On Tyre Bursts

Preamble:
In the 12th March article, if not most, some of you may have read about the interesting facts behind AirCraft Tyres. We even invited Readers to answer at the end, as to what makes an ACT burst at take-off, as distinctly different than a more probable one during landing. However, there was hardly any response – barring one and that too not entirely correct.

So yours truly again e-picked the brains of his TyreGuru – Mr. Sudershan Gusain – and this is how he enlightened me…

Tyre burst or explosion, two different things tho’, is an interesting topic and internationally, very few studies have been made in this direction. Here are some general explanations about them and they apply equally to automotive as well as ACTs:

A tyre burst/explosion is not so common a phenomenon but:
• It is difficult to detect before it happens.
• It may have multiple causes.
• It can have tragic consequences.

Some figures from Canada indicate that tyre explosions account for 1% of all accidents leading to deaths over there.

Before we proceed further, we should distinguish a BURST from an EXPLOSION:

BURST
A Tyre Burst can be defined as due to ‘mechanical deterioration’ of tyre material, thus weakening its ‘structure’, resulting in a sudden and violent release of the air.

The causes of a tyre burst can be classified into 2 categories:

MECHANICAL CAUSES
• Excessive tyre inflation.
• Improper bead seating on the Rim.
• Structural fatigue of the casing.

CHEMICAL CAUSES
HEAT is the main cause that can lead to a burst of chemical origin. Various chemical reactions can happen when heat inside the tyre builds up. Thermal decomposition of rubber then occurs and it chemically breaks the tyre material into its original components viz oil, gas and char.

EXPLOSION
Explosion is a sudden expansion of a gas under pressure. Flammable gases with relatively low self-ignition temperatures can get formed inside a tyre due to heat and/or decomposition of tyre material due to many other causes. And when the internal temperature of a tyre becomes higher than the self-ignition temperature of such gases, an ‘explosion’ can occur. However, for it to happen, the following conditions are to be met:
• Concentration of enough inflammable gas.
• Inside tyre temperature higher than the self-ignition temperature of the gases formed within.
• Oxygen concentration inside the tyre higher than 5.5%.

A chemical explosion of such a nature is much more violent than a burst, as it occurs at much higher pressures - usually ~ 500psi or more.

For a tyre explosion to occur, a high degree of heat is required. The causes of such high heat generation are due to following possibilities:

The most common cause is ‘wheel welding’. Rubber will start to decompose around 250°C. With the increase in internal temperature, the mix of oxygen and flammable gas auto-ignites at around 450°C and an Explosion can occur.

Use of a welding torch to release bolt/nut.

Use of petroleum lubricant or solvent during tyre mounting.

Brakes’ overheat.

Electric discharge either from a high voltage line or lightning.

Fire in ambience.

Severe under inflation or overloading.

Presence of contaminants inside the tyre.

Oil or other combustible fluid ‘absorbed’ by the tire.

If we now go back to the original question i.e. Tyre burst or explosion during take-off, one can probably understand that we should first determine whether it is a burst or an explosion. They key causes in case of an aircraft would be:

These are also the reasons why ‘Nitrogen’ inflation as well as disc brakes is mandatory on Aircrafts.