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Controlling the risk of tyre explosions on a mine site

February 2004

Ian CampbellOperations Support Manager

Tel: 61 (0)8 9473 7500Email: ian.campbell@otraco.com

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Session Outline

What is a tyre explosion?

Causes of tyre explosions.

Tyre explosion mechanisms.

Controlling tyre explosion hazards.

Emergency procedures.

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What is a tyre explosion?

It is the explosive force as a result of the ignition,

of an explosive gas mixture,

inside the air chamber of a tyre.

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Tyre Explosions vs Tyre Bursts

An explosion is due to a chemical reaction which can generates pressures ten times the tyre inflation pressure.

A burst is the release of the inflation pressure due to a structural failure of the casing.

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Tyre Explosions vs Tyre Bursts

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Tyre Explosions vs Tyre Bursts

Burst Explosion

Release of tyre inflation pressure.

Chemical reaction of explosive gas.

Resultant Pressure release

100 - 150 Psi.

Resultant Pressure generated> 1,000 Psi.

Caused by casing rupture due to cuts, penetrations impacts and separations.

Generally caused by heat from an external high energy

source.

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Tyre Explosion

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Tyre Explosion

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Tyre Explosion

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Tyre Explosion

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Tyre Explosion

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16 recorded incidents with EM tyres since 1981.

8 fatalities.

Earthmover Tyre Explosion Incidents

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Typical Causes of Tyre Explosions

Electrification of the vehicle by: Lightning strike, Contact with power lines.

Application of heat from: Welding on the rim, Tyre / vehicle fire.

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Tyre explosion mechanisms

Two Explosion Initiation Processes:

Heat (most common),

Diffusion (extremely rare).

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Heat Initiated Explosions

Heat transmitted to inner liner.

Pyrolysis of inner liner (250oC). This is the decomposition of the

rubber which releases combustible gases.

Concentration of gases (1-8% vol.).

Auto-ignition (430oC).

Note: above temperatures are at atmospheric pressure

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Electrical Arcing / Pyrolysis

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Diffusion Initiated Explosions

Wood in tyre air chamber.

Diffusion of methanol from wood (65oC). 11% denser than air.

Generation of solid combustibles. Mixture of carbon dust with gas.

Concentration of methanol (4% by volume).

Auto-ignition (<65oC).

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Diffusion Initiated Explosions

- Mixture of explosive gases of correct concentration- Initiation point

- Two shock waves/flame fronts

- Typical rupture of tyre (usually both sides)

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Wood Delivered in Tyres

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Controlling tyre explosion hazardsMisconception No.1

Deflating the tyre will prevent an explosion.

THIS IS NOT TRUE

Pressure is not required in the pyrolysis process.

A diffuser (fuse plug) fitted to the rim will therefore not prevent an explosion.

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Controlling tyre explosion hazardsMisconception No.2

Removing the energy source will immediately remove the risk of an explosion.

THIS IS NOT TRUE

Rubber is a very poor conductor of heat and unseen “hot spots” will remain (and pyrolysis continue) long after removal of the external heat source.

An explosion can occur almost immediately, minutes or even hours after the incident.

(10 to 15 minutes is typical for power line contact)

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Controlling tyre explosion hazardsMisconception No.3

There is no risk of an explosion if the tyre is inflated with nitrogen.

TECHNICALLY THIS IS TRUE BUT PROPER IMPLEMENTATION CAN BE DIFFICULT.

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Controlling tyre explosion hazards

Nitrogen inflated tyres have exploded. This is because only a small amount of oxygen is

required (5.5% by volume). Air is often required to seat the beads (because of

the volume required) and may have to be purged by double inflating.

Air can enter from “topping” up inflation pressure in the field.

Use of nitrogen can give a FALSE sense of security. Other hazards related to handling and storage of

nitrogen are introduced.

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Prevention

Never heat or weld rims or wheel with mounted tyre, whether inflated or not.

Use non-flammable tyre lubricants & sealants.

Remove all foreign objects from tyres (wood).

Avoid working near power lines.

Minimise the risk of a tyre fire by: Proper braking procedures. Isolate/change smoking tyres.

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Elimination / substitution controls

Keep power lines and haul road / dump areas separated from each other.

Nitrogen inflation.

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Engineering controls

Emergency escape route from truck.

Controllable nozzles fitted to rear of water trucks.

Fire suppression system.

Tyre temperature monitoring system.

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Administrative controls

Document emergency procedures for: Truck fires, Truck electrification.

Establish the best escape route for each truck type.

Training for: Truck operators, Controllers, Emergency services.

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Emergency proceduresDriver

Inform Control. Park up truck. Shut down. Activate fire suppression system (for fire). Evacuate truck via emergency evacuation route. For electrification do not allow body to be in contact

with the vehicle and ground at the same time. (i.e. jump from the last step / rung.)

Move away from truck in the direction that the truck is facing.

Do not attempt to fight fire with a hand extinguisher.

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Evacuation Path for Driver

Danger Zone(200)

Danger Zone(200 m)

Evacuation Path

(200 m)

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Emergency procedures

Controller Notify emergency services. Inform tyre shop supervisor. Dispatch a water truck for possible fire fighting

duties. Back up water truck to fight fire. (Ensure tank is

between tyre and driver at all times.) Do not attempt to fight the fire with a hand

extinguisher. Cordon off a 200m area around truck. Isolate truck for 24 hrs after incident. Remove and inspect all tyres after incident.

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Thank You