Fire incidents during construction work of tunnels – Modelscale experiments

Anders Lönnermark, Jonatan Hugosson, and Haukur Ingason

Fire Technology

SP Report 2010:86

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Fires in a tunnel during construction -

Model scale experiments

Anders Lönnermark, Jonatan Hugosson and Haukur

Ingason

Abstract

Fires in a tunnel during construction - Model scale

experiments

The report describes a series of model scale tests (1:40 scale) describing the situation

before breakthrough in a tunnel during construction. In such a situation this means that

there is only one access tunnel, the rest is a system of tunnels with no connection to the

surface other than through the inlet tunnel. The tests were carried out in order to

investigate the effects of smoke spread and ventilation in a tunnel during construction.

The tunnel was tested during different ventilation conditions, lengths and slope. The

tunnel consisted of an access part which simulated the access tunnel to the main tunnel.

The access tunnel was sloped and the main tunnel was horizontal, directed in two equal

distances from the access tunnel. The main tunnel had two dead ends, and a ventilation

system that was provided through an air duct in the ceiling. The air duct outlet length and

location was varied in the tests. A total of 36 tests were performed. The fire source was a

propane burner, delivering a heat release rate equivalent to a full-scale fire of 10 MW.

Fibreboard blocks, of different sizes, drenched with heptane were also used to represent

the heat release rate of a construction machine.

The main findings concerned the effect of the ventilation on the fire development. If the

fire occurs before the breakthrough and the fire is too small it will be difficult to obtain

fresh air from the access entrance and the fire will decreases in intensity and finally

extinguish due to lack of oxygen caused by consumption of oxygen and recirculation of

vitiated products back to the fire.

Key words: tunnel, fire safety, model scale experiments, ventilation, construction

SP Sveriges Tekniska Forskningsinstitut

SP Technical Research Institute of Sweden

SP Report 2010:86

ISBN 978-91-86622-36-7

ISSN 0284-5172

Contents

Abstract

3

Contents

4

Preface

5

1

Introduction

7

2

Theory

8

2.1

Scale modelling

8

2.2

Scaling laws

8

3

Experimental setup

10

3.1

Geometry

10

3.2

Measurements

13

3.3

Fire source

15

3.4

Fire positions

16

3.5

Ventilation

17

4

Experimental procedure

18

5

Results

19

5.1

Tunnel A

19

5.1.1

Ventilation

19

5.1.2

Open or closed tunnel end

21

5.1.3

With and without slope

23

5.2

Tunnel A+B

25

5.2.1

Ventilation

25

5.2.2

Fire size

27

5.2.3

Air inlet above the fire

29

5.2.4

Fire position

31

5.3

Tunnel A, A+B, A+B+C

33

5.4

Self-extinguished fires

35

6

Discussion

37

7

Conclusions

38

8

References

39

Preface

This report describes a portion of work in a large research project that was carried out for

the Swedish Civil Contingencies Agency (MSB) during the time period 2008 – 2010. The

work was supported by a national advisory group consisting of numerous representatives

from industry and authorities:

Andreas Johansson, Gothenburg Fire Brigade

Arne Brodin, Faveo Projektledning AB

Bo Wahlström, Faveo Projektledning AB

Kenneth Rosell, Swedish Transport Administration

Kjell Hasselrot, Fireconsulting AB

Lars-Erik Johansson, Swedish Work Environment Authority

Marie Skogsberg, SKB Swedish Nuclear Fuel

and Waste Management Co

Rolf Åkerstedt, SL Stockholm Public Transport

Staffan Bengtsson, Brandskyddslaget AB

Stefan Jidling, Stockholm Fire Brigade

Sören Lundström, MSB Swedish Civil Contingencies Agency

The authors want to thank the advisory group for their efforts during this project and the

Swedish Civil Contingencies Agency (MSB) for their supporting role. We would also

like to thank the technicians that assisted in carrying out the model scale tests:

Sven-Gunnar Gustafsson, Lars Gustavsson, and Tarmo Karjalainen.

1

Introduction

Several large and complex tunnel systems in Sweden are at present either under

construction, at the design stage, or at the planning stage. The consequences of a fire

during the construction stage can be very serious, in the form of injuries, damage to

property, delays to the project or environmental problems. All this imposes demanding

requirements concerning knowledge of what is needed and what can be done to prevent

problems from arising. However, the available knowledge is limited. Therefore a research

project aimed is underway to identify and deal with problem areas.

A tunnel construction site is a workplace for many persons over a long period of time.

Several fires have already occurred at such sites, causing death or injuries to individuals

and losses of and damage to equipment and the structure of the tunnel itself. The

consequences of these fires depend not only on where they occurred in the tunnel, but

also on their intensity, the nature of the fire and facilities, response of the rescue service,

and resources in the form of personnel and equipment. Understanding the fire phenomena

is of great importance when studying these subjects.

Together with the Lund University and the Mälardalen University, SP has conducted a

three-year research project, financed by the Swedish Civil Contingencies Agency (MSB),

to investigate fire safety in a tunnel during construction. The results presented here are

also presented in a summarised form in the main report for that project [1].

A model scale study has been conducted in the project (the results of which are presented

here) in order to better understand the basic fire development phenomena that are at play

in tunnels during construction. The most important aspect of such tunnels is that much of

the time they are under construction no breakthrough, i.e. connection between one or

more tunnels with inlet tunnels, has been obtained. Our traditional understanding of fire

dynamics in tunnels is based on the assumption that tunnels have at least two openings

(which is true only after breakthrough, i.e. for completed tunnels). Therefore we were

interested in phenomena that are related to the geometry, the fuel, the ventilation and

many other parameters. The project group came up with a list of questions to be answered

in a model scale study:

-

How significant is the chimney effect caused by access tunnels used as escape

routes?

-

How do fires behave when there is only one opening?

-

What happens in terms of purely physical events and processes, and how

accurately do present-day computer models reflect the observed behaviour?

-

How should the ventilation system be designed in order to facilitate escape?

-

Can a fire be 'shut in', and thus self-extinguish, and under what conditions is this

possible or even appropriate?

Using model scale experiments is a well know technique [2-13] to investigate the impact

of a variety of different parameters on fire development. The model used in the present

study was built in scale 1:40, which means that the size of the tunnel is scaled

geometrically according to this ratio. This report describes basic scaling theory, the

experimental set-up and test procedures and presents all the results obtained from the

tests.

2

Theory

2.1

Scale modelling

The method of scaling used in the tests presented here is arguably the most widely used

method, i.e. Froude scaling. Clearly, it is neither necessary nor possible to preserve all the

terms obtained by scaling theory simultaneously in model scale tests. The terms that are

most important and most related to the study can be preserved. The thermal inertia of the

material involved, the turbulence intensity and radiation are not explicitly scaled, but we

scale the HRR, the time, flow rates, the energy content and mass. Our experience of

model tunnel fire tests shows there is a good agreement between the model scale and

large scale for many application fields. In scale modelling research it is, however, often

the fundamental behaviour and not the absolutely correct scale modelling of all behaviour

that is important.

SP Fire Technology has a long experience of using scale models and these studies have

clearly illustrated the many advantages of using scale models. SP has, for example, used

scale models for fires in rack storage [2], fires on ferries [3], road tanker fire [4],

reconstruction of the discotheque fire in Gothenburg [5] and in particular for tunnels

[6-12]. These projects have demonstrated that the results obtained using scale models

correlate well with results from full-scale trials where such a comparison has been

possible. Due to the logistical difficulties associated with extremely large scale tests (and

their cost), the use of scale models has been chosen as a suitable vehicle for the

investigations conducted within this project.

2.2

Scaling laws

When using scale modelling it is important that the similarity between the full-scale

situation and the scale model is well-defined. A complete similarity involves for example

both gas flow conditions and the effect of material properties. The gas flow conditions

can be described by a number of non-dimensional numbers, e.g. the Froude number, the

Reynolds number, and the Richardson number. For perfect scaling, all of these numbers

should be the same in the scale model and in the full-scale case. This is, however, in most

cases not possible and it is often enough to focus on the Froude number:

gL

u

Fr

=

2

(1)

where u is the velocity, g is the acceleration of gravity, and L is the length. This method,

often referred to as Froude scaling, has been used in the present study, i.e. the Froude

number alone has been used to scale the conditions from the large scale to the model

scale and vice versa. Information about scaling theories can be obtained for example from

references [14-17]. The scaling of the most important parameters for this study using this

method is presented in Table 2.1.

Table 2.1

A list of scaling correlations for the model tunnel.

Type of unit

Scaling model

a)

Heat Release Rate, HRR (kW)

5

/

2













=

M

F

M

F

Q

_L

L

Q





(2)

Time (s)

1

/

2













=

M

F

M

F

t

_L

L

t

(3)

Energy (kJ)

3













=

M

F

M

F

Q

_L

L

Q

(4)

Heat Flux (kW/m

2

₎

₁

_/

₂

"

"

_











=

M

F

M

F

q

_L

L

q

(5)

Temperature (K)

_{T =}

_F

_T

_M

(6)

a) Index M corresponds to the model scale and index F to the full scale (L

M

=1 and L

F

=20 in the present

case).

3

Experimental setup

To study the environment during a fire in a tunnel under construction, a scale model was

constructed in one of the fire halls at SP. The model scale tunnel was constructed in scale

1:40. Froude scaling was used for the scaling of different parameters (see Chapter 2 for

more information).

3.1

Geometry

When constructing a tunnel or a tunnel system, very often a special access tunnel or

entrance tunnel is constructed. This tunnel is in itself not part of the final tunnel system

but is needed to rapidly reach a point in the system from which the real tunnels can be

constructed. The debris from the blasting is also transported away through the access

tunnel. To limit the length of the access tunnel it may be relatively steep.

A model scale tunnel system (scale 1:40) was designed to include both an access tunnel,

which ended in a T, with the two arms of the T having different lengths. This means that

the system consisted of three parts: A, B and C (Figure 3.1) where the tunnel opening is

located in tunnel A and both tunnel B and C have closed ends. Tunnels A and B were

3.0 m long while tunnel C was 1.5 m long. The height and width of all tunnels was

0.15 m. This corresponds to a cross-section of 6 m × 6 m in real scale. The A tunnel had a

slope of 10° while tunnel B and C were horizontal. In some tests only tunnel A was used,

in some tests all three tunnels and in most cases tunnel A and tunnel B. A ventilation pipe

(0.04 m in diameter) entered tunnel A, reaching 2.25 m into the tunnel, i.e. 0.75 m from

the end of the tunnel when only tunnel A was used. When tunnels A+B or A+B+C were

used, the ventilation tube passed through tunnel A and ended 0.75 m from the end of

tunnel B and 0.75 m from the end of tunnel C (the ventilation tube was divided into two:

one entering tunnel B and one entering tunnel C). In one of the tests with only tunnel A,

the tunnel was positioned horizontally for comparison.

Three different locations of the fire were tested: positions 1, 2 and 3 (see Figure 3.1).

Position 1 was located 0.375 m from the lower end of tunnel A. Positions 2 and 3 were

located 0.375 m and 1.5 m, respectively, from the closed end of tunnel B.

3.00 0.15 3. 00 0. 15 1. 50

A

B

C

1

3

2

x

y

3.00 0.15 3. 00 0. 15 1. 50

A

B

C

1

3

2

x

y

x

y

Figure 3.1

The geometry of model scale tunnel. Dimensions in m.

0.15

0.04

0.

15

Figure 3.2

Cross-section of the model scale tunnel. The ring represents the ventilation

tube. Dimensions in m.

The coordinate system in Figure 3.1 is defined so that x=0 represents the end of tunnel A

and y=0 represents the end of tunnel B. This coordinate system has been used when

presenting the experimental results.

The tunnel was constructed in Promatect H, 10 mm thick with an outer layer of 18 mm

plywood (see Figure 3.4). On one side of tunnel A and tunnel B, several windows were

installed to allow visual observations of the fire and the smoke.

3.00

10°

Figure 3.3

Side view of tunnel A showing its inclination and the ventilation tube

passing tunnel A into tunnel B.

Figure 3.4

The model scale tunnel system before the walls and windows were fully

Figure 3.5

The lower part of section A with the exit of the ventilation tube and some

instrumentation near fire position 1.

3.2

Measurements

In addition to visual observations, a number of measurements were performed during the

tests: gas temperatures and O2, CO, and CO2 concentrations. Below the measurements are

further described.

Gas analysis

The probes for gas sampling were placed 0.188 m after and before the fire, i.e. 0.187 m

and 0.563 m, respectively, from the end of the tunnel when the fire is in that position. In

tunnel B a third position 1.688 m from the end of the tunnel was used. The height of the

measurement was 0.075 m, i.e. half the tunnel height.

Temperatures

Temperatures were measured with thermocouples (type K, 0.25 mm) both near the ceiling

along the tunnel and in thermocouple trees in selected positions. The thermocouple trees

had five thermocouples at heights: 13 mm, 50 mm, 75 mm, 100 mm and 125 mm,

measured from the ceiling.

In a few positions thermocouples with a diameter of 0.8 mm were used. In Table 3.1 this

is written as “TC 0.8mm”. In the same position, an additional thermocouple with a

diameter of 0.25 mm, was also mounted. The height of the two thermocouples was

75 mm. The reason for having two thermocouples of different size was that from these

measurements the “real” gas temperature could be calculated.

The descriptions “Left” and “Right” are defined facing away from the fire towards the

opening. These positions were located 50 mm from the centreline, i.e., 25 mm from the

wall.

Temperatures were measured in many different position and in Table 3.1 all the

measurement positions/channels are described. Distances are given both from the fire and

from the end of the tunnel. Note that the for Tunnel A the distances are measured along

the x-axis and for the Tunnel B+C along the y-axis (see Figure 3.1)

Table 3.1

Description of measurement positions.

No

Distance

from fire

c)

Dist from

_{end of}

tunnel

L, C, R Temperature

Channel

Tunnel

A

1

-0.188

0.187 Left

TC tree

Ch 1-5

2

b)

-0.188

0.187 Centre TC 75mm;

TC 0.8mm

Ch6, Ch 7

Gas: Ch 113, 114, 115

3

-0.188

0.187 Right

TC tree

Ch 8-12

4

0

0.375 Left

TC 13 mm

Ch 13

5

0

0.375 Centre TC 13 mm

Ch 14

6

0

0.375 Right

TC 13 mm

Ch 15

7

0.188

0.563 Left

TC tree

Ch 16-20

8

b)

_0.188

_{0.563 Centre TC 75mm;}

TC 0.8mm

Ch 21, Ch 22

Gas: Ch 116, 117, 118

9

0.188

0.563 Right

TC tree

Ch 23-27

10

0.375

0.75 Centre TC 20 mm

a)

Centre of tube outlet

_{Ch 28}

11

0.5

0.875 Left

TC 13 mm

Ch 29

12

1

1.375 Left

TC 13 mm

Ch 30

13

1.125

1.5 Left

TC 13 mm

Ch 31

14

1.125

1.5 Right

TC 13 mm

Ch 32

15

1.5

1.875 Left

TC 13 mm

Ch 33

16

2

2.375 Left

TC 13 mm

Ch 34

17

2.5

2.875 Left

TC 13 mm

Ch 35

18

b)

_2.5

_{2.875 Centre TC 75mm}

_{Ch 36}

d)

Gas: Ch 108, 119, 120

19

2.5

2.875 Right

TC 13 mm

Ch 37

Tunnel B+C

20

-0.188

0.187 Left

TC tree

Ch 38-42

21

b)

-0.188

0.187 Centre TC tree;

TC 0.8mm

Ch 43-47, Ch 48

Gas: Ch 113, 114, 115

22

-0.188

0.187 Right

TC tree

Ch 49-53

23

0

0.375 Left

TC 13 mm

Ch 54

24

0

0.375 Centre TC 13 mm

Ch 55

25

0

0.375 Right

TC 13 mm

Ch 56

26

0.188

0.563 Left

TC tree

Ch 57-61

27

b)

_0.188

_{0.563 Centre TC tree;}

TC 0.8mm

Ch 62-66, Ch 67

Gas: Ch 116, 117, 118

28

0.188

0.563 Right

TC tree

Ch 68-72

29

0.375

0.75 Centre TC 20 mm

a)

Centre of tube outlet

_{Ch 73}

30

0.5

0.875 Left

TC 13 mm

Ch 74

31

0.938

1.312 Left

TC tree

Ch 75-79

32

0.938

1.312 Centre TC 75mm;

TC 0.8mm

Ch 80, ch 81

33

0.938

1.312 Right

TC tree

Ch 82-86

34

1

1.375 Left

TC 13 mm

Ch 87

35

1.125

1.5 Left

TC 13 mm

Ch 88

No

Distance

from fire

c)

Dist from

_{end of}

tunnel

L, C, R Temperature

Channel

36

1.125

1.5 Right

TC 13 mm

Ch 89

37

1.313

1.687 Left

TC tree

Ch 90-94

38

b)

_1.313

_{1.687 Centre TC 75mm;}

TC 0.8mm

Ch 95 Ch 96

Gas: Ch 108, 119, 120

39

1.313

1.687 Right

TC tree

Ch 97-101

40

1.5

1.875 Left

TC 13 mm

Ch 102

41

2

2.375 Left

TC 13 mm

Ch 103

42

2.5

2.875 Left

TC 13 mm

Ch 104

43

2.5

2.875 Right

TC 13 mm

Ch 105

44

2.625

3 Left

TC 13 mm

Ch 106

45

2.775

3.15 Left

TC 13 mm

Ch 107

46

3.375

3.75 Centre TC 20 mm

a)

Centre of tube outlet

_{Ch 109}

47

3.75

4.125 Left

TC 13 mm

Ch 110

48

3.75

4.125 Centre TC 13 mm

Ch 111

49

3.75

4.125 Right

TC 13 mm

Ch 112

a) At the centre of the air tube opening.

b) Gas measurements of O2, CO and CO2. Only three positions at the same time. When

only Tunnel A was used, the positions 2, 8, and 18 were used. When Tunnel A+B were

used, the positions 21, 27, and 38 were used.

c) For Tunnel B and C, the distance from fire is referring to the fire position located at the

end of the tunnel.

d) In Test 1 to Test 4 the TC in Ch 36 was positioned above the tube while from Test 5 it

was moved to the height 75 mm, i.e., at the sampling point for gas.

3.3

Fire source

Four different fire sources were used including: one propane burner and pieces of fibre

board soaked with heptane and wrapped in a piece of polyethene. Their characteristics are

summarised in Table 3.2. The different fire sources are shown in the pictures in Figure

3.6.

Table 3.2

Summary of properties of the fire sources.

Fire source Size,

L×W×H

[mm

3

_]

Heptane

[mL]

Heat

release rate

[kW]

Time to

HRRmax

[s]

Burning

time [s]

1

Propane

burner

-

1

-

∞

2

10×10×12

0.5

0.4

10

120

3

30×30×24

3

1.3

20

250

4

50×100×48 9

3.2

30

300

The maximum HRRs of 1 kW, 0.4 kW, 1.3 kW and 3.2 kW, represent 10 MW, 4.4 MW,

14 MW and 33 MW, respectively, in full scale.

a)

b)

c)

d)

e)

Figure 3.6

Fire sources used in the test series. The gas burner, a) and b), was mounted

so that only the upper 1 cm was above the floor level. The fire sources made

out of fibre board, c) 0.4 kW, d) 1.3 kW and e) 3.2 kW, were wrapped in

plastics. They were placed on a piece of aluminium foil to facilitate weighing

of the debris after the test.

3.4

Fire positions

To study the effect of the tunnel system and the position of the fire, three different fire

positions were used during the test series:

1. End of tunnel A (0.375 m from the end of tunnel A, i.e. x = 0.375 m)

2. End of tunnel B (0.375 m from the end of tunnel B, y = 0.375 m)

3. In middle of tunnel B, i.e. y = 1.5 m

The fire positions are also shown in Figure 3.1. Fire position 1 was only used in the tests

when only Tunnel A was used. Fire positions 1 and 2 represents a fire near the tunnel

face, while position 3 was included to simulate a fire further from the tunnel face and to

study the effect if this fire led to rupture of the ventilation tube.

3.5

Ventilation

The ventilation in the tunnel was arranged in a similar way as in a real tunnel, i.e. by

leading the inlet air through a circular tube to a position not far from tunnel face. In this

case the tube was made of PVC (PVC-U 50x3.7 DEKADUR) with a outer diameter of

5 cm and inner diameter of 4.2 cm. The end of the tube was positioned 0.75 m from the

end of the tunnel (tunnel face). In some tests this was in Tunnel A (if only Tunnel A was

used), and in the other tests in Tunnel B (and Tunnel C, if used). In the case when the fire

source was placed in position 3 (centre of tunnel B), the air inlet was either at the end of

the tube or above the fire. The air flow was achieved using compressed air controlled by a

rotameter. In addition to the case without ventilation, four different ventilation flows were

used:

1. 0.0 m

3

_/s

2. 0.0001 m

3

_{/s (60 m}

3

_/min)

3. 0.0002 m

3

_{/s (120 m}

3

_/min)

4. 0.001 m

3

_{/s (600 m}

3

_/min)

5. 0.00356 m

3

_{/s (2200 m}

3

_/min)

The values within parentheses is the corresponding value in full scale. In Table 4.1 the

ventilation used in each test is presented.

4

Experimental procedure

In total 36 different experiments were performed. The main parameters varied were the

fire position, tunnel geometry, ventilation rate and the position of the ventilation inlet.

The conditions in each test are presented in Table 4.1.

Table 4.1

Summary of the test conditions during the test series

Test

Tunnel

geometry

Fire size

(kW)

Fire position

Ventilation

(m

3

_/s)

Ventilation

_(L/s)

1 A

1 End of tunnel A

0

0

2 A

1 End of tunnel A

0.0001

0.1

3 A

1 End of tunnel A

0.001

1

4 A

1 End of tunnel A

0.0002

0.2

5

a)

_A

_{1 End of tunnel A}

_0.001

₁

6 A+B

1 End of tunnel B

0

0

7

a)

_A+B

_{1 End of tunnel B}

₀

₀

8 A+B

1 End of tunnel B

0.0001

0.1

9 A+B

1 End of tunnel B

0.001

1

10 A+B

1 End of tunnel B

0.0002

0.2

11 A+B

0.4 End of tunnel B

0.0001

0.1

12

a)

_A+B

_{0.4 End of tunnel B}

_0.0001

_0.1

13 A+B

0.4 End of tunnel B

0.0001

1

14 A+B

1.3 End of tunnel B

0.0001

0.1

15 A+B

1.3 End of tunnel B

0.0001

1

16 A+B

3.2 End of tunnel B

0.0001

0.1

17 A+B

3.2 End of tunnel B

0.0001

1

18 A+B

1.3 Centre of tunnel B

0.0001

0.1

19 A+B

1.3 Centre of tunnel B

0.001

1

20 A+B

3.2 Centre of tunnel B

0.001

1

21 A+B

1 Centre of tunnel B

0.0001

0.1

22 A+B+C

1 End of tunnel B

0.0001

0.1

23 A+B+C

1 Centre of tunnel B

0.0001

0.1

24

b)

_A+B

_{1 Centre of tunnel B}

_0.0001

_0.1

25

b)

_A+B

_{1.3 Centre of tunnel B}

_0.0001

_0.1

26

b)

_A+B

_{3.2 Centre of tunnel B}

_0.0001

_0.1

27

d)

_A

_{1 End of tunnel A}

₀

₀

28 A

1 End of tunnel A

0.00356

3.56

29

b)

_A+B

_{1 Centre of tunnel B}

_0.00356

_3.56

30

b)

_A+B

_{1.3 Centre of tunnel B}

_0.00356

_3.56

31

b)

_A+B

_{3.2 Centre of tunnel B}

_0.00356

_3.56

32 A+B

1.3 Centre of tunnel B

0.00356

3.56

33 A+B

1.3 End of tunnel B

0.00356

3.56

34 A+B

3.2 End of tunnel B

0.00356

3.56

35 A+B

1 End of tunnel B

0.00356

3.56

36

c)

_A

_{1 End of tunnel A}

₀

₀

a) Repetition test

b) Air inlet above the fire

c) No slope

d) Open also at the lower end

The tests with fibre board ignition sources were run until the fire self-extinguished. The

tests with gas were finished by turning off the gas, except for Test 36 when the fire

self-extinguished before the gas was turned off.

5

Results

Main results and observation are stated in this chapter for the different experiments. The

result are divided into different sections dependent of the tunnel geometry and different

parameters studied. The chapter contains summaries and comparisons of the results. More

comprehensive results are presented in Appendix 1.

5.1

Tunnel A

In this section results from “I-shaped” tunnel, tunnel A (see Figure 3.1) are presented.

5.1.1

Ventilation

The different ventilation velocities tested in tunnel A were: 0, 0.1, 0.2, 1 and 3.6 L/s, all

with a fire size of 1 kW (gas burner). For the oxygen concentration 0.188 m from the fire,

on either side, there is no significant difference for four of the ventilation rates (see

Figure 5.1). For the high ventilation of 3.56 L/s there is a difference towards the tunnel

end, where the O2 concentration decreases down to approximately 20 % compared to

17 % for the other ventilation rates. Towards the tunnel opening the ventilation rate of

1 L/s shows the highest O2 concentration of about 20 %, and not the higher ventilation

(3.56 L/s) as would have been expected. A possible explanation for these differences is

that different flow patterns occur. The flames are also affected by the flow field, however

the complete flow field was not visible during the actual test.

O2 concentration at different ventilation rates 0.188m from fire,

towards tunnel end

8

10

12

14

16

18

20

22

0

2

4

6

8

10

12

14

16

18

20

Time [min]

C

on

ce

nt

ra

tio

n [

%

]

0 L/s

0.1L/s

0.2L/s

1 L/s

3.56 L/s

O2 concentration at different ventilation rates 0.188m from fire,

towards tunnel opening

8

10

12

14

16

18

20

22

0

2

4

6

8

10

12

14

16

18

20

Time [min]

C

on

ce

nt

ra

tio

n [

%

]

0 L/s

0.1L/s

0.2 L/s

1 L/s

3.56 L/s

Figure 5.1 O

2

concentration at different ventilation rates, 0.188 m on either side of the fire.

Close to the ceiling (13mm) the temperature increases with a decreasing ventilation rate.

Closer to the bottom of the tunnel the differences are smaller and a higher ventilation rate

gives a higher temperature. A higher ventilation rate results in more mixing which gives a

more even temperature distribution across the height of the tunnel. There is no difference

between left and right side of the tunnel. Figure 5.2 shows the temperature at the left side

of the tunnel 0.188 m from the fire towards the end of the tunnel while Figure 5.3

presents the temperature at the left side of the tunnel 0.188 m from the fire towards the

tunnel opening.

Temperature 13mm from ceiling at different ventilation rates,

0.188m from fire towards tunnel end, left side

0

50

100

150

200

250

300

0

2

4

6

8

10

12

14

16

18

20

Time [min]

Tem

per

at

ur

e [

°C

]

0 L/s

0.1 L/s

0.2 L/s

1 L/s

3.56 L/s

Temperature 50mm from ceiling at different ventilation rates,

0.188m from fire towards tunnel end, left side

0

50

100

150

200

250

300

0

2

4

6

8

10

12

14

16

18

20

Time [min]

Tem

per

at

ur

e [

°C

]

0 L/s

0.1 L/s

0.2 L/s

1 L/s

3.56 L/s

Temperature 125mm from ceiling at different ventilation rates,

0.188m from fire towards tunnel end, left side

0

50

100

150

200

250

300

0

2

4

6

8

10

12

14

16

18

20

Time [min]

Tem

per

at

ur

e [

°C

]

0 L/s

0.1 L/s

0.2 L/s

1 L/s

3.56 L/s

Figure 5.2

Temperature at the left side of the tunnel at 13 mm, 50 mm and 125 mm

Temperature 13mm from ceiling at different ventilation rates,

0.188m from fire towards tunnel opening, left side

0

50

100

150

200

250

300

0

2

4

6

8

10

12

14

16

18

20

Time [min]

Tem

per

at

ur

e [

°C

]

0 L/s

0.1 L/s

0.2 L/s

1 L/s

3.56 L/s

Temperature 50mm from ceiling at different ventilation rates,

0.188m from fire towards tunnel opening, left side

0

50

100

150

200

250

300

0

2

4

6

8

10

12

14

16

18

20

Time [min]

Tem

per

at

ur

e [

°C

]

0 L/s

0.1 L/s

0.2 L/s

1 L/s

3.56 L/s

Temperature 125mm from ceiling at different ventilation rates,

0.188m from fire towards tunnel opening, left side

0

50

100

150

200

250

300

0

2

4

6

8

10

12

14

16

18

20

Time [min]

Tem

per

at

ur

e [

°C

]

0 L/s

0.1 L/s

0.2 L/s

1 L/s

3.56 L/s

Figure 5.3

Temperature at the left side of the tunnel at 13 mm, 50 mm and 125 mm

from the ceiling, 0.188 m from the fire towards the tunnel opening.

5.1.2

Open or closed tunnel end

One of the experiments in tunnel A was carried out with the lower tunnel end open also.

This was made with no ventilation and a fire size of 1 kW. As expected, the O2

concentration 0.188 m from the fire (towards the lower end) was higher in the case when

the tunnel end was open on both sides of the fire. At a position 2.5 m from the fire,

towards the upper opening there was no difference in the O2 concentration between the

two cases.

Figure 5.4 O

2

concentration for open and closed tunnel at different distances from fire.

The temperature 0.188 m from the fire, towards the lower end of the tunnel, is higher

when the tunnel is closed than when it is open, in particular close to the ceiling. For the

case of an open tunnel the temperature is more even distributed across the tunnel height.

Towards the upper tunnel opening, the temperature is fluctuating much more when the

lower tunnel end is open than when it is closed. Close to the ceiling and close to the floor

there is no great temperature difference for the open and closed tunnel, but in the centre

the temperature is higher for an open tunnel.

Figure 5.5 Temperature at different distances from ceiling for open and closed tunnel.

5.1.3

With and without slope

Tunnel A was tested both horizontally, i.e. without slope, and with an inclination of 10°.

In the two cases compared in this section, the forced ventilation was turned off and the

lower end of the tunnel was closed. In Figure 5.6 the O2 concentrations at different

positions are presented for the two cases. It can be seen that the oxygen concentration

decreased rapidly in the case of no slope compared to the tunnel with a slope. When the

concentration reached approximately 11 %, the fire was extinguished and the oxygen

concentration started to increase. Closer to the tunnel opening, 2.5 m from the fire, no

decrease is seen of the oxygen concentration for the tunnel without slope.

Figure 5.6 O

2

concentration for tunnel with and without slope.

When there is no slope, the temperature increases rapidly close to the ceiling and then

decreases after the fire has self-extinguished (see Figure 5.7). Closer to the floor the

temperature increase is much smaller, but similar to that close to the ceiling. In the case

of the tunnel with a slope, the temperature increase is not as great closest to the ceiling.

Closer to the floor the initial part of the temperature curves are similar for the two cases.

The difference close to the ceiling is probably due to differences in position of the flame.

Figure 5.7 Temperature at different distances from ceiling for open and closed tunnel.

5.2

Tunnel A+B

The main geometry during the test series was the access tunnel A connected to the

perpendicular tunnel B.

5.2.1

Ventilation

In this section the results for the five different ventilation cases (0, 0.1, 0.2, 1.0 and

3.56 L/s) are presented. In Figure 5.8 the O2 concentrations for different ventilation rates

are compared. For the lower ventilation rates the oxygen concentration quickly decreases

and the fire self-extinguished. After extinguishment, the oxygen concentration increased

again. For a ventilation rate of 1 L/s, the fire burned well and for a long period of time.

For the highest ventilation rate we also observe the highest level of oxygen.

For the rate 1 L/s the O2 concentration goes down to approximately 16 % 0.188 m from

the fire towards the tunnel end and 2.5 m from fire, towards tunnel opening. At the

location 0.188 m from fire towards the opening, however, the O2 concentration only

decreases to just below 20 %. This could be due to a particular flow pattern, and one

indicator of such a flow pattern in this experiment was that the smoke at the exit was

quite cold and thus low. However, during the experiment particular flow patterns could

not be observed due to lack of smoke (the flame gave no indication of clear differences

between the tests).

Figure 5.8 O

2

concentration at different ventilation rates. Fire in position 2.

The temperature at different heights from the ceiling for the different ventilation rates can

be seen in Figure 5.9. Close to the ceiling the temperature is higher towards the tunnel

opening than towards the tunnel end, in particular for the highest ventilation rate

Figure 5.9 Temperature at different distances from ceiling for different ventilation rates, at

two different positions near the fire.

5.2.2

Fire size

The fire size was varied from 0.4 kW up to 3.2 kW. The fire size of 1 kW was produced

by a gas burner. In this section results from tests with different fire sizes are compared.

The oxygen concentration is shown in Figure 5.10. It can be seen that close to the fire,

towards the tunnel opening, there is no significant change in the oxygen concentration. At

the same distance, towards the tunnel end, the difference is much larger. This is due to the

position of the air inlet and the flow pattern in the tunnel.

Figure 5.10 O

2

concentration for different fire sizes.

The temperature at different distances from the ceiling, 0.188 m on either side of the fire

is shown in Figure 5.11. As expected the temperature is much higher for the larger fire

sizes. The temperatures gradients at the two different sides of the fire are similar to each

other, with the largest difference in the beginning of the tests.

5.2.3

Air inlet above the fire

The air inlet tube, guiding the air to a position near the end of the tunnel, is often made of

plastic in real tunnel construction. In case of a fire such a ventilation tube could burst. It

was therefore interesting to study what consequences could be expected from such a

situation. In this section results for cases with different position of air inlet are compared.

Two different ventilation conditions are presented: one with 3.56 L/s (Figure 5.13) and

one with 0.1 L/s (Figure 5.14). For each case, graphs for three different positions for the

O2 sampling are included: 0.187 m from the tunnel end (Pos 21), 0.563 m from the tunnel

end (Pos 27), and 0.188 m from the fire (towards the tunnel opening; Pos 27 and 38,

respectively), see Figure 5.12 and Table 3.1. This means that in the first and second graph

“Centre” and “End” correspond to the same position of the O2 sampling, while in the

third case the positions are different since they are related to the position of the fire and

not the tunnel end. “Centre” refers to fire position 3 and “End” refers to fire position 2. In

each graph results for three fire sizes (1 kW, 1.3 kW and 3.2 kW) are included. For the

tests presented in Figure 5.13 and Figure 5.14, there was a hole in the tube above fire

position 3, when the fire was in position 3 (but not when the fire was in position 2).

21

27

38

2

3

Figure 5.12

Positions of O

2

sampling (21, 27 and 38) in relation to position of fire (2 and

3).

There are differences between the two ventilation rates. Starting with 3.56 L/s, for the two

cases with sampling position measured from the tunnel end the fire near the end of the

tunnel gave lower O2 concentration than the corresponding cases with the fire in the

centre of the tunnel. The lowest values were measured near the tunnel end. For the case

with sampling 0.188 m from the fire it is interesting to note that the results for each pair

of fire size are almost identical to each other. The results indicate that the fire controls

much of the flow pattern and the conditions near the fire. For the high ventilation rate

much of the inlet air reaches the end of the tunnel despite the hole in the tube.

Figure 5.13

O

2

concentration at different positions (a. 21, b. 27, c. 38 and 27) for

different positions of the fire, different fire sizes and an airflow of 3.56 L/s.

When the fire was in the “Centre” there was a hole in the tube above the

fire.

For the case with 0.1 L/s the results look different. In almost all cases the O2

concentrations for the centre fire position are lower than the corresponding case near the

end of the tunnel. Overall the concentrations are significantly lower than the 3.56 L/s case

above. Note that some of the fires were self-extinguished earlier than in the free-burning

case (see Table 5.1).

Figure 5.14

O

2

concentration at different positions (a. 21, b. 27, c. 38 and 27) for

different positions of the fire, different fire sizes and an airflow of 0.1 L/s.

When the fire was in the “Centre” there was a hole in the tube above the

fire.

5.2.4

Fire position

In this section results for two different fire positions are compared, end of tunnel B (Pos

2) and centre of tunnel B (Pos 3). The air inlet was in all these cases through the end of

the tube near the end of the tunnel, contrary to Section 5.2.3 where there was a hole above

the fire when the fire was positioned at the centre (Pos 3). In Figure 5.15 results for 0.1

L/s are presented and in Figure 5.16 for 1 L/s.

For 0.1 L/s the O2 concentrations 0.187 from the tunnel end are relatively similar for the

two fire positions. The difference is much larger when the air flow rate is 1 L/s, where the

concentration for the fire in Pos 2 is significantly lower than the corresponding one when

the fire is in Pos 3. For sampling position 27 (0.563 m from the tunnel end) the situation

the opposite. Here the concentration are very similar for 1 L/s, while for 0.1 L/s the O2

concentration is lower when the fire (1.3 kW) is in position 3 than in Pos 2.

When the gas sampling is made 0.188 m from the fire (Pos 27 or 38), the O2

concentration is lower when the fire is in the centre, both for 0.1 L/s and 1 L/s.

Figure 5.15

O

2

concentration at different positions (a. 21, b. 27, c. 38 and 27) for

Figure 5.16

O

2

concentration at different positions (a. 21, b. 27, c. 38 and 27) for

different positions of the fire, different fire sizes and an airflow of 1 L/s.

5.3

Tunnel A, A+B, A+B+C

The results obtained using tunnel A+B+C show no significant difference compared to

when Tunnel A+B was used. The fire does not really “see” the extra space. However

compared to tunnel A there is a significant difference in both temperature and oxygen rate

and, as can be seen in Figure 5.17 and Figure 5.18. When the fire is positioned in tunnel

B the oxygen rate is much lower. For the sampling position 0.188 m from the fire towards

the tunnel opening there is a difference between Tunnel A+B and Tunnel A+B+C. For the

temperature there is a difference in the position towards the tunnel end, but not as large as

the difference compared to Tunnel A. Note also the fire burned completely differently in

Tunnel A.

Figure 5.17

Comparison of temperature measurements near the fire in three different

tunnel geometries.

Figure 5.18

Comparison of O

2

concentration measurements near the fire in three

5.4

Self-extinguished fires

In many of the test cases, the oxygen concentration decreased to such a low level that the

fire was self-extinguished. In Table 5.1 a summary of the conditions where this occurred

is presented. In the table some cases when the fire was extinguished later than the time

reach in the free-burn test (see Table 3.2) are also included; these are given in italics. The

mass consumed during a test is also included, when available. In some cases the mass loss

continued long after the fire (flame) was extinguished and no exact mass loss could be

presented.

Table 5.1

Summary over all case where the fire was self-extinguished.

Test

case

Tunnel

Fire

size

(kW)

Fire

position

Ventilation

(L/s)

Expected

_extinguish

time (min:sec)

Time when

extinguished

(min:sec)

Consumed

mass

a)

_(g)

6

A+B

1

2

0

Never

2:37

-

7

A+B

1

2

0.1

Never

2:41

-

8

A+B

1

2

0.1

Never

2:39

-

10

A+B

1

2

0.2

Never

2:53

-

11

A+B

0.4

2

0.1

2:00

2:41

NA

12

A+B

0.4

2

0.1

2:00

2:20

0.7 (0.7)

13

A+B

0.4

2

1

2:00

2:30

0.6 (0.7)

14

A+B

1.3

2

0.1

4:10

2:24

5

c)

_(9.3)

15

A+B

1.3

2

1

4:10

5:12

7.8 (9.4)

16

A+B

3.7

2

0.1

5:00

2:03

7.2 (82.8)

17

A+B

3.7

2

1

5:00

7:39

NA

c)

18

A+B

1.3

3

0.1

4:10

2:53

6.7 (9.2)

19

A+B

1.3

3

1

4:10

3:56

7.3 (9.2)

20

A+B

3.7

3

1

5:00

6:16

NA

c)

21

A+B

1

3

0.1

Never

2:27

-

22

A+B+C 1

2

0.1

Never

2:46

-

23

A+B+C 1

3

0.1

Never

2:55

-

24

A+B

1

3

0.1

Never

3:02

-

25

A+B

1.3

3

0.1

4:10

4:01

6.8 (9.0)

26

A+B

3.7

3

0.1

5:00

2:23

NA

c)

30

A+B

1.3

3

3.56

4:10

4:11

NA

31

A+B

3.7

3

3.56

5:00

5.56

41 (82.9)

32

A+B

1.3

3

3.56

4:10

6:54

6.7 (9.5)

33

A+B

1.3

2

3.56

4:10

4:13

6 (9.2)

34

A+B

3.7

2

3.56

5:00

6:31

30.4 (82.8)

36

b)

_A

₁

₁

₀

_Never

_2:32

_-

a) Value within parentheses represents mass before test.

b) No Slope

c) Mass continued to decrease also after extinguishment.

NA = Not available

Observe that in tests 29 and 35 the burner was turned off and the fire did not

self-extinguish as might be concluded from looking at the graphs. It can be can observed that

all times when the fire did self-extinguish, the ventilation rate was very low. Furthermore

the fire is placed in Tunnel B in all cases except for test 36, which was different to all

other tests as it did not have any inclination, i.e. Tunnel A was horizontal. It can also be

noted that when the fire size is 0.4 kW it is not extinguished even though the ventilation

rate is low (0.1 L/s in test 11 and 12)

6

Discussion

In the test series a scale model was used. It was constructed as an access tunnel (10°)

reaching a horizontal T-shaped tunnel. In a real construction situation the tunnel system

can be very complicated and will vary from site to site. The number of tunnels starting

from the bottom of the access tunnel as well as the lengths of each tunnel will be site

specific. However, generally the basic concept is similar, i.e. a sloping access tunnel is

constructed to reach a starting point for horizontal tunnels (these tunnels can of course

also have a slope), each with a closed end before the breakthrough. Therefore, the general

trends and conclusions should be valid.

Similarly, the installations for “comfort” ventilation might vary between different sites,

but a very common way to solve the issue is to guide the inlet air through large tubes near

the ceiling from large fans outside to a position near the work site at the closed tunnel

end. The ventilation affects both the flow pattern and the development of the fire. A large

fire might have the power to start a circulation of the air all the way from the opening,

while a smaller fire will not. If the ventilation rate is low this could lead to

self-extinguishment of the fire.

Further, the ventilation creates a flow near the ceiling. Therefore, the ventilation affects

the flow pattern and together with the forces from the fire, creates a circulation “behind”

the fire. This in turn leads to a recirculation of vitiated fire products. The consumption of

oxygen together with the recirculation of vitiated products can also cause the fires to

self-extinguish. The flames try to find oxygen and it was observed in some cases during the

test series how the flames extended into the ventilation tube in search of oxygen in the

entering fresh air. For these reasons (availability of oxygen and flow pattern) the position

and flow rate of the ventilation are important for the conditions during a fire in a tunnel

under construction. During the test series, the effect of a simulated hole (caused by the

fire) on the ventilation tube was also studied. An effect could be seen, which might have

been larger if it had been combined with an obstruction of the ventilation tube after the

hole. This was, however, not tested during the test series.

7

Conclusions

The report describes a series of model scale tests in scale 1:40 describing the situation

before breakthrough in a tunnel during construction. The tunnel was constructed as an

access tunnel (10°) reaching a horizontal T-shaped tunnel. In a real construction situation

the tunnel system can be very complicated and will vary from site to site. The number of

tunnels starting from the bottom of the access tunnel will be site dependent and vary.

However, generally the basic concept is similar, i.e. a sloping access tunnel is constructed

to reach a starting point for more horizontal tunnels (these tunnels can of course also have

a slope) with closed end before the breakthrough. Therefore, the general trends and

conclusions should be valid. The “comfort” ventilation will also vary between different

sites, but a very common way to solve the issue is to guide the inlet air through large

tubes near the ceiling from large fans outside to a position near the work site at the closed

tunnel end. The ventilation therefore affects both the flow pattern in the tunnel and the

development of the fire.

Ventilation before breakthrough consists of mechanical comfort ventilation and after

breakthrough is dominated by natural ventilation. Comfort ventilation transports fresh air

through the ventilation pipes of plastic to the workplace where drill or blasting is carried

out (at the dead end). The fresh air is in turn, transported back from the workplace to the

tunnel portal. The model scale experiments show that if the fire occurs before the

breakthrough and the fire is small (a few MW) it will be difficult to obtain fresh air from

the entrance. Therefore the fire is totally dependent on the oxygen delivered by the

comfort ventilation system. If the comfort ventilation is shut off, the consequences will be

that the fire decreases in intensity and finally extinguishes due to lack of oxygen caused

by consumption of oxygen and recirculation of vitiated products back to the fire.

A large fire might have the power to induce circulation of the air all the way from the

opening, while a smaller fire will not. If the ventilation rate is low this could result in

self-extinguishment of the fire. The ventilation creates a flow near the ceiling. This affects the

flow pattern and together with the forces from the fire, creates a circulation “behind” the

fire.

It was observed that when the fire self-extinguished, the ventilation rate was very low. In

many of the test cases, the oxygen concentration decreased to such a low level that the

fire was self-extinguished. The results for tunnel A+B+C showed no significant

difference compared to when Tunnel A+B was used, i.e. the fire does not really “see” the

extra space. However, compared to tunnel A there was a significant difference in both

temperature and oxygen rate. When the fire was positioned in tunnel B the oxygen rate

was much lower. For the sampling position 0.188 m from the fire towards the tunnel

opening there was a difference between Tunnel A+B and Tunnel A+B+C. For the

temperature there was a difference in the position towards the tunnel end, but not as large

as the difference compared to Tunnel A.

8

References

1.

Ingason, H., Lönnermark, A., Frantzcih, H., and Kumm, M., "Fire incidents

during construction work of tunnels", SP Technical Research Institute of Sweden,

SP Report 2010:83, Borås, Sweden, 2010.

2.

Lönnermark, A., and Ingason, H., "Fire Spread in Large Industrial Premises and

Warehouses", SP Swedish National Testing and Research Institute, SP Report

2005:21, Borås, Sweden, 2005.

3.

Larsson, I., Ingason, H., and Arvidson, M., "Model Scale Fire Tests on a Vehicle

Deck on Board a Ship", SP Swedish National Testing and Research Institute, SP

Report 2002:05, Borås, Sweden, 2002.

4.

Ingason, H., "Small Scale Test of a Road Tanker Fire", International Conference

on Fires in Tunnels, pp. 238-248, Borås, Sweden, October 10-11, 1994.

5.

Ingason, H., Wickström, U., and van Hees, P., "The Gothenburg Discoteque Fire

Investigation", 9th International Fire Science & Engineering Conference

(Interflam 2001), 965-976, Edinburg, Scotland, 17-19 September, 2001.

6.

Ingason, H., "Model Scale Tunnel Fire Tests - Longitudinal ventilation", SP

Swedish National Testing and Research Institute, SP REPORT 2005:49, Borås,

Sweden, 2005.

7.

Ingason, H., "Model Scale Tunnel Fire Tests - Sprinkler", SP Technical Research

Institute of Sweden, 2006:56, 2006.

8.

Lönnermark, A., and Ingason, H., "The Effect of Cross-sectional Area and Air

Velocity on the Conditions in a Tunnel during a Fire", SP Technical Research

Institute of Sweden, SP Report 2007:05, Borås, Sweden, 2007.

9.

Ingason, H., "Model scale tunnel tests with water spray", Fire Safety Journal, 43,

7, pp 512-528, 2008.

10.

Lönnermark, A., and Ingason, H., "The Influence of Tunnel Cross Section on

Temperatures and Fire Development", 3rd International Symposium on Safety

and Security in Tunnels (ISTSS 2008), 149-161, Stockholm, Sweden, 12-14

March, 2008.

11.

Lönnermark, A., and Ingason, H., "The Effect of Air Velocity on Heat Release

Rate and Fire Development during Fires in Tunnels", 9th International

Symposium on Fire Safety Science, pp 701-712, Karlsruhe, Germany, 21-26

September 2008.

12.

Ingason, H., and Lönnermark, A., "Effects of longitudinal ventilation on fire

growth and maximum heat release rate", Proceedings from the Fourth

International Symposium on Tunnel Safety and Security, pp 395-406, Frankfurt

am Main, Germany, 17-19 March, 2010.

13.

Lönnermark, A., and Ingason, H., "Fire spread between industry premises", SP

Technical Research Institute of Sweden, SP Report 2010:18, Borås, Sweden,

2010.

14.

Heskestad, G., "Modeling of Enclosure Fires", Proceedings of the Fourteenth

Symposium (International) on Combustion, 1021-1030, The Pennsylvania State

University, USA, August, 1972.

15.

Quintiere, J. G., "Scaling Applications in Fire Research", Fire Safety Journal, 15,

3-29, 1989.

16.

Saito, N., Yamada, T., Sekizawa, A., Yanai, E., Watanabe, Y., and Miyazaki, S.,

"Experimental Study on Fire Behavior in a Wind Tunnel with a Reduced Scale

Model", Second International Conference on Safety in Road and Rail Tunnels,

303-310, Granada, Spain, 3-6 April, 1995.

17.

Heskestad, G., "Physical Modeling of Fire", Journal of Fire & Flammability, 6,

p. 253 - 273, 1975.

Appendix 1 Time-resolved graphs

In this section graphs from each test are presented. The position in the tunnel is described

by a x or y coordinate, where x = 0 is at the end of tunnel A and y = 0 is the end of tunnel

B (see Figure 3.1). The descriptions “Left” and “Right” are defined by looking from the

fire towards the opening. These positions are 50 mm from the centreline. In one graph the

temperatures at different distances relative to the fire are compared.

Gas analysis

The gas concentrations are measured at three positions, all at a height of 0.75 m, which is

half the tunnel height. Two gas analysers are placed at 0.187 m and 0.563 m from the end

of the tunnel. When the fire is placed in the end of the tunnel (position 1 and 2) these

positions represent a distance of 0.188 m before and after the fire. A third position of

measurement at 2.875 m from the end of the tunnel in tunnel A and 1.687 from the end of

the tunnel in tunnel B is also used.

Comparison of thermocouples

At two locations in each tunnel, two different kinds of thermocouples where used at the

same position, with diameters 0.8 mm and 0.25 mm, these are marked with “TC 0.8” and

“TC 0.25”. At all other positions, thermocouples with a diameter of 0.25 mm were used.

Some of the positions with thermocouples of different size were relatively close to the

fire and there the effect of the radiation from the fire can be seen.