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How Building Material can Influence the Spread of Fire in High Rise Construction

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High rise buildings present several unique challenges not found in traditional low rise buildings; longer egress times and distance, evacuation strategies, fire department accessibility, smoke movement and fire control. The multiple floors of a high-rise building create the cumulative effect of requiring great numbers of persons to travel great vertical distances on stairs in order to evacuate the building.
High-rise buildings have garnered significant attention in the fire safety world over the years. The public, code bodies, local, regional and central governments, as well as the design, build, and ownership communities are all affected by high-rise building safety. In India, Fire safety regulations are articulated in the BIS (BUREAU OF INDIAN STANDARDS).
Very recently a particular residential sky scraper in Dubai was in the news for catching fire in the densely populated Marina district on July 20th, 2016, sending thick plumes of smoke into the air and burning chunks of the building tumbling to the streets below.
According to news reports, it was the latest in a string of dramatic infernos that have raced up the sides of skyscrapers in and around the Middle East’s commercial hub, which is home to the world’s tallest tower, the BurjKhalifa.
The afternoon blaze began several stories off the ground of the 945-foot (288 meter) Sulafa Tower and spread rapidly as hot wind gusts fanned the flames. Hundreds of Marina residents fled to the cavernous streets around the tower as firefighters raced to the scene.

 

Building made with Wienerberger'sPorotherm Smart Bricks, Bangalore
Building made with Wienerberger’sPorotherm Smart Bricks, Bangalore

Multiple high rise buildings have been struck by similar fires across the United Arab Emirates in recent years. While the initial causes may differ, building and safety experts blame the fires’ rapid spread on a popular type of cladding used to cover the buildings that can be highly flammable, particularly if installed without fire breaks. Another very prominent recent fire was a New Year’s inferno at a 63-story luxury building known as The Address Downtown Dubai, which is near the 2,717-foot (828-meter) BurjKhalifa and the city’s biggest shopping mall. Police say faulty wiring sparked that blaze.
A precise risk to fire in high rise buildings cannot be quantified as such due to lack of data but it can be estimated to greater accuracy upon careful examination of the factors that make up “Fire-Risk” and thereby identifying the higher potential of fire risks in high rise building.
Risk is defined by the probability that an event will happen multiplied by the consequences of that event when it does
happen. This is shown in the following equation:
Risk= Probability x Consequences
The risk to life & property is calculated on the basis of all probable fires occurring in all probable locations in the building by examining the consequences of all these fire scenarios. In this respect, it becomes easily evident that the risk of fire in high rise apartment buildings is significantly higher than in low rise buildings given the potential for:
– More fire locations
– Greater consequences of the fire itself (Stack effect)
– To a greater number of Occupants
– Difficulty in accessing the fire by fire brigades
– Evacuating occupants from the building, especially those who are trapped on the floors above the actual fire
– Impact of wind in higher altitudes fanning the fire allowing rapid spread of fire
– And let’s face it, the response time by helicopters to come for rescue as shown in Hollywood movies, may not be as easily replicated in India.
Hence, it is of utmost importance that care should be taken, at the design stage itself, even before the actual construction of the building to evaluate processes that can help mitigate fire risks to the building and its occupants. Every country has a standard building code which includes fire safety procedures.
In this context it is important to understand the difference between ‘reaction-to-fire’ and ‘fire resistance’.
Reaction-to-fire mainly deals with materials: if they burn (combustibility); how easily they burn (ignitability and flame spread); and what happens when they burn (smoke development and resulting toxicity).
Reaction-to-fire focuses on the response of materials during the development of a fire, so, for example, concrete, paper, wood, plastic and paint will each register very different reaction-to-fire performances. The result is often a material classification that is used by designers to ensure the right material is in the right place with the aim of preventing a fire from starting, or limiting its spread.

 

Clay Ventilated Façade tiles from Wienerberger's Aspect Range
Clay Ventilated Façade tiles from Wienerberger’s Aspect Range

Fire resistance, on the other hand, mainly addresses building systems (such as walls, floors, ceilings, and doors) and their compartmentation abilities – for instance, when a fire is fully developed in a space or room, how long will it take for that fire to burn through a system into an adjacent space? Fire resistance performance is always measured in terms of ‘time’ and is used by designers to make sure potential fire spread from one compartment to another is quantified. This is an important consideration when designing a building because it will enable people to get out in time, as well as limiting damage to property.
Often the choice of building materials can go a long way in minimizing the destructive impact of fire and give enough time to the residents for evacuation.
The fire resistance of a building material refers to the length of time a walling element is about to resist a fully developed fire.
Fire resistance is the ability of a material or an assembly to withstand fire or give protection from it. Walls may be required to provide a barrier to the spread of fire or perform structurally when exposed to fire, or both. Model codes reference the ability of a material or assembly to maintain its particular fire-resistant properties as its fire resistance rating, expressed in hours.
As clay bricks or blocks are made in a fire kiln, they’re already highly resistant to fire. Clay blocks like Porotherm, which are fired at 10000C have a high fire resistance compared to other conventional walling material with over 240 minutes or 4 hours of FRP or Fire Resistance Period for an 8 “ thick block wall. To the owner of a clay brick building, this means peace of mind and substantial savings over time on insurance premiums. Depending on the construction and thickness of the wall, a clay brick wall can achieve a 1-hour to 4-hour fire-resistance rating.
When a masonry wall is subjected to fire, which is usually only on one side, a thermal gradient is created through the thickness of the wall and the expansion of the material causes bowing towards the fire source. If this bowing extends far enough it can cause collapse of the wall. Even if the wall does not collapse, it can crack because of internal stresses caused by restraint of the thermal expansion, or it can heat up sufficiently to allow flammable material on the side away from the fire to ignite. Both these consequences can cause the fire to spread. (et al. Think Brick Australia, Designing of Clay Masonry Walls for Fire Resistance)…
A number of serious building fires have triggered significant public concern over the safety of façade materials as well. Whether or not the façade of the building has a fire resistance capability, it must also perform in at least two other important fire-related functions.
Firstly, the materials used have to limit flame spread – and it is lamentably apparent that some of the materials used on the buildings in the recent fires were not suitable.
Secondly, where ‘compartmentation’ is required by the fire safety strategy, the gap between the façade and the building (typically at the floors), must be sealed to limit fire spread between rooms. This is called ‘perimeter firestopping’. It is extremely important, but can become ineffective if the materials used in the façade enable the fire to bypass this seal.
When looking into the flame spread characteristics of a façade, it is important to evaluate the materials used in its manufacture. In particular, the combustibility, ignitability and spread of flame across the surface must be evaluated.
Clay facades or terracotta facades have a process of strict raw material processing, high pressure extrusion forming, undergoing intense heating in over 12000C temperatures, with very stable & even physiochemical properties, giving them the characteristic fire resistant property. As curtain wall materials terracotta panels have features of fire safety, acid & alkali resistance, scratch and wear resistant along with high compressive strength.

 

 

Appaiah Monnanda
Appaiah Monnanda

Appaiah Monnanda
Managing Director, Wienerberger India.

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