In many states, laws exist that allow the electrical contractor to design fire alarm systems for projects he is selling and installing for a customer. When you decide to perform the fire alarm system design portion of a project, you should be familiar with the detector coverage requirements of the National Fire Alarm Code and the requirements of your locally adopted building and fire codes.
In general, building and fire codes do not require complete or total detection coverage to be designed and installed in a building. However, the owner may have certain fire protection goals that may dictate this type of coverage, or the owner’s insurance company may have more stringent detector coverage requirements than any code. The point here is to ask questions of the owner and ensure you understand all relevant requirements.
NFPA 72-2007 recognizes that there are many different types of detector coverage. The code breaks detector coverage down into three primary types: total or complete, partial and selective coverage.
According to the code, total coverage includes 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.” The code requires detection in all accessible and inaccessible areas that contain combustible material, and if the area is inaccessible, it must be made accessible and protected.
The code does allow detectors to be omitted in combustible blind 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.)”
It is important for the contractor to remind the owner of the limitations of a fire alarm system that does not have total or complete coverage.
For example, as stated in the annex of NFPA 72-2007, “If there are no detectors in the room or area of fire origin, the fire could exceed the design objectives before being detected by remotely located detectors. When coverage other than total coverage is required, partial coverage can be provided in common areas and work spaces such as corridors, lobbies, storage rooms, equipment rooms, and other tenantless spaces. The intent of selective coverage is to address a specific hazard only … . It should also be noted that fire detection by itself is not fire protection. Also, protection goals could be such that detection being provided for a specific area or hazard might require a form of total coverage for that particular area or hazard. That is, it might be necessary to provide detectors above suspended ceilings or in small closets and other ancillary spaces that are a part of, or an exposure to, the area or hazard being protected.”
Typically, a contractor will be providing partial detection where a building or fire code, the Life Safety Code, or the authority having jurisdiction will require protection of only selected areas. The code still requires that this designed and installed partial or selective coverage comply with all requirements for detector spacing and installation.
Finally, you will find owners who have existing buildings and have asked that you design and install what is essentially a nonrequired system. Some contractors assume if the system is not required by any code, then the requirements of NFPA 72-2007 do not have to be followed. This is a little like saying that because a surgical operation is elective, one can let a veterinarian perform the surgery instead of an experienced surgeon.
NFPA 72-2007 states in section 22.214.171.124.1 that “detection installed for reasons of achieving specific fire safety objectives, but not required by any laws, codes, or standards, shall meet all of the requirements of this Code, with the exception of prescriptive spacing criteria … .” The code does provide some relief, stating that where nonrequired detectors are installed for achieving specific fire safety objectives, additional detectors that are not necessary to achieve the fire safety objectives (goals) of the owner will not be required.
So, the bottom line to avoiding costly mistakes when designing a fire alarm system for your customer is to know the requirements of NFPA 72-2007 thoroughly, including those related to detector coverage.
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.