System Sensor BS5839 manual Corridors, Corridor being 7.5m and 5.3m respectively, Sloping Ceilings

Guide

>10% of Ceiling Height

Treat as separate room

>250mm <10% of Ceiling Height

Minimum

500mm

Minimum

500mm

however along the roof apex spacing the lesser of the two figures should be used, in this example 10.5m +18%. Where the slope finishes within the adjusted detection radius, the standard distance to the next row of detectors, 10.5m, should be used. Care must be taken when placing the next row that no gaps are left in detection coverage.

Max 600mm

15m

Application

Normal Detector Spacing, eg. 10.5m max for “simple” layout.

Height < 250mm

Minimum 2 x

height

		40°
18°
	.35m 25%
	9	+
		.5
.5m	7
	=
7

Normal Detector Spacing, eg. 10.5m max for “simple” layout.

Figure 2.4.3: Detector Spacing around isolated ceiling obstructions

2.4.4.Partitions and Racking

Where the gap between the top of a partition or section of racking and the ceiling is greater than 300mm, it may be ignored. If the gap is less than 300mm it should be treated as a wall.

To maintain a free flow of smoke and heat to the detector, a clear space should be maintained for 500mm in all directions below the detector.

>300mm : No effect <300mm :Treat as wall

10.5m		12.39m =10.5+18%
.85m		18%
8	+
	.5
=7

Figure 2.4.5. Spacing of Smoke Detectors under a

Pitched Roof

2.4.6.Corridors

In corridors less than 2m wide, detectors should be spaced at a distance of 15m for smoke detectors and 10.6m for heat detectors, with the maximum dimension to a wall at the end of

Minimum 500mm Clear

Partition

Racking / Shelving

the corridor being 7.5m and 5.3m respectively.

In narrow rooms and corridors greater than 2m wide, due to the way that the coverage radii of detectors intersect with the walls of the corridor, the spacing between detectors will increase. Figure 2.4.6 shows how, for a room 6m wide, the spacing for smoke detectors can be increased from the standard 10.5m.

Figure 2.4.4. Partitions

2.4.5.Sloping Ceilings

Where the ceiling is pitched or sloping, the slope of the roof tends to speed the rise of smoke or heat to the apex, hence reducing the delay before the detectors are triggered. For sloped roofs with a pitch height greater than 600mm for smoke detectors, or 150mm for heat detectors, a row of detectors should be placed within a maximum vertical distance of 600mm or 150mm for smoke or heat detectors respectively from the roof apex. Sloped roofs rising less than 600mm for smoke detectors or 150mm for heat detectors may be treated as a flat ceiling.

Since the smoke or heat tends to rise faster up the slope, it is permissible to use a greater spacing for the row of detectors mounted in the apex of the roof: For each degree of slope of the roof, the spacing may be increased by 1% up to a maximum of 25%. Where, as in figure 2.4.5, the roof slopes are unequal the spacing down the slopes can be unequal,

6.88m13.75m

6m

7.5m

Note: Detectors are mounted in the centre line of the room

Figure 2.4.6. Smoke detector spacing in corridors greater

than 2m wide

14

Note: This document is based on the recommendations of BS5839 Part 1: 2002. It is intended only as a guide to the application of fire detection systems.

Reference must be made to relevant national and local standards.