I have written numerous articles regarding the code requirements for fire alarm system installations. Most contractors assume that the fire alarm system requirements as outlined in the building codes are the maximum required and, unfortunately, do their client a disservice when they make that assumption. If you really want to expand your fire alarm system book of business, then you need to review a few basic fire protection guidelines that will help make your installations more reliable and lead to increased sales and profits. The information you need can be found in NFPA 72, National Fire Alarm and Signaling Code, Chapter 17 and its associated Annex A material.

Smoke detectors for early warning

The first thing you should do is to explain to your customer that the fire alarm system required by the codes is a minimal design and will not guarantee the continuity of their business operations. Early in your discussions with your customer, focus their attention on a better system by simply asking, “What do you want left after the fire?” Although it may sound flippant, the question is a serious one, and their answer will guide your design.

In simple terms, if they desire early warning using smoke detection, there must be detectors close enough to the fire to detect the smoke. In most cases, that means your early warning design will include additional smoke detection. Obviously, if there are no or limited smoke detectors in the room or area of fire origin, the fire could exceed your early warning objectives. Detectors located remotely from the fire origin will not meet your design goals. Too many owners believe a single smoke detector located in a hallway outside offices or apartments will provide early warning of a fire regardless of the location of the origin. Smoke moves in a plume and travels throughout the space based on the heat generated from a fire. This concept means that a smoldering fire with little heat generated will be the most difficult to detect.

Conversely, a rapidly burning fire will generate more smoke that will travel throughout the space. If the detector is in that space, you will detect the fire. However, if the fire is in an enclosure that will confine the smoke movement and that does not have a detector present, detection will be delayed, certainly beyond the time one would expect to get “early warning” of the fire.

Your customers generally have this misunderstanding of a smoke detector’s ability to detect smoke.

Spacing smoke detectors

When you install smoke detection in a space, you place the detectors approximately 30 feet apart. This recommended spacing has been in NFPA 72 almost since its inception but has no basis in research. However, from our experience, when we space the detectors 30 feet apart on a smooth, flat, 10- or 12-foot ceiling and the smoke is generated in the smoke detector’s location, detection occurs at an acceptable time.

Even if the code allows the placement of smoke detectors on ceilings higher than 12 feet, you need to understand that there can be a considerable delay in detection as ceiling height increases. As smoke rises from a fire, it cools. If it cools to the ambient temperature of the space, there will likely be smoke stratification, and the smoke may never reach the detector. We have long recommended not using spot-type smoke detectors in areas where the ceiling height exceeds 15 feet for two reasons: smoke detection will be delayed (if it even occurs) and the higher the detector placement, the less likely it will be serviced and maintained as required. Smoke detectors that are not maintained are prone to false alarms, which can end up costing you money and negatively impacting your reputation.

Another reason to install more smoke detection than required by the building codes is the increase in the use of plastics over wood in our environment. This means fires will burn faster and will negatively affect the evacuation time from the building.

Other considerations for smoke detector placement

These discussions regarding additional smoke detection are important regardless of occupancy. Although more smoke detection for increased life safety in residential environments may seem obvious, your customer, upon reflection, may realize that staying operational after a fire is just as important as life safety. Indeed, there may be specific areas of a customer’s property that, in their opinion, would warrant more smoke detection coverage. The code recognizes this need and allows for partial or selective coverage as described in Section 17.5.3.3.

For example, your customer might want to add detection to meet certain performance goals or to address a particular hazard or need, but that detection is not required by the code. In these instances, you need to remember that once you have installed the necessary detection for this application, acceptance testing, annual testing and ongoing maintenance in accordance with the code is required.

Understanding the basics of fire protection will allow you to better serve your customers’ fire alarm system needs.