The Technical Basis for Sprinkler "Trade-offs"

 

By Richard Schulte

Schulte & Associates, Evanston, Ill.

The debates over building fire safety, which have been occurring since the development of the International Building Code began, are rather interesting, given that the actual theory behind building fire safety is relatively simple. The principal means of protecting building occupants from fire has always been evacuation of the room of fire origin followed by either building evacuation or the relocation of occupants exposed to the fire to a safe area within the building. In addition to evacuation, there are essentially only two other concepts used to provide protection of building occupants from fire: passive fire protection and active fire protection.

Passive fire protection consists of both structural fire protection and building compartmentation. Active fire protection includes sprinkler protection, extinguishing systems other than sprinkler systems, smoke detection, heat detection and fire alarm systems.

Structural fire protection is used to delay or prevent the partial or total collapse of a building structure when the structure is exposed to fire. Structural fire protection is also used to extend the time that is available for building evacuation or that is necessary to allow the occupants exposed to the fire to be relocated to a safe area. In addition, structural fire protection is also used to protect firefighters from building collapse when interior manual firefighting is necessary (i.e. in high-rise buildings).

Building compartmentation is used to prevent or delay the spread of heat and other combustion products generated by the fire from the compartment of origin to other areas of the building. Compartmentation may consist of floor construction, corridor separations, elevator lobby separations, residential unit separations, floor opening enclosures and exit enclosures.

While active fire protection includes smoke detection, heat detection, smoke control systems and fire alarm systems, the term is usually used to refer to sprinkler protection. Sprinkler protection performs a number of functions with respect to the protection of the building and its occupants. Sprinkler systems are specifically designed to protect the building structure from significant damage. In addition, sprinkler systems are designed to limit the size of the fire that develops: Sprinkler operation typically limits the fire spread to the area of origin. By virtue of the fact that sprinkler protection limits fire spread to a relatively small area, sprinkler protection also limits the quantity of smoke generated by the fire. (The quantity of smoke generated by a fire is proportional to the size of the fire. In general, larger fires generate greater amounts of smoke than do smaller fires. Hence, sprinkler protection is a very efficient and effective form of smoke control.)

Given the above descriptions of the functions of both active and passive fire protection systems, it can be seen that sprinkler protection essentially performs the same functions as passive fire protection. It should be obvious that sprinkler protection is a far more efficient and effective means of protecting a building and its occupants than passive fire protection, since sprinkler protection performs not only a structural fire protection function but also is capable of limiting the spread of fire to the area of origin.

Up until the early 1970s, it was an accepted fact that sprinkler protection was only a property protection feature and that sprinklers were too slow to operate to be able to provide any protection for building occupants. In other words, up until the early 1970s, it was thought that the only two means of protecting the occupants of a building were evacuation and passive fire protection. After a series of major fires occurred in (unsprinklered) high-rise buildings in the early 1970s (and probably even earlier), this presumption about sprinkler protection was challenged. It became increasingly obvious that the key to protecting high-rise buildings from fire was not fire resistive building construction, but, rather, sprinkler protection. And if sprinkler protection could be used to protect the occupants of high-rise buildings from fire, then sprinkler protection could also be used to protect the occupants of low-rise buildings. Some even went so far as to say that sprinkler protection could be used to protect the occupants of single-family homes from fire.

The major roadblock to installing sprinkler protection in high-rise buildings in the early 1970s was cost. (Architects also objected to the appearance of sprinklers.) Since passive fire protection and sprinkler protection essentially perform the same functions, and since sprinkler protection provides protection to the building occupants that is superior to that provided by passive fire protection, the obvious way to reduce the cost of installing sprinkler protection in high-rise buildings was to allow reductions in the requirements for passive fire protection when sprinkler protection was provided. Other means of reducing the cost of installing sprinkler protection were also employed, including modifying the minimum requirements for sprinkler installations.

Among the reductions in passive fire protection included in the high-rise provisions developed in the late 1970s were reductions in the hourly fire resistance ratings for structural fire protection and shaft enclosures, the elimination of the requirement for spandrels or flame barriers, the elimination of the requirements for fire dampers at penetrations of shaft enclosures, the elimination of the requirement for a horizontal exit on each floor and the use of a mechanical smoke control system as a substitute for remotely operated exterior windows. These reductions in passive fire protection produced significant cost savings and made the installation of sprinkler protection in high-rise buildings economically feasible.

Were the reductions in passive fire protection when sprinkler protection was provided included in the high-rise provisions developed in the early 1970s technically sound? We now have more than three decades of experience with sprinklered high-rise buildings, and a major fire has never occurred in a high-rise building protected throughout by a sprinkler system. We also know that when many existing unsprinklered high-rise hotels were retrofitted with sprinkler protection in the early and middle 1990s, fire fatalities in high-rise hotels were virtually eliminated. These facts about the success of sprinkler protection provided for high-rise buildings certainly seem to indicate that reductions in passive fire protection when sprinkler protection is provided are a valid concept in high-rise buildings. And if sprinkler "trade-offs" are a technically sound concept in high-rise buildings, then this concept should also be a technically sound approach in low-rise buildings.

The only question that remains is whether or not eliminating the reductions in passive fire protection when sprinkler protection is provided will result in a significant increase in the level of safety of buildings protected by sprinklers. If few, if any, fire fatalities occur in sprinklered buildings where sprinkler "trade-offs" are utilized, then it follows that the level of fire safety for buildings constructed without the reductions in passive fire protection can't be significantly greater than buildings where the "trade-offs" are utilized. Hence, why "saddle" building owners (and ultimately the American public) with additional construction costs if no significant increase in the level of safety will actually be provided?

The fact that many people currently participating in the development of our building codes do not know the history of the development of sprinkler "trade-offs" does not bode well for future building codes. Building codes should be a practical reflection of minimum acceptable standards for building safety. If codes simply reflect the inclusion of any and all forms of fire protection features, without regard to cost, effectiveness or need, then the code does a disservice to the public. The fire safety provisions contained in building codes should be based upon sound engineering principles, not just on opinions about what is necessary to provide a "fire-safe" building.

Richard Schulte is a 1976 graduate of the fire protection engineering program at the Illinois Institute of Technology. After working in various positions within the fire protection field, he formed Schulte & Associates in 1988. His consulting experience includes work on the Sears Tower and numerous other notable structures. He has also acted as an expert witness in the litigation involving the fire at the New Orleans Distribution Center. He can be contacted by sending e-mail to rschulte@plumbingengineer.com.