Office Building Smoke Control: Pressurization Fundamentals

A fire in your office building is a serious event that requires quick and determined response. Even if no actual flames are involved, the production of smoke from a flammable source can compromise employee and customer safety. Office building smoke control processes should be included in the design of all building fire safety systems. Preventing smoke from flowing up or down in elevator shafts and stairwells is a major component of office building smoke control. Here is a basic look at how this type of smoke control can be achieved.

Elevators and Stairwells

Smoke traveling either through elevators or stairwells can put building occupants at risk, even if they are several floors away from the fire or source of smoke. When a fire safety and smoke control system is being designed, the characteristics of both elevators and stairwells must be factored in.

Pressurized elevator shafts and stairwells are prime methods for controlling smoke flow. In many buildings, both elevator shafts and stairwells are pressurized. Even if the elevator is the only pressurized smoke control area in the building, the following smoke control techniques can still be used to improve occupant safety. Engineers and designers should remember that the movement of elevator cars can change pressures inside the elevator shaft and take this into consideration during office building smoke control design.

Other factors to include in the analysis and design include the quality of the building’s envelope, or seal; air leaks and their location; and air flow and pressurization differences that can result from opened elevator or exterior ground-floor doors. Many fire safety engineers rely on CONTAM, computer software designed to simulate and analyze the multiple elements of an effective office building smoke control system.

Basic Smoke Control Systems

Basic office building smoke control systems provide for one or more dedicated fans that pressurize elevator shafts and stairwells. The disadvantage of these systems is that in buildings with tight seals or even marginally leaky walls, the pressurization is not always sufficient. Buildings with very leaky walls are more likely to be able to handle the airflow needed to produce enough pressurization in both stairwells and elevator shafts.

Exterior Vent Systems

Exterior vent (EV) systems are designed to provide enough ventilation and exterior air leakage to provide sufficient amounts of pressurization in elevator shafts and stairwells. Properly sized vents are usually placed in the building’s exterior walls. In cases where internal walls create flow resistance, ducts can be installed that will allow enough airflow to achieve correct pressurization.

Floor Exhaust Systems

Floor exhaust (FE) systems use relatively small amounts of supply air in the elevator shafts, with the majority of the exhaust and venting being done on the floor where the fire occurs. This allows pressurization to be kept at optimum levels on the floor where it is most necessary. Typically, this type of system also will provide exhaust for one or two floors above and below the source of the fire. Contact your local building code and fire safety organizations for help with this type of smoke control system, as its limited pressurization will probably require some level of approval.

Ground Floor Lobby Systems

Ground floor lobby (GFL) systems provide for a closed elevator lobby only on the ground floor of the building, not on every floor except for the ground floor, as is more common. GFL systems can significantly reduce the pressure differences across elevator doors at the ground floor. These pressure differences can cause elevator doors to jam, so reducing them during a fire is vital. In some cases, a vent is placed between the enclosed lobby and the building serves to prevent excessive pressure differences for both lobby doors and elevator doors.

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