What are the Basics of Fire Suppression Systems?

Fire suppression systems are important components of building design, and it is critical that architects understand fire protection requirements and the types of systems that are used to satisfy those requirements. The topic itself is far deeper and more extensive than can be covered here. This blog post is intended merely to introduce ARE^® candidates to some of the basic concepts, systems, and system components of fire suppression and sprinkler system design.

For any project on which the architect works, it is necessary to understand the particular code requirements which are adopted in the jurisdiction in which the project is located. Among the specific codes which may govern fire protection requirements are the IBC, IFC, and the NFPA codes and standards. For even those well acquainted with fire protection, it is critical to review the codes on a project-by-project basis since the codes are highly specific and detail oriented. Topics related to fire protection which are outside of the scope of suppression and sprinkler systems (active fire protection), such as requirements related to construction type, wall fire ratings, assemblies, and smoke protection (passive fire protection) will not be discussed here, though it should be mentioned that the necessity or requirements for fire suppression systems may depend upon these other building features. Portable fire extinguishers will also not be discussed here, though they are also an important component of fire protection in buildings with which the architect should be familiar.

The intention behind fire suppression systems is to extinguish fires within a building should they occur to prevent loss of life and injury and to limit damage to the building and property. In the event of a fire, an automatic detection system activates the fire suppression system. The codes classify fires into four types, and the specifics of the system design will depend upon which type of fire the code requires to be considered for the project. Class A fires are those which occur when there is combustible or flammable solids present, such as wood or paper, which would act as the fuel source for the fire. Class B fires occur when combustible liquids, such as gasoline or propane, would be the fuel source. Class C fires are those which are due to electrical causes, as may occur with transformers or other equipment. In this case, water should not be used to put out the fire. Class D fires are those in which metals act as a medium for the fire. Class K fires relate to those which may occur in a kitchen and may involve combustible oil or grease.

Codes also distinguish between hazard levels, which are related to building occupancy, uses, and material that may be stored in the building. Specifically, these are light hazard, ordinary hazard, and extra hazard. These can generally be understood as risk levels in terms of destruction should a fire occur for a particular project and are determined by a number of factors. The specifics of how these classifications are to be applied depend upon the specifics of the code provisions which are applicable.

Once the requirements for which the fire suppression system should be designed are understood, a particular type of system can be selected. There are 3 basic types of systems based on their extinguishing medium: water, gas, and chemical-based systems. Water-based systems are most typically used due to the ease of access to a supply of water. These systems will require that the water be at an adequate water pressure. If it is not, then the use of fire pumps to increase the pressure will be necessary. Gas-based systems may utilize inert gases such as carbon dioxide or nitrogen. Chemical-gas based systems are also possible, but their use depends upon whether they are permitted by the particular jurisdiction in which the project takes place. Gas-based systems are sometimes used when there are concerns about the possible extent of water damage on a particular project if a water-based system were to be used or if there is some concern about a chemical reaction occurring between water and chemicals located at a project. The third possibility is a chemical-based system. It is also often used where there are concerns about the use of water for a particular project, and it's sometimes used, for example, in kitchen areas or where there is the possibility of Class B fires. These systems may be of the "dry" (or powder) type or the "wet" type, with the choice depending on the class of fire it is necessary to design for. It should be noted that these chemical-based systems can require a large amount of clean-up effort if the system should be activated.

There are several different types of sprinkler systems which the architect should be familiar with. These include wet-pipe, dry-pipe, pre-action, deluge, antifreeze, and high-pressure water spray systems. In a wet-pipe system, the pipes contain water which is under pressure with sprinkler heads opening and releasing this water when the heads detect a particular level of heat present. The pipes in a dry-pipe system, by contrast, are not filled with pressurized water prior to activation but rather with air that is under pressure. If a sprinkler head opens when heat is detected, the air pressure within the pipes lowers and a valve is opened which causes water to then flow through the piping and out of the heads. Pre-action systems also contain air rather than water prior to heat detection, but the air is not pressurized. It is, however, a two-stage system, unlike the dry-pipe system. Firstly, a pre-action valve is used to release water when it is activated by a separate detection system. Then the water will be discharged where sprinkler heads have opened due to heat detection. This type of system is sometimes used when there is concern about accidental activation of sprinkler heads. A deluge system has sprinkler heads which are already open. As with the pre-action system, a separate detection system is utilized to activate the system, but in this case, the sprinkler heads all release water when that detection system is activated. It should be noted that the detection systems of the pre-action and deluge type systems could be heat-based but may also be based on the presence of smoke. Antifreeze systems are similar to wet-pipe systems, but the pipes are filled with antifreeze rather than water. This type may be selected when the pipes are in unheated spaces where the possibility of water freezing is a concern. Lastly, high-pressure water spray systems (also called high-pressure mist systems) discharge water in small droplets. It uses a pump which is activated by a fire detection system. Advantages to high-pressure misting systems include significantly less water consumption, smaller pipes, and rapid heat absorption. Each of these system types can employ several different sprinkler head types. These include upright, pendent, concealed pendent, flush pendent, and horizontal sidewall type sprinkler heads.

In addition to automatic sprinkler systems, buildings may be required to have standpipes and fire department connections. Standpipe systems are networks of pipes, often placed in stairwells, from which hoses may be connected for use, typically by firefighters. The fire department connection (also called FDC or Siamese connections) is located on the outside of a building at street level. It also is used by firefighters who can connect hoses at the outside of the building.

Fire suppression systems play an important role in protecting the health, safety, and welfare of the public. As such, it is important for architects to understand how these systems work, the code requirements for their use, and the various types and components of these systems.