Corridor Strobe Spacing Chart
How to space fire alarm strobes in a corridor 20 ft wide or less, per NFPA 72 (2022 edition, §18.5.5.8): a 15 cd minimum with a placement rule instead of the room-size candela table. Wider corridors fall back to the wall-mounted room table. The synchronization requirement applies wherever strobes share a field of view.
Corridor spacing rules (≤ 20 ft wide)
| Rule | Requirement |
|---|---|
| Minimum candela (corridors ≤ 20 ft wide) | 15 cd |
| Maximum spacing between appliances | 100 ft |
| Distance of first/last appliance from each end | Within 15 ft |
| Corridors wider than 20 ft | Use the room-spacing (wall) table instead |
| Offsets, legs, and turns | Add appliances so the viewing path is never interrupted |
Corridor length → minimum 15 cd strobes
| Corridor length | Min 15 cd strobes |
|---|---|
| 0–30 ft | 1 |
| 31–130 ft | 2 |
| 131–230 ft | 3 |
| 231–330 ft | 4 |
| 331–430 ft | 5 |
| 431–530 ft | 6 |
How corridor spacing works
A corridor is a special case: rather than sizing candela to the space, NFPA 72 lets you use the smallest standard strobe (15 cd) and instead controls coverage by spacing. Put a strobe within 15 ft of each end so no one steps into an unlit stretch, then no more than 100 ft between strobes down the run. This holds for corridors up to 20 ft wide; anything wider is treated as a room and sized from the wall strobe candela chart.
The corridor-length table is just that spacing arithmetic worked out: with a strobe 15 ft from each end and 100 ft between, one strobe reaches 30 ft, and every strobe after that adds another 100 ft. Recent editions dropped the printed table because the two spacing rules already produce it.
Synchronization
Any time more than two strobes fall within a person's 135° field of view — common at corridor intersections and in open areas — they must flash in synchronization, and the requirement crosses system boundaries: strobes on two different fire alarm panels in the same space still have to be in sync. All strobes flash between 1 and 2 Hz. The rule exists to avoid the overlapping random flash rates that can provoke photosensitive seizures.
Common questions
What candela strobe is required in a corridor?
In a corridor 20 ft wide or less, NFPA 72 (2022 edition) allows a 15 cd strobe regardless of the corridor's length. Instead of the room-size candela table, corridors use a spacing rule: a strobe within 15 ft of each end and no more than 100 ft between strobes. A corridor wider than 20 ft reverts to the room (wall) spacing table.
How far apart can corridor strobes be?
No more than 100 ft apart, and the first and last strobe must be within 15 ft of each end of the corridor. Those two rules give the corridor-length lookup: one strobe covers up to 30 ft, two up to 130 ft, three up to 230 ft, and so on — each added strobe extends coverage by the 100 ft maximum spacing.
When do strobes have to be synchronized?
When more than two strobes (or groups of strobes) fall within a person's field of view — taken as 135° — they must flash in synchronization, even if they are on separate fire alarm systems. Synchronization prevents the random overlapping flashes that can trigger photosensitive seizures. All strobes flash between 1 and 2 Hz.
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