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.