Atriums are among the most striking architectural features in modern commercial buildings, creating a sense of openness, light, and spatial grandeur. Yet, their defining characteristic—a large, open vertical volume connecting multiple floors—presents some of the most complex fire safety challenges in building design.
Unlike conventional buildings where floors act as fire barriers, atriums create a direct pathway for fire and smoke to spread vertically, potentially endangering occupants on every floor simultaneously.
This guide explores the unique challenges and design strategies for fire safety in atriums and large-volume spaces.
◆ Section 1: Defining the Atrium and Its Challenges
An atrium is a large open space within a building that extends through multiple stories, typically with a glazed roof or ceiling. Atriums are often considered “the heart of a building,” designed to create a sense of grandeur and connection between spaces.
Unique Fire Safety Challenges:
| Challenge | Description |
|---|---|
| Vertical Smoke Spread | Smoke generated on any floor can rise rapidly through the open volume, endangering occupants on upper floors. |
| Smoke Buoyancy | The temperature difference between hot smoke and ambient air creates strong buoyancy forces that drive smoke upward. |
| Large Air Volumes | The sheer volume of air in an atrium makes smoke management more complex. |
| Glass Wall Vulnerability | Glass walls and doors are common in atriums but provide limited fire resistance. |
| Stack Effect | Warm air naturally rises, creating a “chimney” effect that can rapidly draw smoke upward. |
Research Insight: The temperature difference between a burning surface and the ambient environment is the primary factor influencing smoke movement in atriums. When ambient air is cooler, the density difference between hot smoke and surrounding air increases, enhancing buoyancy forces and driving smoke upward.
◆ Section 2: The NFPA 92B Framework
The primary standard for smoke management in atriums and large-volume spaces is NFPA 92B, the Standard for Smoke Management Systems in Malls, Atria, and Large Spaces.
Key Focus Areas of NFPA 92B:
| Aspect | Description |
|---|---|
| Performance Criteria | Establishing system performance to maintain a tenable environment. |
| System Testing | Requirements for testing new and retrofitted systems. |
| Design Tools | Use of Computational Fluid Dynamics (CFD) and zone models for design. |
| Smoke Exhaust Calculations | Data and equations for calculating smoke exhaust requirements. |
| Smoke Barriers | Location and design of smoke barriers. |
Pro Tip: The 2009 edition of NFPA 92B is the most current and fully adoptable edition. It reflects the state-of-the-art in smoke management system design for large-volume spaces.
◆ Section 3: Compartmentation and Smoke Barriers
One of the most critical aspects of atrium design is the separation of the atrium from adjacent spaces. IBC Chapter 4 (Special Detailed Requirements Based on Occupancy and Use) provides the primary requirements for atrium separation.
General Requirement:
Atrium spaces shall be separated from adjacent spaces by a 1-hour fire barrier constructed in accordance with IBC Section 707, or a horizontal assembly in accordance with Section 711.
Exceptions:
The IBC provides several important exceptions to the 1-hour fire barrier requirement, allowing for more open designs while maintaining fire safety:
| Exception | Description |
|---|---|
| 1. Glass Wall with Sprinkler Protection | A fire barrier is not required where a glass wall forming a smoke partition is provided, with automatic sprinklers along both sides of the separation wall (or on the room side only if there is no walkway on the atrium side). Sprinklers must be located 4–12 inches from the glass and at intervals not greater than 6 feet. |
| 2. Glass-Block Wall | A glass-block wall assembly complying with Section 2110 and having a 3/4-hour fire protection rating. |
| 3. Three-Floor Exception | A fire barrier is not required between the atrium and adjoining spaces of up to three floors, provided such spaces are accounted for in the design of the smoke control system. |
| 4. No Smoke Control Required | In certain occupancies, a fire barrier is not required where the atrium is not required to be provided with a smoke control system. |
Australian Code (NCC) Requirements:
The National Construction Code (NCC) in Australia provides similar provisions, requiring bounding walls to have an FRL of not less than 60/60/60. These walls must extend from the floor of the storey to the underside of the floor next above or to the underside of the roof.
◆ Section 4: Smoke Control Systems
Smoke control is the primary active fire protection strategy for atriums.
General Requirements:
Smoke control systems in atriums must be designed to maintain a tenable atmosphere in all paths of travel to exits during the period of evacuation.
Key Elements of Atrium Smoke Control Systems:
| Element | Description |
|---|---|
| Smoke Exhaust | Mechanically powered exhaust fans that remove smoke from the atrium. |
| Makeup Air | Air introduced at the lowest level to balance pressure. |
| Sprinkler System | Floor of the atrium must be protected by sprinklers (quick response type). |
| Automatic Detection | Smoke control systems are activated by automatic fire alarm, sprinkler operation, or manual switch. |
| Glazing Protection | Wall-wetting sprinkler systems protect glass walls from thermal fracture. |
| Pressurization | A velocity of not less than 0.1 m/s towards the atrium well must be maintained on all storeys where the bounding wall is set back from the atrium well. |
Smoke Exhaust Design Assumptions:
Smoke exhaust systems for atriums are typically designed on the basis of the sprinkler system limiting the size of a fire to:
| Occupancy Type | Heat Output | Fire Perimeter |
|---|---|---|
| Class 2, 3, 5 or 9 (Residential, Educational, Healthcare) | 1.5 MW | 7.5 m |
| Class 6, 7 or 8 (Retail, Commercial, Storage) | 5 MW | 12 m |
Makeup Air Requirements:
Uniformly distributed makeup air must be provided from outside the atrium at or near the lowest storey level, and from relief air from non-fire storeys. This makeup air must be introduced in a manner that prevents disturbance of the smoke layer due to turbulence.
Pro Tip: A discharge volume sufficient to maintain a velocity of not less than 0.1 m/s towards the atrium well must be provided on all storeys where the bounding wall is set back from the atrium well.
◆ Section 5: Sprinkler Protection Requirements
General Sprinkler Requirements:
| Requirement | Details |
|---|---|
| Atrium Floor | The floor of the atrium must be protected by sprinklers with quick response type sprinkler heads. |
| Glazed Walls | Sidewall pattern sprinkler heads together with overhead sprinklers where dictated by the dimensions of the atrium. |
| Glass Wall Protection | Water spray protection must be provided along both sides of the glass wall, or on the room side only if there is no walkway on the atrium side. |
| Sprinkler Spacing | Sprinklers shall be located between 4 inches and 12 inches away from the glass and at intervals along the glass not greater than 6 feet. |
Minimum Sprinkler Flow Requirements (Australian Code):
| Location | Minimum Flow Rate |
|---|---|
| Atrium Side of Glazing (set back > 3.5 m) | 0.25 L/s.m² |
| Atrium Side of Glazing (set back ≤ 3.5 m) | 0.167 L/s.m² |
| Side Away from Atrium | 0.167 L/s.m² |
◆ Section 6: Stage and Platform Provisions
Atriums often contain stages, platforms, and other performance spaces that require additional fire safety provisions. The 2021 IBC provides specific requirements for stages and platforms in atriums.
Key Stage Requirements:
| Requirement | Details |
|---|---|
| Proscenium Wall | A minimum 2-hour fire-resistance-rated proscenium wall is required where the stage height is greater than 50 feet. |
| Stage Curtain | Proscenium opening must be protected with either a fire curtain or a water curtain. |
| Stage Ventilation | Stages larger than 1,000 square feet in area, or with a height greater than 50 feet, must have emergency ventilation to control smoke. |
| Separation | Dressing rooms, storage rooms, and other backstage areas must be separated from the stage and from each other. |
Platform Requirements:
| Requirement | Details |
|---|---|
| Permanent Platforms | Must be constructed of materials as required for the building’s type of construction. |
| Fire-Retardant-Treated Wood | Permitted in Type I, II and IV buildings when no more than 30 inches above the main floor, no more than one-third of the floor area of the room, and no more than 3,000 square feet. |
| Temporary Platforms | May be constructed of any approved material but may not be used for storage. |
◆ Section 7: Means of Egress
Egress from atriums requires special consideration due to the open configuration and potential for smoke spread.
General Requirements:
| Requirement | Details |
|---|---|
| Open Floor Connecting Up to 3 Stories | Permitted if the space is sprinklered and one of those storeys is at a level with direct egress to a road or open space. |
| Balcony Egress | Paths of travel along balconies to required exits must maintain a tenable atmosphere during evacuation. |
◆ Section 8: Activation of Smoke Control Systems
Smoke control systems in atriums must be activated by one of the following means:
| Activation Method | Description |
|---|---|
| Automatic Fire Alarm | Operation of an automatic fire alarm system. |
| Sprinkler System Operation | Activation of the sprinkler system. |
| Manual Start Switch | A manual start switch located in the fire control room, emergency control centre, adjacent to sprinkler control valves, or incorporated in the Fire Indicator Panel. |
Pro Tip: The location of manual start switches must be clearly identified and accessible to building occupants and firefighters.
◆ Section 9: Design Checklist
Use this checklist to verify fire safety provisions in atrium design:
| Item | Status | Notes |
|---|---|---|
| Smoke Control System (NFPA 92B) | ☐ | Designed and installed in accordance with NFPA 92B. |
| Separation from Adjacent Spaces | ☐ | 1-hour fire barrier or approved exception. |
| Sprinkler Protection | ☐ | Atrium floor, glazed walls, and stage areas. |
| Glazing Protection | ☐ | Water curtain or wall-wetting sprinkler system. |
| Smoke Exhaust System | ☐ | Designed for assumed fire size (1.5 MW or 5 MW). |
| Makeup Air System | ☐ | Introduced at lowest level, velocity ≥ 0.1 m/s. |
| Stage Provisions | ☐ | Proscenium wall, curtain, and ventilation where required. |
| Means of Egress | ☐ | Tenable atmosphere maintained on balconies. |
| Activation Means | ☐ | Automatic and manual start switches. |
◆ Section 10: Common Mistakes and How to Avoid Them
| Mistake | Why It’s a Problem | How to Fix |
|---|---|---|
| Inadequate Smoke Control Design | Smoke spreads vertically, endangering all floors. | Use NFPA 92B and CFD modeling for accurate design. |
| Ignoring Glazing Protection | Glass walls fail under fire exposure. | Provide water curtains or wall-wetting sprinklers. |
| No Makeup Air | Smoke exhaust becomes ineffective. | Provide makeup air at the lowest level. |
| Insufficient Egress Capacity | Evacuation takes too long. | Ensure tenable conditions are maintained on balconies. |
| Not Testing Systems | Systems fail when needed. | Test smoke control systems regularly. |
◆ Conclusion
Atriums are magnificent architectural features that require specialized fire safety strategies. By understanding the challenges of vertical smoke spread, providing robust smoke control systems, ensuring proper compartmentation, and protecting glazed walls, you can design atriums that are both beautiful and safe.
Take Action Today:
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Understand the definition of an atrium and how it triggers special requirements.
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Design a smoke control system in accordance with NFPA 92B.
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Provide separation between the atrium and adjacent spaces using a 1-hour fire barrier or approved exception.
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Protect glazed walls with water curtains or wall-wetting sprinklers.
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Ensure makeup air is provided at the lowest level.
Continue Reading from Our Series:
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Read more about: How to Design Fire Safety for Underground Buildings and Basements
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Learn more: How to Design for Fire Safety in High-Rise Buildings
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Related guide: Understanding Smoke Control Systems in Commercial Buildings