Time to vent
16 September 2019
With more than half of fire fatalities resulting from the inhalation of smoke and toxic gases, Scott Couldrey explores the benefits of smoke vents in helping to prevent loss of life with.
SMOKE IS a killer!In the event of a building fire, it’s the biggest threat to life: 53% of fire fatalities are caused by asphyxiation from the inhalation of smoke and toxic gas(1).
When a fire starts indoors, smoke can get trapped, rapidly filling the space. These fumes can quickly overwhelm anyone caught within the building. Thankfully, smoke vents can help reduce the accumulation of smoke. Within 60 seconds, the vent can be open, allowing cool air into the building while letting hot air and smoke escape thanks to automatic sensor controls. This reduces the risk of inhalation while also improving visibility to aid escape. Evacuation times are decreased, and better visibility is provided for fire fighters supporting rescue efforts.
In the absence of ventilation, smoke fills the room and is drawn back down from the ceiling by convection as temperatures rise, leading to potential – and particularly dangerous – ‘flashover’. This is the stage of a fire whereby a room or other confined area becomes so heated that the flames flash over and through the vapours being produced by heated combustible contents in the space.
Recent disasters have made people increasingly aware of the devastating impact of inhaling toxic gases, but there is still more work to be done in raising the awareness and use of smoke vents.
Adhering to regulations
Government legislation around smoke vents is complex. To perform their potentially life-saving task effectively, manufacturers must adhere to strict testing, tracking and installation regulations. These include: the BS EN1201-2 European Standard that specifies requirements and test methods for natural smoke and heat exhaust ventilators; the Approved Document B2013 and The Regulatory Reform (Fire Safety), which provide further regulation and guidance for buildings other than dwelling houses, while BS 9991 and BS 9999 provide assistance in more complex buildings. It can be a regulatory minefield and is therefore imperative that guidance is sought from industry professionals that are specialists in this area and are abreast of the latest guidelines and legislation.
Key points include:
Smoke vent opening for a lobby or stair vent must project a minimum of 300mm above the roof level, with no additional restrictions on location or height of upstand.
Smoke vent opening for a smoke vent shaft must project a minimum of 500mm above the roof level or any surrounding structure within 2.0m, and must be 2.5m above the ceiling level of the floor it serves.
Single Leaf Smoke Vents must open to at least 140-degrees for compliance. However, 160-degree units are also available and are a preferred solution for many specifiers
Aerodynamic Area (Aa) and Geometric Area (Av) must be provided for ventilation units
Every individual vent must have a CE compliance label applied
Selecting the right smoke vent
Smoke vents can be used in almost all buildings and are typically found in large structures with high occupancy, such as apartment blocks, warehouses, high-rise buildings, offices, universities, schools and student halls.
There are a variety of solutions available suited to different applications: smoke vents, automatic opening vents (AOVs), as well as smoke and heat exhaust ventilation systems (SHEVs). Smoke lid vents, for example, are most suited to smoke shaft applications and rapidly expel toxic gases in situations where no extra light is needed.
Options include but are not limited to:
Industrial/commercial properties with large roof areas: double leaf smoke vents can clear vast quantities of smoke quickly, with each leaf opening to approximately 90 degrees.
High security properties: roof louvre smoke vents offer high resistance to wind load and added security. In addition, they provide a good level of impact resistance in the open or closed position. Situated at roof level, the vent disperses both heat and smoke. These vents can also be fitted on exterior walls, providing an air inlet to replace exhausted air.
Façade ventilation: window louvre smoke vents installed in the façade increases natural daylight while its wide operating parameter can provide as much as 1.5m2of air for ventilation. This solution can be used in high wind environments as well as normal conditions.
Stairwells: a vital yet very dangerous area in the event of a fire. With a smoke vent, stairwells can provide a safer means of escape (MOE) and essential access for the emergency services. Essentially, the vents reduce smoke build up in the stairway and corridors leading onto the stairs for safe evacuation of large volumes of people. The stairwell ventilators are controlled by clearly visible manual switches at stairway entrances for use in emergency situations. It’s recommended that a ‘break glass’ switch or firefighter override switch is also fitted. An automatic opening ventilation system can also significantly improve safety in a fire as these will open when a detector or switch on a smoke control panel is triggered.
There are different requirements for variations in staircases and these will depend on the number of stairs, levels and the travel distance to the stairway.
Corridors: In residential buildings and apartment blocks, a corridor automatic opening vent (AOV) utilises the external wall of the building to expel smoke, particularly where build-up is close to escape stairwells. Located high on the external wall, corridor smoke vents support the discharge of smoke as it naturally rises and escapes through the vent.
Smoke shaft vents: There are many smoke ventilation solutions for ‘smoke shafts’, which support ventilation of escape routes in tall buildings. The ventilation options can be integrated either at the roof level or on internal floors of the building. An efficient control system ensures that only the smoke vents on the affected floor are activated to efficiently expel accumulating smoke.
When choosing a smoke vent, its location, the type of ventilator, and method of installation within the fabric of the building must all be taken into careful consideration. Expert advice should be sought to ensure the correct product and specification is used.
Form and function
Smoke vents come in a variety of guises to suit all property styles. Additionally, alongside the safety benefits, smoke vents can also support day-to-day improvements in the environment, such as adding ventilation and letting in natural light.
Aesthetic options for smoke vents include:
Polycarbonate: one of the most popular options, it can be used to glaze a variety of smoke vents, including automatic opening vents (AOVs) and Smoke & Heat Exhaust Ventilation Systems (SHEVS). These solutions are fully certified to BS EN 12101-2, are available in dome and pyramid designs, and can have double or triple skins for optimal thermal performance and resistance to condensation. Polycarbonate also offers excellent light transference and clarity, so occupants can see the sky above while benefitting from its thermal properties.
Glass: as a smoke vent glazing material, glass offers both visual and performance-related benefits and enhancements across the board. The most obvious appeal is the flat glazed appearance and the ability to have a lower profile product at roof level. This helps keep the smoke vent as attractive from both the roof level and below the installed unit, which is important for buildings where smoke vents are located on communal roof garden areas.
When used in vertical applications (in facades and external walls), glazed roof louvres are a great way to introduce natural light within commonly overlooked areas of a building, assisting in the safe evacuation of occupants during an emergency. Smoke vent mechanism options include single leaf, double leaf and glazed louvre vent.
Solid lid Smoke Vents:Although there are advantages in having a glazed solution to allow natural light in to a building, this is not always needed. A solid lid unit can be used in areas that are positioned above or within a smoke shaft vent where light is not required, or other sources of light are available within the same zone. Several types of mechanism are available: single leaf, double leaf, roof louvre, solid blade and shaft vent door.
Smoke vents can be supported by control panels.These can be activated by and respond to various accessories depending on the building’s particular requirements. Single zone control panels are designed to operate the electric opening systems for both fire and comfort ventilation, whilst dual zone control panels are designed to control the operation of larger fire and comfort ventilation electric opening systems.
Certified in accordance with EN 12101-10 2005 Class A, the control panels typically come in 24V DC, 5 or 8 Amp output and have a 72-hour battery back-up. They also incorporate a visual LED indicator to alert when they’re activated, along with ‘open’ and ‘close’ commands on the front panel. They may be networked as part of a building management system or may sit as a complete standalone system.
Remember: fire burns but smoke kills!Ultimately, whatever the appearance of the smoke vent, its quality, performance and life-saving functionality is critical. Always seek expert advice to ensure the correct vent is selected for the application. Smoke vents could help save lives and reduce the shocking fatality statistics we have today.
1 Home Office Fire statistics data tables - FIRE0504: Fatalities from fires by cause of death
Scott Couldrey is managing director at the National Domelight Company (NDC). For more information, visitwww.smokevent.co.uk