The burning issue
Tall buildings have challenges when it comes to fires butÃ‚Â the supertallÃ‚Â can be designed super safe.
Tall buildings have unique challenges when it comes to fires. James Boley finds out how GCC architects can design the supertall to be super safe.
Buildings have to deal with all sorts of stresses. Earthquakes, hurricanes and other natural disasters can demolish an icon in a matter of minutes. There's only so much that a building can withstand when facing the forces of nature.
Other catastrophes, however, are preventable or can be mitigated with greater success. Fire has the potential to cause absolute disaster, but good design can minimise the damage and save lives. While the risk of fire will always exist in a building, architects and engineers have the skills to design buildings so that even if the unthinkable happens, safety can be maintained.
A building's fire defence can be either active or passive. Active fire defences include the use of sprinkler systems and fire extinguishers. Passive defences are when the very fabric and design of the building can help keep people safe during a fire. It's through these passive defences that architects can make the biggest difference.
Although a building is a significant financial, and perhaps emotional, investment, some architects are pragmatic about what is really important.
"You don't really care if a building burns down, as long as the people are out and life is preserved," says Peter Weismantle, associate director of SOM and senior technical architect on the Burj Dubai.
Therefore, the most critical function for a building in a fire is to provide its occupants with both the time and the means to escape to safety. This can be achieved by specifying the right materials, and by designing the interior of a building to make escape both quick and safe.
The great escape
Needless to say, during a fire, the priority is to remove occupants from danger areas. Fire escapes provide safe passage for a building's occupants, so care needs to be taken with their design and specification.
Frequently within tall buildings, fire escapes are located in the core of the structure, away from the premium space at the edge of the building, which affords the best view.
Locating fire escapes in the core means that it can be difficult to naturally ventilate the area. However, there are other solutions to help keep clean air in fire escapes.
"The way around this is to provide pressurisation to those staircases and lobbies, so you can keep those stairs inside," says Andrew McCracken, senior consultant, Bodycote Warringtonfire Consultancy.
Pressurisation also helps eliminate another tall-building-specific issue for fire escapes. Stack effect-where the warm air on the outside of a building is sucked into the building-is a particularly common phenomenon in the Middle East.
"In a home, in a cold climate, you can feel the warm air rushing out the chimney. We have that effect in Dubai but it's the opposite," explains Weismantle.
"The building air is cold, the outside is hot, and the air tends to want to rush out the bottom of the building."
Pressurisation can prevent this happening.
Fire escapes also need to be considered in terms of efficient and effective evacuation. Tall buildings frequently have a phased evacuation policy, due to the impracticality of evacuating thousands of occupants simultaneously.
"You might have the fire floor and two floors above that would leave," says McCracken. "The stairs would then be sized to cater for the number of people involved in that phased evacuation of those floors. That means the stairs wouldn't need to be sized to evacuate everybody all at once."
A building's design can significantly influence the materials an architect specifies. McCracken says that depending on how a building is designed- or fire engineered-can help reduce the minimum requirements for materials.
"A code might ask for 4-hour fire resistance for elements of the structure," says McCracken. "Depending on the number of windows in the building and in each fire enclosure, and how much ventilation can be provided by those windows breaking...you [may not] actually need 4-hours fire resistance."
This can have a massive impact on the overall budget of a design, since materials that are fire-rated to last longer, cost more.
"If you've a building where the code asks for a 2-hour fire resistance standard, and it can be reduced to 60 minutes through fire engineering, that's a massive saving on a tall building," says McCracken.
This reduction can also lead to selecting more aesthetically pleasing or sustainable materials. Global aluminium product supplier SchÃƒÆ’Ã‚Â¼co provides aluminium doors which are smoke and fire-rated for 30 minutes. "For a lobby, [30 minutes] is adequate escape time," says Sam Brooks, SchÃƒÆ’Ã‚Â¼co technical manager.
Steel doors and compartments can provide fire protection for two hours, but where this has been reduced, through fire engineering, aluminium can be considered.
"If it's a visual thing, or aesthetic thing, it's worth looking at aluminium," adds Brooks.
Brooks points out that this technique is popular throughout Europe, especially in Germany. "In Europe there are standards that require areas to be rated to different degrees," he says.
Developers note that European standards tend to be higher than those in the region.
"The local codes are very rudimentary because they really haven't experience in the building types, so the local authorities are very pleased to go with internationally recognised codes," says Weismantle.
These codes also place greater emphasis on the quality of insulation in a building.
"If you have a high-rise building, the insulation should only be of the highest standards," says Vincenz.
"Some of the high-rises in the UK and Europe only allow the top-rated products."
The Middle East is, to some extent lagging behind the US and Europe with regard to codes, but in terms of permitting material, the outlook is very positive.
"All of the thermal insulation needs material approval from Dubai Municipality. Otherwise it's not allowed in Dubai," says Vincenz. "[The UAE] does that better than a lot of other countries."
Suppliers recommend the use of better fire-rated materials for insulation, including rock wool or glass foam, which is relatively new to the region.
Glass foam retains all the fire-resistant properties of glass as well as all the dynamic capabilities of insulation.
"I don't know any other insulation that has a zero flame spread index and a zero smoke development index," says Vincenz.
Getting the right insulation can make a huge difference. Materials such as Foamglas can be used to establish a secondary fire barrier behind the faÃƒÆ’Ã‚Â§ade, thus reducing the spread of a blaze.
Architects also need to bear in mind the effects of vapour transmission. From the stack effect, the cold air inside the building causes air from the outside to flow into the building.
Non-waterproof insulation needs to be protected with a waterproof aluminium skin, otherwise, the material can get wet from condensation, which ultimately impairing its fire resistance.
As the construction boom continues throughout the Middle East, there's never been a greater need to ensure that buildings remain fire safe. Supertall projects like the Burj Dubai are leading the way to a new standard of fire safety in design.
The better equipped architects are to rise to the challenge of keeping the supertall super safe, the better the future for both buildings and occupants.
"In the ME, as in many other parts of the world, reinforced concrete is the standard building method and so there's very little steel at the Burj Dubai," explains Weismantle.
"Reinforced concrete serves us well up to the top of the occupied floors. We've taken the reinforced concrete up to level 154.
Above that, we've introduced steel because the floorplate gets so small." The steel on the upper levels is sprayed with cementicious fireproofing.
The Burj Dubai uses the International Building Code and the US National Fire Prevention Association code 101.
"It's a comprehensive set of codes and standards for all the systems in the building, specifically focused on fire safety and means of escape."
However, Weismantle points out that codes are merely a starting point because they are simply for a minimum standard. "From day one on the Burj Dubai, we put together suggested enhancements that go beyond the code."
The shape of the Burj Dubai has proved beneficial in terms of providing means of escape.
There are fire escapes in each of the three wings of the building, instead of being concentrated in a single core. "We have more capacity than we actually need," says Weismantle.
Another important element of the fire escapes is refuge points. Climbing down the entirety of the world's tallest building would pose a challenge even to the super fit, so every thirty floors, the escape stairs open out into an enclosed, smoke controlled refuge.
"People can go down 30 floors and wait for the firefighters to contain the fire without having to go all the way down the building," explains Weismantle.
The fire escape also has LED screens at various points that firefighters can use to send messages and instructions to people in the building.