Many Twitter users expressed dismay this week at the 鈥渓oss鈥� of Notre Dame following the blaze that engulfed the top of the Paris cathedral on 15 April. But, thankfully, the situation isn鈥檛 as disastrous as that: most of the building is still intact thanks to its clever design, and hundreds of millions of euros have already been pledged for restoration.
It took around 17 hours, and the efforts of 1000 firefighters and a 500-kilogram robot, to extinguish the fire. Although the spire was destroyed, the Gothic cathedral鈥檚 timber roof was built above a stone vault that medieval architects had designed to stop fires from spreading to the rest of the building. That made it more resilient than cathedrals with timber ceilings such as York Minster in the UK, which suffered a fire in 1984.
When it comes to protection against fires, engineers think about six elements, including prevention, detection, evacuation, and suppression. Notre Dame only used prevention: keeping ignition sources, such as work by electricians, away from flammable parts of the building, says Guillermo Rein, a fire engineer at Imperial College London.
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Unfortunately, fires in historic buildings often start during renovation work, when such precautions may be set aside. While the media has speculated that ongoing renovation work may have been to blame for the Notre Dame fire, the company doing it has said that none of its employees were on the site when the blaze broke out at around 6.45 pm.
Once it started, there was little to stop the fire from tearing through the timber roof. And although the stone walls, vault and flying buttresses aren鈥檛 flammable, they may have suffered structural damage. 鈥淭he masonry may have heated up and expanded, which it can do without collapsing. As the masonry cools down and shrinks it may deform,鈥� says Robert Bowles from the Institution of Structural Engineers. The water used to extinguish the fire could also have caused damage.
President Emmanuel Macron has pledged to rebuild the cathedral in five years, and the amount pledged for such efforts by firms and wealthy families is expected to surpass 鈧�1 billion.
Bowles thinks Macron鈥檚 deadline is possible聽鈥� it took a similar length of time to fully repair Windsor Castle in the UK after a fire in 1992.
The reconstructed roof should have extra protection built in, says Rein. 鈥淲e do this with iconic buildings all around the world.鈥� These could include smoke detectors, barriers in cavities and possibly sprinklers, although they would be costly to install.
The shock of seeing a historic monument in flames has prompted questions about other vulnerable buildings. UK politicians are warning that the Houses of Parliament could face a similar fate unless renovations are carried out urgently. The building鈥檚 antiquated heating, lighting and power systems raise the risk of a serious fire. However, following a catastrophic fire in the 1830s, the building was designed so its extensive timber panelling isn鈥檛 structural. 鈥淚f it burns, the building will not fall down,鈥� says Bowles.
But fires in buildings that are less globally iconic can arguably be even more devastating. When fire hit the National Museum of Brazil last year, the majority of its 20 million artefacts were burned聽鈥� a loss that will forever impair efforts to understand human history and the natural world.
