What happened to the scaffolds in the Notre-Dame and Børsen fires?

The Notre-Dame and Børsen fires: what happens to scaffolding in a fire?

It truly feels like déjà vu: exactly five years and one day after Notre-Dame Cathedral burned down, Copenhagen’s Old Stock Exchange suffered a devastating fire on April 16^th 2024, which destroyed large parts of the historic building. Like the cathedral in Paris, the Copenhagen landmark was scaffolded for renovation work at the time of the fire.

What remains now is a largely destroyed historical structure, several tons of debris, and scaffolding completely deformed by the heat of the fire. In the following, we will clarify what exactly happens to a scaffolding in a fire and which influences it can withstand.

Can scaffolding melt in a fire?

When a building is burning, temperatures can typically reach around 1000°C. During the Notre-Dame fire, for example, the scaffolding was exposed to temperatures even exceeding the 1000°C degree mark in some areas. At such temperatures, a metal scaffold does not melt yet, which would only occur at 1400°C to 1500°C. However, the heat is sufficient to make the material more malleable and thus severely deform it - especially when the weight of the scaffold itself acts on the material. This resulted in an unstable, nearly 200-ton network of 40,000 metal scaffold parts at Notre Dame, which had to be painstakingly dismantled within 6 months.

Similar dismantling work began just two days after the fire at the Copenhagen Old Stock Exchange (called ‘Børsen’ by locals). Here too, the scaffolding was deformed by the heat and partially collapsed. With a large pair of shears attached to a crane, attempts were made to cut the severely deformed and unstable scaffolding into parts and remove it. However, the endeavor soon suffered a setback when the shears plunged into the debris.

Just shortly before the failed scaffold dismantling, the exterior facade of the historic building collapsed after attempts were made to support it with containers filled with concrete blocks in an effort to stabilize it.

Does scaffolding collapse in a fire?

Whether scaffolding collapses in a fire, as partially occurred at the Old Stock Exchange, depends on factors such as how and where it was anchored. If a wall or roof to which scaffolding was attached and secured collapses, it is very likely that the scaffolding will also come down. Backdraft or other explosions, caused by gas cylinders and propane tanks used for welding or tarring, can also lead to the collapse of scaffolding. Additionally, heavy falling debris, such as roof truss, can damage scaffolding to the point of instability and, ultimately, collapse.

For example, during the Notre Dame fire on April 15, 2019, the scaffolding itself withstood the collapse of the spire and roof even though it was heavily damaged by the heat.

Can scaffolding itself catch fire and become a fire hazard for its surroundings?

It is actually rather unlikely that a burning scaffold will ignite objects in its immediate vicinity. This is because zinc on the scaffold would only begin to burn and detach from the steel at temperatures above 450°C. At this point, it could run down or splatter from the scaffold, potentially igniting flammable objects nearby or underneath. However, considering that at such temperatures, the immediate surroundings of the scaffold are likely already engulfed in flames, a fire directly caused by the scaffold is not very probable.

While it’s not very likely that the scaffold itself would contribute to inflaming its surroundings, it's more plausible that it could delay firefighting efforts. If firefighters cannot get close enough to the fire because the scaffolding is blocking their path, it could make it more difficult for them to extinguish the fire.

How can fires on construction sites be prevented?

The cause of the fire at the Old Stock Exchange in Copenhagen is currently still unclear. Similarly, the exact cause of the fire at Notre Dame has not been definitively determined to this day. Possible causes of fires on construction sites like these could include short circuits, work involving heat, or carelessly discarded cigarette stubs. To prevent accidents like these, effective measures can be implemented, ranging from the basic minimization of fire risks to regular fire safety checks. For more information on the safety measures that can be taken on construction sites to prevent fires, read our next blog article.