Balancing active and passive fire protection
Fire protection engineers can and should consider the building's construction, fire suppression systems, and smoke control when designing fire protection systems.
- Understand the differences between active and passive fire protection systems.
- Learn which codes pertain to these systems.
- Know that each AHJ has different requirements.
Like most people, I am regularly asked what I do for a living. When I respond that I am a fire protection engineer, the response is either a blank stare expecting me to explain further or a comment to effect of: “Oh right. Sprinklers.”
Fire protection engineering is not just about active protection like automatic sprinklers and fire alarm systems. While the suppression side of fire protection engineering is well known because of the excitement of watching water or other suppression agents suppress or extinguish fire, it is by no means the extent of fire protection. People are also familiar with the annoying horns and strobes of the fire alarm system.
Fire protection involves multiple forms/means of protection that include both active and passive elements. Active fire protection can involve automatic sprinklers, clean agent suppression systems, standpipes for manual suppression, and fire alarm and smoke management systems. Passive fire protection primarily involves construction elements that either limit the spread of fire by containment, or provide fire-resistive protection to structural elements to mitigate high heat that would otherwise cause them to fail. To fully understand how we can best balance active and passive fire protection features, we will first look at minimum requirements that govern building construction.
Building and fire codes
In the realm of building construction, most fire protection requirements are established in building and fire codes. Model building codes, such as the International Building Code (IBC) promulgated by the International Code Council, establish minimum requirements for buildings based on how they are occupied and what type of construction is used. For example, a standard single-family residential home is permitted to be constructed of wood with very limited requirements for fire-resistive construction. A 10-story apartment building, on the other hand, would require noncombustible steel and concrete with most of the structural elements requiring 2-hour fire-resistive construction or better.
Additionally, model building codes often dictate the type of fire protection aspects required. Using the same example as above, a single-family residential home historically has not required automatic sprinklers but does require smoke alarms. As a high-rise building, a 10-story apartment building would require automatic sprinklers, standpipes, a fire detection and voice alarm evacuation system, secondary power supplies, and some form of smoke management. Both examples are buildings where people live. The primary differences are the size of the buildings, ease of evacuation, and quantity of people within them.
Building and fire codes establish the minimum requirements as governed and adopted by the respective jurisdiction in which the building is to be constructed. Specific building code requirements vary from state to state, county to county, and city to city. The local authority having jurisdiction (AHJ) responsible for buildings and construction is tasked with monitoring construction so that the level of fire protection is not less than that adopted by its state, county, or city. Where multiple jurisdictions such as state, county, and city each have their own adopted codes, typically the city’s code is not permitted to be less stringent than that of the county or state. Engineers must review with the local jurisdiction what the minimum requirements are and be aware that there may be additional requirements.
It is important to establish that the model building codes are often the basic, minimum requirements. Environmental, social, economic, climatic, and other influences may dictate levels of active and passive protection as well. Many U.S. jurisdictions have implemented requirements for automatic fire sprinklers for single-family residential homes. The reasons for requiring automatic sprinklers may vary depending on the size of the home, the location of the home, or the stature of the local fire department. Large homes in excess of 10,000 sq ft may require sprinklers simply because of their size, the total fuel load, and complexities fire departments face in responding to a fire that size. Some jurisdictions have made sprinklers a requirement for all single-family residential homes to lessen the burden on the fire department. Sprinklers have proven effective enough in single-family homes to establish laws requiring them so fire departments will not necessarily have to increase the quantity of stations within a specified area. The response time can marginally increase with the understanding that sprinklers are provided.
Alternatively, some jurisdictions may enforce more stringent passive fire protection requirements depending on their circumstances. In areas where there is higher potential for conflagration, a jurisdiction may require that buildings have noncombustible or limited combustible construction. Wildland urban interface fires have thousands of homes, a fact that weighs on the minds of the AHJs that govern building construction in those areas. As a result, some of those jurisdictions require minimum clearances around structures, providing a natural passive barrier to limit/restrict fire from impinging on structures. Clearances may require vegetation that is more resistant to fire, noncombustible landscaping, and even noncombustible construction of the structure itself.
How does one balance the active and passive features of fire protection in the best interest of the project? The question is best answered by highlighting that the building and fire codes establish the minimum level of protection required. Therefore, it depends on the project, and understanding what is most important to protect.
As the term “fire protection engineering” suggests, one of our primary focuses is on protection from fire. In the building and construction industry this primarily relates to keeping people and buildings safe from fire. As in most industries, the safety of people comes first and property protection is secondary. Protecting the occupants of the building from the effects of fire is the primary objective, but designers should also be conscious of emergency responders when designing. Ideally, all occupants of the building are capable of self-preservation and can escape on their own. In reality, emergency responders are called on daily to risk their lives saving and protecting people and property.
Because firefighters train regularly, they know and understand the fire phenomena. While their tactics and strategies typically use the equipment they maintain, they also often rely on buildings’ active and passive fire protection features. In high-rise buildings, firefighters stage and attack from minimum 2-hour fire-resistance rated stair enclosures where the building’s standpipe outlets are maintained. Therefore, as designers, it is important to recognize that stair enclosures will not be used solely by building occupants, but also by emergency responders.
In concert with protecting people, the design must protect property. While property loss from fire is devastating regardless of size, some fire losses are more difficult to recover from financially and emotionally. Priceless artifacts in museums are often well protected from fire, theft, and other elements. Because people want to look at and admire the artifacts, active and passive protection requires a design cognizant that people will need to evacuate in a fire scenario. Conversely, data centers that maintain billions of dollars of financial transactions may have zero occupants 95% of the time, but may have equal or more robust protection in place to safeguard against losses.