Journal of Heat Island Institute International Vol. 9-2 (2014)

Academic Article

Propagation of tracer gas in a subway station controlled by naturalventilation
Jonathan Spiegel*1Markus Brüne*1 Nils Dering*1 Andreas Pflitsch*1Brian Agnew*2 Roberto Paliacin*2 Malcolm Irving*3Zi Qian*2*1 Department of Geography, Ruhr-University Bochum, Germany* NewRail, School of Mechanical and Systems Engineering, Newcastle University, UK*3 Nexus, Newcastle upon Tyne, UK2Corresponding author: Jonathan Spiegel, jonathan.spiegel@rub.deABSTRACT
To minimize risk from passengers and emergency rescue teams in occurrence of an event of the release of
toxic agents or a fire scenario, an understanding of the dispersion process inside subway systems is valuable
information. To gather knowledge about the airflow conditions in the subway system of the Tyne and Wear Metro in
the centre of Newcastle upon Tyne, air velocity and tracer gas dispersion were obtained during a nightly experimentin the absence of train movement. Results indicate that dispersion ways and passenger routes often overlap.
Key Words : natural airflow, tracer gas experiment, chimney effect, subway station, sensor platform

noticeable (Pflitsch et al., 2011).

1. Introduction

The complex system of air currents is influenced by a variety of
Recent research focusses on the effect of the piston wind as afactors. Mainly by the outside weather conditions. Thispassive way to ventilate subway systems. But this is only one

weather-related influence is in complete contradiction to thepart of the complex system of air currents in the underground.

conventional method of applying a permanent uniform airflow

Beside the piston effect and an active ventilation, a naturalto the boundaries of numerical simulations.

ventilation based on background airflows occurs in subway

Temperature differences within the subway system and between

systems (Pflitsch et al., 2002). The understanding of this naturalsubway and outside atmosphere have a strong influence on

background airflow is helpful to obtain a pleasant environment

underground air currents. High temperature gradients usuallyfor passengers and is highly important to identify the dispersion

lead to stronger and more stable airflows in the tunnel system.

paths

InsufficientThis effect can be observed especially in winter months when

understanding of the variable background airflow can hinder

the temperature inside the system lags behind the changing ofeffective rescue of passengers and endanger the life of

the outside temperature. Large temperature differences between

emergency response teams.

inside and outside, preferably during periods of extreme cold or

In the past it was assumed, that air currents in the undergroundheat leads to strong compensating airflows between inside andonly come about the movement of trains. These currents wereoutside (Pflitsch et al., 2013). During cold weather conditions,described as unsteady, alternating and decisive for airflows

when the outside air is a much colder than the air in the subway,

inside subways stations. For some time the existence of a naturalstrong chimney effects can be found at connections to thebackground airflow, which is independent of train movement

surface or at vertical structures within a subway station. (Spiegeland ventilation, was observed in several subway systems.

et al., 2014)

of

smoke

andother

toxicagents.

(Pflitsch 2001). This background airflow is a highly complex
system of air currents with spatial and temporal variation, which

2. Case study Monument Station, Newcastle upon Tyne

can be defined as an independent airflow system. It is always
present but mainly masked by the movement of trains. ShortThis paper examines the Monument station of the Tyne andtime after termination of traffic (about 1-3 minutes) it occurs

Wear Metro in Newcastle upon Tyne, a light rail system in North- 103 -

East England and only one of four underground metro systems

tracer gas dispersion in the Monument station. Monumentin the UK.

station is the most complex station within the system, consisting

The underground area of the subway system is located entirelyof two platform levels and a main concourse with connections towithin the city centre of Newcastle upon Tyne. It consists of athe surface. The north-south line (platforms 1 and 2) is at thenorth-south running line with tunnel openings north of Jesmondlowest level (see Fig. 1). Both platforms are connected with theStation and south of Central Station with opening to the Tyne

station concourse and with a direct connection that allow

Bridge. The east-west running line has tunnel openings afterchanging platforms without moving through the main concourse.

Manners Station and St. James. All these stations are each

Unlike previous studies in which air samples were taken withadjacent to Monument station, which is the main interchangesyringes (Pflitsch et al., 2013), which were afterwards analysed

station. The underground area is a total of 4km long and consists

in a laboratory, this experiment was accomplished with a newof six stations.

measuring system. The new sensor platforms were part of theThe Experimental setting was intended to examine air flow andresearch project "Measuring system for the determination of theFig. 1 Experiment setting, (a) 3d view, (b) 2d view of Monument Station- 104 -propagation of hazardous materials in critical infrastructures andthe train service and examine the propagation based on thecomplex buildings for the prevention of civil disasters" fundednatural background airflow. All instruments were placed onby the German Federal Ministry of Education and Researchtemporary stands at different locations (see Fig. 1) on all(BMBF, Grant number 13N11673) and were able to measureplatforms and the main concourse.

concentrations of 0.05 ppm to 50 ppm (optical measurementThe Release Point of the tracer gas was at the lowest level in the(SF6).

middle of platform 1. A gas sensor was placed at every in- andrange)

ofthetracergassulfurhexafluoride(Potje-Kamloth, 2014).

outlet of the tunnel, at the connections to the main concourse andAll measurements were taken during operational break in thethe other platform level and at two places in the middle of thenight between 21st and 22nd February 2014. The release oflevel. As on the other level, platform 3/4 was equipped with gas

tracer gas started at 2:29 (UTC) and ended at 2:33. In total

sensors at each in- and outlet. The position of the velocity

1.53kg SF6 was released. The measurement lasted till 3:10. Thesensors can be seen in Figure 1.

time slot was chosen as not to disrupt the normal operation ofThe goal of the experiment was to examine, how fast dispersion

Fig. 2 Temporal development of tracer gas concentrations at 19 different locations inside Monument station during tracer gas
experiment. Night from 21th to 22th February 2014

- 105 -

of hazardous substances will contaminate a whole subway

three exits to the surface show a medium concentration of SF6.

station and which parts of the station were affected and which

Remarkable is that the central stairway from the lower level toparts stay free of contamination. Similar experiments in otherthe concourse, despite the short distance to the release point,

subway systems showed, that within 5 minutes nearly moststays free over the entire period. In an emergency, this would beevacuation routes were contaminated.

the ideal escape route from the lower level through theconcourse, which shows no contamination until 10 minutes aftergas release, to the surface. An important result shows the3. Results

contamination of the stairway connection between the twoFigure 2a-d show the temporal development of tracer gas

platforms. This stairway would have been uncertain from thedispersal during the experiment. The tracer gas was emitted onbeginning.

the lower platform in the middle of track 1, from where it spread

The main reason for the rapid propagation to the upper level can

within the first minute to the adjacent tunnel of track 1. The

be found in chimney effects supported by a clear inflow of warmother parts of the station were not affected at this time. After

air from the southward tunnel at the lower level. Figure 3 shows

three minutes the gas spread via the stairway, connecting the two

a steady inflow of approx. 1 m/s for the ultrasonic anemometer 8

platforms, with a very high concentration over 50 ppm. Up toand a smaller inflow of 0.25 m/s at ultrasonic 9 on the lower

this time, only the parts near this stairway and the adjacent arealevel. A negative value always means air is flowing towards theto the northward tunnel were involved.

ultrasonic, while positive means a flow in opposite direction of

After six minutes only the northern area of the lowest level was

the ultrasonic. The upper level shows a small but steady outflow

affected, while the remaining parts stay free of concentration.

of 0.4 m/s in direction of St. James. The ultrasonic placed in

The upper level is now completely filled with tracer gas while

front of the stairway between upper and lower level shows athe concourse stays clear.

strong airflow of 1.25 m/s from the lower to the upper level. The

After 19 minutes, the concentration has almost completely

exit Blackett Street in the concourse demonstrates a strong

disappeared from the lower level. The upper level is still

airflow to the surface with 1.5 m/s, interrupted by various dips

partially affected but with a rather low concentration. However,of cold air. The connection between concourse and the two

the tracer gas has moved from the upper level via the central

platform levels shows different airflow patterns. The connection

stairway to the concourse and contaminated a large area. Allfrom the concourse to platform 1/2 shows a steady flow with 1

Fig. 3 Variation of Air Velocity at the Monument Station- 106 -m/s from the lowest level to the concourse while the otherconnection is alternating with slightly more movement from theCongress of Biometeorology (2002).
(2) A. Pflitsch, Investigations on air currents in undergroundupper level to the concourse (see Fig. 3). The concourse level

publicwith connected shops is relatively over warmed to the rest of thestation and therefore pulls air out of the lower parts, whichtransportationsystems,

inMeteorologischeZeitschrift 10 (4) (2001).
(3) A. Pflitsch, M. Brüne, B. Steiling, M. Killing-Heinze, B.

results in chimney effects.

Agnew, M. Irving and J. Lockhart, Air flow measurements

Beside chimney effects within the station, the stable windin the underground section of a UK light rail system, in:conditions on the lower level can be explained by the tunnel

Applied Thermal Engineering 32, 22–30 (2011).

geometry. Northwards the tunnel rises up to the station after the(4) A. Pflitsch, M. Brüne, M. Killing-Heinze, J. Ringeis, B.

next at approx. 25m. The relatively light warm air within theAgnew, and B. Steiling, Natural Ventilation as a Factor

tunnel system is moved up to a chimney effect through the rising

Controlling the Dispersal of Airborne Toxins in Subwaytunnel. The same situation occurs on the upper level, where theSystems in a Disaster Situation, Journal of Transportationnext station St. James is about 10m higher than Monument

Safety & Security 5(1), 78-92 (2013).

station.

(5) J. Spiegel, M. Letzel, T. Flassak and A. Pflitsch, Dispersionof Airborne Toxins in a highly complex Subway Station, inProceedings of the 6th International Symposium on Tunnel4. Conclusion and further work

Safety and Security 2014, 255-263 (2014).
Previous measurements inside the tunnels have shown the(6) Potje-Kamloth, K. (2014): Finding the ideal escape andpresence of a strong background airflow that is driven by aemergency route,chimney effect based on the inclination of the tunnel (Pflitsch et.

http://www.imm.fraunhofer.de/content/dam/imm/de/documal., 2011). This background airflow was also responsible for theents/pdfs/PD_MAusKat_final.pdf (December 11, 2014).

dispersion of the tracer gas experiment.
The influence of the tunnel geometry and chimney effects within(Received Dec. 11, 2014, Accepted Dec. 27, 2014)

the subway station on the propagation paths could be clarified.
Knowledge of these processes shows how wrong it may be to
expel static escape routes. A system that identifies escape routes
dynamically and assigns the safest way out of the compound,
may save lives in fire or disaster.
The use of new measurement technology significantly expands
the possibilities for the implementation of tracer gas experiments.
Due to a limited number of syringes that can be analysed in alaboratory, air samples could yet only be taken every minute
over a time period of 20-40 minutes. With the new automatic
sensor technique it is now possible to take samples with atemporal resolution of 1-2 seconds, when the time period is only
limited by the battery service life of approx. 10 hours. This
allows completely different experiments, such as the spread oftracer gas from one station to the neighbouring stations or theoutlet of tracer gas inside a moving train to investigate thespreading from the train into the approached stations. Suchexperiments could be accomplished yet and will be published innear future.
The tracer gas experiment in this station has shown a clear
situation of tracer gas contaminated and free areas.
References(1) Pflitsch, M. Brüne and H. Küsel, Spatial variability andDynamic changes in air temperature distribution withindifferent

subwaystations,

Biometeorology/Aerobiologyand

15thConf.

16thInternationalon- 107 -