Smouldering mega-fires in the Earth system (Forest Ecology 2011)

8/3/2019 Smouldering mega-fires� in the Earth system (Forest Ecology 2011)

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Dr Guillermo Rein

School of Engineering

University of Edinburgh

Smouldering mega-fires

in the Earth system



22 Oct 1997 smoke plume, NASA TOMS satellite

Page et al. Nature 420, 2002

Sign at NTU Singapore, 2011



National Geographic 2008/ AP Photo/MODIS

2008 - The Evans Road fire, NC

burned for 7 months

1 0 0 k m

During worst drought on record

16,500 ha burned (2x year avg.)

1 m deep into the soil Stopped by flooding and excavation



2009 Tablas de Daimiel National Park, Spain



World Map of Peatlands Contain more terrestrial carbon than the forests or the

atmosphere

Gore, 1983



Russian summer mega fires, 2010



1999 A Belenky / SPT

July 1999: Anomalous climate conditions led to a smouldering fire at the wild-urban

interface. Peat fires burned South of the city for weeks and haze covered five districts.

Other peat fires elsewhere in Russia forced President Boris Yeltsin to change holiday

resort.

Days in July 1999



August 1972: Moscow and Alaska



Flameless

Low peak temperature (~600°C)

Low heat of combustion (~5 kJ/g) Creeping propagation (~1 mm/min)

Heterogeneous combustion at fuelpores

Peat (esp. dry) Incomplete combustion

Rein, Intern. Review Chemical Engineering 2009

Smouldering Combustion

sssashchar OH CH , , NH H , C CH COO H COOC +++++→+ ∑ ...)( 33834222

JB Nielsen, wikipedia JL Torero, UCB

smouldering/flaming



Most persistent fires on Earth

Smouldering fires are the easiest to ignite

Ignition with 50% smaller heat sources (8 vs. 15 kW/m2)

Self-heating possible at ambient temperatures <30 ºC

Smouldering fires are most difficult to suppress

Larger amounts of water (>50% more kgH2O/kgfuel)

Much longer sealing hold-on times (~100 days)

Lower critical oxygen concentration (<16%)

The oldest continuously burning fire on Earth is asmouldering coal seam in Australia ignited >6,000

years old (most probable natural causes)



video speeded up 600 times

1 s video = 10 min experiment

Smouldering spread30 x 30 x 5 cm layer of peat

Top view, Visual camera Top view, Infrared camera



igniter

t i m e



igniter

lS

t Sresidual layer

of char and ash

0hundisturbed peat

leading edge

trailing edge

Spread and in-depth burning

iS

in-depth



Ammt ′′= &&

Mega-fire spread

32

03

t SSdt mmlit t

ρ π

== ∫ &

constant)(~densityandratedepth-inrate,spread,,

timeburningandareaFire,

burnof depthandarea)unitperand(total,nconsumptiofuel,,

area)unitperand(total,rateburning,

0 =

=

=′′

=′′

ρ il

b

SS

t A

hmm

mm&&

m t

t o t a l f u e l

c o n s u m p t i o n

t , time

biht Sdt mm 00 ρ ρ ==′′=′′ ∫ &

m ” f u e l c o n s u m p t i o n

p e r u n i t a r e a

t , time

00

ρ h

flaming

smouldering

00

ρ h

( )

220

0

2

t SSm

Sm

t S A

lit

i

l

πρ

ρ

π

=⇒

=′′

=

&

&

3t

2t



Depth of Burn hb

The depth of burnt hb

increases linearly with time

Maximum value h0 is given by the location of the inertlayer, very moist layer (>125%MC) or firefightingattempts

Depth of burn of 5 cm leads to ~7 kg/m2

Values reported in the literature from 0.1 to 5 m

Most typical average is 0.5 m (=75 kg/m2)

In-depth spread over thick peat layers leads to 40to 90 times larger fuel consumption than flaming

fires

0.5mm/min)~atspreaddepth-(in t Shib

=



Lost Mass and Ignition

for a 8% inert



Carbon Emissions flux

Carbon emissions from fires are 3,000 times larger the natural respiration fluxfrom peatlands

Hadden, PhD Thesis 2011



National Geographic 2008/ AP Photo/MODIS

Flaming fires consume

grasslands, shrubs and

forests. These take 10-102

yearsto grow back and sequester back

the carbon = Renewable & Carbon

Neutral

Flaming vs. Smouldering

Smouldering fires consume peat,

organic soils and coal. These take 104

to 109 years to grow again =Not Renewable & Carbon Positive

Smouldering fires burn

pre-fossil and fossil fuels



Feedback Mechanism in the Earth System

the topics I work on



Smouldering phenomena involve the burning of fossil fuels and are carbon-positive.

This creates a positive feedback mechanism in theclimate system

Moisture deficit and self-heating of carbonaceous media areenhanced under warmer climates

Drier and warmer organic matter leads to more frequentsmouldering fires.

Warmer temperatures at high latitudes are alreadyresulting in large smouldering fires in the Arctic(e.g., Alaska 2010).

Feedback Mechanism in Earth

System



Conclusions1. Accidental burning of fossil fuels (incl. natural sources)

2. Equivalent on average to ~15% of man-made carbonemissions

3. Positive feedback mechanisms between smoulderingfires and climate change

Very large fires of organic matter (mostly peat) haveburnt since past millennia for long periods of time(months, years, decades)

Possible acceleration due to drying/drainage

In terms of fuel consumption, these are mega-fires Concepts as fire exclusion or prescribe burning cannot

apply



ThanksThanks

Belcher et al, PNAS 2011

Rein et al, Catena 2008

Hadden, PhD Thesis 2011Rein et al., Proc Combustion Institute 2009

Rein, Int Review Chemical Engineering 2009



Bing35 m high pile of oil-

shale and coal wastes,formed in the 1920snear Glasgow, has

been smouldering fortwo years

spread

~1 m/month

drying frontoxidation front

off-gassing vent

spread

Smoulder bing since 2008



Belcher et al, PNAS 2011

Critical Oxygen Concentration

15% O2 17% O2

Smouldering mega-fires in the Earth system (Forest Ecology 2011)

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