Travelling fires pose huge risk to open building spaces

Scientists say that the lesser known ‘travelling fires’ shouldn’t be ignored now as they pose a huge risk to open building spaces including modern day offices and warehouses.

‘Travelling fires’ are those fires that can travel within large buildings and rather than engulfing entire rooms at once, they travel within the open space. The way these fires travel can cause structural damages and could even lead to buildings collapsing much like typical fires.Travelling fires are likely to be especially prevalent in large spaces with ample fuel and fewer doors and interior walls, like open-plan offices and warehouses.

Structural engineers design buildings to survive fires use guidelines like standard fire and Eurocode parametric fires. Using these guidelines, they typically focus on the fires that engulf whole rooms at once, known as flashover fires.

According to the new study published in the journal Fire Technology, open spaces are also vulnerable to travelling fires – a lesser-known fire type that burns locally and moves across an entire floor over time. According to researchers, with more and more buildings beings designed with open spaces, it is important to better understand how fires behave in these spaces.

Scientists found that buildings with open plans are in fact vulnerable to travelling fires, but this fire type is not yet weighted as heavily as flashover fires when designing buildings. Scientists urged engineers to understand that protecting against travelling fires could be just as important as protecting against more typical ones. By considering both fire types, engineers can be confident that they are considering the worst-case scenario.

Travelling fires

Traditional engineering guidelines for assessing fire safety in new buildings are based on observational experiments of fire dynamics in compartments much smaller than 100m2. These experiments have led to the assumption that flashover fires should be the main objective in structural design against fire. However, due to the lack of experiments in larger compartments, the potential significance of travelling fires in larger compartments is poorly understood.

To put travelling fires to the test, Imperial researchers designed the largest compartment fire experiment ever conducted, known as x-ONE. Using a disused 380m2 open-space concrete farm building in Poland, they started a fire at one end and measured its behaviour as it spread across the 35.5-metre-long compartment. Before doing so, they applied fire protection to columns to prevent structural damage and laid down a bed of fuel to feed the fires.

Within 12 minutes, the fire had spread the length of the compartment and had increased in speed from 0.33 to 16.7 centimetres per second as the size of the fire increased. It burned out after 25 minutes. Despite the size increase, the fire did not reach flashover.

The researchers reported that the fire dynamics observed during x-ONE differed greatly from the fire dynamics reported in small-scale compartment fires in previous studies. The findings also challenge flashover fires as the sole worst-case scenario in designing buildings.

They say this highlights the need for further experiments in large compartments to understand open-space fire dynamics and continue improving the safe design of modern buildings.

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