Sprinkler System Types and Impact on Building Fires

By Matthew Hartsell

It's 3:30 a.m., and you have been dispatched to a report of a multifamily structure fire in your engine company's first-due response area. Dispatch is reporting a fire has been called in on the fourth floor of the apartment building. You think to yourself that you have been to this location before. It's a new construction four-story apartment building that is fully protected by a sprinkler system. You think to yourself that this will be a quick incident, that it's probably just a single 1¾-inch attack line or even a water pressure extinguisher to hit the hotspots, shut down the sprinkler system, ventilate, and that's it.

As your engineer turns into the apartment complex, you see a well-developed fire on the fourth floor and fire showing through the roof. The quick-knockdown fire turns into a two-alarm fire with multiple aerials doing an exterior defensive attack. What happened? How could this fire develop so quickly in a modern structure that was fully protected by a sprinkler system? Or was it?

As company officers, it is important that we take the time to get our crews out to perform prefire plans on existing structures and look at what is being constructed in our response area. In the scenario at the beginning of this article, the company officer thought he was familiar with this particular structure. He had been there before and seen for himself that the structure was equipped with a sprinkler system, and the sprinkler system functioned exactly as it was designed to operate. The problem was with the design and intended purpose of the system. It was a sprinkler system that met the requirements of National Fire Protection Association (NFPA) 13R, Standard for the Installation of Sprinkler Systems in Low-Rise Residential Occupancies. This structure had a sprinkler system that was designed to protect lives but not designed to protect property.

There is much more we should be aware of as company officers than just if there are sprinklers or not in a structure. We need to know what that sprinkler was designed to do but, more importantly, what limitations it has, how to identify the system, and our actions to overcome those shortcomings. Let's review sprinkler system types as identified by the NFPA.

This is the primary and oldest standard for sprinklers in the United States. This system promotes life safety, property conservation, and protection for the contents of the structure (NFPA 13 1.2.1 2022). This means that sprinkler coverage extends to all areas of the structure including the unoccupied areas such as attics, closets, and voids. NFPA 13 systems offer the fire protection that we usually think of when we see that a structure is fully protected by a sprinkler system. Typically, these types of systems are found in many commercial buildings, high-rise residential structures, large hotels, health care or educational facilities, and many other older structures.

NFPA 13 systems are also designed to flow the needed water for the greatest hazard present in the structure from multiple heads at once without impacting the gallon-per-minute (gpm) flow from those heads. It delivers water in such a manner that will prevent further spread of the fire no matter where or what is burning. In many cases, these systems are using large, powerful water supply risers and fire pumps to meet these gpm requirements.

According to the NFPA, sprinkler systems are designed to target the greatest hazards of the structure and its contents and prevent further fire extension. These are broken down into five hazard classifications based on the contents or processes of the structure. These hazard classes are what are used for the design and hydraulic calculations of the sprinkler system so that is capable of stopping the growth of a fire.

This type of system was developed with the primary focus being on life safety by giving occupants the needed time to exit the structure by preventing flashover from occurring (NFPA 13R 1.2.2 2022). It is not designed to prevent the building or its contents from being involved in fire. NFPA 13R systems typically do not require having sprinkler coverage in areas of the structure that are uninhabited such as closets, attic areas, void areas between floors, small bathrooms, and awnings. These systems have limited capabilities in fire extinguishment and perhaps zero capabilities in certain areas of the building. You would find this type of sprinkler in residential-type structures including multifamily homes, apartment buildings, condos, and small hotels that are four stories or less.

The design requirements of this type of system are typically based on the flow of up to four heads in a single occupied compartment of the structure and generally have far less gpm capability than a similar sized structure equipped with a NFPA 13 system. Also, these systems are usually offered to eligible structures as a cost reduction over the NFPA 13 system, as the reduced coverage areas and lower gpm require less material and equipment to function, but it is still able to achieve improving life safety of the structure.

This type of system was also developed with life safety being the primary function and not designed to protect the contents or the structure. The system accomplishes this by preventing flashover from occurring but not necessarily extinguishing the fire (NFPA 13D 1.2.2 2022). Also, similar to the 13R system, it does not provide coverage to the entire structure but only to the inhabited areas. NFPA 13D is what is typically installed into one- and two-family homes. The gpm flow requirements are even lower than that of the 13R systems, with calculations based on the flow of up to two heads per compartment.

What is unique to the NFPA 13D system is that, in most cases, it does not have its own water supply to the structure for fire protection. It is supplied from the domestic water supply that is used to supply other fixtures in the home such as sinks, toilets, and showers typically found in the residential home setting. This is because of the low gpm requirements and requires less overall maintenance, as the system is constantly flowing water to supply these fixtures and not stagnant within the sprinkler piping. Similar to the NFPA 13R system, the 13D was designed to be installed at cost savings over the two other systems. Lower cost of the system makes it attractive to homeowners during the building phase, which is a good thing, as these systems also improve the life safety of the home.

We know both from education and real-world experiences that all types of sprinkler systems save lives. There are numerous studies of how effective sprinkler systems are at saving lives and property. They are also becoming more common in new construction and renovations of older structures, but all systems can only work as designed. It is important to know and understand what the system was designed to do and what its limitations are.

Identifying the different NFPA ratings of sprinkler systems can be as easy as reading the latest inspection tag on the sprinkler system riser. In many cases, the companies doing the inspection will label what kind of system it is and what requirement it meets. In other cases, there may be a sign on the system indicating its design elements, such as number of heads, rated gpm flow and duration, and what NFPA code it was designed to meet.

It is possible to identify which buildings would likely have a 13R sprinkler system by looking at exterior construction. If it is new construction, four stories or less, and a residential occupancy, it is quite likely equipped with a 13R. If the structure is a one- or two-family residence equipped with a sprinkler system, it is likely a 13D. Any type of high-rise, large commercial buildings, and many mercantile stores will have a 13 system. If you have a chance to inspect these buildings, ensure that you check the uninhabited spaces such as attics, elevator rooms, closets, or bathrooms. If no sprinklers are present, it is likely a 13R or 13D system.

Another option, if your organization has designated fire inspectors or building construction inspectors, is discussing the building with them, which can lead to answers on what the sprinkler system is capable of achieving. This is a great option if access to the structure is limited or difficult to obtain. They may even give you some insight as to what your locality's codes are for installing sprinklers, as some local ordinances may have limitations on what structures are eligible to have a 13R system that is more stringent than the requirements in NFPA. Ultimately, your local officials and authority having jurisdiction will have the final say for sprinkler system requirements in your response area.

Knowing the type of sprinkler system the building has is an important part of response tactics for fires. Of course, we are going to focus efforts on rescue and fire confinement/extinguishment in the event of a fire. However, if it is a large structure with a well-developed fire, we will have a few other priorities as well, such as supplying the fire department connection as early as possible in the incident to boost the gpm and pressure on a 13R system and opening void areas to check for extension into those uninhabited areas that may not have sprinkler coverage; these acts can contribute to stopping the fire before it grows.

In the opening example, the fire officer thought the building was protected by a sprinkler system, and it certainly was. The problem was that the structure had a 13R system. The fire, which had started in a nonsprinkler-covered bathroom, extended through a bathroom vent fan into a nonsprinkler-covered attic space, which was an open area of lightweight wood trusses. The fire quickly advanced through the open area attic.

It is important for the company officer to actively conduct prefire plans and be involved in the plans review process for new construction. This ensures that you are ahead of the game in locating and preparing for possible fires in your response area in these types of residential buildings. Would this have changed the situation encountered in the opening scenario? No, but the officer would have been better able to mentally prepare for the incident by knowing there is greater potential for extended firefighting efforts or multiple rescues.

The NFPA even suggests that we, as officers, have a thorough knowledge of the property equipped with sprinkler systems that we may encounter in our response area (NFPA 13E 5.1.2 2020). NFPA 13E is another great resource if you would like to learn more about fighting fires in structures equipped with sprinkler systems.

Sprinkler systems save lives. There is no question about that. However, we should allow the sprinkler system to assist us with our goal of saving lives and property, not expect to have the sprinkler system do our job for us. Get out into your response area and have a solid working knowledge of the target hazard buildings by understanding their fire protection systems and what they are meant to accomplish. In the end, you will make yourself more knowledgeable and better equipped to serve your firefighters, department, and community.

BIO:

Matthew Hartsell has been a civilian firefighter for the Department of Defense since 2006. He has worked at several different Navy bases but currently is in NSA Naples, Italy, where he is a captain and has been a company officer since 2014. He has spent a large portion of his career studying fire protection systems and has degrees in fire science and business leadership.