otraco (international) pty ltd · report on lightning strike / tyre explosion 2.3.3 emergency...

REPORT

ON

HAULTRUCK LIGHTNING STRIKE

&

SUBSEQUENT TYRE EXPLOSION

IN

APRIL 2004

Report compiled by: Tony Cutler, Technical Manager

Report date: June 2004

Report on Lightning Strike / Tyre Explosion

TABLE OF CONTENTS 1. INTRODUCTION.......................................................................................1

1.1 Otraco’s experience regarding tyre fires and explosions.....................1 1.2 Acknowledgements ...............................................................................1

2. INCIDENT, FINDING & RECOMMENDATIONS ..................................2

2.1 Incident .................................................................................................2 2.2 Finding ..................................................................................................2 2.3 Recommendations .................................................................................3

2.3.1 General ...........................................................................................3 2.3.2 Prevention.......................................................................................3 2.3.3 Emergency procedure.....................................................................4

3. TYRE EXPLOSION MECHANISMS ........................................................5

3.1 Difference between tyre blow-out and tyre explosion .........................5 3.1.1 Tyre blow-out..................................................................................5 3.1.2 Tyre explosion.................................................................................5

3.2 Improved understanding of tyre explosion mechanisms.....................6 4. INSPECTION OF TRUCK, SITE, TYRES & RIMS .................................8

4.1 Inspection of truck ................................................................................8 4.2 Inspection of site .................................................................................11 4.3 Inspection of exploded tyre.................................................................11 4.4 Inspection of other tyres off truck ......................................................15

4.4.1 Charring to liner of position 2 (right front) tyre .........................15 4.5 Inspection of wheel rims.....................................................................16

5. INVESTIGATION PROCESS..................................................................17

5.1 Initial investigation ............................................................................17 5.2 Ongoing investigation.........................................................................17

APPENDICES

Appendix I – Dynasphere Lightning Protection System.........................19 Appendix II – EM Tyre explosion incidents database.............................21 Appendix III – Recommended Emergency Procedure Guidelines ..........30


1. INTRODUCTION In April 2004 a parked Terex/Unit Rig MT4400 (240T) haultruck was found, after a lightning storm on an Australian minesite, with a catastrophically failed outside rear tyre (40.00R57 size) and severe damage to the truck. The truck had been parked because of the impending lightning activity and the operator had been taken to a safe area until the storm had passed. No one was injured in the incident. Otraco1 has conducted an investigation into the incident. This report chronicles that investigation, its findings and recommendations.

1.1 Otraco’s experience regarding tyre fires and explosions Prior to this incident, Otraco has led the investigations into six incidents involving earthmover (EM) tyre explosions. Our first investigation was the Tasmanian Cleveland Tin fatality in 1981, and our most recent the Chilean Radomiro Tomic fatality in 2000. As a result of the Cleveland Tin investigation, Otraco established the principal tyre explosion mechanism (pyrolysis2); we have recently, with the technical assistance of two universities in Chile3, established a second, very rare tyre explosion mechanism (diffusion4). In 1987 we organised, together with the Western Australian Mines Department and Mt Newman Mining Company, the first conference on earthmover tyre fires and explosions. Causes of tyre explosions in cases previously examined by us have included the use of an oxyacetylene torch to loosen corroded wheel nuts, a haultruck having contacted overhead power-lines, dragging brakes initiating a haultruck tyre fire, and wood packing material being left inside a haultruck tyre. Apart from cases that we have personally investigated, Otraco has maintained a database of tyre fires and explosions that have come to our attention since the early 1980s. Information from these records has assisted us with our investigations, and has allowed us to better understand tyre explosion mechanisms and to formulate recommendations related to tyre fires and explosions.

1.2 Acknowledgements Otraco is grateful to Mr Grant Kirby, Principal of Lightningman Pty Ltd, for providing technical expertise in relation to lightning strikes. We also thank mine site personnel for material provided, and Terex personnel who supplied valuable information and technical assistance as well as some of the photographs used in this report.

1 Otraco is responsible for tyre management for the Argyle, Newman, Fimiston, Telfer, Murrin Murrin, Tarmoola, Tom Price, Paraburdoo/Channar, Marandoo, Brockman, Yandicoogina, Pannawonica, West Angelas, Cadia and Saraji mines in Australia, Kelian mine in Indonesia, and Escondida and Mina Sur mines in Chile. 2 Pyrolysis is the chemical decomposition of a compound caused by high temperatures. 3 Universidad de Santiago and Universidad de Chile. 4 The diffusion process is based on a difference in the chemical composition of elements present.

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2. INCIDENT, FINDING & RECOMMENDATIONS

2.1 Incident A Terex/Unit Rig MT4400 (240T) haultruck was parked in an isolated5 lay-by on the minesite in April 2004, because of impending lightning storm activity in the area6. The truck’s operator was picked up and taken to a safe area until the storm had passed. When an operator returned to the truck three hours later, the operator found that the position 3 (left outside rear) tyre had failed catastrophically and that severe damage had been caused to the truck – including damage to the main hydraulic tank, the operator cabin and to the walk-platform over the engine. The doors to the electrical cabinet on the walk-platform had been blown open, and the covers of both rear wheel motors had been blown off and were lying on the ground. Because of the isolation of the lay-by in which the truck was parked, it was not known if the truck has been struck by lightning or if some other condition had caused the catastrophic failure of the tyre. Subsequently, while the truck was being repaired and undergoing further examination, damage to electrical wiring and circuitry components was discovered. It was also found that the inner liner of the failed position 3 tyre had undergone extensive pyrolysis. The inner liner of the position 2 (right front) tyre had also suffered pyrolysis, although not as severely as for the position 3 tyre. The position 2 tyre had not failed.

2.2 Finding The conclusion of this investigation is that the truck was struck by lightning whilst parked in the lay-by during the lightning storm and that its position 3 tyre exploded. The tyre explosion was due to the auto-ignition of an explosive mixture of flammable gases that had built up inside the air chamber of the tyre following pyrolysis of the rubber inner liner material lining the air chamber. The pyrolysis was causing by electrical earthing of the lightning current-flow via the tyre. It is probable that the tyre exploded simultaneously with, or within seconds of, the lightning strike. The air-blast from this tyre explosion caused the observed damage to the truck components. The electrification of the truck, due to the lightning strike, caused the damage to the trucks electrical wiring and circuitry. While the inner liner of the position 2 tyre had also undergone pyrolysis (although not as severely as for the position 3 tyre) the position 2 tyre did not explode. This was because one or more of the conditions required for an explosion to occur (adequate oxygen, an explosive concentration of flammable vapour, a source of ignition, and sufficient molecular energy to sustain the explosive reaction) did not occur in the case of this tyre. 5 Far from any offices or other manned facilities. 6 The mine employs Storm Tracker, a lightning detector unit monitored in the mine control room, to measure the distance of lightning activity from the mine. With the assistance of Storm Tracker, the mine shift supervisor determines if and when mining equipment should be parked for safety reasons.

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The mine site’s policy to park haultrucks and other rubber tyred equipment during lightning activity was sensible and fortuitous. Without doubt, it avoided certain injury (and possible death) to the truck driver in this incident.

2.3 Recommendations

2.3.1 General • The exploded tyre, off position 3 of the haultruck should be scrapped. • The position 2 tyre, which did not fail but whose inner liner has suffered

partial pyrolysis, should be returned to service on a rear position and be closely monitored:

a) to determine whether it loses inflation pressure at an unacceptable rate (the main function of the inner liner is to prevent excessive permeation of the inflation air into the tyre’s carcass), and

b) for any indication of subsequent carcass separation. • Should there be any significant problem in either area, then the tyre should be

permanently removed from service. • All other tyres and rim components off the haultruck may be returned to

service.

2.3.2 Prevention • The mine site’s policy to monitor lightning activity and to park mining

equipment and remove operators to a safe area if lightning activity approaches the mine has proven, through this incident, to be a prudent procedure. We recommend that it be continued.

• Consideration should be given to parking trucks in an area (eg. close to the mine office) that could be readily monitored for lightning strike.

• Consideration should also be given to the installation of a system that renders an area safe from lightning strike, eg. Dynasphere System or similar, as is installed in the ROM pad area7 at another Australian operation (refer Appendix I).

• It would be very useful to have a system that could detect whether a unit of equipment (or a particular area of the minesite) has been struck by lightning – in the event, for example, of a parked and unoccupied haultruck being struck by lightning creating the danger of a tyre explosion at some time after the lightning strike8 (eg. after the driver has returned to the truck). Otraco understands9, however, that no such detection device is commercially available.

7 At that mine site, five terminals, each fitted to a 22 metre high pole, are installed at the ROM area providing a lightning safe zone of approximately 55 metres effective radius per terminal. Lightningman Pty Ltd (phone: +61-(0)8-9316 1902), who provided lightning related expertise for this investigation, can supply further details. 8 From Otraco’s records of lightning strikes and tyre explosions, this scenario appears to be unlikely because reports indicate that almost always (if not in all cases to date) tyre explosions have occurred simultaneously with or within seconds of the lightning strike, rather than several minutes to several hours later, as usually occurs with other heat/energy-initiated tyre explosions, such as those caused by power-line contact, truck or tyre fire, oxyacetylene heating of wheel components, etc. However the possibility of a delayed tyre explosion following a lightning strike cannot be ruled out. 9 As advised by Lightningman Pty Ltd.

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2.3.3 Emergency procedure

• Otraco has recently revised its recommended general emergency procedure guidelines covering incidents of Truck/Tyre Fire and Truck Electrification. A copy of the revised guideline is attached as Appendix III.

• In the event of a suspected truck electrification or tyre explosion, all relevant data, including photographs, should be collected immediately to assist in the incident investigation and to further the industry’s knowledge regarding tyre explosion mechanisms.

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3. TYRE EXPLOSION MECHANISMS

3.1 Difference between tyre blow-out and tyre explosion A tyre blow-out (also referred to as a tyre impact or tyre burst) is totally different from a tyre explosion. This difference is often not adequately understood in the mining industry.

3.1.1 Tyre blow-out A tyre blow-out results when the casing/carcass of the tyre cannot hold the inflation pressure (typically 100 psi to 150 psi for large haultruck radial tyres during operation) contained within the tyre. This usually occurs when the tyre casing is weakened due to an operational injury (eg. running over a rock) or due to a manufacturing defect. While a tyre blow-out usually occurs when a truck is in motion, it can, rarely, occur when the truck is stationary.

3.1.2 Tyre explosion A tyre explosion is a chemical explosion involving energy many orders of magnitude greater than that of a tyre blow-out. A shock wave creating pressures typically in excess of 1,000 psi is what causes the tyre to rupture in a tyre explosion. While a tyre explosion may occur when the truck is in motion or stationary, most explosions have occurred on stationary trucks.

3.1.2.1 Pyrolysis related tyre explosion The most common cause of tyre explosion involves pyrolysis of a section of rubber compound (usually the inner liner of the tyre that lines the tyre’s inflation chamber) due to a heat/energy source. The most common heat/energy sources arise from:

• equipment contact with high voltage overhead power-lines, • equipment or tyre fires, • application of heat to wheel components (eg. using an oxyacetylene torch to

loosen corroded wheel nuts), and • lightning strike.

Pyrolysis of rubber can produce flammable gases (eg. styrene and butadiene). An explosion will occur if the following conditions exist concurrently:

• there is an explosive concentration of flammable gases10, • there is an adequate concentration of oxygen to support combustion of these

gases, • there is an ignition source, and • there is sufficient molecular energy to sustain the explosive reaction.

If the other three conditions exist, then the flammable gases will explode if there is a hot-spot of sufficient temperature to auto-ignite the gas mixture. A flame or spark is not required if the hot-spot temperature exceeds the auto-ignition temperature of the gas mixture.

10 All ignitable gases/vapours have Lower Explosive Limit (LEL), also referred to as a Lower Flammable Limit (LFL) – although these terms are not equivalent in the strictest sense – below which the ratio of gas/vapour to oxygen is too low for combustion to occur (the lower explosive limit of styrene is 0.9% by volume). Most (but not all) ignitable gases/vapours also have an upper limit of concentration (UEL or UFL) beyond which ignition also will not occur. Above this concentration, the mixture is “too rich” to burn.

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3.1.2.2 Diffusion related tyre explosion Tyre explosions have also been known to occur without the involvement of pyrolysis of rubber in the tyre. This second process is called diffusion. At least one tyre explosion is known to have been caused by leaving a large amount of packing wood inside a haultruck tyre. Wood gives off methanol (wood-alcohol) in the tyre’s inflation chamber by a process of diffusion. The abrasion between the wood and tyre inner liner during operation of the tyre adds small particles of carbon and rubber to the methanol gas, which can increase the volatility of the mixture. Methanol vapour is 11% more dense than air so it will collect at the bottom of the tyre, increasing its concentration; the explosion vapour range of methanol vapour is 6% (LEL) to 36.5% (UEL) by volume. This mixture, under the pressure conditions of eight atmospheres (120 psi) inside the tyre’s inflation chamber, requires a temperature of less than 65 degrees Celsius (which is within the normal temperature range of the inflation chamber of the tyre during its normal operation) to auto-ignite.

3.2 Improved understanding of tyre explosion mechanisms Otraco has investigated, in detail, six previous incidents involving EM tyre explosions. However this investigation has been the first involving lightning strike. The results of this investigation have added considerably to our knowledge of the mechanics of tyre explosions – particularly in the case of lightning strike, which is among the four most common causes of EM tyre explosions (along with power-line contact, truck/tyre fire and the application of heat to rim or wheel components). Most tyre explosions involving the application of heat or energy, apart from lightning strike, occur several minutes to several hours after initial application of the energy, whereas there are documented cases of lightning strike initiated tyre explosions having occurred at the instant of the lightning strike. The large area of inner liner that suffered pyrolysis in the exploded tyre in this April 2004 incident, provides the probable reason for this. In most (non-lightning) events only a small area of inner liner (immediately adjacent to the heat source) undergoes pyrolysis; hence a significant period of time is required to build up an explosive concentration of flammable gas from this pyrolysis. In the case of lightning strike, enormous amounts of energy may be involved (typically millions of volts and thousands of amperes of electrical current11) which can cause instantaneous pyrolysis of a large portion of the inner liner of a tyre producing the required concentration of explosive gas and a simultaneous explosion. For a detailed explanation of the pyrolysis tyre explosion mechanism, we refer the reader to Otraco’s April 1990 report to Argyle Diamond Mines (ADM) concerning the explosion of a tyre on a 150T haultruck following contact of the truck with overhead power lines12.

11 The National Lightning Safety Institute (NLSI), an international organisation dedicated to providing lightning safety information to the public, notes that “lightning’s characteristics include current levels approaching 400 kA with the 50% average being about 25 kA, temperatures to 15,000 C, and voltages in the hundreds of millions”. 12 The ADM report is available from Otraco. General release of this report was authorised by Argyle Diamond Mines Pty Ltd in 1990 in the interests of safety and the dissemination of information relating to tyre explosions and their causes.

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Otraco’s September 2000 report to Corporacion Nacional del Cobre de Chile (Codelco) concerning the explosion of a tyre on a 240T haultruck details the diffusion tyre explosion mechanism13.

13 The Codelco report is not yet available for general release.

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4. INSPECTION OF TRUCK, SITE, TYRES & RIMS

4.1 Inspection of truck A Terex/Unit Rig MT4400 haultruck was found in the condition shown in photos 1 to 5, when an operator returned to the truck in April 2004 after a lightning storm. The position 3 (left outside rear) tyre had failed catastrophically – at that stage it was uncertain whether the tyre had blown-out or exploded14. Both wheel motor covers, on the position 3 (outside left) and position 6 (outside right) rear tyres had been blown out of their retaining clips and were lying on the ground beside the respective tyres.

Photo 1 – Haultruck immediately after the incident was discovered (note blown-off left wheel cover, blown-out headlights & piece of ruptured tyre in foreground)

There was severe damage to the truck. The hydraulic tank positioned vertically immediately in front of the left rear tyres had been badly deformed. The driver’s cabin was badly damaged, including the windscreen and rear windows having been deformed/blown-outwards. The walk-platform covering the engine had been deformed. The electrical cabinet on the walk-platform was deformed and the doors had been blown15 open. All of this damage appears to have been caused by the air/shock-blast from the ruptured tyre; there was no evidence of pieces of ruptured tyre (small pieces were spread about the site) having caused this damage through direct contact with the damaged truck parts.

14 A tyre explosion is totally different from a tyre blow-out (also termed an impact or a burst) – discussed in Section 3 of this report. 15 It is possible that this occurred due to a reduction in air pressure (as is often associated with explosions or similar catastrophic discharges) outside the electrical cabinet, rather than due to an increase in air pressure inside the cabinet. The same pressure differential scenario may have applied in relation to the driver’s cabin.

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As far as Otraco is aware, no obvious point of lightning strike to the truck was noticed at the time of discovery of the incident.

Photo 2 – Exploded position 3, left outside rear tyre (note torn mud-flap in foreground)

Photo 3 – Damaged hydraulic tank & blown-off left wheel cover (the right side wheel cover was also blown off)

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Photo 4 – Damaged driver’s cabin (note outwardly deformed windscreen & rear window)

Photo 5 – Buckled walk-platform (note blown-open doors on electrical cabinet) After the truck had been transferred to the haultruck workshop for repair, Terex personnel discovered heat damage to electrical wiring and faulty circuitry components. This damage was, according to the Terex personnel, consistent with an external source of electrification.

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The point or area of lightning contact to the truck was never identified16.

4.2 Inspection of site An inspection of the site of the incident produced large quantities of small pieces of inner liner that had been expelled from the rupture zone of the tyre. All of these inner liner particles had suffered heat decomposition. Otraco found some pieces of tyre 50 metres or so from where the tyre exploded. We were advised that particles had been found, immediately after the incident, up to 100 metres from the tyre.

4.3 Inspection of exploded tyre The exploded tyre, that was fitted to position 3 (left outside rear) of the haul truck was a Michelin 40.00R57 XDR (E4 rock lug tread pattern) Type B4 (standard tread compound) tubeless tyre17.

What was particularly interesting, following close examination of the inner liner of this tyre, was that while most of the inner liner exhibited signs of heat degradation, there was a distinct elliptical shaped section of inner liner that showed no sign of heat damage whatsoever. This elliptical section was approximately 2 metres long (in line with the centre tread of the tyre) and 1.2 metres wide (from one sidewall to the other). It was located in that section of the tyre that formed the “bottom” of the tyre at the time of the tyre’s explosion. Liquid sealant is used to minimise air loss and to reduce rim corrosion in all haultruck tyres on site (approximately 80 litres is used for a 40.00R57 tyre), and this sealant would have covered an elliptical section (of approximately the dimensions noted above) of inner liner at the bottom of the tyre. It appears that the sealant protected the area of inner liner that it was covering – in the stationary tyre prior to the explosion – from the heat degradation (pyrolysis) suffered by the rest of the inner liner of the tyre, as shown in figure 1. There was also a pre-existing separation in the tyre’s casing; this separation was not related to the explosion.

Pre-existing casing separation

Front of truck Figure 1 – Elliptical zone (yellow) of inner liner, at bottom of tyre, unaffected by heat degradation

16 As discussed in Section 5 of the report, this phenomenon is not unique to this incident. 17 Bridgestone tyres were fitted to the two front positions and Michelin tyres to the four rear positions.

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Photos 6 to 11 show the exploded tyre and sections of inner liner cut from it. Photo 6 shows the point of rupture at the site of the pre-existing casing separation.

Photo 6 – Position 3 (exploded) tyre: Exterior view showing point of rupture Photo 7 shows the view of this separation/rupture point from inside the tyre’s air chamber. The ruptured steel casing cords are visible.

Photo 7 – Position 3 tyre: Interior view showing point of rupture at the pre-existing casing separation

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Photo 8 shows the outline (marked with chalk) of the elliptical shaped area of inner liner that was at the base of the tyre (at the time of the tyre explosion) and hence protected from pyrolysis by the liquid sealant in the tyre.

Photo 8 – Position 3 tyre: Chalk line delineating elliptical zone of sealant protected inner liner (no pyrolysis) & zone of pyrolysis (outside the ellipse)

Photo 9 shows areas from which sections of inner liner were cut for more detailed examination.

Photo 9 – Position 3 tyre: Sections of inner liner removed at the pyrolysis/no pyrolysis interface

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Photo 10 shows two sections of inner liner – one cut from the zone of pyrolysis outside the elliptical zone protected by the sealant, and the other cut from the protected (non-pyrolysis zone) within the elliptically shaped area.

Photo 10 – Position 3 tyre: Inner liner from zones of pyrolysis (left) & non-pyrolysis (right) Photo 11 shows a single section of inner liner that covers the interface between the zones of pyrolysis and non-pyrolysis inside the tyre.

Photo 11 – Position 3 tyre: Inner liner showing areas of non-pyrolysis (left) & pyrolysis (right)

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The elliptical area of inner liner that had not undergone pyrolysis was intact; the ruptured area of the tyre was totally contained within the zone of pyrolysis.

4.4 Inspection of other tyres off truck Apart from inspecting the exploded position 3 tyre, the five other tyres were removed, stripped and inspected. Sections of the inner liner of the position 2 (right front) tyre had also suffered pyrolysis. The four remaining tyres showed no signs of pyrolysis, heat or other relevant damage.

4.4.1 Charring to liner of position 2 (right front) tyre The position 2 (right front) tyre had suffered partial pyrolysis of its inner liner; however it had not exploded18. This tyre was a Bridgestone 46/90R57 VRDPz (E4 rock lug tread pattern) E1A (standard tread compound) tubeless tyre.

Photos 12 and 13 show the inner liner of the position 2 tyre.

Photo 12 – Position 2 (partially pyrolised but unexploded) tyre: Inner liner showing finger marks through carbonised rubber residue

18 It is common in cases of truck electrification, through either lightning strike or contact with overhead powerlines, for a tyre or tyres to suffer some pyrolysis of the inner liner but not explode (even though one or more other tyres on the truck may have exploded). In the case of the unexploded tyres it is most probable that one or other of the conditions of an explosive concentration of gases or of an ignition source (eg. a hot spot of sufficient temperature) have not occurred concurrently.

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Photo 13 – Position 2 tyre: Inner liner close-up showing signs of pyrolysis

4.5 Inspection of wheel rims There was no significant damage to any of the haultruck’s six wheel rims.

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5. INVESTIGATION PROCESS

5.1 Initial investigation Otraco’s initial investigation, and that conducted by another party, suggested that the position 3 tyre had ruptured due to a blow-out rather than due to a tyre explosion. The main reason for this, despite the incident having occurred during a lightning storm and the considerable damage to the truck, was that the tyre had ruptured in the area of a significant pre-existing casing separation (approaching a metre in length). The condition of the inner liner of the tyre, which appeared burnt and powdery, was deemed to have been caused most probably from operational conditions (eg. heat from the braking system, etc).

5.2 Ongoing investigation However Otraco’s ongoing investigation uncovered evidence that conclusively points to a tyre explosion. The reason that the tyre had ruptured at the area of the pre-existing casing separation was because this was the weakest point of the tyre19, and hence the natural point of rupture. The following observations are relevant:

• The inner liner of the position 3 (exploded) tyre was burnt (had undergone pyrolysis) over its whole surface apart from an elliptical area, of approximately 2 metres by 1.2 metres centred circumferentially along the centre tread section of the tyre. The inner liner material within this elliptical shape exhibited normal inner liner physical appearance and texture. It was located precisely in the area of the tyre that comprised the tyre’s footprint at the time of the explosion20. The tyre had liquid sealant in it21, which was expelled from the tyre as it exploded and was splattered widely over the truck’s chassis and components. The sealant apparently protected this elliptical section of inner liner in the footprint area of the tyre from pyrolysis.

• Sections of the inner liner of the position 2 (right front) tyre had also undergone pyrolysis (although not to the same extent as for the exploded tyre); however the position 2 tyre had not exploded.

• The four other tyres on the truck appeared in a “normal” condition for operating tyres; their inner liners showed no sign of degradation, apart from what would normally be expected in an operating tyre.

• During repairs to the driver’s cabin, heat damaged wiring was discovered that was consistent with the truck having been electrified from an external source. There was also damage to circuitry in the truck’s electrical cabinet.

In every case, known to Otraco, of an earthmover tyre explosion following mining equipment electrification (whether by contact with high voltage overhead power-lines or through lightning strike) the exploded tyre has shown signs of pyrolysis of its inner

19 Where there is no pre-existing damage/weakness, a tyre explosion usually results in shoulder section rupture(s) – generally to both shoulders – directly opposite to (180 degrees in circumference from) the point of initiation of the explosion; i.e. the shock waves initiate from the ignition zone, travel in opposite directions around the circumference of the tyre’s inflation chamber, and meet opposite the ignition zone rupturing the shoulder areas of the tyre. 20 This was readily determined based on the known orientation of the tyre at the time of the incident. 21 The standard amount of sealant used in a 40.00R57 tyre is 80 litres.

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liner. In some cases only one tyre has exploded; in other cases more than one has exploded. It is common for unexploded tyres to show signs of inner liner pyrolysis; it is also common for some unexploded tyres to show pyrolysis while other unexploded tyres on the same truck show no signs of pyrolysis or any other indications of having high voltage/current earth via them. In cases investigated or recorded by Otraco of electrical current from an external source grounding to earth via an earthmover tyre, we have noted the following:

• The electric current usually passes over the surface of the tyre (whether this be the exterior surface, eg. the tyre’s sidewall; or the interior surface, i.e. the inner liner) rather than through and along the internal casing structure of the tyre – whether it be the steel-cord/rubber casing material of a radial tyre or the nylon-cord/rubber casing material of a bias ply tyre.

• In cases where the current passes over the surface of the inner liner it appears then to transverse the casing from the inner liner to the tread surface, and earth at the tyre’s contact zone on the ground.

• In these cases there is often a small earthing mark (sometimes as small as a centimetre in diameter or less) visible on the inner liner at the point where the current passed from the inner liner, through the thickness of the tyre’s casing and tread, to ground. However there is often no indicator mark on the tread of the tyre where the current exits to ground.

While the number of earthmover tyre related electrification cases examined by Otraco has been small in absolute terms, our observation that electrical current, particularly from lightning strikes, tends to earth via the surface of a material rather than through its internal structure appears to a commonly observed phenomenon in the case of materials that are generally regarded as being poor electrical conductors (such as tyres).

Lightning strikes may or may not cause noticeable damage at the point of contact with a vehicle. In the case of a lightning strike to a haultruck at another Australian mine site in January 2001, the point of strike (the position 6, right outside rear, wheel rim) was evidenced solely by a burn mark that could be wiped away by hand, leaving no permanent visible damage. We found no clear evidence of the point/area of the lightning strike to the haultruck in this April 2004 incident; however, given that there was considerable rainfall at the time of the incident, any evidence could have been obliterated, consistent with the January 2001 case referred to above (and other documented lightning strike incidents worldwide).

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Appendix I

Appendix I – Dynasphere Lightning Protection System The Dynasphere Lightning Protection system is installed on the ROM pad of at least one Australian mine. The system on that site comprises five air-terminals, each installed on a 22 metre high freestanding pole (refer photo 14). The overall protection zone afforded by the five air-terminals is shown in figure 2.

s

Photo 14 – Two

Figure 2 – Lightn

Two of the five air-terminal pole

of the five Dynasphere Air-Terminal poles used at an Australian mine site

ing protection zone (within red circles) afforded by the five air-terminals

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Appendix I

Thunderstorms are an almost daily event during summer at this mine site, and the Dynasphere system protects most of the ROM pad against lightning strike (the ROM pad is elevated and hence particularly exposed).

This allows ROM operations to continue safely during lightning storms. Alternatively, equipment operators can park within the protected zone of the ROM pad if it is thought to be too dangerous to leave this area.

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Appendix II

Appendix II – EM Tyre explosion incidents database This list of EM tyre explosions is by no means comprehensive. Numerous other EM tire explosions have almost certainly occurred. The list represents incidents for which Otraco has received confirmation of at least some of the factors responsible for the explosion and of the consequences of the explosion.

Cleveland Mine, Tasmania, Australia

Year: 1981 Tire: Michelin 26.5R25 radial tire Position: not applicable (wheel not attached to truck) Truck: Wigtruck underground haultruck Source: Oxy-acetylene heat applied to rim

Events The tire exploded approximately 10 minutes after heat was applied to frozen wheel nuts using an oxyacetylene torch. The fitter applying heat was killed instantaneously; another was seriously injured.

Otraco conducted an investigation at the request of the mine. It was established that heat being applied to the wheel nuts was transmitted via the rim to the bead of the tire causing pyrolysis of a section of the tire's liner near the bead. The released gases exploded a short time later (estimated at around 10 minutes after heating started).

The tire was ruptured circumferentially around a 90° arc on one shoulder just below the line of the breaker belts. The rupture occurred diametrically opposite the zone of pyrolized liner.

Subsequent chemical analysis of the liner rubber established that pyrolysis commences at about 250°C releasing an explosive mixture of styrene and butadiene vapours which auto-ignites at approximately 430°C. Only 20gm of liner material would have needed to pyrolyze to yield an explosion pressure equal to the burst pressure of the tire (350psi).

Intercor Mine, Colombia, South America

Year: 1986 Tire: 36.00x51 Position: Not known Truck: Wabco 170C Source: A wheel fire initiated by a brake problem

Events The tire fire was initiated by a brake problem. The truck was driven into the maintenance area with the wheel on fire and was allowed to continue burning for 20 to 30 minutes before extinguishment. The outside of the tire was reported to be cool enough to touch when the tire exploded some 30 to 35 minutes after the fire had been extinguished.

Three people were killed.

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Appendix II

Drayton Mine, NSW, Australia

Year: 1986 Tire: Michelin 33.00R51 radial tire Position: 1, Left front Truck: Komatsu HD1200M haultruck Source: Contact with 33kv overhead power lines

Events The tire exploded approximately 10 minutes after the truck contacted a 33kv overhead power line. The truck had tipped its load under a 33kv power line touching the line. The truck earthed via the left front tire, starting a grass fire. The driver, who was unaware that his truck had contacted the line, drove back to the loading point two kilometres away. As he applied his brakes at the loading area, the tire exploded.

The explosion tore off the truck's access ladder and air cleaner, throwing these items 175-200 metres. The truck cabin door was bulged and the windows blown out. The driver was not hurt.

The tire was ruptured in a similar manner to the Tasmanian tire, except that it burst on both shoulders. The rupture occurred through about 90° of arc opposite the area in the crown of the liner where pyrolysis had occurred.

Otraco postulated that electrical earthing occurred through the rim across to the steel bead, via the steel body cords to the crown area corresponding with the ground contact patch, and then through the tread rubber to earth. Michelin, at the 1987 Tire Fire and Explosion Seminar conducted by Otraco, WA Mines Department and Mt Newman Mining, suggested that the current path was probably from the rim through the tire liner and then through the casing and tread to earth.

Kalgoorlie, WA, Australia Year: 1987 Tire: 37.25x35 Position: Not known Equip: Cat 637 scraper Source: A tire fire caused by diesel spillage

Events The tire exploded after a diesel spillage caught fire. A man who attempted to put the fire out was injured.

Ipswich, Qld, Australia Year: 1987 Tire: 27.00R49 radial tire Position: Not known Truck: Cat 777 haultruck Source: Lightning strike

Events The tire exploded after lightning struck the truck.

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Appendix II

Leigh Creek Mine, SA, Australia

Year: 1987 Tire: Bridgestone 36.00-51 bias ply tire Position: 4, Left inside rear Truck: Terex 33-11 haultruck Source: Not established (possibly internal heating due to tire separation)

Events The tire exploded after the truck had been parked up for 3.25 hours. The truck had worked the previous shift.

Within 10 minutes of the tire exploding, it caught fire. The fire could not be extinguished and the truck was completely gutted. The remaining tires burnt out but did not explode. Tire fragments were thrown distances of up to 200 metres. No one was injured.

After the examination of numerous possible causes, ETSA (the mine operator) concluded that carbon dust on the tire's liner may have undergone slow combustion due to a combination of high ambient temperature and localised heating at the site of a cut or ply separation. The combination of rubber pyrolysis and sufficient heat led to the explosion.

Newman Mine, WA, Australia Year: 1987 Tire: Bridgestone 36.00-51 bias ply tire Position: 3, Left outside rear Truck: Dresser (Wabco) 190T haultruck Source: Apparent misuse of service brake combined with broken park brake line

Events The tire exploded after catching fire due to a dragging brake. The fire was fuelled by escaping hydraulic oil. The left wheel motor caught fire. The driver stopped and evacuated the truck but did not shut it down. The fire quickly spread to the left front and left outside rear tires. The left outside rear tire subsequently exploded.

The force of the explosion blew the outer flange off the rim. Tire fragments were hurled distances of up to 100 metres. The exploded tire was largely destroyed by fire. No one was injured in the explosion.

Bougainville Mine, Papua New Guinea Year: Several incidents involving tyre explosions occurred pre-1989 Tires: 36.00x51s Position: Various Truck: Euclid R170 haultrucks Source: At least one incident involved a tyre fire resulting in a tyre explosion

Events There were several tyre explosions on Euclid R170 haultrucks, one of which resulted in a fatality. In at least one case the truck tyres had been inflated with nitrogen (it is probable that either air had been inadequately flushed from the tyre during inflation with the nitrogen, or air was subsequently added to the tyre – such

23

Appendix II

that the oxygen concentration was greater than the 5.5% by volume limit necessary to support combustion or an explosion).

Pine Creek Mine, NT, Australia Year: 1989 Tire: 24.00R35 radial tire Position: 1, Left front Truck: Cat 773 haultruck Source: Lightning strike

Events According to eyewitnesses, the tire exploded at the same instant that the truck was struck by lightning. The tire was reportedly propelled 45 metres from the truck. The bead seat band was thrown 40 metres hitting a Bobcat loader causing sufficient damage to the loader that it was subsequently scrapped. The lock ring was thrown 70 metres imbedding itself in the wall of a transportable hut.

A section of liner, reportedly 90° from the area where the tire ruptured, was pyrolyzed. The bead bundle of the exploded tire was completely severed at the point of rupture. There was no visible damage to the tread of the tire, however the undertread belts were subsequently found to be separated for 60% of the tires circumference.

Inspection showed that two other tires, the right front and the right outside rear, had also suffered pyrolysis of the inner liner.

Argyle Mine, WA, Australia (refer photo 15) Year: 1989 Tire: Michelin 33.00R51 radial tire Position: 1, Left front Truck: Cat 785 haultruck Source: Contact with 33kv overhead power lines

Events The haultruck was carting material from the mine area to a rehabilitation area. While pulling away from the tip point with its body up, the truck contacted 33kv overhead power lines. The driver braked to a stop and was advised to remain in the cabin because the truck was still in contact with the power lines. The position 1 (front left) tyre exploded approximately 12 minutes after initial contact with the power lines. The tyre was projected off its rim and through a steel mesh fence bordering the road. It landed 7 metres from the truck. Rim components (lock ring, bead seat band and outer flange) were hurled distances of up to 40 metres from the truck. A section of tyre weighing several kilograms was thrown over 100 metres hitting a transportable hut. The truck was considerably damaged by the explosion.

The truck driver, who was sitting in the truck cabin at the time of the explosion, was cut by broken glass. Fortunately, the air blast from the explosion was directly mainly in a sideways direction out from the tyre and not in an upwards direction towards the driver’s cabin. Three observers were shaken by the explosion.

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Appendix II

Mt Pleasant Mine, WA, Australia

Year: 1990 Tire: Bridgestone 24.00R49 radial tire Position: 5, Right inside rear Truck: Not known Source: Contact with 33kv overhead power lines

Events The tire exploded 8 minutes after the truck had contacted 33kv overhead power lines.

The tire was severely damaged by the explosion rendering little evidence of the precise failure mechanism, viz. arcing or pyrolysis. However the two tires on the left rear showed signs of arcing – a hole on the liner, but neither pyrolysis of the liner nor any visible evidence of arcing of the external tread.

Nottingham, England Year: 1990 Tire: Not known Position: Not known Equip: Not known, thought to be a front end loader Source: Oxy-acetylene heat applied to wheel brakes

Events The tire exploded while workmen were using oxy-acetylene cutting equipment on the brakes of the machine in an engineering factory. The blast tore the roof off a nearby building.

Two men were killed instantaneously; a third died shortly afterwards. Other workers further away were hurled to the ground but escaped serious injury.

Candelaria Mine, Chile, South America Year: 1999 Tire: Bridgestone 37.00R57 radial tire Position: 3, Left outside rear Equip: Dresser 685 haultruck Source: Thought to result from an internal separation of the tire

Events The tire exploded rupturing both shoulders of the tire. The tire caught fire after the explosion. No major damage was reported to either the haultruck or the wheel rim.

The tire had been checked half an hour before the explosion. Both this tire and its mate had been found to be seriously under-inflated; both had been reinflated to the correct operating pressure before the explosion.

No injuries were reported to either the driver or any persons within the immediate area.

Alumbrera Mine, Argentina, South America

Year: 1999 Tire: 40.00R57 radial tire Position: Not known

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Appendix II

Equip: Cat 793 haultruck Source: Contact with overhead powerlines

Events Tire exploded after the truck contacted overhead powerlines. No-one is believed to have been injured.

Radomiro Tomic Mine, Chile, South America (refer photo 16) Year: 2000 Tire: Bridgestone 40.00R57 radial tire Position: 1, Left front Equip: Cat 793 haultruck Source: Packing wood left in tyre

Events The position 1 (left front) tyre exploded as the truck was braking at a waste dump. The air-blast from the explosion crushed the driver’s cabin, killing the driver.

Freeport Mine, Irian Jaya, Indonesia (refer photo 17) Year: 2002 Tire: Bridgestone 50/90R57 radial tire Position: 5, Right inside rear and Position 6, Right outside rear Equip: Komatsu 930E-I haultruck Source: Contact with high voltage overhead power lines

Events The truck was dumping underneath high voltage power lines when the truck body contacted the power lines. The right rear tyres exploded consecutively approximately one minute after contact with the power lines; tyre sections were expelled up to 20 metres from the truck. The front right tyre caught fire.

The truck driver, hearing the explosions, evacuated his truck immediately and was not injured.

Peak Downs Mine, QLD, Australia (refer photo 18) Year: 2003 Tire: Bridgestone 37.00R57 radial tire Position: 1, Left front Equip: Cat 789 haultruck Source: Failed wheel hub resulting in truck fire

Events The truck caught fire following a position 5 (right inside rear) hub failure causing the position 5 wheel to become loose. The wheel rubbed on the chassis and other brackets causing heat. The wheel severed the brake cooling line bringing oil in contact with hot surfaces causing ignition. The operator felt a vibration. When he pulled up he noticed flames. He operated the fire suppression and exited the truck. The emergency squad attended the scene. During the fire, the position one tyre exploded, blowing the hub off. The wheel hub flew a considerable distance landing on a lower bench. No one was injured.

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Appendix II

Yandicoogina Mine, WA, Australia (refer photo 19)

Year: 2003 Tire: 33.00R51 radial tire Position: 1, Left front and Position 2 Right front Equip: Cat 785 haultruck Source: Burst diesel fuel line

Events A diesel fuel line apparently burst spraying fuel onto a turbo-charger causing a truck fire that then spread to the tyres, resulting in both front tyres exploding. The explosions caused serious damage – the position 1 tyre explosion caused the driver side ladder to be blown back up the front of the truck and the position 2 tyre explosion blew this wheel assembly completely off the truck, landing a considerable distance away. The truck was subsequently burnt to the ground.

No one was injured.

Australian Mine (refer photo 20) Year: 2004 Tire: Michelin 40.00R57 radial tire Position: 3, Left outside rear Equip: Terex/Unit Rig MT4400 haultruck Source: Lightning strike

Events The haultruck was parked due to an impending lightning storm. When an operator returned to the truck three hours later, the position 3 tyre was discovered to have exploded causing severe damage to the truck.

No one was injured.

Other incidents There have been reports of EM tyre explosions in Zambia and Canada although little information is available regarding these incidents. There have almost certainly been EM tyre explosions in other countries with a significant mining industry (notably the USA) however no specific incidents have come to Otraco’s notice. Lack of safety awareness In some of the cases documented above, people have attempted to fight truck or tyre fires using portable extinguishers or have inspected trucks immediately following contact with overhead power lines – totally unaware of the potential for a delayed tyre explosion. The two worst incidents (each involving three fatalities) followed:

a) In one case, deliberate application of heat to wheel brakes while a tyre was still fitted to the wheel. Note that deflating the tyre, prior to applying heat to the wheel, would not have avoided the tyre explosion.

b) In the other case, people standing around a tyre that had been extinguished and which subsequently exploded some 35 minutes after extinguishment of the tyre fire.

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Appendix II

Photo 15 – Argyle Mine 1989

Photo 16 – Radomiro Tomic Mine 2000

Photo 17 – Freeport Mine 2002

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Appendix II

Photo 18 – Peak Downs Mine 2003

Photo 19 – Yandicoogina Mine 2003

Photo 20 – Australian Mine 2004

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Appendix III

Appendix III – Recommended Emergency Procedure Guidelines

Introduction Haultruck tyre fires and explosions are becoming more common worldwide – probably due to a general industry push for increased productivity and the growing population of bigger trucks and tyres (tyres tend to approach their operating limit more quickly in large truck applications). Certainly bigger tyres create the potential for larger, more dangerous explosions. The industry standard haultruck electrification and tyre fire emergency procedure, upon which many site specific procedures are based, was developed by Otraco in the late 1980s. Major changes are required to it to take account of the industry’s updated knowledge of tyre explosions; these changes have been included in the revised emergency procedure shown over-page. Procedures in place on some minesites, and pressure relief valve products currently being marketed, demonstrate a dangerous lack of understanding of tyre explosion mechanisms (eg. deflating a tyre does not remove the risk of explosion). This, together with experience of typical operator reactions to haultruck electrifications and truck or tyre fires, and the lessons learnt from a recent fatality, has prompted Otraco’s review of the procedure. There is no point in having a procedure that does not take account of human nature and what actually happens on most minesites. It is also important to incorporate improved understanding and knowledge gained from the plethora of tyre explosion incidents, many that have resulted in fatalities, over the past few years. For example, if the driver of an affected truck can evacuate his or her truck quickly (generally within five minutes of the initiating incident occurring, eg. contact with overhead power lines) he or she is likely to be able to have cleared the hazard area before a tyre explosion occurs. The longer a driver stays on the truck, the greater the risk of being injured. The following procedure should be taken as a guideline only in formulating the specific emergency procedure for any minesite. A risk analysis should be conducted for the particular minesite and a specific procedure should be produced for the minesite in light of that risk analysis. It is equally important that everyone working on the minesite is inducted in the procedure, and that regular refresher courses and training exercises are conducted.

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Appendix III

January 23, 2004

Recommended Guidelines for

Truck Electrification and Tyre Fire Emergency Procedure 1. Warning A tyre can explode at any moment after the application of heat to the tyre or rim, eg. through truck electrification or tyre fire. Deflating a tyre, including the use of a pressure relief-valve device, does not remove the risk of a tyre explosion. 2. Truck Driver Upon becoming aware of truck electrification (eg. from lightning, power lines etc.) or a tyre fire, the driver should:

a. Advise Mine Control, for example: • State "Emergency; Emergency; Emergency", • Identify yourself with your call sign and name, and state your

location, • State the nature of emergency (eg. tray in contact with power

line).

b. Park the truck quickly, if possible in an area where it has the least exposure to manned facilities or passing traffic, so that:

• The truck is clear of any power lines with which it came into contact,

• There is an evacuation path in front of the truck, • If possible, a water truck will have easy access to any wheel

affected by fire.

c. Shut down the truck.

d. If there is a fire, activate the fire suppression system (if one is fitted).

e. Evacuate the truck as follows: • Exit the cabin, preferably via the passenger seat door. • Get off the truck via an emergency evacuation system22 if one is

fitted; otherwise via a standard access-way (furthest from any point of truck or tyre fire).

• Once on the ground move quickly away from the truck in a direction coincident with the longitudinal axis of the truck (ie. moving in the direction that the truck is facing). Move to a point at least 200 metres from the truck.

22 Eg. an emergency ladder or stairs, or an electrically insulated slide, fitted to the front centre of the truck. In the case of a ladder or stairs, the driver should jump, from a platform at the bottom of these, to the ground so that he or she is not simultaneously in contact with truck and ground – to avoid possible electrocution.

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Appendix III

• Do not attempt to extinguish a tyre fire with a portable

extinguisher. • At all times avoid contact with any power line lying or hanging

over the truck or ground.

3. Mine Control Upon notification of truck electrification or a tyre fire, Mine Control should contact the Controlling Supervisor apprising him or her of the situation. 4. Controlling Supervisor The Supervisor should:

a. Notify the Emergency Services Officer of the situation.

b. Inform the Tyre Shop Supervisor of the situation.

c. Establish adequate road blocks for the area at a minimum distance of 200 metres from the park up location.

d. Dispatch a water truck to the road block and assume control of fire

fighting and/or cool down operations (if necessary).

e. Obtain specific particulars from the truck driver in regard to time frames, strength of flames, heat, sparks and the amount of smoke from the tyres, etc.

5. Water Truck Driver The Water Truck Driver should, on notification from the Controlling Supervisor:

a. Provide a water service as requested by the Controlling Supervisor.

b. If directed, reverse the water truck in, onto the affected wheel – at all times shielding the water truck driver’s cabin with the body of the water truck.

• Under no circumstance should the water truck driver proceed anywhere near the affected unit until he/she has received authorisation from the Controlling Supervisor.

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otraco (international) pty ltd · report on lightning strike / tyre explosion 2.3.3 emergency...

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