For almost a millennium, Notre-Dame Cathedral has stood proudly on Paris’ central Île de la Cité, a symbol of the city’s history, culture, and romanticism. On Monday, April 15th, 2019, thousands who lined the banks of the Seine and millions more across the world watched on in a mixture of disbelief, heartbreak, and helplessness as the Gothic masterpiece burned before their eyes.
The fire has fortunately not claimed any lives but has robbed the landmark of its 19th-century spire, roof, and potentially priceless stained glass windows and interior ornamentation and artwork. At the time of writing, it appears that the main structure of Notre-Dame Cathedral has been saved and preserved, owed to the efforts of 500 firefighters deployed to the disaster.
As many watched the operation in real time, former St. Louis Fire Commander and CNN contributor Gregg Favre took to the internet to offer a professional explanation of the challenges facing the fire crews in Paris, and the many aspects for dealing with a structural blaze of this magnitude. His expert angle makes for informative reading to architects and the public alike, detailing aspects from design to accountability to the science of how fire burns through buildings.
The first issue identified by Favre is in the timber construction of old churches. Cathedrals like Notre-Dame are characterized by a heavy timber construction with large, open spaces and very few fire stops to seal openings in the building. With no passive fire protection system in place, the fire is liable to tear uninterrupted through the building, with the timber structure as its fuel. In cases where the fire starts high on the structure, the Fire Department can save walls and impinged areas. However, with the Notre-Dame fire, the peak and inaccessibility of the roof led to its surrender, with 66% of the roof lost.
In fires of this magnitude, firefighters will often aim to create a “trench cut,” also known as “strip ventilation.” A trench cut is a long narrow ventilation hole that acts as a break on the roof of the structure from peak to gutter, creating a chokepoint that prevents the fire spreading to an area not yet ablaze. Favre explains that because of the steep peak of the Notre-Dame roof, and the advanced fire conditions, a trench cut was not feasible.
Fire crews at Notre-Dame also faced the obstacle of what apparatus to use to fight the fire. Due to the delicate condition of the roof, aerial water dumps from planes and helicopters were ruled out, with the force of the water likely to lead to structural failure. Arial waterways such as hooks and ladders with pre-piped hoses would struggle to reach the roofline, and even if they did, would struggle to create an angle that would effectively tackle the fire, due to the height of the structure.
The difficulty of fighting the fire from the outside leads to the need for crews to enter the building. However, as Favre explains, this creates numerous issues. The primary apparatus for interior operations is a large 2.5” fire hose, which is heavy, difficult to maneuver, and largely ineffective in a fire on the scale of Notre-Dame. Placing crews inside the building also runs the obvious risk of injury, with elements from the heavy timber roof likely to collapse.
With an iconic structure such as Notre-Dame, which sees 80,000 daily visitors, accountability and life safety is a primary concern for fire crews. As the structure was undergoing renovation, there was a probability that more people would have been onsite than normal. The crews would have immediately confirmed that all Cathedral staff, construction workers, and visitors were accounted for. If people were unaccounted, responders would plan a rescue task, and confront difficult questions such as how many responders should be placed in danger for unconfirmed reports.
Favre also considers the science behind how fires burn. The four elements of a blaze are oxygen, fuel, heat, and a chemical chain reaction. The elimination of one of these elements, be it through cooling material, removing fuel or oxygen, or interrupting the chemical chain reaction, will lead to the fire’s suppression. The Notre-Dame fire presented no opportunity to achieve this. Removing the fuel was impossible due to the bounty of flammable materials inside, particularly the timber frame roof. The intensity of the fire was also advanced enough to make controlling heat and chemical reactions too challenging. As the roof had been destroyed early in the fire, there was also an uncontrollable flow of oxygen to the fire, which as Favre points out, would have also been the case even if the roof was intact, due to the Cathedral’s open, airy interior.
The restoration works underway at the Cathedral, apart from being linked to the fire starting, also presented a further obstacle for firefighters. It was likely that additional unprotected construction materials were present throughout the Cathedral due to the renovations, including materials deemed explosive, sensitive to water, hazardous, and dangerous if airborne.
Favre’s final detail, which was witnessed by shocked onlookers during the Notre-Dame fire, was the risk of collapse of building elements. As the roof and spire of the Cathedral fell, crews needed to assess where collapsing elements were likely to fall. The towers and walls of the Cathedral, though made of stone, were likely to be weakened as the roof and spire collapsed, leading to the evacuation of adjacent streets, and the careful positioning of responders and trucks. If there is a risk of a wall of fire leading to the igniting of a surrounding building, crews also need to plan for how to tackle a developing situation on many fronts.
Favre’s reading of the fire demonstrates the intricate planning, dangers, and shifting variables that firefighters face during blazes on a scale of Notre-Dame. It is a testament to the resolve and skill of the Pompiers de Paris that despite these adverse conditions, the fire was prevented from causing irreversible damage or collapse of the main structure, or its iconic bell towers. As a result, the resilient Gothic masterpiece, which has withstood riots, revolutions, and wars, will live to fight another day.
Gregg Favre is a former Deputy Director of Missouri Department of Public Safety, and former Command Staff at the St. Louis Fire Department. Follow him on Twitter here.
