Architects and their clients love atriums in their buildings, and with good reason. The natural daylight, interconnectivity, and view of the outside environment have been shown in respected studies to significantly increase productivity in the workplace and help students score better on exams in educational settings. Architecturally, an atrium can reflect the exterior scale of the building making for a very dramatic design. There is one thing, however, that architects hate about an atrium: the code required smoke control system. Why? Because smoke control systems are a complex and often costly, building code required component of an atrium.
In a article for the National Institute of Building Sciences by Todd Gritch, AIA ,ACHA and Brian Eason, AIA of HKS Inc. the technical issues of fire protection and smoke control in atriums are summarized. Here are some of the key issues they point out.
A successful atrium design must have a smoke control system. It is critical to life safety. Atrium buildings break with orthodox concepts of safety because of their open and interconnected nature. Because of its critical nature, both NFPA 101 “The Life Safety Code” and The International Building Code have extensive code provisions for Atriums. A significant difference however, is that the IBC is prescriptive and arbitrarily limits the number of floors that may be open to the atrium to three. The Life Safety Code is more performance oriented and will allow the number of floors open to atria without enclosure to be based upon the results of the required engineering analysis.
One of the basic atrium requirements is an engineered smoke control system. It is also recognized that some form of boundary is required to assist the smoke control system in containing smoke to just the atrium area. This could be a wall, shutter, or rated curtain. Both the Life Safety Code and IBC require that the atrium space be separated from adjacent areas by fire barriers having a fire rating of 1 hour or equivalent. Both codes accept adjacent spaces to be separated by properly constructed glass walls where automatic sprinklers have been installed to protect the entire surface of the glass.
Smoke Control Guidelines:
Fire records have shown that smoke is the primary threat to life during a fire in buildings. Smoke is by far the most rapidly developing threat during a fire. That means proper smoke control in an atrium building is an absolute must. NFPA 92B, quantifies the physics associated with atrium smoke control and presents methodologies for system design in an understandable and useful format. The guidelines of NFPA 92B allow the system designer to design a system and prepare associated documentation to access for adequacy in meeting the performance criteria. NFPA 92 provides a set of calculations that can be performed by the FPE to determine the quantity of exhaust necessary to evacuate the smoke generated by the largest anticipated fire size. However, a fire protection engineer (FPE) can assist in determining the smoke control system parameters.
Hire an Engineer:
An FPE involved early in the atrium design is the best source of potential fire detection and prevention system selection options. FPEs are knowledgeable about all of the atrium code issues. The codes and standards that address smoke control systems for atria are based on similar research and fundamental fire size and smoke generation models. ASHRAE 1999 Applications, Chapter 51 provides a broad design basis for smoke management and general directions for the designer.
Do a Computer Model:
Currently the most comprehensive method of determining complex smoke management criteria is with computer fire modeling (Reference ASHRAE 1999 Applications, Chapter 51.12). In many instances the results of the computer modeling will result in lower exhaust quantities being required, and therefore lowering initial project costs. The model allows multiple fire origins to be evaluated. The resulting smoke removal system needs to be adequate for all anticipated fire origin locations. Computer modeling and visualization are important tools for understanding the processes of fire behavior. Even when the exhaust quantities are determined by use of a computer fire model, smoke management systems can be well designed in adherence to all other requirements of NFPA 92.
There are lots of solutions to achieve proper smoke control whether through a mechanical active smoke exhaust/evacuation system or some strategically placed smoke curtains. But whatever the choice, an atrium in your building will have lasting beauty and productivity benefits that are well worth the effort.