Andy Tegart, John MacLeod, Andrew HalnonDeanmac Emergency Services

A brief review of Australian surface coal mine fires and their mitigations and control

Introduction

• Over 100 large open cut coal mines on the east coast of Australia, most in QLD and NSW

• 1365 coal mines in the US• Various types of coals with

different rates of spread• Significant recent fires such as

Hazelwood Mine, highlight the critical risk of fires to local communities from product of combustion

Surface Coal Mine Fire History

• International experience • US Surface Mine Fires (NOISH) 10

years (1990-1999)– 215 Number of fires– 1 Fatality– 93 Injuries

• Coal mining is a high risk operation

0

20

40

60

80

Jul'85

Sep'85

Nov'85

Jan'86

Mar'86

May'86

Jul'86

Sep'86

Nov'86

Jan'87

Mar'87

May'87

Jul'87

Sep'87

Nov'87

Jan'88

Mar'88

May'88

Jul'88

Sep'88

Nov'88

Jan'89

Mar'89

May'89

Number of Fire's Between Morwell and

Yallourn Open Cut Mines

Summer Season Morwell Yallourn

Open Cut Coal Mines

• Different risks to underground coal mining

• Considerable size and scale– Progressively have become the major

production source• Most of coal mine fire research initially

developed from 1910 in the US by Bureau of Mines– Coal mine fire research has been active

internationally for over 100 years and a large body of research exists

– NIOSH Fire Suppression Facility in US (Lake Lynn Laboratory) is world class enabling large scale experiments

• The  Australian  Coal  Industry’s  Research  Program (ACARP) established in 1992

Coal Chemistry – Coal Lithotypes

Brown Coal– Lignite

Black Coal– Anthracite– Bituminous– Sub-Bituminous

Bituminous Coal Physical Characteristics (Average)

Density 1330 𝐾𝑔/𝑚

Specific Heat 1.05 𝐾𝐽/𝐾𝑔 − 𝑘

Coal Conductivity 0.24 𝑊/𝑚 − 𝑘

Heat of Pyrolysis 209 𝐾𝐽/𝐾𝑔

Lignite Coal Physical Characteristics (Average for Latrobe

Valley)

Density 1120 𝐾𝑔/𝑚

Specific Heat 1.38 𝐾𝐽/𝐾𝑔 − 𝑘

Coal Conductivity 0.52 𝑊/𝑚 − 𝑘

Porosity 38.9%

Fire Science- Heat Transfer

• All combustion reactions are exothermic• Ignition (with much smaller heat sources 8 𝑘𝑊/𝑚 )

– Temperature, particle size– Oxygen availability– Coal + O2 -> CO2 + Heat

• Smouldering combustion – Flameless– Low peak temperature (often 500-700°C)– Low heat of combustion (i.e. 31 KJ/Kg bituminous coal) – Creeping propagation– Incomplete combustion

𝐶 𝐻 𝑂 + 113 𝑂 → 100𝐶𝑂 + 37 𝐻 𝑂 + 4.2 × 10 𝐽𝑘𝑚𝑜𝑙 𝑂

In-depth Spread

• Smouldering fires spread in area and in depth

• Char is both a product and reactant in pyrolysis and oxidation reactions

• Volumetric eventho

St leading edgeSd in-depth

trailing edge

residual layer of char and ash

Two speed Fire Spread Model

Sub - Surface Coal

• Conduction through coal type and pyrolysis of coal

• Radiation• Thermal mass (insulated from

heat loss)• Coal can smoulder indefinitely at

< 2% oxygen concentrations (NIOSH)

• Coal fire spread rates 0.0086 –0.0145 m/sec

Coal Surfaces

• Dynamic pressure (atmospheric driven)

• Fine coal dusts and particles vectors

• Spontaneous heating of coal dependent on oxidation rates (time needed)– Ambient temperatures (30°C)

• Lignite coal fire spread observed at 5 m/sec

Smoke- Devolatisation

Char, 30

Carbon

Monoxide, 12.8

Carbon

Dioxide, 7.9Water Vapour, 9.2Ethylene, 1.8

Methane, 1.85

Hydrogen, 0.95

Tar, 35.5

PRODUCTS OF DEVOLATISATION

• Significantly higher CO/CO2 products than flaming combustion• POC levels vary between coal types and mining material fuel

Smoke – Air Toxins and Health Impacts

• Static surface mine fire, large fuel volumes, day and night production in calm, low lying conditions may result in high exposure levels

• Smoke irritates, obscures vision, exacerbates respiratory or cardiac diseases

• Major POC matter – PM10 and PM2.5 (greatest impact on health)– Gases: PAH, SO2, NO2, CO2

– Air toxins: VOC and metals• Bituminous coal (smouldering) – Bureau of Mines US

– Particle concentrate 1.0 (10 𝑝/𝑐𝑚 )– Mass particle concentration 3.2 (mg/𝑚 )– Diameter of average particle 0.16 μm

Smoke – Air Toxins and Health Impacts

• CO is a narcotic gas, highly toxic• High exposure to PM2.5 serious threat to the sensitive people

Detection and Suppression

• Detect early, locate and mapping• Significant difficulty to suppress

– Large amounts of water • > 50% Kg H2O / Kg Fuel

– Lower critical oxygen concentration 10% -> 2%

– Large thermal mass– Can persist for months/years sub-

surface– Sub-surface can consume 50 times

more fuel than surface fires

Control Measures- Mitigation

Lessons learned Reduce ignition sources• Oxidation by coal rank• Mining equipment• Human activity• Limit size and

compartmentation • Wetting fuel – agent and

additives• Make fuel inert• Coal dust at PM2.6 becomes

airborne

Best Practise and Guidelines

Conclusion

• Surface mine fires are generally preventable• Surface mine fires continue to occur, illustrating the potential for

disaster to still occur– Highlights the importance of eliminating potential fire hazards and

improved fire control

• Large scale and deep seated (firmly established) surface coal fire are notoriously difficult to extinguish, costly and resource intensive

• Products of combustion cause hazards to human health and safety is of paramount concern

Questions