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RAC issues warning over exploding petrol tank reports

Published 27 June 2018

The RAC is warning drivers about fake emails and social media posts that falsely link cars to a recent spate of fires that only occur in hot weather and heatwaves.

The reports circulating online claim that filling up a car to the brim with petrol in high temperatures will increase the risk of a fuel tank explosion; however, the RAC has dismissed these claims as a social media hoax.

>>>Top 10: The most-common MoT failure points

All fuel systems on modern cars are designed to cope with any expansion of fuel, or vapour coming from the fuel and there is no chance of a fire being caused. 

“There is no risk of explosion from filling up a fuel tank fully and drivers should have no concerns in doing so"

“There is no risk of explosion from filling up a fuel tank fully and drivers should have no concerns in doing so,” said RAC spokesperson Rod Dennis, “we’d recommend people avoid the temptation to share misinformation like this via social media.”

The false reports claim that there were five cases of fire in June due to cars being refuelled to the brim. The fake news is, more often than not, linked to a video of a car on fire as proof. However, technical experts at the RAC has rubbished the reports and said the videos are unrelated to the emails and social media posts in question.

>>>Top tips for getting your car through the MoT

While the hot weather won’t cause petrol tanks to explode, it can lead to problems for drivers who neglect their car’s general maintenance, with both the engine coolant and oil being worked harder in the summer months. Extreme temperatures can also increase the risk of blow-outs for tyres that are in a poor condition or under-inflated.

In 2017, 385,000 three-year-old cars failed their first MoT, with the vast majority of problems being linked to poor maintenance, with unsafe brakes, lights and tyres.

Comments

Watkins247    on 2 July 2018

Wouldn't it be less likely to explode if brimmed as less space for fuel vapour to form and also air(oxygen) will be excluded from the tank.

Craig Ponting    on 2 July 2018

Correct... Full tanks less likely to cause problems... Ask any fuel tanker driver and he will say the same

Gary Malins    on 2 July 2018

It seems that many people are only too keen to share scare stories without looking at them properly, the version of this story which I've seen comes from Islamabad!

DrTeeth    on 2 July 2018

Incorrect! There is not a maximum or minimum level of oxygen or fuel vapour that will increase the chance of an explosion.The concentration of oxygen is what counts rather than its absolute quantity.

One can argue, that as lliquids are not generally compressable, that a full tank is more likely to explode than an empty one.

The concentration of vapour above a liquid is always constant, as long as even a little bit of the liquid remains.

Essexman    on 2 July 2018

I'm reminded of the Jeremy Clarkson demonstration of shooting through both a car petrol tank and a Jerry Can of petrol- nothing except a very small leak.

Too many people get their facts from Movies - but a growing number rely on Social Media - Hooray!

dombat    on 2 July 2018

Our so called heat wave is nothing compared to many countries, it's just warm like Spain or Greece. Do cars explode all the time in death valley or around the equator? No.

StephenWestSussex    on 2 July 2018

Not explosions but leaks - I had two instances last year of petrol pouring onto the road from my Skoda Superb, and pressurised fuel gushing out when I eased the cap. Another owner had a similar problem and we believe it was narrowed down to an 'AHK' valve. Lot of (warranty) work to resolve it. I had to call the Fire brigade second time because of danger of explosion with the amount of fuel. So it may have been 'fake news', but the complexity of modern cars does sometimes lead to undesirable outcomes.

Edited by Stephen Hales on 02/07/2018 at 15:49

lesatwa5    on 2 July 2018

With regard to Dr Teeth's post explaining the flammabilty of vapours in air, here is my offering:

Flammable vapours have an "explosive range", defined by the upper and lower explosive limits:

The lower explosive limit (LEL) is the lowest concentration of gas or vapour which will burn or explode if ignited.

The upper explosive limit (UEL) is the highest concentration of gas or vapour which will burn or explode if ignited.

So,between the LEL and the UEL, there is a window of concentration where the mixture is explosive. Below the LEL, the mixture is too lean to burn. Above the UEL, the mixture is too rich to burn.

It is also important to emphasise that it is not enough just to be in the explosive range for an explosion to occur- there must also be a source of ignition present.

As far as the relative compressibility of vapours and liquids are concerned it is true that, unlike gases or vapours, liquids are relatively incompressible. However, in industries where pressure vessels are used, and are certified to a particular pressure specification, they are generally tested against that specification by pressurising the system with water. If the vessel fails during such testing, then the water will be released from the failure point – but this is not an “explosive” event.

If the vessel were to be tested using say, air instead of water, and similarly failed, the stored energy release from the compressed gas would be very significant, and very hazardous. This would be an “explosive event”.

Given the above, if a tank completely full of petrol is subjected to excessive heat flux (and the tank is not freely-venting) then the expanding liquid could cause the tank to fail. This in itself would not be an “explosive” event.

The concentration of vapour above a liquid is a function of the vapour pressure expressed by that liquid, and this is a function of the temperature of the liquid.

Generally speaking, the higher the temperature, the higher that vapour pressure, and concentration of the vapour in the headspace above the liquid will be.

Dr Les.

Model Flyer    on 3 July 2018

We had lessons in science at shcool that would de-bunk this story, probably not taught these days due to the health and safety people /snowflakes . A tin filled with gas or flammable vapour with a hole on the top . The gas that escaped from this hole was ignited and left . Once the ratio of air and vapour in the tin was correct the mixture exploded and the tin went sky ward . Simple science, as Dr Les says its the vapour that burns or explodes and this has to be within a cirtain vapour :air ratio . A more worrying problem is that most of this generation are addicted to their mobile phones etc and believe everything they read on FB, youtube and social media..

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