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Theoretical and Experimental Study of Critical Velocity for Smoke Control in a Tunnel Cross-Passage

An Erratum to this article was published on 24 May 2013


Theoretical analyses and model-scale experiments have been conducted to investigate the critical velocity in a tunnel cross-passage which is defined as the minimum ventilation velocity through the fireproof door to prevent smoke from flowing into a cross-passage. The effect of the fireproof door geometry, heat release rate, ventilation velocity and fire source location were taken into account. The critical velocity in a tunnel cross-passage varies approximately as 3/2 power of the fireproof door height, as one-third power of the heat release rate and as exponential law of the ventilation velocity, almost independent of the fireproof door width. The critical Froude Number mainly ranges from 5 to 10 and consequently as it is not a constant value it is not very suitable to predict the critical velocity in a tunnel cross-passage. A dimensionless correlation that can correlate well with the experimental data was proposed.

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Figure 11


A :

Area (m2)

C d :

Coefficient defined in Equation 14

c p :

Heat capacity of air (kJ/kg K)

Fr cc :

Critical Froude Number

g :

Gravitational acceleration (m/s2)

H :

Height (m)

l :

Length (m)

m :

Mass flow rate (kg/s)

Q :

Total heat release rate (kW)

Q c :

Convective heat release rate (kW)

T :

Temperature (K)

V :

Ventilation velocity (m/s)

V cc :

Critical velocity in a tunnel cross-passage (m/s)

ρ :

Density (kg/s)

a :

Cross-section no

b :

Cross-section no

c :

Cross-section no

d :

Fireproof door in a cross-passage

f :

Smoke flow

r :

Full scale

o :


m :

Small scale

t :


* :



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This work was sponsored by the ministry of railway of the People’s Republic of China which is gratefully acknowledged. The authors would also like to thank adjunct Prof. Zhihao Xu and adjunct Prof. Zhihui Deng for their help in these experiments. Acknowledgement to SP Tunnel and Underground Safety Centre for the support to the project.

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Correspondence to Haukur Ingason.

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Li, Y.Z., Lei, B. & Ingason, H. Theoretical and Experimental Study of Critical Velocity for Smoke Control in a Tunnel Cross-Passage. Fire Technol 49, 435–449 (2013).

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  • Tunnel fire
  • Cross-passage
  • Smoke control
  • Critical velocity