, but the panel was programmed differently, or the zoning changed in a renovation and nobody updated the plan.
- Alert signal treated as background noise. In two-stage buildings, occupants sometimes learn to ignore the alert pattern. Training should explain what it means and what to do while it sounds.
- Speakers added without checking amplifier capacity. Each new speaker draws power from an amplifier with a fixed rating and a standby battery. Additions need a recalculation, not just a wire pulled to the nearest speaker.
- Messages that no longer match the building. A message that names an exit or assembly area that has since changed sends people the wrong way.
- Tenant fit-outs that block sound. New walls and closed offices can leave a room without an audible or intelligible signal. Every fit-out should include a check of signal coverage and re-verification of the affected area.
The system is only half of it. Two-stage and voice systems depend on people: trained staff who know what the alert signal means, a fire safety plan that matches the system's programming and regular drills. Review the plan whenever the programming changes. See our guide to emergency response plans.
How ehZee can help
We design single-stage, two-stage and voice evacuation systems as part of our fire alarm system design service, including speaker layout, zoning, message wording and the sequence of operation, with drawings sealed by a licensed professional engineer where required. Our guide to how a fire alarm system works covers the basics.
Common questions
Can we convert a single-stage system to two-stage?
Sometimes, if the panel supports it and the building has staff to respond at all hours. It also needs approval from the authority having jurisdiction, a revised fire safety plan, staff training and verification of the changed sequence.
Why can't people understand our voice messages?
Usually because of too few speakers turned up too loud, hard surfaces, high background noise or a message that is too long. An intelligibility review of the problem areas normally points to added or relocated speakers and adjusted settings.
Who records the messages?
Messages are written as part of the design and agreed with the owner and, where required, the fire department. They are then recorded and loaded by the system supplier and checked during verification.
Do voice systems still need strobes?
Yes, in the spaces where the code requires visible signals. A voice message does nothing for someone who cannot hear it, so strobes are laid out alongside the speakers and are activated with the evacuation message. Some systems also use text displays to repeat the instruction.