Balancing passive, active fire protection
Fire protection engineers should consider the building's construction, fire suppression systems, and smoke control when designing active and passive fire protection systems.
- Explain the International Code Council (ICC) and NFPA’s elements and integration of both passive and active fire protection to reinforce one another.
- Assess the differences between active and passive fire protection systems and learn which codes pertain to these systems.
For more than 2 decades, the concept of balancing passive and active fire protection has been debated in the code-development hearings in the United States, including the International Code Council (ICC), NFPA, and legacy code organizations. Typically, there are proposals to require sprinkler protection in certain buildings and, in many instances, there is an attempt to offset the cost by reducing or eliminating one or more passive fire protection features.
In some instances, the sprinkler protection may already be required and fire data is used in an attempt to substantiate the reduction or elimination of one or more passive fire protection features. While there are other forms of active fire protection, sprinkler systems seem to be at the forefront of the discussion regarding balanced fire protection.
A historic perspective of balanced fire protection
As evidenced by the testimony at code-development hearings, some people define balanced fire protection as "one of everything." One of everything could include sprinklers, automatic detection, and fire-resistance-rated construction. Others may not promote the concept of one of everything. Rather, they will support retaining existing passive fire protection feature requirements due to the fact that the active fire protection feature is not 100% reliable.
However, the word "balanced" can be defined as being in proper proportion. For the purposes of this article, the concept of proper proportion will be used in trying to define the phrase "balanced fire protection."
There have been code-change proposals submitted to eliminate a passive fire protection feature in an area in which sprinkler protection is not even provided. For example, proposals have been submitted to eliminate draft-stopping in a combustible attic space if the building is protected throughout with an automatic sprinkler system complying with NFPA 13R: Standard for the Installation of Sprinkler Systems in Low-Rise Residential Properties, even though sprinklers are not provided in the attic space. While an NFPA 13R sprinkler system certainly may reduce the number of fires that spread to the attic space, should the fire start in the attic space—or spread to the attic despite the sprinkler system—there would be no protection feature in the attic space to offset the omission of the draft-stopping. One might argue that such a provision does not offer balanced fire protection.
With respect to balanced fire protection, it may be less clear when a prescriptive requirement for a 1-hour fire barrier or 1-hour fire partition is reduced to a nonrated assembly due to the presence of an automatic sprinkler system. Prior to requiring sprinkler protection in all new hospitals, codes generally required a 1-hour corridor if the building, or smoke compartment, was not protected with sprinkler protection.
Those same codes often reduced the corridor-wall requirement to an assembly capable of "resisting the passage of smoke" if the building, or smoke compartment, is protected with an automatic sprinkler system.
Consider these ideas to determine whether the fire protection system is in balance: If a fire occurs in the building protected with a sprinkler system, what happens if the wall is not capable of resisting the passage of smoke due to some compromise in the integrity of the wall? As a separate consideration, what happens if the sprinkler system fails to effectively control the fire? If a fire occurs in the building that is not protected with a sprinkler system, what happens if the 1-hour fire partition is compromised? Does the code have a proper proportion of passive and active fire protection? Are there any tools to assist in answering these questions?
Passive and active fire protection features often complement each other. For example, John R. Hall Jr., PhD, noted in his report, High-Rise Building Fires, that the U.S. experience is such that there is a lower risk of fire and associated losses in high-rise building fires than in other buildings of the same property use. He noted that this experience is most likely due to the increased presence of sprinkler protection and fire-resistance-rated construction in high-rise buildings.
NFPA 550: Guide to the Fire Safety Concepts Tree was developed by the NFPA Committee on Systems Concepts. The committee was established to be responsible for developing system concepts and criteria for fire protection in buildings. The committee subsequently was discharged in 1990 and the responsibility for NFPA 550 was reassigned to the NFPA Standards Council. With the exception of updating reference standards, there have been essentially no technical changes to the guide since the first edition. Obtain free access to the 2012 edition of the code and graphics at www.nfpa.org/550.
At the top of the Fire Safety Concepts Tree in Chapter 4, the "or" gate indicates that the desired fire safety objectives can be achieved by either preventing the fire or managing the fire. For purposes of this article, the focus will be on the "Manage Fire Impact" branch of the tree. Note that this branch contains two offshoot branches connected by an "or" gate: "Manage Fire" and "Manage Exposed." The objectives of the Manage Fire branch are to reduce hazards related to fire growth and spread, thus reducing the impact of the fire. The Manage Exposed branch includes coordination involving the items specified in the fire safety objectives, such as people, property, or other valued items.
The Manage Fire branch then contains three more branches: "Control Combustion Process," "Suppress Fire," and "Control Fire by Construction." Whereas all of the branches identified are connected by an "or" gate, if one is able to be 100% effective with any of the branches, the others are not needed.
Fire experience in the United States has indicated that we are not 100% successful with either of the two major branches of the tree, with the two branches under Manage Fire Impact, or with the three branches within the Manage Fire branch. Therefore, prescriptive codes generally contain requirements related to preventing fires, controlling the combustion process, suppressing the fire, controlling the fire by construction, and managing those exposed to the fire.
The remainder of the article will focus on proportioning or balancing the Suppress Fire and Control Fire by Construction branches. However, before we continue with these two branches, it should be noted that passive fire protection features and active fire protection systems also play a role within the Manage Exposed branch of the tree.
Managing the fire risk
If we go back up to the top of the tree, everything is focused on the fire safety objectives. In a performance-based design approach, the interested stakeholders in the project would define the fire-safety objectives. With a prescriptive code approach, fire-safety objectives generally are not stated explicitly, although the purpose of the codes is to provide a reasonable or acceptable level of safety. If a fire protection engineer were to use NFPA 550 in evaluating proposals to change a prescriptive code, he would need either probability or frequency data to evaluate the code-change proposals.
It’s a challenge to find sound probability data for many of the branches of the tree. For that reason, the Society of Fire Protection Engineers Engineering Guide to Fire Risk Assessment recommends the use of frequency data instead of probability data. Data sources, such as the National Fire Incident Reporting System (NFIRS), can provide frequency data for many of the branches of the tree. The use of frequency data also can be helpful if cost is a consideration, because the cost-benefit analysis for a specified period of time can be estimated. Even frequency data will not be available for all considerations, especially those involving smoke spread, because it is no longer a factor included in the NFIRS database. Modern prescriptive codes are based more upon a qualitative risk assessment with considerations similar to those contained in NFPA 550.
For example, the requirement for corridor walls in hospitals was mentioned previously. Looking at NFPA’s Fires in Health Care Facilities report for the period 2006 to 2010, there were an estimated 1,430 structure fires in hospitals and hospices with no civilian deaths. Of those 1,430 fires, 40 (or 8 fires/year) spread beyond the room of origin. What cannot be determined is whether the spread beyond the room was to an adjacent room or to the corridor. The database also does not identify whether the boundary walls of the rooms had a fire-resistance rating or not. One civilian injury and no fire deaths were associated with the fires that spread beyond the room of origin. Ironically, the average property loss per fire was lower for the fires that spread beyond the room of origin than it was for those contained to the room of origin.
The NFPA report also indicates that automatic sprinkler systems were present in 64% of the fires in hospitals and hospices during the time period. The report does not break down the reliability of the sprinkler system just for hospital fires. However, the overall reliability of the sprinkler system operating and being effective when the fire was large enough to activate a sprinkler in all health care facilities was 86%, as indicated in the report High-Rise Building Fires.
It should be noted that health care facilities, as used in the NFIRS database, include nursing homes, hospitals, mental health facilities, clinics, and doctor’s offices. A specific data report could be requested for sprinkler protection for hospital fires, but the dataset will start to become relatively small (in this case, 915 fires, or 183/year).
Despite all of the data, we are still not able to quantitatively apply the Fire Safety Concepts Tree to this one scenario involving balancing passive and active fire protection as it relates to corridor walls in hospitals. Here is an example of what we can ascertain from the data:
From the code-development perspective, if a proposal was submitted to reduce the amount of passive fire protection currently required because of the above data summary, one could point to NFPA 550 and ask what is being done to retain the current level of safety. Is something being done to improve the reliability of the sprinkler system or is the reliability considered acceptable?
Is something being done to prevent some of the fire from occurring? Is something being done to better control the combustion process? If the answer to these three questions is no, the designer has to assume the level of risk of a fire spreading beyond the room of origin during a hospital fire will increase if the passive feature is eliminated.
If a proposal was submitted to increase the amount of fire protection currently required, the typical question that will be asked is how will the risk improve and at what costs. Unfortunately, the current data system in the United States does not provide an easy way to quantify the impact on the level of risk in this instance. A more detailed review of the 40 incidents might result in some better information, but more on an anecdotal basis than a statistical basis due, in part, to the limited number of incidents.
Consider design methods
Ultimately, many of us would prefer to use performance-based design methods and fire risk assessments for all of our projects. The reality is that most clients will accept a building that complies with the prescriptive code, and there is an assumption that the prescriptive code balances passive and active fire protection features to provide an acceptable level of safety.
When the client or design professional is seeking an alternative to the prescriptive code, or when the client wants a design based upon risk assessment, the limitations of data will often result in the use of a comparative risk assessment. When done properly, a comparative risk assessment should properly balance passive and active fire protection features. To the extent the design profession wants to advance the use of true performance-based design methods, we may need to start with developing a better data system that provides us with the information that is needed.
This is not a criticism of the NFIRS, but rather a recognition of the limitations of the existing system that was not originally developed to support performance-based design methods. The increased use of true performance-based design methods also should result in an improved balance between passive and active fire protection features.
William E. Koffel is president of Koffel Associates, a fire protection engineering design/consulting firm, and is recognized as an expert in the fire protection/life safety aspects of codes and standards. He is a member of the Consulting-Specifying Engineer editorial advisory board.
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