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19 October 2018

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Fires in Tunnels: Researching the spread of heat and smoke with Windmill Software

Fires in road tunnels cause serious explosions and loss of life. The main source of casualties in recent tunnel fires in China and elsewhere was the release of toxic substances from incomplete combustion of fuels. A study published next month in Tunnelling and Underground Space Technology will say that the key to solving tunnel safety problems is to understand smoke flow patterns and thermophysical properties of fires in tunnels.

To this end, instead of working with a small-scale smoke tunnel model or numeric simulations, researchers from Chongquing Jiatong University have constructed a full size mock-up of a tunnel fire. This gives a much more relisting reflection real-life fires in tunnels.

Full size smoke tunnel

Road tunnel fires are mainly caused by vehicles and their load. The researchers thus set fire to gasoline and diesel to simulate oil surface burning caused by fuel leakage following vehicle collision.

Full size smoke tunnel

For both oil pool fires and burning vehicles the scientists measured the height of the smoke layer at various intervals in their 150 m x 14.5 m x 7.1 m tunnel. They also monitored the velocity with which the smoke spread, the carbon monoxide concentration of the smoke and the radiant heat flux - the amount of heat transferred.

To monitor the heat transferred the researchers used Windmill software. They set up total heat flux sensors 8 m, 18 m and 48 m from the fire source and 1.5 m above the ground. These were from Captec and comprised a thin foil heat-flow sensor that indicates the heat flux when the temperature changes, and a circulating water-cooled heat receiver. The engineers connected the sensors by copper wire to the acquisition module and transmitted the data using the Windmill RS485/232 data acquisition system. Windmill continually collected and logged the data.

The immersed-tube tunnel of the Hong Kong - Zhuhai - Macao Bridge is the longest immersed highway tunnel and the only deeply buried tunnel in the world, with a length of 5664 m. It is 40 m underwater and is designed to last 120 years. The research results will help ensure people are safely evacuated in the event of a fire in the tunnel by predicting the behaviour of thermal parameters in different situations.

Further Reading

Full-scale immersed tunnel fire experimental research on smoke flow patterns. P.X, S.P.Jiang, R.J.Xing, J.Q.Tana Tunnelling and Underground Space Technology Volume 81, November 2018, Pages 494-505
https://doi.org/10.1016/j.tust.2018.08.009

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