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July 27, 2022
Floor-to-floor systems were a commonly specified method for smoke control in high-rises, especially in Florida. Unfortunately, this outdated approach has been wrongfully applied to the modern era as it is still specified in contemporary buildings occasionally. This has led to several misunderstandings about its use and application amongst architects, engineers, code officials and building owners/operators.
A floor-to-floor smoke control system provides negative pressure on the fire floor and positive pressure on the floors above and below. This is known as the “sandwich method” of smoke control or zoned smoke control. The goal of this pressurization method is to control or restrict smoke movement beyond the zone/floor of fire origin.
For the past few decades, floor-to-floor smoke control systems have been provided as a form of smoke control for high-rises in the United States. This includes Florida, which defines a high-rise as “any building having occupied floors more than 75 feet (22,860 mm) above the lowest level of fire department vehicle access.”
Floor-to-floor is a dated code provision, going back to the BOCA Basic Building Code, which hasn’t been used in Florida since the Florida Building Code superseded all local building codes in 2002. This has led to several misunderstandings about floor-to-floor smoke control. Let’s address each one now.
One of the biggest misconceptions about floor-to-floor smoke control systems is that they are required in new construction high-rise buildings, specifically in the state of Florida.
But according to the Florida Building Code (FBC) and Florida Fire Prevention Code (FFPC), the only time this type of system would explicitly be required is as an exception to providing fire service access to elevator lobbies, as mentioned in the FBC:
“Where a fire service access elevator is required, a 1-hour fire-rated fire service access elevator lobby with direct access from the fire service access elevator is not required if the fire service access elevator opens into an exit access corridor that is no less than 6 feet wide for its entire length and is at least 150 square feet with the exception of door openings, and has a minimum 1-hour fire rating with three-quarter hour fire- and smoke-rated openings; and during a fire event the fire service access elevator is pressurized and floor-to-floor smoke control is provided.”
- 2020 Florida Building Code, Building, 7th Edition, Section 3007.6
Some engineers and architects may look at the code and think they need to utilize floor-to-floor smoke control to satisfy other code provisions. But this approach should only be implemented under unique circumstances, as identified in the exception above.
Because floor-to-floor smoke control systems are complex, they are prone to sequencing issues. Many integrations are involved for these systems to work, and any misprogrammed smoke control system can mess up the entire sequence, potentially activating the system in the wrong part of the building. The worst-case outcome of improper sequencing would be pressurizing the zone/floor of fire origin and forcing smoke throughout the building.
As an example, the chance for failure increases when you’re dealing with 400-500 input devices (smoke detectors) that all need to be sequenced correctly. Conversely, a more straightforward system is easier to manage and less likely to fail.
As discussed in the Smoke Control Handbook, in some fires, the first smoke detector documented to activate has been one or more floors above the fire floor. This can happen due to a variety of factors:
As a result, the fire floor is pressurized while the floor above is exhausted. This could severely exacerbate the fire and smoke conditions on the fire floor.
The FBC does require the egress stairs in high-rise buildings to be protected as a smokeproof enclosure, most commonly provided through a pressurization system. However, there is potential that concurrent use of an inadequately designed or improperly performing floor-to-floor smoke control system can negate the pressure differential required to protect the egress stairs, jeopardizing all occupants of the building. In fact, the Handbook of Smoke Control Engineering explicitly warns against the use of floor-to-floor smoke control.
Floor-to-floor smoke control systems are not intended to fully exhaust the smoke produced in the zone/floor of fire origin and provide tenable conditions for egress. All modern high-rise buildings are provided with automatic fire sprinkler systems, ideally for controlling a fire in the early stages and limiting smoke production.
These suppression systems, paired with methods of passive protection (i.e. fire/smoke barriers) and active systems (stairwell pressurization), are intended to provide a safe and tenable environment for occupants non-intimate to the fire location. The addition of a floor-to-floor system does not necessarily provide any additional benefit to life safety; as noted in our second misconception, these systems can actually do more harm than good.
A floor-to-floor system is an active smoke control system – one that is subject to the higher standards for life safety systems. This means, for example, that it must be provided with a dedicated smoke control panel, and all components must be connected to a standby power source, meet higher equipment rating requirements, monitor for power and operational status, and additional conditions.
Passive smoke control occurs through physical barriers constructed within the building. These include walls and floors in strategic and code-required locations. Every floor in a high-rise building is constructed to possess a fire-resistance and smoke resistance rating. Any penetration in these assemblies must be sealed in a specific manner to maintain the rating of the floor assembly. A high degree of integrity in these floor and wall assemblies that are intended to resist the passage of fire and smoke are often times more beneficial and reliable than a complex mechanical smoke control system.
Floor-to-floor smoke control systems are often confused with post-fire smoke removal and post-fire evac systems. But post-fire systems are not life safety systems. Instead, they are intended to assist the fire department in removing smoke from the building after the fire is suppressed and occupants have already egressed to safety. Post-fire smoke removal systems do not have to meet the higher requirements for a life safety system the way a floor-to-floor smoke control system does. Due to this confusion, sometimes a floor-to-floor smoke control system is unnecessarily provided, increasing both the initial construction cost of the building and the cost of ongoing maintenance.
Floor-to-floor smoke control systems often have issues with dependability and longevity due to the inherent complexity, including the numerous electronic components required for the system to operate correctly. If a fan fails, the controls are wired incorrectly, or a control board is damaged, the system won’t work, and an inoperable smoke control system provides no benefit to the occupants or the owners of the building.
To help mitigate the likelihood of catastrophic failure, life safety smoke control systems must undergo periodic testing. This ensures the system is operating as intended and provides an opportunity to identify maintenance needs before an emergency situation. These recurring maintenance and testing costs are significantly higher in a building with a floor-to-floor smoke control system compared to alternative smoke control options.
Floor-to-floor smoke control systems are a liability and a risk to occupants and building owners.
As a building owner, think of your smoke control system as a car. For example, assume your primary objective when you set out car shopping is to find a reliable and economical vehicle with a high safety rating to get your family from A to B. This typically describes a four-door family sedan with a four-cylinder engine and an automatic transmission. The benefits that you’ll realize as the owner of this vehicle are reasonable maintenance costs, flexibility in mechanics that can work on your car when needed and typically reliable operation over several hundred thousand miles.
Alternatively, you could opt for a high-performance sports sedan to get your family from A to B. However, with the higher initial price tag also comes higher service bills, more limited options of qualified mechanics, and more complex systems that could render your family car inoperable when something fails. If a component is installed incorrectly, serviced incorrectly, or not maintained, you are left in the dust.
In the smoke control world, when practical, aim for the reliable and economical family sedan, sticking to methods of passive smoke protection and the most often utilized approach to smokeproof enclosures, the egress stair pressurization method. This increases the likelihood of system operability throughout the life of the building. A simple design and interaction between components allow contractors to become familiar with the fundamental concepts and functionality of system components quickly and replace components as needed without compromising system functionality.
On the other hand, that high-performance, complex sports car system may only be serviceable by specific vendors or contractors and will have more intensive controls and interfaces between components. Throughout the life of the building, if any of these components, controls or interfaces are not fully understood, modifications could reduce the reliability of the system, potentially rendering the system ineffective or, in the worst-case scenario, actively facilitating smoke spread throughout the building. Ultimately, this defeats the purpose of the smoke control system, which is to contain smoke within a specific area of the building during a fire emergency.
With so many misconceptions and warnings about floor-to-floor smoke control systems, you’re probably wondering if there’s a better approach or if there is a need at all
Research and testing have shown that stairwell pressurization and elevator lobbies (or elevator pressurization systems) provide sufficient control of the vertical movement of smoke throughout high-rise buildings.
These smoke control methods, adopted by the modern Building Code, combined with the utilization of passive fire and smoke protection features, including fire or smoke dampers and listed firestop assemblies for penetrations, ensure the continuity of horizontal assemblies and the protection of vertical enclosures.
Floor-to-floor smoke control systems were once popular in high-rises and remain in service for many buildings. However, they are an outdated approach that creates an unnecessary expense and can lead to dangerous situations if they have not been designed or maintained properly. That’s why it’s important to understand your options during the development of a high-rise, so you know what kind of smoke control system is required.
Since most modern high-rises are required to have some kind of smoke control system in place, you should understand the implications of simple or complex systems so you can make an informed decision. As an owner or developer working on a new construction building, it is also in your best interest to be familiar with the design principles of your building’s fire protection and life safety systems so you are aware of and anticipating the future maintenance and testing needs of the system(s). Hire a licensed fire protection engineer and life safety consultant like Performance Based Fire to help in the design and evaluation of smoke control systems.
Performance Based Fire offers comprehensive smoke control services for high-rises. To learn more about our approach to stairwell pressurization, contact us.
