The National Fire Alarm Code does not require anyone to install a fire alarm system. That statement sometimes surprises contractors who have been told by a fire official to install a fire alarm system in accordance with NFPA 72. In fact, the requirement for a fire alarm system in a new building comes from the building code in force in the jurisdiction. Generally, an engineer has designed the system based on the building code, and once the system has been mandated, you must install it in accordance with the National Electrical Code (NEC) and the National Fire Alarm Code.

If you, as a professional electrical contractor, are asked to design a system for an existing property and have no idea where to start, there are two avenues from which to choose. The first is to look at the building code or Life Safety Code to determine the minimum fire alarm system requirements for the occupancy in question. The second option is to sit with the owner and determine his or her fire protection goals. Of course, the fire official may have recommendations as well, and it always is a good idea to involve him or her early in the decision-making process.

Once you have determined which type of fire alarm system the owner desires, you would look to NFPA 72-2007 to determine the detector coverage and the installation requirements. The code recognizes that there are several different types of detector coverage and many types of detectors to choose from, depending on the fire protection goals of the owner.

For instance, you can choose total or complete coverage. This type of coverage is not mandated by a building code but may be required by an insurance company in order for it to insure your customer. The code defines total coverage as providing detection in “all rooms, halls, storage areas, basements, attics, lofts, spaces above suspended ceilings, and other subdivisions and accessible spaces as well as the inside of all closets, elevator shafts, enclosed stairways, dumbwaiter shafts, and chutes.” In addition, where inaccessible areas contain combustible materials, they must be made accessible and provided with detection.

The code provides some relief, however, from the inaccessible combustible spaces if any of the following conditions exist:

“(1) Where the ceiling is attached directly to the underside of the supporting beams of a combustible roof or floor deck

(2) Where the concealed space is entirely filled with a noncombustible insulation (In solid joist construction, the insulation shall be required to fill only the space from the ceiling to the bottom edge of the joist of the roof or floor deck.)

(3) Where there are small concealed spaces over rooms, provided any space in question does not exceed 4.6 m2 (50 ft2) in area

(4) In spaces formed by sets of facing studs or solid joists in walls, floors, or ceilings where the distance between the facing studs or solid joists is less than 150 mm (6 in.)”

Detectors also are not required below an open grid ceiling if the openings in the grid constitute 70 percent of the area of the ceiling, are ¼ inch or larger in the least dimension, and the thickness does not exceed the least dimension.

Detectors are not required in concealed, accessible spaces above suspended ceilings used as return air plenums as defined in NFPA 90A, Standard for the Installation of Air-Conditioning and Ventilating Systems. This allowance can be used only if there is smoke detection at each connection from the plenum to the central air-handling system.

And, finally, where total coverage is required, detectors can be omitted from such areas as underneath open loading docks or platforms and their covers and for accessible under-floor spaces if all of the following conditions exist:

(1) Space is not accessible for storage purposes or entrance of unauthorized people and is protected against the accumulation of windborne debris.

(2) Space contains no equipment, such as steam pipes, electric wiring, shafting or conveyors.

(3) Floor over the space is tight.

(4) No flammable liquids are processed, handled or stored on the floor above.

Keep in mind that total or complete coverage is not required by any of the occupancy-based codes, but it still may be in the best interest of the owner to protect the entire facility.

The minimum requirement in the building codes is defined as partial coverage. NFPA 72-2007 states that, “Where codes, standards, laws, or authorities having jurisdiction require the protection of selected areas only, the specified areas shall be protected in accordance with this Code.”

It is also important that you be aware of the limitations of detection.

Electrical contractors need to understand the coverage concepts outlined in the National Fire Alarm Code to ensure they meet their customers’ goals and provide code-compliant fire alarm system installations.

MOORE, a licensed fire protection engineer, frequent speaker and an expert in the life safety field, is a co-editor of the current National Fire Alarm Code Handbook. Moore is a principal with Hughes Associates Inc. at the Warwick, R.I., office.