A tragic truth about building codes is that they are often based on the tough lessons learned from disasters that could have been avoided. Fire safety is a perfect example of this phenomenon. Consider the Great Chicago Fire of 1871, which was supposedly started by Mrs. O’Leary’s cow knocking a lantern into hay, fueled by the massive number of constructions of wood and other combustible materials hastily erected to serve Chicago’s rapidly growing population, and finally stopped when it ran out of fuel. The fire destroyed one-third of Chicago’s buildings and killed 250 people. As a result, fire and building codes changed the spacing and material requirements that were used for reconstruction. In 1903, The Iroquois Theater in Chicago was packed for a matinee performance of Mr. Bluebeard when a spark from an arc light ignited a muslin curtain. Blocked exit doors, unfamiliar locking devices, doors that opened into the building, shut vents, and iron gates blocking the exit stairways all contributed to the more than 600 casualties that occurred. The Iroquois Theater Fire is recognized as the deadliest single-building fire in the history of the United States. After the fire, federal and state standards for exiting pathways, exit doors, exit signs, maximum seating, and the use of the panic bar were created.
Photo courtesy of Jennifer Baker/Jenn’s Breathtaking Moments
Automatic smoke vents were installed on the roof of the Cincinnati Music Hall when the 140-year-old facility underwent a major renovation.
This course will take a closer look at the use of one fire-safety technology—automatic smoke vents—in large, single-story, undivided buildings. It will review the accident that showcased the vulnerability of these types of space, explain why automatic smoke vents are an optimal fire-response solution in these scenarios, explore how the codes changed to require these technologies in different types of space, review today’s code requirements, and provide insight into the product options that can be selected to best match the venting solution with the needs of the project.
The 1953 General Motors Fire
In 1953, there was a terrible fire at a very large General Motors (GM) plant in Livonia, Michigan, where GM Hydra-Matic transmissions were manufactured for many of the company’s biggest brands, including Cadillac, Oldsmobile, Pontiac, Chevrolet, and Lincoln. The expansive, open building covered roughly 1.5 million square feet and was 866 feet wide. Just four years old, the manufacturing plant was considered state of the art for the early post-World War II era.
At the time of the fire, the building and production processes were deemed fully up to all established fire and safety codes, and the building itself was said to have “the most modern fire-prevention and fire-quenching equipment.” However, a Fire Engineering article published in September 1953 reported that the building “was enlarged several times, and there were no effective fire stops to divide up the large floor area. Also, the sprinkler system did not cover the entire plant.” Later reports indicate that no more than 20 percent of the building was sprinklered, and there were no fire walls, partitions, or roof vents.
The cause of the fire was determined to be a spark from a welder’s cutting torch that ignited oil and a highly flammable liquid used as a rust inhibitor for transmission parts in a conveyor drip pan. In the Fire Engineering article “Michigan’s Costliest Fire Destroys Auto Parts Plant,” the writer says, “The fire spread rapidly down the metal trough to a storage tank, which exploded. Before the explosion, employees tried to fight the fire with hand extinguishers, and reportedly they had almost controlled the blaze when someone stretched in a hose line and turned water on the trough, almost instantly spreading fire over the area. The tank explosion touched off additional blasts in other tanks, and the fire communicated rapidly to other oil-loaded machines, which flared up, further spreading the blaze and driving plant workers outside.” The flammable oils, grease, and chemicals present on the production floor further fueled the destructive flames. The fire spread quickly throughout the open room building and engulfed the sprawling four-block plant.
Unfortunately, many aspects of the building’s design hindered an effective fire response. Fire-hose streams were only able to penetrate 75 feet into the 866-foot-wide structure. Without a way to escape, the smoke, heat, and fire were trapped inside the building, creating temperatures intense enough to melt and warp metal girders and cause structural damage to roof trusses, which ultimately led to the fail of the building.
In the end, most of the 1.5-million-square-foot plant was destroyed, with the exception of an office building and small power plant on the campus. In 1953, this fire was recognized as one of the nation’s largest individual insured fire losses, with damages estimated at roughly $35 million. Six men died and many others were injured. As a result of this fire, changes were made to the fire code in an effort to prevent losses of life and property from occurring on this magnitude again in large, single-story, undivided buildings.
The Fire Risk in Large, Single-Story, Undivided Buildings
In many types of structures, including high-rises, hotels, and commercial buildings, compartmentalization is a key component of the fire-containment strategy designed into the building. The idea is that if the smoke and flames are trapped on a single floor or section of a structure, building occupants will be able to escape safely, and it will be easier for firefighters to locate and address the fire. Large, undivided buildings, such as warehouses or convention centers, are not naturally compartmentalized, and so they require special consideration and fire-managing technology in their design.
Photo courtesy of The BILCO Company
Automatic smoke vents protect property and aid firefighters in bringing a fire under control by removing smoke, heat, and noxious gases from a burning building.
Here’s a quick description of how smoke, fire, and hot gases move through a large, undivided building. When a fire develops, a smoke plume comprised of hot gases and smoke rises upward into the space directly above the fire. When the smoke plume impacts the ceiling, the hot gases and combustion products spread out horizontally under the ceiling surface, quickly reaching areas of the building that are removed from the immediate location of the fire. The rapid flow of hot gas moving in a shallow layer beneath the ceiling surface is referred to as the ceiling jet. The smoke layer flows under the ceiling jet. As the fire continues to burn, more smoke and hot gases rise to the ceiling. Ambient air is also entrained into the smoke plume. As a result, the layer of hot gas and smoke at the ceiling thickens, and the temperatures of the ceiling jet and smoke layer rise. As the temperatures increase across the surface of the ceiling, sprinklers open, including many that are not over flames. This has two undesirable effects. It decreases the water pressure being applied to the actual flames, and it soaks much of the interior unnecessarily. The accumulation of smoke inside the building limits visibility, which can make it more difficult for occupants to escape and firefighters to gain access to the fire. The intense heat building at the ceiling will eventually begin to weaken the structure, increasing the potential danger to the people and firemen on the scene and the amount of damage caused by the fire.
Many researchers have worked to quantify the flow, temperature, and velocity of ceiling jets. While there are many variables that must be considered in determining the temperature and velocity of a ceiling jet in a specific situation, the ceiling height of a building is an important contributing factor. “As a rule of thumb, the thickness of the ceiling jet flow is 5 to 12 percent of the ceiling-to-fire-source height. Within this ceiling jet flow, the maximum temperature and velocity occurs within 1 percent of the distance from the ceiling to the fire source,” explains David D. Evans in the SFPE Handbook of Fire-Protection Engineering, Second Edition. Fires in buildings with taller ceiling heights will create thicker and potentially more destructive ceiling jets.
The relationship between the size of the ceiling jet and the ceiling-to-fire-source height of the building helps to illustrate why managing the presence of hot gas and combustibles at the ceiling level of these large open buildings is so important. And it becomes even more so as the size of the warehouses and other undivided building types continue to grow. According to NAIOP, the Commercial Real Estate Development Association, “Twenty years ago, the average ceiling height for a new warehouse was 25 feet clear. Today, in newly constructed structures larger than 300,000 square feet, 32 feet clear is typical. In mega-sized distribution buildings, 36 feet is common, with clear heights rising past 40 feet in some cases.”
Allowing intense heat to build up inside large, single-story facilities creates a number of problems and can contribute to structural damage. Designers can use automatic smoke vents to prevent the accumulation of incredible heat at the ceiling and better protect the property and the lives of the people inside it.
A tragic truth about building codes is that they are often based on the tough lessons learned from disasters that could have been avoided. Fire safety is a perfect example of this phenomenon. Consider the Great Chicago Fire of 1871, which was supposedly started by Mrs. O’Leary’s cow knocking a lantern into hay, fueled by the massive number of constructions of wood and other combustible materials hastily erected to serve Chicago’s rapidly growing population, and finally stopped when it ran out of fuel. The fire destroyed one-third of Chicago’s buildings and killed 250 people. As a result, fire and building codes changed the spacing and material requirements that were used for reconstruction. In 1903, The Iroquois Theater in Chicago was packed for a matinee performance of Mr. Bluebeard when a spark from an arc light ignited a muslin curtain. Blocked exit doors, unfamiliar locking devices, doors that opened into the building, shut vents, and iron gates blocking the exit stairways all contributed to the more than 600 casualties that occurred. The Iroquois Theater Fire is recognized as the deadliest single-building fire in the history of the United States. After the fire, federal and state standards for exiting pathways, exit doors, exit signs, maximum seating, and the use of the panic bar were created.
Photo courtesy of Jennifer Baker/Jenn’s Breathtaking Moments
Automatic smoke vents were installed on the roof of the Cincinnati Music Hall when the 140-year-old facility underwent a major renovation.
This course will take a closer look at the use of one fire-safety technology—automatic smoke vents—in large, single-story, undivided buildings. It will review the accident that showcased the vulnerability of these types of space, explain why automatic smoke vents are an optimal fire-response solution in these scenarios, explore how the codes changed to require these technologies in different types of space, review today’s code requirements, and provide insight into the product options that can be selected to best match the venting solution with the needs of the project.
The 1953 General Motors Fire
In 1953, there was a terrible fire at a very large General Motors (GM) plant in Livonia, Michigan, where GM Hydra-Matic transmissions were manufactured for many of the company’s biggest brands, including Cadillac, Oldsmobile, Pontiac, Chevrolet, and Lincoln. The expansive, open building covered roughly 1.5 million square feet and was 866 feet wide. Just four years old, the manufacturing plant was considered state of the art for the early post-World War II era.
At the time of the fire, the building and production processes were deemed fully up to all established fire and safety codes, and the building itself was said to have “the most modern fire-prevention and fire-quenching equipment.” However, a Fire Engineering article published in September 1953 reported that the building “was enlarged several times, and there were no effective fire stops to divide up the large floor area. Also, the sprinkler system did not cover the entire plant.” Later reports indicate that no more than 20 percent of the building was sprinklered, and there were no fire walls, partitions, or roof vents.
The cause of the fire was determined to be a spark from a welder’s cutting torch that ignited oil and a highly flammable liquid used as a rust inhibitor for transmission parts in a conveyor drip pan. In the Fire Engineering article “Michigan’s Costliest Fire Destroys Auto Parts Plant,” the writer says, “The fire spread rapidly down the metal trough to a storage tank, which exploded. Before the explosion, employees tried to fight the fire with hand extinguishers, and reportedly they had almost controlled the blaze when someone stretched in a hose line and turned water on the trough, almost instantly spreading fire over the area. The tank explosion touched off additional blasts in other tanks, and the fire communicated rapidly to other oil-loaded machines, which flared up, further spreading the blaze and driving plant workers outside.” The flammable oils, grease, and chemicals present on the production floor further fueled the destructive flames. The fire spread quickly throughout the open room building and engulfed the sprawling four-block plant.
Unfortunately, many aspects of the building’s design hindered an effective fire response. Fire-hose streams were only able to penetrate 75 feet into the 866-foot-wide structure. Without a way to escape, the smoke, heat, and fire were trapped inside the building, creating temperatures intense enough to melt and warp metal girders and cause structural damage to roof trusses, which ultimately led to the fail of the building.
In the end, most of the 1.5-million-square-foot plant was destroyed, with the exception of an office building and small power plant on the campus. In 1953, this fire was recognized as one of the nation’s largest individual insured fire losses, with damages estimated at roughly $35 million. Six men died and many others were injured. As a result of this fire, changes were made to the fire code in an effort to prevent losses of life and property from occurring on this magnitude again in large, single-story, undivided buildings.
The Fire Risk in Large, Single-Story, Undivided Buildings
In many types of structures, including high-rises, hotels, and commercial buildings, compartmentalization is a key component of the fire-containment strategy designed into the building. The idea is that if the smoke and flames are trapped on a single floor or section of a structure, building occupants will be able to escape safely, and it will be easier for firefighters to locate and address the fire. Large, undivided buildings, such as warehouses or convention centers, are not naturally compartmentalized, and so they require special consideration and fire-managing technology in their design.
Photo courtesy of The BILCO Company
Automatic smoke vents protect property and aid firefighters in bringing a fire under control by removing smoke, heat, and noxious gases from a burning building.
Here’s a quick description of how smoke, fire, and hot gases move through a large, undivided building. When a fire develops, a smoke plume comprised of hot gases and smoke rises upward into the space directly above the fire. When the smoke plume impacts the ceiling, the hot gases and combustion products spread out horizontally under the ceiling surface, quickly reaching areas of the building that are removed from the immediate location of the fire. The rapid flow of hot gas moving in a shallow layer beneath the ceiling surface is referred to as the ceiling jet. The smoke layer flows under the ceiling jet. As the fire continues to burn, more smoke and hot gases rise to the ceiling. Ambient air is also entrained into the smoke plume. As a result, the layer of hot gas and smoke at the ceiling thickens, and the temperatures of the ceiling jet and smoke layer rise. As the temperatures increase across the surface of the ceiling, sprinklers open, including many that are not over flames. This has two undesirable effects. It decreases the water pressure being applied to the actual flames, and it soaks much of the interior unnecessarily. The accumulation of smoke inside the building limits visibility, which can make it more difficult for occupants to escape and firefighters to gain access to the fire. The intense heat building at the ceiling will eventually begin to weaken the structure, increasing the potential danger to the people and firemen on the scene and the amount of damage caused by the fire.
Many researchers have worked to quantify the flow, temperature, and velocity of ceiling jets. While there are many variables that must be considered in determining the temperature and velocity of a ceiling jet in a specific situation, the ceiling height of a building is an important contributing factor. “As a rule of thumb, the thickness of the ceiling jet flow is 5 to 12 percent of the ceiling-to-fire-source height. Within this ceiling jet flow, the maximum temperature and velocity occurs within 1 percent of the distance from the ceiling to the fire source,” explains David D. Evans in the SFPE Handbook of Fire-Protection Engineering, Second Edition. Fires in buildings with taller ceiling heights will create thicker and potentially more destructive ceiling jets.
The relationship between the size of the ceiling jet and the ceiling-to-fire-source height of the building helps to illustrate why managing the presence of hot gas and combustibles at the ceiling level of these large open buildings is so important. And it becomes even more so as the size of the warehouses and other undivided building types continue to grow. According to NAIOP, the Commercial Real Estate Development Association, “Twenty years ago, the average ceiling height for a new warehouse was 25 feet clear. Today, in newly constructed structures larger than 300,000 square feet, 32 feet clear is typical. In mega-sized distribution buildings, 36 feet is common, with clear heights rising past 40 feet in some cases.”
Allowing intense heat to build up inside large, single-story facilities creates a number of problems and can contribute to structural damage. Designers can use automatic smoke vents to prevent the accumulation of incredible heat at the ceiling and better protect the property and the lives of the people inside it.
Introducing Automatic Smoke Vents
There are, generally, two categories of automatic smoke and heat-removal systems: mechanically opened and gravity opened.
Photo courtesy of The BILCO Company
Mechanically opened automatic smoke vents in double-leaf models ventilate larger areas.
Mechanically opened automatic smoke vents consist of covers that are over-sprung by a mechanical lift assist and held closed by a latching mechanism with a fusible link. The fusible link—the same technology commonly used as the trigger mechanism in fire sprinkler systems and automatic fire doors—melts at a specific temperature, opening the vent doors when temperatures at the ceiling reach a certain level. When released, engineered lift assistance opens the steel or aluminum covers and locks them in an open position, allowing the heat, smoke, and toxic fumes gathering at the ceiling to escape the burning building. Once the fire has been put out, the vents can easily be reset from the roof level. These automatic smoke vents are the most common solution used for smoke and heat removal in large, single-story, undivided buildings.
Gravity-opened vents, also referred to as melt-out domes, do not open by mechanical means. When the heat from the fire reaches the dome material, it shrinks the material until it falls into the building, providing a hole in the roof through which the heat and gas can escape. There are a few notable disadvantages in selecting this technology over the automatic smoke vents. The melt-out domes cannot be designed to activate in response to a fire alarm or smoke detector. They cannot be reset, and the dome material could contribute to the fire as it falls into the building. Melt-out ventilation is less common but offers a cheap alternative to mechanically operated smoke vents.
When a fire-venting strategy is implemented in a large, single-story, undivided building, the progression of a fire event is dramatically different, and the damage can be much more contained. The automatic smoke vent or vents located closest to the source of the fire open first, providing the most direct exit for the hot gases and smoke produced in the combustion zone. This reduces the spread of hot gases and smoke throughout the facility, and it slows the thickening rate of the ceiling jet and the smoke layer. With sufficient venting area, the thickening rate can be arrested and even reversed.
With the development of the ceiling jet and smoke layers better controlled, occupants will have time to evacuate safely, and firemen can enter the building and fight the blaze from the floor.
The Evolution of Automatic Smoke Vent Use and Regulation
After the GM fire in Livonia, in recognition of the catastrophic damage that could occur when fires start in large, single-story, undivided spaces, building codes and common design practices changed. There were new restrictions on roof tar buildup, a required separation of hazardous operations, sprinkler requirements in industrial buildings, a mandated fire coating for steel-frame trusses, and new requirements around the use of automatic fire doors. It also became a widespread practice to install automatic smoke vents into the ceilings of storage buildings, manufacturing facilities, and warehouses. To provide guidance on the design of these life-safety systems, the Standard for Smoke and Heat Venting, authored by the National Fire Protection Association (NFPA), was also created. The standard is referred to as NFPA 204.
NFPA 204: Standard for Smoke and Heat Venting, 2024 Edition
Initiated in 1956, the first guide dedicated to smoke and heat venting was officially adopted by NFPA in 1960 and has undergone regular revisions since then. The 2002 edition was converted from a guide to standard, and the 2024 Edition is its latest iteration. As it describes in Chapter 1, “This standard shall apply to the design of venting systems for the emergency venting of products of combustion from fires in buildings.” Provisions are included to address appropriate designs for both non-sprinklered, single-story buildings and sprinklered buildings.
Photo courtesy of The BILCO Company
Smoke vents are available in single-leaf models for smaller, more confined areas like stairwells or elevator shafts.
The standard identifies design objectives for smoke and heat venting systems and explores vent design constraints, methods of operation, and vent dimensions and spacing, as well as information on air inlets, draft curtains, mechanical smoke exhaust systems, and required inspection and maintenance. Ultimately, NFPA 204 helps designers meet selected performance objectives related to a specific building and a specific set of circumstances. Those performance objectives include designing a vent system that will “slow, stop, or reverse the descent of a smoke layer produced by fire in a building by exhausting smoke to the exterior.” By controlling the smoke layer, a well-designed vent system will provide occupants with a safe path of travel to a safe area, facilitate manual firefighting, and reduce the damage to buildings and contents that results from exposure to smoke and hot gases.
Although NFPA 204 is technically referred to as a standard, it does not specify under which conditions venting is to be provided or required. The decision whether to provide venting in a building depends on the design objectives set by a building owner or occupant and on local building and fire code requirements.
2024 International Building Code (IBC) Section 910
While NFPA 204 guides the design of automatic venting systems where they are required, the 2024 International Building Code (IBC) Section 910: Smoke and Heat Removal addresses the specific types of buildings that require these automatic smoke and heat vents.
910.2 Where Required
Smoke and heat vents or a mechanical smoke removal system shall be installed as required by Sections 910.2.1 and 910.2.2. Exceptions include:
- Frozen food warehouses used solely for storage of Class I and Class II commodities where protected by an approved automatic sprinkler system.
- Areas of buildings equipped with early-suppression fast-response (ESFR) sprinklers.
- Areas of buildings equipped with control-mode special-application sprinklers with a response time index of 50 (m · s) ½ or less that are listed to control a fire in stored commodities with 12 or fewer sprinklers.
910.2.1 Group F-1 or S-1
Smoke and heat vents installed in accordance with Section 910.3 or a mechanical smoke-removal system installed in accordance with Section 910.4 shall be installed in buildings and portions thereof used as Group F-1 or S-1 occupancy having more than 50,000 square feet of undivided area. In occupied portions of a building equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1 where the upper surface of the story is not a roof assembly, a mechanical smoke removal system shall be installed. Exception: Group S-1 aircraft repair hangars.
910.2.2 High-Piled Combustible Storage
Smoke and heat removal required by Table 3206.2 of the International Fire Code (IFC) for buildings and portions thereof containing high-piled combustible storage shall be installed in accordance with section 910.3 in unsprinklered buildings. In buildings and portions thereof containing high-piled combustible storage equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1, a smoke- and heat-removal system shall be installed in accordance with Section 910.3 or 910.4. In occupied portions of a building equipped throughout with an automatic sprinkler system in accordance with an automatic sprinkler system in accordance with Section 903.3.1.1, where the upper surface of the story is not a roof assembly, a mechanical smoke removal system in accordance with Section 910.4 shall be installed.
In summary, the 2024 IBC requires the installation of smoke and heat vents in factories, industrial buildings, and storage facilities that have more than 50,000 square feet of undivided area and where the upper surface of the story is a roof assembly. Table 3206.2 of the IFC (referenced in the code language above) requires smoke and heat removal in high-piled storage areas holding commodity classes I-IV that are greater than 12,000 square feet or considered nonpublic accessible and between 2,501 and 12,000 square feet in size. High-piled storage areas containing commodities deemed High Hazard must have a system for smoke and heat removal if the area is larger than 2,501 square feet or identified as nonpublic accessible and between 501 and 2,500 square feet. The IBC and IFC also contain provisions that state the minimum ratio of area of vents provided to the floor area and the maximum spacing of vents.
UL 793 Standard for Automatically Operated Roof Vents for Smoke and Heat
In addition to standards that dictate where automatic roof vents must be included and the standards that guide designers in creating systems that meet certain performance objectives, there are standards that provide construction and performance criteria that the manufacturers of automatic smoke vents must meet. Underwriters Laboratories (UL) develops standards that help companies demonstrate safety, confirm compliance, and deliver quality in a wide array of product types. The UL 793 Standard for Automatically Operated Roof Vents for Smoke and Heat defines certain requirements for automatically operated roof vents in both the mechanically opened and gravity-opened categories.
Photo courtesy of The BILCO Company
Acoustical smoke vents are designed to guard against noise intrusion and are ideal for concert halls, theaters, and other interior applications that require limited noise from the outside.
As stated in the scope of UL 793 Standard, “The vents covered by these requirements are operated manually or automatically in the event of fire to remove smoke and heat from the building. Automatic operation does not depend upon electrical power or other energy sources that may be interrupted during a fire, but rather on operation of a heat-responsive device or on the action of a plastic cover shrinking and falling from place due to fire exposure or the like. These vents are not intended for use as general-purpose building ventilation devices.” The UL standard contains requirements for vent construction, performance, marking, and installation and operating instructions.
The Benefits of Automatic Smoke Vents
Designing large, single-story, undivided industrial, manufacturing, and storage facilities to meet codes and effectively manage a fire, protecting people and property inside, is an especially important topic today, as the online shopping trend has resulted in a proliferation of large warehouse spaces across the nation. But automatic smoke vents also offer incredible life-saving benefits to other large, undivided venues where the upper surface of the main story is the roof, such as convention centers, arenas, stadiums, performance theaters, and auditoriums.
Photo courtesy of The BILCO Company
By allowing the heat, smoke, and gases to escape a burning building, automatic smoke vents allow an increased evacuation time, decrease the risk of smoke inhalation, enhance visibility for firefighters, and protect the structure from damaging heat.
Increased Evacuation Time and Decreased Risk of Smoke Inhalation
By removing smoke, heat, and gases from a burning building, automatic smoke vents can offer people in the building more time to safely exit the premises and decrease the risk of smoke inhalation, which is recognized as the number one cause of death related to fires.
Enhanced Visibility for Firefighters
Providing smoke, hot gases, and products of combustion with a path to exit the building, instead of trapping them inside, also improves the visibility that firefighters have of the interior once they arrive on the scene, and enables them to more quickly locate the fire and formulate a plan to contain it.
Release Noxious and Potentially Explosive Fumes
Fires also release dangerous gases into the air, including carbon monoxide, which is lethal, and fire smoke often contains a whole host of other toxic threats like hydrogen cyanide and inorganic acids. Exposure to these toxicants can be the principal cause of death found in victims of fires. During fires, potentially explosive fumes can also be released. Automatic smoke vents remove noxious and potentially explosive gases from the area, making the burning environment safer for people and firefighters to travel through it.
Protects Against Secondary Ignitions and Lateral Fire Spread
Intense heat is one of the components that can cause a secondary ignition in a fire, which causes the fire to move through a building laterally away from the initial area of combustion. Automatic smoke vents allow the heat and smoke to escape the building, eliminating the potential for the problematic buildup of intense heat and helping to keep the fire from spreading from its original location.
Protect the Structure from Damaging Heat
When fires start, a smoke plume of hot gases and smoke rises directly above the area of combustion until it hits the ceiling. Unable to break through the ceiling, the hot gases remain trapped at the horizontal surface, getting thicker and hotter as the fire burns. Exposure to the intense heat in those gases can damage structural elements in the building. Automatic smoke vents slow the buildup of these hot gases at the ceiling and can even reverse it, protecting the structure from the damaging levels of heat that can be produced.
Reduced Damage to Buildings and Their Content
Smoke detectors and sprinkler systems are installed in the ceiling because smoke and hot gases produced by fires first rise to the ceiling before spreading horizontally across the surface and through the building. As previously discussed, this can cause sprinklers to activate that are not directly over a fire condition, which can result in unnecessary water damage to contents and property not directly involved in the fire. When automatic smoke vents closest to the actual zone of combustion open, they pull the hot gases and smoke out of the building so that they don’t travel further away from the fire and set off these additional sprinklers, which reduces the damage caused to the building and the contents inside.
Many architects and engineers, fire authorities, and insurance carriers agree that specifying automatic vents for modern industrial and commercial structures offers a significant benefit and dramatically improved outcomes in the protection of lives and property. The first step is learning how to select the right automatic smoke vent for a specific project.
Selecting the Right Automatic Smoke Vent for a Project
Automatic smoke vents are an important and effective fire management tool for buildings with large expanses of unobstructed space, such as convention centers, auditoriums, retail stores, schools, theaters, manufacturing facilities, and warehouses. However, the types of buildings included on this incredibly diverse list have unique needs that may be best addressed with slightly different automatic smoke vent solutions. Let’s take a closer look at some of the options and features available, and identify the types of projects that need them.
Photo courtesy of The BILCO Company
Vents can be supplied with polycarbonate covers to add daylight into a building and reduce energy costs.
Built-In Skylight
Most automatic smoke vents feature a cover constructed from solid aluminum or steel. In addition to melt-out dome models, mechanical automatic smoke vents are available with translucent polycarbonate covers that allow daylight to penetrate into the interior, while the covers are in the closed position, effectively transforming the smoke vent into a fire-responsive skylight. These daylighting covers are designed to resist UV degradation and offer superior insulation performance. These solutions are often sought to provide access to daylight for reduced energy costs and to improve the interior environment in manufacturing facilities, large atriums, and even schools.
Acoustical Sound-Rated
While outside noise may not be particularly disruptive to manufacturing and storage activities, the experience created in theaters and auditoriums can be materially diminished by unwanted noise intrusion. Automatic smoke vents that have achieved a sound rating can be used to help soundproof the interior space. Look for products that have sound transmission class (STC) and outdoor–indoor transmission class (OITC) ratings. These ratings indicate how well a device attenuates airborne sound, making these products ideally suited for concert halls, theaters, auditoriums, and other interior applications where exterior noise infiltration needs to be minimized.
Thermally Broken Smoke Vents
New thermally broken smoke vents can be specified to add energy efficiency. During summer months, heat from an extremely hot roof exterior wants to radiate through the smoke vent into the cooler building interior. While standard smoke vent insulation helps to reduce this heat gain, the metal construction of the smoke vent itself facilitates the temperature transfer, which can lead to increased utility costs and condensation issues on the underside of the vent. In winter or colder months, this same energy transfer principle results in heat loss from inside a building as well as increased energy expenses.
In order to increase energy efficiency, thermally broken smoke vents are designed with an element of low conductivity integrated between interior and exterior surfaces of the cover and frame to reduce temperature transfer. As an added benefit, these same thermally broken components dampen vibration for improved acoustic performance against outside noise.
Leading manufacturers can provide a thermally broken vent product featuring up to three inches of polyisocyanurate insulation with an R-value of 20+ in both the cover and curb for superior energy performance, and a special cover gasket to minimize air leakage. The product should be UL labeled to ensure reliable smoke vent operation in an emergency.
Electric Activation
Automatic smoke vents can also be designed to be activated in response to a smoke detector or fire alarm in addition to the fusible link activation that will open the vents when the fusible link mechanism melts. These automatic smoke vents include an electric latching mechanism, which enables the vents to open when they receive a electric signal from the smoke detector or fire alarm control panel. This feature can be especially useful in applications where the smoke vents are more centrally located and will ensure that if there is a fire in the building, even if it is not located near the vents, the vents will be open, and smoke and hot gases will be able to escape.
Motorized or Winch Operation
Sometimes it’s nice or necessary to open the automatic smoke vents to ventilate a work area, even if there is no fire. Automatic smoke vents can be equipped so that they can be opened on demand too. Motorized smoke vents can be opened with push-button control, or a rigging can be installed at the floor level which will allow an operator to use a manual winch to open the vents.
Photo courtesy of The BILCO Company
Smoke vent options include motorized operation for daily natural ventilation in manufacturing environments.
Explosion Vents
Automatic smoke vents have also been designed to respond to explosions as well as fire, and they are available as either explosion vents or as combination fire/explosion vents. The explosion release mechanism is preset and factory tested to release in response to pressure on the underside of the covers.
The incredible damage that resulted from the 1953 GM Livonia plant fire provided the nation with an important example of how dangerous fires in large, single-story, undivided buildings can be when there is no way to remove the layers of smoke and hot gas building up at the ceiling. The lessons learned from that incident led to the practical inclusion of automatic smoke vents in large single-story factories and, eventually, the code-mandated inclusion of these technologies in large industrial, manufacturing, and storage facilities. Automatic smoke vents are a powerful fire-response solution that can deliver significant protection to the people and property inside a burning building and help create an environment that allows firefighters to access and contain a fire as quickly and safely as possible.
For more information on the code-required equipment and best practices for incorporating automatic smoke ventilation into the roof design of a specific project, contact the local fire-protection authority or reach out to a reputable smoke vent manufacturer for assistance. Both resources will help designers to save lives and fight fires in large, single-story, undivided buildings.
Jeanette Fitzgerald Pitts has written nearly 100 continuing education courses exploring the benefits of incorporating new building products, systems, and processes into project design and development.
