Photos © Ryan Leasure
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.
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.
