Strobe / visual signal device

A strobe is a visible signal device, a flashing appliance that supplements the audible alarm signal. Ontario Building Code Article 3.2.4.19, Sentence (1), makes them mandatory on noise-based triggers rather than disability-based ones: where the ambient noise level is more than 87 dBA, where occupants use ear protection devices or are located in an audiometric booth or a sound-insulating enclosure, and in assembly occupancies in which music and other sounds associated with performances could exceed 100 dBA. Ontario also carries clause (1)(i), requiring visible signals in living spaces in a suite of residential occupancy in a Group C major occupancy apartment building, which NBC 2020 does not have. Visible devices are required in addition to audible ones, never instead of them.

Last updated: September 2026

What a visible signal device is for

A strobe exists for the cases where sound will not do the job. In Canadian code terms it is a visible signal device, and Article 3.2.4.19 of Division B of Ontario's 2024 Building Code is the article that decides when you need one. It is the counterpart to Article 3.2.4.18, which handles the audible side.

The heading of the article is worth reading literally. It is called Visible Signals, and Sentence (1) requires the devices in addition to audible signal devices. There is no reading of it in which a strobe substitutes for a horn. If you take a level reading that fails in a space, adding strobes does not fix it. See audibility for what the level has to be.

The triggers are about noise, not about who is in the room

This is the single most misunderstood point about Canadian visible signalling, and it is where imported American practice does real damage.

Ontario's triggers in Sentence (1) include:

Clause	Trigger
(b)	Assembly occupancies in which music and other sounds associated with performances could exceed 100 dBA
(c)	Any floor area in which the ambient noise level is more than 87 dBA
(d)	Any floor area in which occupants use ear protection devices, are located in an audiometric booth, or are located in sound-insulating enclosures

Every one of those is a statement about the acoustic environment. None of them is a statement about occupant hearing ability. Under United States practice, visible notification in public and common use areas is driven largely by accessibility law rather than by ambient noise, which is why an American design guide will place strobes in corridors and washrooms where Ontario's Article 3.2.4.19 does not. That is a contrast, not a requirement you can carry across the border. The wider version of that argument is in NFPA 72 versus CAN/ULC-S524.

Ontario building projects still have accessibility obligations from other law. They just do not come out of Article 3.2.4.19.

The Ontario-only apartment clause

Ontario carries an extra clause, 3.2.4.19.(1)(i), requiring visible signal devices in living spaces in a suite of residential occupancy in a Group C major occupancy apartment building. NBC 2020 has no equivalent.

This is the clause most often missed, because it is missed in a specific way: a consultant designs from the national code or from a template built on it, the clause is not there, and nothing in the drawing review catches it until somebody reads the Ontario text. If you work from national documents, check Ontario versus the National Building Code before you assume the two match.

What it costs you on the circuit

Strobes are the heaviest load on a signal circuit. A horn draws modest current, a strobe draws a pulse at every flash, and a corridor full of them will drive the alarm load on that NAC far harder than the horns do. Two consequences show up late if you ignore them early: the battery calculation fails on alarm load, and the last device on the run drops out of its listed voltage window because of voltage drop.

What the Code does not specify

Article 3.2.4.19 tells you when a visible device is required. It does not tell you the candela rating, the mounting height, the spacing, the flash rate, or whether devices in the same field of view have to be synchronized. Those sit in the ULC installation and product standards, which are copyrighted and sold, and we do not reproduce them or fill the gap with the American figures.

Neighbouring entries: the notification appliance family generally, and the horn on the audible side.

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