Ventilation for Smoke Control, Fire Control &

Life Safety in TunnelsDr. Ricky Carvel

BRE Centre for Fire Safety EngineeringUniversity of Edinburgh

• Tunnel ventilation was invented as a pollution control system• Edge Hill railway tunnel, UK (1870) – extract fan• The Holland Tunnel, USA (1927) – fully transverse• The Queensway Tunnel, UK (1934) – semi-transverse• Bargagli-Ferriere Tunnel, Italy (1971) – jet fans

• Why do we use it as a fire safety system?• Is it a fire safety system?

Tunnel Ventilation?

What Happens When You Blow on a Fire?

What Happens When You Blow on a Fire?

What Happens When You Blow on a Fire?

Backlayering

This Strategy Generally Works for Road Tunnels

The strategy is to protect the queue

Does It Work for Rail Tunnels?

Where is the queue we need to protect?Can the vehicles ‘ahead’ just drive away?

What Should We Do with Ventilation Here?

• What would happen if we turned the ventilation system up?

• What would happen if we turned the ventilation system off?

• How would this affect the fire, the smoke, the people?

Ventilation vs. Sm

oke Ventilation

Good

Bad

Smoke control

Critical ventilation velocity

But…

• Blowing on a fire doesn’t just move the smoke. It also influences the fire dynamics!

• Do we care?

Ventilation vs. Fire Size

Ventilation velocity [m/s]0 2 4 6 8 10

Critical ventilation velocity1

2

4

8

Fire Enhancement Factor

Single lane tunnel

Two lane tunnel

See my PhD thesis or

FSJ papers 2001 fordetails...

Ventilation vs. Fire Grow

th

See paper in ISTSS 2008

or Handbook of Tunnel Fire

Safety…

Time

Hea

t Rel

ease

Rat

e

‘Delay’ phase

0

2

6

10Length of delay (min)

8

4

Ventilation velocity [m/s]0 1 2 3 4 5

Critical ventilation velocity

See paper in ISTSS 2008

or Handbook of Tunnel Fire

Safety…

Ventilation vs. Fire Grow

th

Ventilation velocity [m/s]0 1 2 3 4 5

See paper in ISTSS 2008

or Handbook of Tunnel Fire

Safety…

‘Growth’ phase

0

5

15

25Grow

th rate (MW

/min)

20

10

Critical ventilation velocity

Ventilation vs. Fire Grow

th

Example data for two lane tunnel, 5 m vehicle separation.

Ventilation velocity [m/s]0 1 2 3 4 5

0

20

60

100

Probability of spread (%)

80

40

Medium fire[32-64 MW]

Critical ventilation velocity

Ventilation vs. Fire Spread

See paper in 4th Int ConfTunnel FireSafety, 2004

Ventilation vs. Fire

Ventilation

Good

Bad Peak Fire Size

Delay duration

Growth rateFire Spread

Smoke control

Critical ventilation velocity

So What Should We Do?

What should we do?• That depends on one thing:

•How nasty is the smoke?

• For decades, fire strategies have been developed to keep smoke away from people and people away from smoke.

• Rarely have we stopped to ask questions about the properties of the smoke. Is smoke bad for you?

Which Smoke?

• If we blow on the fire, we get:• Fast growing, large fire, that is reasonably well ventilated

and we blow the smoke away from half (?) the people

• If we don’t blow on the fire, we get:• Slower growing, smaller fire, that is underventilated

and we expose all (or most) of the people to smoke

Which Is the Better Strategy?

How to Decide?

• There is really no ‘one size fits all’ solution.• This is what Performance-Based Design is all about.• We studied the case of a typical, 18 carriage, modern, high-speed,

inter-city passenger train, stopping due to fire in a tunnel with cross passages. (Disclaimer: Conclusions are not transferrable to other situations)

(The problem with trying to show trains on screen is that they’re just too long…)

If the fire is on carriage 2:

If the fire is on carriage 9:

About 375m

Ventilation

No forced ventilation

FED = 1

FED = 0.3

Ventilation

No forced ventilation

FED = 1

FED = 0.3

So What Does This Mean?• For this very specific scenario:

• If the fire is near the middle of the train:• with natural ventilation, everyone escapes through tenable smoke• with forced ventilation, half the passengers are completely fine, half

may be exposed to problematic levels of smoke.• If the fire is near the end of the train (but still with some people on both sides of it):

• with natural ventilation, everyone escapes through tenable smoke• with forced ventilation, most of the passengers are completely fine,

but the small number downstream of the fire are unlikely to survive!

Do you know where the fire is?If in doubt, use natural ventilation!

Why?

• You can’t divorce smoke control from fire dynamics!

An Introduction to Tunnel FiresShort CourseEdinburgh, UK5-6 September 2016www.edinburghfire.com/tunnel-fires/

BRE Centre for Fire Safety Engineering