Potter Releasing Systems - Manual (Page 51)

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Smoke/Heat Detector Replacement
See NFPA 72
Detector placement is critical to early warning functions. In order to provide an effective early warning of a developing
fire situation, smoke detectors should be installed in all areas of the protected premises. Local codes or ordinances may
not be adequate for early detection. The location, quantity and zoning of detectors should be engineered to provide
maximum life safety, as opposed to meeting minimum requirements of local codes.
Defining The Smoke Chamber
The continuous, smoke resistant perimeter boundary of a room or area to be protected. Between the upper surface of the
floor and the lower surface of the ceiling. The smoke barrier does not have to be a solid structure from floor to ceiling. A
solid structure that extends 18” or more from the ceiling would constitute a smoke barrier.
Open “grid” material is considered solid when:
• The openings are less than ¼” in the least dimension.
• The thickness of the material exceeds the least dimension.
• The openings constitute less than 70% of the area of the perforated material.
For Areas With Smooth And Flat Ceilings Ten Feet In Height
All points on the ceiling shall have a detector within a distance equal to .7 times the listed spacing.
Spot type detectors shall be located on the ceiling or, if on a sidewall, between the ceiling and 12” down form the ceiling
to the top of the detector.
The distance between detectors shall not exceed their listed spacing. There shall be detectors within one-half the listed
spacing, measured at right angles, from all side walls.
Detectors shall not be recessed mounted unless specifically listed for recess mounting.
Spot type smoke detectors must be a minimum 36” from air diffusers, and may not be in a direct airflow exceeding their
air velocity, regardless of distance.
Detectors shall be supported independently of their attachment to circuit conductors.
Spot type detectors should be mounted at least 6’ from florescent lights.
Except in cases where “stratification” is expected, detectors shall never be mounted more than 12” below ceiling level.
Detectors must be wired to ensure supervision of the detector head. Removal of the detector head must cause a trouble
condition on the panel.
Ceilings
Smooth Ceiling Spacing - Spot Type Smoke Detectors
In the absence of specific performance-based design criteria, smoke detectors shall be permitted to be located using
9.1 m (30 ft) spacing. NFPA72, 2010 17.7.3.2.3.1
Solid Joist and Beam Construction
Solid joists shall be considered equivalent to beams for smoke detector spacing guidelines. NFPA72 2010, 17.7.3.2.4.1
Level Ceilings
1. For ceilings with beam depths of less than 10 percent of the ceiling height (0.1 H), smooth ceiling spacing shall be permitted.
Spot-type smoke detectors shall be permitted to be located on ceilings or on the bottom of beams.
2. For ceilings with beam depths equal to or greater than 10 percent of the ceiling height (0.1 H), the following shall apply:
a. Where beam spacing is equal to or greater than 40 percent of the ceiling height (0.4 H), spot-type detectors shall be
located on the ceiling in each beam pocket.
b. Where beam spacing is less than 40 percent of the ceiling height (0.4 H), the following shall be permitted for
spot detectors:
i. Smooth ceiling spacing in the direction parallel to the beams and at one-half smooth ceiling spacing in the
direction perpendicular to the beams.
ii. Location of detectors either on the ceiling or on the bottom of the beams
3. For beam pockets formed by intersecting beams, including waffle or pan-type ceilings, the following shall apply:
a. For beam depths less than 10 percent of the ceiling height (0.1 H), spacing shall be in accordance with
17.7.3.2.4.2