What’s the Best Way to Keep Smoke out of a Stairwell?
Stairwell pressurization was the topic of our most recent Coffee Break webinar, and we posed this question to Scott Blackmon of RM Manifold Group (the makers of products by U.S. Draft Co. and LFSystems).
Our Coffee Break webinar series features HVAC experts delivering insider knowledge about products, systems, and more. Contact your SVL sales engineer for an invite to our upcoming Coffee Breaks.
Protecting Life and Property
A stairwell pressurization system aims to create an environment that will allow people to escape a burning building. These systems should also improve visibility in the stairwell and adjacent corridors.
Stairwell safety became national news after a fire at the MGM Grand in Las Vegas in 1980 when over 60 people died, mainly in the stairwells. Forty-two years since that tragedy, many buildings are still not adequately equipped for these scenarios. Earlier this year, 17 were killed, and 63 were injured at the Twin Parks Housing in the Bronx, New York, which had no stairwell pressurization system. In both incidents, a small fire created suffocating smoke in the stairwell and killed people attempting to flee.
Which Codes and Standards Apply to Stairwell Pressurization?
The following codes and standards should be consulted in the deployment of these systems:
- Handbook of Smoke Control Engineering, Chapters 10 and 20
- NFPA 92, Chapters 4 and 6, and Appendix F
- ANSI/UL864, Sections 47–50
- International Building Code Section 909
Methods for Stairwell Containment
Passive systems rely on gravity and doors opening and closing, whereas active systems use mechanical means to pressurize the stairwell to inhibit smoke from entering. The components of these active systems include supply fans, exhaust fans, dampers, and building controls.
NFPA 92 highlights two types of active systems:
In a single-point injection system, a supply air fan dumps air into the stairwell at a single point. This works best for buildings under 100 feet tall. NFPA suggests using modeling software to analyze buildings taller than 100 feet to determine the efficacy of a single-point injection system. The supply fan is located anywhere in the stairwell, usually on the rooftop but sometimes at ground level.
In a multiple-point injection system, a fan delivers air through a duct to multiple points in the stairwell. The industry consensus is that system is the correct choice for tall buildings and may include multiple supply fans. Code requires one air injection point every three floors, but many designs have injection points on every other floor.
System Control Types
Blackmon differentiates between three types of controlled systems for proper stairwell pressure:
A non-compensated system is a single-point injection system. Supply air comes in, thus providing one pressure difference with all doors closed. It is a single supply fan run at a single speed.
A compensated system uses dampers and controls to adjust to various combinations of doors opening and closing, keeping the airflow and pressure spikes under control but not changing the fan speed.
Finally, a compensated system with a modulated supply airflow uses VAV or similar technology to vary the supply fan speed to control the pressure spikes.
Active Compensated Stairwell Pressurization System (ACSP)
Blackmon recommends an ACSP solution from RM Manifold group. It features fast-acting relief dampers that reduce over-pressure spikes in the system. A dedicated UL864-listed Point Logic controller provides proper stairwell pressurization.
The system comprises a control panel, three pressure transducers (for monitoring zones within the stairwell), a two-second actuator for the relief damper, and a VFD. It is compatible with any fan listed for smoke control systems.