🔥 Atrium Exhaust Airflow
🏗 Stair Pressurization Airflow
Sizing Breakdown
Full Calculation Table
| Component | Basis | Value | Result |
|---|
How to Use the Smoke Control Calculator
Enter atrium floor area and the vertical height from the design fire source to the design smoke layer.
Choose a fuel load category or enter a custom heat release rate confirmed against your project's fire engineering analysis.
Enter the number of pressurized stairwells, door leakage area, and target design pressure differential.
Click Calculate Smoke Control to see estimated atrium smoke exhaust airflow and stairwell pressurization fan sizing.
Understanding Smoke Control System Design
Smoke control systems protect building occupants and firefighters by managing where smoke goes during a fire event, rather than simply removing heat like a conventional exhaust system sized through the exhaust fan sizing calculator. Two common strategies appear in Canadian commercial buildings: atrium smoke exhaust that actively removes smoke from a large connected volume, and stairwell pressurization that keeps smoke out of protected egress paths entirely.
The Mass Flow Plume Method for Atrium Exhaust
As a fire burns, its convective plume rises and entrains surrounding air, growing in volume and cooling as it travels upward toward the design smoke layer height. The mass flow plume method, the calculation approach set out in NFPA 92, estimates how much air this plume entrains by the time it reaches the smoke layer, which sets the minimum exhaust airflow needed to keep the smoke layer from descending into the occupied space below. Taller atriums generally need somewhat less exhaust per unit of fire size, since the plume has more distance to entrain air and cool, though the relationship depends on specific atrium geometry and is not simply proportional to height.
Design Fire Size Depends on Fuel Load and Sprinklers
Design fire heat release rate reflects the atrium's fuel load, which depends heavily on what combustible content is present and whether the space is sprinklered. Sprinklered atriums with typical light-to-moderate combustible content commonly use design fires in the 1 to 5 megawatt range, though specific values must be confirmed against your jurisdiction's fire code requirements and, for many projects, a project-specific fire engineering analysis rather than assumed from a general guideline.
Stairwell Pressurization: A Different Approach
Rather than actively exhausting smoke from a large volume, stairwell pressurization maintains the egress stairwell at higher pressure than adjacent floor areas using a dedicated fan, so smoke cannot infiltrate the stairwell even when a door briefly opens during evacuation. This calculator estimates required stair fan airflow using an orifice flow relationship through the door leakage area at your specified design pressure differential, similar in principle to the approach used in the building pressurization calculator but applied specifically to stairwell life safety design, and verified in the field the same way any life-safety system is verified, through a commissioning checklist before the building is occupied.
National Building Code of Canada Requirements
The National Building Code of Canada requires smoke control or smoke management provisions for certain building configurations, particularly atriums connecting multiple floors and high-rise buildings above specified height thresholds. Provincial codes adopt and sometimes amend these requirements, and specific applicability depends on building classification, height, and occupancy. This calculator provides a preliminary estimate for early design purposes only; final smoke control design must be performed by a qualified fire protection engineer following the exact code requirements, testing standards, and safety factors applicable to your specific project.
Related Life Safety and Pressurization Tools
Smoke control interacts closely with general building pressurization, since both involve managing airflow balance and pressure differentials throughout the building. See the building pressurization calculator for broader HVAC-driven pressure control beyond life-safety-specific smoke systems, and confirm any healthcare-specific isolation pressurization needs with the hospital HVAC calculator.
Frequently Asked Questions
The mass flow plume method estimates smoke exhaust airflow by calculating how much air a fire's convective plume entrains as it rises from the fire source to the design smoke layer height, based on the design fire heat release rate and the height of rise. Taller atriums generally need less exhaust airflow per unit of fire size because the plume entrains more air and cools before reaching the smoke layer, though this relationship is not linear and depends on specific atrium geometry.
Design fire heat release rate depends on the atrium's fuel load, sprinkler protection status, and applicable code requirements, commonly ranging from 1 to 5 megawatts for sprinklered spaces with typical combustible content, though specific values should always be confirmed against your jurisdiction's fire code and any project-specific fire engineering analysis rather than assumed from a general rule of thumb.
Stairwell pressurization maintains the egress stairwell at higher pressure than adjacent floor areas, so that even when a stair door briefly opens during evacuation, positive pressure limits smoke infiltration into the stairwell that occupants need for evacuation and firefighters need for access. This differs from atrium smoke exhaust, which actively removes smoke from a large volume space rather than simply preventing its entry into a protected egress path.
The National Building Code of Canada and provincial building codes require smoke control or smoke management provisions for certain building configurations, particularly buildings with atriums connecting multiple floors and high-rise buildings above specified height thresholds. Specific requirements vary by building classification, height, and provincial code adoption, so confirm exact applicability and design criteria with your authority having jurisdiction and a qualified fire protection engineer.
Related HVAC Tools
Broader HVAC pressure control
Healthcare isolation pressurization
Related pressurization cascade approach
General building air handling
Large-volume high-bay spaces
General exhaust considerations
Common atrium building type
Broader building load analysis