If you were watching TV on New Year's Eve, amid all the spectacular
fireworks displays in cities around the world you might have also seen an
unplanned spectacle: the blaze climbing
up one side of the 63-story Address Hotel in Dubai, the largest city of the
United Arab Emirates (UAE). While
the Address Hotel is not the tallest skyscraper in the world (that honor goes
to the Burj Khalifa, also in Dubai), it's tall enough to attract global
attention as it was enveloped in flames during the night. Amazingly, no fatalities were reported,
although numerous people suffered smoke inhalation or minor injuries while the
hotel was being evacuated. The
main reason for the absence of serious casualties was that the fire was
confined almost entirely to the "sandwich panels" or cladding on the
outside of the building. Why they
could catch fire—and why entire buildings are covered with flammable material
in the first place—are topics worth pursuing.
As most people know, modern skyscrapers depend on a hidden
steel skeleton for mechanical strength, not on the exterior surfaces, which can
be chosen for properties other than their ability to support the building. At first, high-rise architects stuck to
the traditional stone, concrete, and brick for facades, but in the 1950s, they
began to experiment with lighter-weight and cheaper materials, such as glass and
aluminum. Properly handled and mounted, aluminum makes a fine, long-lasting
sheathing material, and so does glass.
Then a couple of decades ago, someone had the idea of sandwiching a few
millimeters of plastic—polyethylene or some other heat-softening—between two
thin foil-like claddings of
aluminum, making something cheaper and lighter but just as good-looking as
solid aluminum. Thus the sandwich
panel was born.
Now, most heat-softening (thermoplastic) plastics can burn
very easily, and some attempts were made to introduce fire-retardant materials
into the plastic core of sandwich panels to make them fire-resistant. Apparently, these attempts did not convince
U. S. building-code authorities that the new sandwich panels were safe enough
to use in high-rises. A comment on
an architect's chatroom I found indicates that these types of panels are prohibited
in the U. S. for use on buildings taller than about four stories. But other countries either had no such
laws, or came to realize the potential for disaster too late.
What can happen is this. If you have a whole building encased in this stuff, and one
panel near the bottom happens to catch fire somehow (fireworks seem to be a
popular way to do this), you are in big trouble. Aluminum has a low melting point and melts away from the
plastic cladding as soon as the flame reaches it, exposing more plastic to air
and letting the fire feed on itself.
Hot air and flames travel upward to the next panel and so on, and in the
case of a 63-story building, there's plenty of upward to travel through. This is what happened, apparently, not
only to the Address Hotel, but to several other similarly-clad high-rises in
Dubai and elsewhere in the last few years. The architect-chatroom website where this problem was
discussed has numerous pictures of burned-over building exteriors in Dubai,
China, and elsewhere—all fires in which sandwich panels played a critical role.
Fortunately, the fires that these panels support tend to
stick to the outside, and most of the time, people inside the buildings have
time to evacuate before anyone gets killed. But nobody wants to leave a building under duress while
dodging falling pieces of burning plastic and metal on your way out. And it's very costly to clean up the
resulting mess and re-cover the structure with something that won't burn as
easily next time.
Both Australia (where such a fire happened in Melbourne in
2014) and the UAE have changed their building codes to require sandwich panels
to pass certain fire-retardant tests.
There are two problems with this, however. One, it's not clear exactly how fire-retardant a panel has
to be in order to resist spreading a fire on a tall building. The only sure way to know is to build
such a building and try to set fire to it, and this experiment is beyond the
resources of most building-code-writing organizations. Second, such codes generally apply only
to new construction, and are not retroactive. So anyone who's already built a skyscraper with flammable cladding
doesn't have to take the cladding down and replace it with something
better. That is, until it catches
fire. Judging by the fact that the
Address Hotel fire was the third such conflagration in Dubai in three years, it
may be only a matter of time until the others light up too.
Modeling how fires start and spread is still an inexact
science, and it is understandable that pressures from the building industry
allowed dangerous sandwich panels to be installed in many places around the
world, despite the hazards involved.
But it takes only one or two fires like this to demonstrate that there's
a serious problem. The almost
universal tradition of not making building codes retroactive makes sense,
because taking stuff out of an existing building to replace it can be more
expensive than the original building cost. Better in that case simply to condemn the thing and tear it
down, but that's an extreme measure too.
So what's the best that can be done in the present
situation? There may be some lower-cost
ways to reduce the chances that a fire in existing sandwich panels will spread,
possibly by installing some kind of fire-break strip at selected heights. But that would be pretty speculative
and might not work. Another
proposal has been to install fire sprinklers on balconies near sandwich panels,
because many of the buildings are high-rise apartments, and I bet there has
been more than one numskull who's tried to light a barbecue grill on his
balcony and let the fire get out of hand.
If a building has potentially flammable sandwich panels, the owners
better make sure that all the fire alarms and protection systems are
operational, and conducting regular fire drills might not be a bad idea
either. But owners will be
reluctant to advertise the fact that their building is a giant firework waiting
for someone to light the fuse.
We can also be thankful that U. S. building codes flat-out
prohibit the use of sandwich panels in high-rise structures. Yes, it forces builders to use more
expensive materials, and drives the cost up compared to construction costs in
other countries. But we've had
enough towering infernos in this country to last us a long time, and we don't
need any more.
Sources: I referred to a Reuters report by
Andrew Torchia carried on Jan. 2, 2016 on the Yahoo News website http://news.yahoo.com/dubai-blaze-raises-questions-over-gulf-skyscraper-design-160747983--finance.html#. The architect's chatroom with a comment
about the U. S. prohibition of sandwich panels and photos of similar fires in
other countries is at http://www.skyscrapercity.com/showthread.php?t=1801571. A report of a sandwich-panel-fueled
fire in a Melbourne building in 2014 appeared on the Australian website http://www.architectureanddesign.com.au/news/non-compliant-cladding-fuelled-melbourne-apartment
on Apr. 28, 2015. I also referred
to the Wikipedia article on sandwich panels.
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