Ensuring occupant comfort and safety with smoke vents

by sadia_badhon | May 1, 2019 11:19 am

by Thomas Renner

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The architects responsible for designing a state-of-the-art theater in Utah between 2015 and 2017 faced a unique challenge in trying to limit noise intrusion. An adjacent interstate and planes arriving and departing from
a nearby airport made for noisy neighbors for patrons attending events at the Hale Centre Theatre[2] in the city of Sandy.

“The sound issue was pretty intense,’’ said architect Lyle Beecher. “We knew noise was going to be an issue.”

Beecher’s firm, Utah-based Beecher Walker, designed the $80-million Hale Centre Theatre, which opened in November 2017. A critical element of the solution for Beecher and his team was the installation of 20 acoustical smoke vents to guard against noise intrusion. The vents feature a sound transmission class (STC) rating of 46. This figure denotes how well a building partition attenuates airborne sound and roughly reflects the decibel reduction in noise a building component can provide.

STC ratings are included on the doors, windows, partitions, and even floors. They are generally much lower than 46 on doors and windows—a hollow door can have an STC rating of around 20 to 25, while windows are usually in the STC 26 to 28 range. Most smoke vents that are not acoustically rated have an STC value of 30 or less. The vents used at the Hale Centre Theatre include 75-mm (3-in.) thick fiberglass insulation, exceeding the 25-mm (1-in.) thickness of many smoke vents and helping contribute to their acoustic performance.

Construction materials limiting noise are particularly important at theaters and other performance venues, where interference from external forces can ruin events for guests who sometimes pay exorbitant prices to watch shows.

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“In this instance, there are even helicopters that fly directly overhead,’’ Beecher said. “The air traffic was one of the primary concerns we had when we discussed which roofing components to use. Those acoustical smoke vents are the only thing stopping noise from the outside at the loading level. We could not have any noise infiltrating the building.”

The smoke vents are also supported by other acoustical elements, including 0.6-m (2-ft) thick concrete walls with carpeting installed. Additionally, the door bottoms included acoustical treatments.

The acoustical smoke vents atop the Hale Centre Theatre do more than limit noise intrusion. They are also a crucial safety feature in a venue that can host more than 1300 guests in its two auditoriums. Vents enable the escape of smoke, heat, and gases in a burning building.

“Vents will allow for the removal of heat and smoke and potentially slow the spread of fire,’’ said Steve Martin, battalion chief for the Columbus Fire Department in Ohio. “They will also permit firefighters to see and enter the building to possibly extinguish the fire early, preventing the entire building from becoming a loss.”

The vents used at the Hale Centre Theatre include gas spring operators that open the covers in snow and wind. They also have built-in dampers to ensure smooth opening and eliminate the possibility of operational, roofing, or structural damage.

“The vents solved a tremendous challenge for us,’’ Beecher said. “The most important thing is to make sure people are safe. Those vents create a passive smoke-ventilation system that leads up through the loading level. It keeps the smoke out of the theater so everyone can exit safely.”

The scoop on smoke vents

Regulations for smoke vents in commercial structures are outlined in National Fire Protection Association (NFPA) 204, Standard for Smoke and Heat Venting. This standard provides calculations to determine the required dimensions and spacing of smoke and heat vents. The number of smoke vents depends on the size of the building or area protected, the height of the ceilings, and the depth of the expected smoke layer, according to Robert Solomon, PE, division director for NFPA. The number of smoke vents required is also determined by local building and fire codes and the type of commercial structure.

In one example, fire destroyed a building owned by Dick Cold Storage, a business in Columbus, in 2016. More than 400 firefighters rushed to the blaze, but the building did not have smoke vents.

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Without smoke vents, Martin and his team made the decision to let the fire burn itself out once they knew no one was inside. The scene was simply too dangerous to allow firefighters to enter the building. It was not until 18 hours later the fire was finally extinguished. Smoke vents would not have prevented the fire, but they would have allowed firefighters to be more aggressive in tackling the blaze. The building may not have been destroyed if smoke vents had been in place.

“Two of the biggest challenges we face in fighting any fire are heat and smoke. The heat of the fire radiates on everything surrounding it, causing the flames to spread and creating rapid degradation of structural elements,” said Martin. “Buildings that do not lend themselves to ventilation, such as cold-storage buildings, are especially dangerous to firefighters. If there is no known life-safety issue, firefighters will retreat to a defensive position and fight the fire from outside the building instead of going inside.’’

The new Dick Cold Storage building has 18 smoke vents spaced out across 10,637 m² (114,500 sf). The Hale Centre Theatre, by contrast, required 20 acoustical vents over 12,356 m² (133,000 sf). The activation requirements were the same in both applications.

“A cold-storage facility may have a greater fuel load than a theater, which correlates to a design with a higher expected heat release rate, greater temperature outputs, and an increased smoke production rate. It may require larger, more closely spaced vents,’’ Solomon said. “The design influences the number, size, spacing, and activation requirements. The theater scenario is largely directed at stages and the vents are essentially a key occupant life-safety feature.”

Without vents to exhaust it, smoke is contained within a building, explained William Koffel, PE, FSFPE, president of the fire-protection engineering firm, Koffel Associates.

“This could impact egress, cause increased property damage, and hinder the efforts of first responders,’’ he said.

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When a fire occurs, if the incident commander determines ventilation is necessary and appropriate, firefighters will manually cut holes in the roof to serve as roof vents. However, many structures (such as the cold-storage building) are light steel construction and there may be concerns with the integrity of the roof upon which the firefighters need to work.

How smoke vents work

Underwriters Laboratories (UL)-listed smoke vents are required to open automatically and be equipped with both an interior and exterior pull release allowing firefighters to open them manually. Automatic smoke vents can be actuated either by fusible links or electrically via a heat or smoke detector or sprinkler water flow switch.

Some automatic smoke vents include a positive hold/release mechanism ensuring reliable vent operation when a fire occurs. The vent automatically releases upon the melting of a UL-listed 74 C (165 F) fusible link. The curb-mounted fusible link housing allows the latch to be quickly and easily reset from the roof level.

It is also critical smoke vents open in snow and wind. If a fire occurs in inclement weather, they must operate as planned.

“NFPA 204 requires opening mechanisms to remain free and clear and undergo periodic inspection, testing, and maintenance,’’ Solomon said. “Additionally, NFPA 204 requires automatic vents to be fail-open, meaning if there is a failure in the mechanism of the vent, it will automatically open.”

Solomon added the expanded use and installation of roof-mounted solar photovoltaic (PV) arrays has the potential to impede the operation of vents.

“Anytime vents and PV systems are being installed together, including circumstances where the array is being installed on an existing building with vents, great care must be taken to ensure the array will not prevent the vent from operating or obscuring the vent area,’’ he said.

To ensure the two systems function cohesively, design/construction professionals should ensure they are familiar with the dimensions for both vents and the PV array. When the building is being designed, they should also ensure they allow enough space for all components to work properly. Architects will have to confirm the vents are spaced out over an equal distance across the roof.

Know the standard

Among the most important sections in NFPA 204 is one requiring vents to be designed so they can be inspected visually. Section 5.2.4, “Vent Design Constraints,” states the supporting structure and means of actuation must be designed to allow this.

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“This is very important as too often, mechanical equipment is installed in a manner that makes regular inspection, testing, and maintenance very difficult or infeasible,’’ said Solomon. “The vent layout as presented on the contract plans is also critical. The vent size, arrangement, and geometry are often based around the location of draft curtains and intended storage configurations. Deviations for the vent location may impact their effectiveness. Any changes from the original design need to be carefully evaluated.”

The decision to provide smoke and heat vents should be made by an engineer, as there are cases in which their inclusion is not appropriate.

“Vents should not be provided if the building is equipped with an early suppression, fast response (ESFR) sprinkler system or if an alternative means of smoke ventilation is provided, such as an active smoke-control or smoke-evacuation system,’’ Solomon said. “The benefits of smoke and heat vents are also highly dependent on the size and geometry of the building and the expected size of the fire.  They are most effective in large, open spaces with high ceilings with a significant fuel load.”

Vents operate best in such spaces because large, open areas allow for the escape of smoke and gases and do not contribute to the rapid buildup of smoke within the building.

Vents versus sprinklers

Smoke vents and sprinkler systems serve different fire-protection and life-safety purposes. Sprinklers control or suppress a fire until the fire department can respond to extinguish it. Smoke vents allow for smoke and heat to leave the building, which can help increase the safe egress time for building occupants. They will also allow for increased visibility for both occupants and firefighters and reduce interior temperatures for firefighting operations.

“Proper operation of an automatic sprinkler system should result in a reduction in the amount of smoke produced,’’ Koffel said. “There are fire scenarios, especially in storage occupancies, in which a considerable amount of smoke is still produced.”

This can be mitigated with the inclusion of an appropriate number of smoke vents, which open with the melting of a link.

According to Solomon, there is also some concern vents may create a vacuum effect and bring more outside air into the building or pull a fire in the direction of a smoke vent, helping it continue to grow and spread.

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“While smoke and heat vents do increase entrained air into the building, the benefits from the significant reduction of the amount of smoke and superheated gases in the space usually outweigh the possible fire growth due to the entrained air,’’ he explained.

A critical piece of fire protection

Whether the project in question is a theater in Utah or a cold-storage building in Ohio, smoke vents can be an essential part of a fire-protection plan. Lives and businesses can be saved. Theaters, especially those as technologically sophisticated as the Hale Centre, can be susceptible to fire. Technological features introduce more elements that could cause a fire, such as wiring, increased electrical load, and electric cables.

Stage technology has become so advanced, NFPA’s research affiliate, the Fire Protection Research Foundation, wrote a report[8] in 2009 addressing fire-protective measures at theaters. According to the report, “it is desirable a fire-safety curtain and roof vents are activated prior to sprinklers,” and the vents should be “tied to a relatively responding rate-of-rise heat detectors, preferably ceiling mounted.”

“Smoke vents were such an important part of this,’’ Beecher said about the Hale Centre project. “We know they will operate if there is an actual fire. We needed to make sure if a fire did occur, everyone could exit safely.”

Cold-storage constructor Tippmann Innovation designed a state-of-the-art facility for Dick Cold Storage, and the smoke vents give Don Dick, its CEO, peace of mind a tragedy of similar proportions will not hurt his business.

“We were surprised at how quickly the team at Tippmann Innovation was able to meet with us after the fire,’’ said Dick. “Their combined expertise and experience allowed us to immediately begin making plans to replace our warehouse. The upgraded technologies in the new facility allow us to have peace of mind about the future growth and safety of the warehouse.”

In many commercial industries, smoke vents play an integral part in fire-protection plans. They can be an important piece of equipment in saving lives and protecting property.

Thomas Renner writes frequently on building, construction, and manufacturing for U.S. trade publications. He has been a journalist for more than 30 years, held executive positions at several newspapers, and won notable awards for his work. Renner can be reached at trenner@catalystmc.com[9].

Source URL: https://www.constructionspecifier.com/ensuring-occupant-comfort-and-safety-with-smoke-vents/

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