1. Fire Detector Placement
Chapter 14
Page 425

2. Objectives
Describe how detectors are listed by Underwriters Laboratories (UL)
Explain why detectors are not permitted to be positioned too close to the corners of a room where the ceiling meets the wall
Determine the spacing of detectors in a room with a smooth flat ceiling
Determine locations of detectors in a room with unusually configured walls

3. Objectives Space detectors in a corridor
Discuss rules for placement of detectors on sloped ceilings
Determine the locations of detectors on ceilings with solid joists or beams
Explain why detectors are not permitted to be located too close to supply air ducts

4. Objectives
Describe the effect of floor-mounted partitions on a ceiling jet
Determine the optimum locations for beam detectors, flame detectors, gas detectors, and duct detectors

5. Heat Detector Listings
Heat detectors are listed by UL as follows:
Heat detector type
Temperature rating
Listed smooth ceiling spacing between detectors
Listed smooth ceiling spacing to wall or partition
Contact arrangement
Detector model number

6. Smoke Detector Listings
Smoke detectors are listed by UL under category UROX as follows:
APPLICATION
DETECTOR TYPE
COMPATIBILITY RESTRICTIONS
INSTALLATION CRITERIA

7. Spot-Type Detector Spacing
Corner Placement for Spot-Type Detectors: The 4-Inch Rule
Smooth Ceiling Spacing of Spot-Type Detectors
Spot-Type Detector Spacing for Unusual Wall Configurations
Spot-Type Detector Spacing in Corridors

8. Spot-Type Detector Spacing
Figure Ceiling jet dynamics for corner fires; NFPA 72 prohibits spot detectors being placed within the “blind spot”

9. Spot-Type Detector Spacing
Figure Illustration of .7 Smax rule, or “circle of coverage”

10. Ex. 14-1: Ceiling Spacing of Spot-Type Detectors

11. Ex. 14-2: Ceiling Spacing of Spot-Type Detectors – Spacing Less than Listed Spacing

12. Ex. 14-2: Ceiling Spacing of Spot-Type Detectors – Spacing Less than Listed Spacing

13. Ex. 14-2: Ceiling Spacing of Spot-Type Detectors – Spacing Less than Listed Spacing

14. Spot-Type Detector Spacing
Spot-Type Detector Spacing for Smooth Peaked Ceilings
Spot-Type Detector Spacing for Smooth Shed Ceilings
Spot-Type Detector Spacing for Solid Joist Construction

15. Spot-Type Detector Spacing
Figure Sectional view of a peaked ceiling; a detector must be placed within 3 feet (900 mm) of the roof peak,
and spacing is measured along the floor, not along the slope

16. Spot-Type Heat Detector Spacing for Beamed Construction Body Of NFPA 72
Spot-Type Heat Detector Spacing for Beamed Construction—Annex of NFPA 72
NFPA 72 requirements
Effect of Ceiling Height on Spot-Type Heat Detectors

17. Ex. 14-3: Detector Placement for Beamed Construction

18. Ex. 14-3: Detector Placement for Beamed Construction

19. Spacing Of Line-Type Heat Detectors
Spacing requirements (see Table 14-1, Page 441):
Line-type detectors on a ceiling must be not more than 20 inches from the ceiling
Line-type detectors are mounted to the bottom of solid joists
Line-type detectors are mounted to the bottoms of beams, where beams are less than 12 inches deep and less than 8 feet apart on center

20. Spot-Type Smoke Detector Spacing
Spacing near Air Vents
Spacing near Floor-Mounted Partitions
Spot-Type Smoke Detection for Raised Floors and Suspended Ceilings
Spot-Type Smoke Detectors in High Air Movement Areas
Spot-Type Smoke Detectors for Smoke Control Systems

21. Spot-Type Smoke Detector Spacing P.443
Figure Smoke detector spacing for beamed construction

22. Projected Beam Smoke Detector Spacing P.451
Beam detectors work on the following principles:
Beam detector consists of sender and receiver
NFPA 72 (2007) requires that
The sender and receiver be mounted firmly to avoid movement of the projected beam and possible unwanted alarms
The projected beam remain unobstructed by storage, ceiling-mounted equipment, or other objects that would result in a trouble condition on the FACU and prohibit the detectors from sensing smoke

23. Projected Beam Smoke Detector Spacing
Smoke obscures the projected beam and reduces transmission of the infrared beam to the receiver
Beam detectors are for indoor use, and are to be mounted to stable surfaces
Mirrors can be used with projected beams, per manufacturer’s instructions, provided that mirrors are mounted to stable surfaces

24. Projected Beam Smoke Detector Spacing
Spacing for smooth ceilings must be per manufacturer’s instructions
For beamed construction, some manufacturers require that beam detectors be mounted in each beam pocket if
Beam depth exceeds 18 inches
Support beam spacing is greater than 8 feet

25. Projected Beam Smoke Detector Spacing
For solid joists less than 8 inches in depth, some manufacturers require that the ceiling be considered as a smooth ceiling
NFPA 72 requires beam detectors on sloped ceilings be installed parallel to peak

26. Projected Beam Smoke Detector Spacing
Figure Sloped ceiling installation for beam detectors

27. Flame Detector Placement
A flame detector can perceive a fire that is viewed within its cone of vision
Its ability to sense a fire depends on
Position of the fire within the cone of vision
Distance from the fire to the detector
Size of the fire
Matching the spectral response of the detector to the spectral emissions of the fire

28. Flame Detector Placement
Each flame detector is listed for a specific viewing angle that defines the cone of vision
Placement of flame detectors usually requires considerable field experience and consultation with the manufacturer

29. Gas-Sensing Detector Placement
May sense a potentially hazardous condition in advance of ignition, or may sense gaseous combustion by products
Spaced in accordance with NFPA 72 (2007) and their listing
NFPA 72 has replaced detailed spacing requirements on gas-sensing fire detectors

30. An Engineering Approach To Heat Detector Placement
Best way to ensure detection in a building
Conduct fire testing in numerous areas
Determine best detector
Determine best detector locations
Calculated Heat Detector Placement per NFPA 72 Annex B (2007 Edition)

31. Summary The placement of detectors must consider
Type of fire
Dynamics of the ceiling jet
Attributes of the detector
Properties of the ceiling or surface onto which the detectors are mounted
NFPA 72 provides minimum requirements for the spacing of detectors

32. Summary
Designers must analyze the anticipated fire and the space requiring detection
Annex B of NFPA 72 provides engineered approach to positioning detectors
Specific requirements for
Heat detectors
Smoke detectors
Beam detectors
Gas detectors