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15 Jun 2017

By Dr Clive Fraser

Most car owners will not hesitate to option up their vehicle with fancy alloy wheels.

After all they are shiny and will lift the appearance of even the most ordinary sedan.

We used to call them “Mags” because that’s what they were originally made from.

“Mags” was a term that was simply short for magnesium, the 12th element in the Periodic Table.

In England in 1618 an Epsom farmer noticed that his cows wouldn’t drink from a well because of the water’s bitter taste.

The contamination was from hydrated magnesium sulphate which we now call Epsom Salts.

Doctors know that ingesting 300-400mg a day of magnesium from nuts, whole grains and leafy green vegetables will keep those essential enzyme systems running.

And whilst the average adult body contains 25 grams of magnesium, the average car contains much more.

With a melting point of 650°C it’s worth remembering that magnesium is also highly flammable with flame temperatures reaching 3,100°C.

Burning magnesium also reacts with nitrogen, carbon dioxide and water so don’t try to use these to put the fire out as they will only intensify the combustion.

Stronger and 75 per cent lighter than steel magnesium was perfectly suited to the manufacture of automobiles.

Because of its light weight from the 1930’s onwards magnesium was used in the fabrication of wheel rims.

But corrosion could let air leak through the rims and that flammability issue did cause problems when cars crashed.

A fire from a ruptured fuel tank could easily ignite the magnesium wheels and there really was no practical way of putting the fire out.

The most catastrophic example of this occurred at the 1955 Le Mans 24 hour endurance race.

A crash involving an Austin-Healey and a Mercedes 300SLR made mostly of Elektron (90 per cent magnesium) resulted in at least 84 fatalities.

The exact number of casualties is unknown, but may have been as high as 130 due to the catastrophic damage at the scene.

The body and wheels of the Mercedes burnt for hours and attempts by officials to douse the blaze with water only made the fire worse.

Having come from a family of firefighters I can remember my father’s stories of attending VW Beetle engine fires.

The air-cooled engine compartment was very prone to over-heating which damaged rubber fuel lines which in turn would leak and catch fire.

As the VW Beetle engine was made of magnesium alloys the resulting engine-bay fires were spectacular.

Fast forward to today and modern magnesium alloy wheels don’t have exactly the same flammability issues of their predecessors.

But the next time someone tells me that my wheels look “hot”, I’ll check their temperature before accepting the comment as a compliment.

BCF (bromochlorodifluoromethane) anyone?

Safe motoring,
Doctor Clive Fraser

Published: 15 Jun 2017