Using CONTAM Analysis for Stair and Elevator Pressurization

Performing a CONTAM analysis before construction can identify potential design issues and optimize pressurization systems.

What is the benefit of using CONTAM modeling during the building design process?

“During a fire, smoke and other gases can travel through stairwells and elevator shafts and spread to other floors, which can make it difficult for occupants to evacuate and can also cause damage to the building,” explains fire protection consultant Lana Benny of TERPconsulting. During the design process, TERPconsulting’s fire protection specialists use CONTAM, a software program developed by the National Institute of Standards and Technology (NIST), for modeling indoor air quality and ventilation in buildings and simulating the movement of air and gases through a building’s ventilation system during a fire to model stair and elevator pressurization. “To prevent the spread of smoke and gases, stair and elevator pressurization counteracts this effect by using ventilation to create a positive pressure differential between the stairwell or elevator shaft and the rest of the building, making it easier for occupants to evacuate,” Benny explains.

What building parameters does CONTAM modeling take into account?

CONTAM modeling considers factors such as the layout of the building, the size and location of the stairwells and elevator shafts, and the pressure and flow rates of the ventilation system. “The output of the model includes predictions of door pressure differentials and airflow rates of stair and/or elevator doors during a fire, which can be used to assess the effectiveness of the stair and elevator pressurization system and to identify areas where improvements may be needed,” explains Benny.

“By ensuring that stairwells and elevator shafts are positively pressurized during a fire, occupants can evacuate safely, and the spread of smoke and other gases can be minimized. This process works by using ventilation systems to create higher air pressure within stairwells and elevator shafts compared to the surrounding areas and, in turn, preventing smoke and gases from infiltrating pathways and ensuring they remain relatively clear for evacuation,” elaborates Benny.

When should a CONTAM analysis be performed?

A CONTAM analysis is especially beneficial when designing a high-rise building that requires a pressurization system for the stairwells and elevators. “It can help to prevent the spread of smoke and fire and consider wind as well as stack effect,” says Benny. CONTAM assists TERPconsulting’s fire protection designers in predicting what smoke and other harmful gases will do during a fire or other hazardous event in a multi-story building. Several examples of well-known high-rise buildings that have utilized CONTAM to evaluate stair and elevator pressurization include the Taipei 101 tower in Taiwan, the Petronas Towers in Kuala Lumpur, Malaysia, and The Shard in London.

TERPconsulting’s fire protection experts perform a CONTAM analysis before construction begins to identify potential design issues and optimize the performance of the pressurization system. “Fire protection professionals can use CONTAM to model the airflow patterns during a fire and evaluate the effectiveness of the pressurization system in controlling the spread of smoke and toxic gases. This information can be used to optimize the system’s design, ensuring it effectively protects occupants during a fire,” explains Benny.

Which International Building Code (IBC) offers guidance for an active smoke control system?

IBC Section 909.1 clarifies that smoke control can be provided utilizing mechanical (active) or passive systems. Active smoke management systems use mechanical equipment to control the spread of smoke by exhausting smoke from the building and/or creating a pressure difference across a barrier. The active smoke control systems proposed for the high-rise building will be limited to smokeproof enclosures with mechanical pressurization systems for the stairs in the building under IBC Section 909.20.

What is stack effect?

Tall buildings are often affected by stack effect, which is natural air movement caused by temperature differences between the building’s interior and exterior. During seasons requiring heating, warmer indoor air will rise through the building, whereas during the cooling season, cooler interior air will flow downward. “Stack effect becomes more pronounced as building height increases, and the condition can affect the intended smoke control system operation,” says Benny.

“Since CONTAM can be used for this analysis, the stack effect is incorporated into the model by assigning inputs such as exterior temperatures based on weather history, interior design temperatures, and elevation parameters of the building. The model can calculate the flows within shafts and the associated pressure differences created by stack effect, and the fan capacities can be adjusted to determine the appropriate values for maintaining the required door pressure differences,” explains Benny. “This allows clients, designers, and architects to install an appropriately sized supply fan, distribute injection points throughout the building, and install relief vents to pressurize these systems effectively.”

Can CONTAM analysis help determine if a building design meets pressurization criteria or other fire protection codes?

The experts at fire protection engineering firm TERPconsulting recommend that architects and builders request a CONTAM analysis when designing a building that requires compliance with fire protection codes and IBC pressurization requirements, as mandated in Chapter 9 of the 2021 edition of the International Building Code (IBC) Section 909.21.1. “The IBC requires that high-rise buildings have pressurized stairwells and elevator shafts to prevent the spread of smoke and fire. These requirements typically include specific door pressure criteria for stairs and elevators that must be met to ensure the safety of occupants during a fire,” explains Benny. “To ensure that these pressurization systems meet the required door pressure criteria, a CONTAM analysis would be best suited.”

What pressurization requirements are mandated by International Building Code (IBC)?

Stair pressurization systems must be designed in accordance with IBC Section 909.20. For smokeproof enclosures, the minimum allowable pressure differential for a pressurized interior exit stairway is 0.1” water gauge (w.g.) positive pressure relative to the adjacent occupiable space per IBC Section 909.20.5. The maximum allowable pressure differential is 0.35” w.g. positive pressure relative to the adjacent occupiable space per IBC Section 909.20.5. The maximum allowable door opening force is 30 lbs. per IBC Section 1010.1.3.

A CONTAM analysis can help architects and fire protection professionals like those at TERPconsulting ensure that their designs meet these requirements by simulating the airflow patterns and evaluating the performance of the building’s ventilation and pressurization systems. This analysis can help identify potential issues or areas where the design may fall short of meeting the door pressure criteria or other fire protection codes.

“By simulating the airflow patterns during a fire, TERPconsulting’s fire protection experts can identify potential issues and design effective pressurization systems to prevent the spread of smoke and fire in buildings,” says Benny, summing up the benefits of performing a CONTAM analysis.