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How this is calculated#

The tool lays out fire detectors in a rectangular room or a corridor. It reads NZS 4512:2010 Clause 405.3 for point heat, line heat, point smoke and beam smoke detectors.

1. Spacing. The tool reads the spacing for the detector type along and across the room.
2. Wall distance. It reads the greatest distance from a wall. It uses that as the setback in the layout.
3. Grid. It divides each room side by the spacing and rounds up. That gives the grid.
4. Count. It multiplies the two grid numbers. The result is the number of detectors, lines or beams.
5. Worst distance. It finds the point furthest from any detector. It compares that distance with the limit in Cl 405.3.
6. Sloping roof. The tool gives the distance from the apex of a sloping roof.

Cl 405.2.1 keeps a detector at least 200 mm from a wall or partition.

Worked example#

• Room of 20 m by 12 m with point smoke detectors. The grid is 2 by 2, so the tool gives 4 detectors. Spacing is 10 m both ways. The worst distance is 7.07 m against a 7 m limit. The tool warns, and asks you to reduce the spacing.

Limits#

The tool does not check ceiling height or obstructions. It does not place detectors in voids. NZS 4512:2021 supersedes the 2010 edition. Check the current edition before you rely on a layout.

See also: Sounder level calculator, Fire alarm cabling and Fire alarm battery.