With advancements in construction and building technology, high-rises have become the norm in the metros owing to rapid urbanization and lack of space. With further advancements, such buildings that were predominantly concrete structures with a higher wall-to-window ratio, are now being enveloped by materials like glass and aluminium. They are also being built greener and faster, compared to the conventional concrete and window buildings.
Architectural changes over time
However, these types of buildings pose a higher risk of fire due to their height, higher occupancy loads, a mixed bag of interior fit-outs and usually, an inadequate fire strategy in their design. Unfortunately, many buildings that are above 15 meters or so, and super tall buildings that scale 200 meters or more, have insufficient facilities for smoke ventilation during a fire emergency as usually these aspects are not given the required amount of importance.
On the other hand, the older buildings, which are more concrete and windows with open-to-sky areas, smoke will not tend to collect during a fire, as there are channels for smoke to pass through outside. Concrete buildings were also not clad with ACP in the earlier days, which is a growing concern in modern day buildings, where smoke can spread from a fire can spread from floor-to-floor, and also due to the secondary debris.
Many modern glass-enveloped buildings also have aluminium composite panels, which can lead to a catastrophe in the event of a fire. Often, there is little to no focus on having separate smoke shafts to extract smoke from the occupant areas, lift lobbies, and corridors and direct it to the building’s roof, unlike the glass façade buildings seen in Europe and America. This is the reason why we have Top Hung Open Out.
Considering the varied applications as given in this article, and their implementation being more cost-effective than that of Mechanical Extraction, including maintenance, when done right, and given the ongoing trend of Glass Façade Buildings, we see Automatic Opening Vents (AoVs) as the best solution for ensuring smoke extraction in all building types.
Manual Vents fitted with handles, which most people wrongly think is for natural ventilation. This is not the right way to place vents nor is it expected that an occupant or a fire officer will open the vents when there is a fire in the building. Smoke will tend to settle at the person’s waist as the opening is kept at a low level. In many cases, the vents are also too large to be opened by an individual and are often stuck due to poor maintenance, or sometimes the handles are removed in highly data-secure properties. Such manual systems are difficult to operate and are therefore useless in an emergency.
Vent as per present NBC norms
As per the current NBC norms, openable panels shall be provided on each floor and spaced not more than 10m apart, and measured along the external wall from centre-to-centre of the access openings. Such openings shall be operable at a height between 1.2 m and 1.5 m from the floor and be in the form of openable panels (fire access panels) of size not less than 1000mm x 1000 mm opening outwards. The warning ‘Fire openable panel - open in case of fire - do not obstruct’ shall be of at least 25mm letter height and marked on the internal side. The panels shall not be limited to cubicle areas and also be located in common areas/corridors to facilitate access by the building occupants and the personnel for smoke exhaust in times of distress.
Today, we have systems that can automate vents during the initial stages of a fire in commercial glass façade buildings. These vents are placed in occupant areas, lift lobbies, end of corridors, stair tops, and in public buildings using make-up air vents on vertical façades and smoke vents or hatches on the roof, based on Stack-Effect Principles. Products must be tested and certified as per EN12101 clauses and annexes.
A more sustainable solution in smoke ventilation is a smaller / shorter vent with a larger angle of opening
For Commercial Glass Façade Buildings, the automatic vents which are in the Occupant Areas, are to be of Bottom Hung Open Out and placed as close to the false ceiling as possible, as this would be the smoke extraction zone. In Hotels, Schools, and Hospitals too, the automatic vents in lift lobbies and at the end of corridors can be of the same Bottom Hung Open Out type or a square-shaped Side Hung Open Out.
In Escape Stair locations, where pressurization or no means of smoke ventilation is provided, a provision for Bottom Open Vents at the top of the stair vent, will act as a stack effect.
In large public buildings like Malls, Airports, and Railway Stations that have large open spaces, with double and triple height sections, provision should be made for Make-up Air Ventilation on the vertical façade using low-level Top Hung Open Out Vents. These can be on areas of the glass façade covering the building with designed Effective Free Areas kept in mind (entrance and canopy areas can also be used), combined with roof smoke extraction units or high-level Façade Vents Bottom Hung Open Out, which will automatically open for the smoke to be released from the roof area, if the building does not have a mechanical smoke extraction system.
Atria ventilation with make-up air ventilation & roof or top of façade automatic extractors; Typical system schematic will vary based on the fire strategy
In both these cases, the following care must be taken while calculating the sizes and number of openings, and care should also be taken when considering the cable type, size, and distance:
- Size of the vent to be shorter and wider, rather than taller, as this will give more angle of opening.
- Number of vents to be calculated based on 2.5% of floor area for commercial buildings, and 3-3.5% for the larger public utility buildings.
- For the Free Areas, we can only use Effective Smoke Release and not Punch Window.
- Cables are to be of Fire Survival or Fire Rated Low Smoke Copper Armoured with Cable Trays, if required, and based on MEP/Fire Specifications.
- The diameter of the cables is to be chosen based on the distance of AoV from its respective control panel, to avoid voltage drop issues.
- A proper maintenance schedule and AMCs must be kept in place for the system to function as designed when called for during an emergency.