Fire Technology

, Volume 54, Issue 3, pp 625–647

# The Use of Positive Pressure Ventilation Fans During Firefighting Operations in Underground Stations: An Experimental Study

• K. Lambert
• S. Welch
• B. Merci
Article

## Abstract

Positive pressure ventilation (PPV) fans are widely used by the fire service during firefighting operations in buildings. Fans are positioned to create a flow through the enclosure. This flow can remove the smoke after the fire or affect the direction of the smoke to support firefighting operations. In subway stations, it is less common to use PPV fans. Here, 106 full-scale tests with up to four fans have been performed in a training building that represents a subway station. The fans were used as extraction fans. The generated flow through the subway station has been measured. The critical velocity for a hypothetical tunnel (W × H: 3.17 × 4.15 m) attached to the subway station has been calculated as 2.37 m/s. Reaching the critical velocity has been used as criterion for ‘success’. All combinations with four fans exceed this velocity, supporting the idea that the fans could be used to facilitate a firefighting operation. The location of the fans was varied. Combinations with three fans on the platform and one at the top of the staircase performed better than combinations with two fans on the platform, one on the landing and one at the top of the staircase. There is an optimum value for the distance between the fans on the platform and the first step of the staircase. This value depends on the angle of inclination of the fans. The fans were not capable of creating a flow that exceeded the critical velocity in the station itself (L × W × H: 60 × 7.15 × 4.53 m). However, a velocity of 2.40 m/s corresponds to a flow rate that will limit the backlayering distance in the station to 15 m. This was only achieved by tests with four fans (three on the platform and one at the top of the staircase).

## Keywords

Positive pressure ventilation PPV Fire service intervention Full-scale experiments Subway stations

## List of symbols

$$c_{p}$$

Specific heat of air (kJ/kg K)

ɛ

Reduction in critical velocity due to an obstruction

F

Flow rate (m3/s)

g

Gravitational acceleration (m/s2)

H

Tunnel height

$$\bar{H}$$

Hydraulic tunnel height

$$L_{b}$$

Backlayering distance (m)

$$\rho_{0}$$

Ambient density (kg/m3)

Q

Heat release rate (kW)

$$Q^{*}$$

Dimensionless heat release rate

$$T_{0}$$

Ambient temperature (K)

$$V_{cr}$$

Critical velocity (m/s)

$$V_{ctr}$$

Critical velocity in the obstructed tunnel (m/s)

$$V_{cr}^{*}$$

Dimensionless critical velocity

$$V^{*}$$

Dimensionless ventilation velocity

## Notes

### Acknowledgements

This paper is a summary of the thesis of Karel Lambert [21], performed in the context of the International Master of science in Fire Safety Engineering (IMFSE) at the universities of Ghent, Lund and Edinburgh. The first author strongly acknowledges the financial support from EACEA during his studies in IMFSE, the material support of the Brussels fire department, the Frankfurt Fire Department and Ghent University. The authors also acknowledge Associate Professor Stefan Svensson (Lund University) for their valuable comments during the research. Finally, the authors thank Nathalie Van Moorter for the illustrations in this paper.

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## Authors and Affiliations

• K. Lambert
• 1
• 3
• S. Welch
• 2
• B. Merci
• 3
1. 1.Brussels Fire DepartmentBrusselsBelgium
2. 2.The University of EdinburghEdinburghUK
3. 3.Department of Flow, Heat and Combustion MechanicsGhent University – UGentGhentBelgium