Two-stage system

A two-stage fire alarm system sounds an alert signal first, addressed to designated persons, and an alarm signal follows automatically if that alert is not acknowledged within 5 minutes of its initiation. Ontario's Building Code requires it in a Group B occupancy, other than a Group B, Division 3 building 3 storeys or less in building height, and leaves it as an option in most other buildings. The escalation is conditional on acknowledgement rather than on the clock alone, and Ontario adds an exception for Group B, Division 2 occupancies that has no equivalent in the National Building Code 2020. Choosing two stage where the occupant load exceeds 1 000 also pulls in a one way voice communication system.

Last updated: September 2026

What it is

Two signals, in order. Operation of any manual station, waterflow detecting device or fire detector causes an alert signal to sound. The alert is a staff signal and the alarm is the everybody out signal: the Code's definitions describe an alert signal as advising designated persons of a fire emergency, and an alarm signal as advising occupants that a fire emergency exists. The whole point of the arrangement is to put a staff response in front of a building wide one.

Those two definitions are quoted in our guide from the revoked O. Reg. 332/12, so treat them as wording that explains the concept rather than as the current statutory text.

The 5 minutes is not a timer

This is the part most trade explanations get wrong. The Code makes the alarm signal sound automatically if the alert signal is not acknowledged within 5 minutes of its initiation. The escalation is conditional on acknowledgement, not on the clock alone. Calling it a flat five minute delay implies the general alarm is coming regardless, which is not what the sentence says. The 5 minutes is the window in which acknowledgement has to happen.

There is an exception, and it is Ontario's. The clause opens by excepting Group B, Division 2 occupancies, meaning care and treatment. In those buildings the automatic escalation does not apply. NBC 2020 has no such carve out.

What the Building Code does not say is what happens after acknowledgement: how long an acknowledgement holds, what re-triggers escalation, or how the panel handles any of it. Article 3.2.4.4 is silent, and the answer is not in the Building Code.

The other three parts of the clause

The key at the manual station. Manual stations on a two stage system must be equipped so that use of a key or similar device causes an alarm signal that continues to sound after the key is removed. It is not a hold to run function. Once keyed, the general alarm stays up.

Hotels. In a building containing a hotel, the alarm signal sounds in the initiating fire zone and the alert signal sounds throughout the hotel and such parts of the building as are needed to alert hotel staff. NBC 2020 has no equivalent clause at all.

Zone coding is permitted, not required. A coded alert identifying the zone of alarm initiation, repeated in its entirety not less than 4 times, then a continuous alert. All three are alert signals, and zone coding changes nothing about the escalation.

Where it is mandatory, and what it drags in

Article 3.2.4.3 requires two stage in a Group B occupancy, except that a Group B, Division 3 building 3 storeys or less in building height may be single or two stage. Group F, Division 1 and schools are locked to single stage. Everything else is the designer's call.

Before you choose it in a large building, read Article 3.2.4.23. Where a fire alarm system is required, a one way voice communication system must be installed where a two stage system is installed and the occupant load exceeds 1 000, excepting Group B, Division 1 and Group F, Division 1 major occupancies. Both conditions are cumulative, and it is easy to miss when the staging looks like a free choice.

Provenance. The provisions above are read from the free 2024 Building Code Compendium Volume 1, the 16 January 2025 update. The Ontario amendment document actually in force is dated 17 July 2026 and is not published online.

What goes wrong

Programming the escalation as an unconditional countdown. Missing the Group B, Division 2 exception on a care and treatment job. Missing the hotel split and sounding one signal throughout. Treating zone coding as a requirement. And loading a manual station with no key function on a system that needs one.

Neighbouring terms

The alert and alarm patterns are delivered by the NAC. The full side by side, with the Code text quoted and every Ontario departure from NBC 2020 tabled, is in single stage versus two stage fire alarm systems.

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