Burning car

[kahunabean]

This morning I watched (and tried to help !) as my neighbour's car caught fire and burnt out. As we waited for the fire brigade to come we thought the petrol tank would explode - but it didn't, and the firemen just walked up to it pretty calmly to put it out . The tyres ahd all exploded so it was a pretty serious fire. Does anyone know why the petrol tank didn't go, hollywood style ? Is it cos u need a petrol/air mix and the tank has only petrol ? My neighbour said the tank was half full. Is the tank really well protected to avoid an explosion ? It was definitely petrol, not diesel.

[gazzawazza]

I've attended hundreds of car fires and quite honestly I'm having trouble trying to remember one that did go up Hollywood style!

I've often wondered about this myself. Tyres often go pop, I suppose simply because they can quickly become exposed to direct heat impingement which not only weakens the integrity of the tyre but also heats the air inside it causing it to expand and eventually burst.

I feel sure there will be built in safeguards to prevent the petrol tank from rupturing due to heat. I would imagine there will be a maximum amount of petrol you can put into a tank even when full which will allow some space for expansion of the fuel due to heating and I'm sure there will also be some sort of relief valve which can reduce pressure but in normal circumstances poses no danger.

You're right in saying you need a petrol/air mix, but if the tank did rupture and petrol escaped it is almost certain that somewhere near the spillage the correct mixture would be present, and obviously with a source of ignition so close ignition would almost definitely occur. It may be, however that because it is only the petrol and air that is in the correct mixture that will ignite it may only show as a sudden flare up of flame (which I have seen many many times) and nothing on the scale of a Hollywood style explosion.

[gazzawazza]

I also meant to say that the tanks will be designed to rupture (slow release of petrol) rather than explode which would spread the fuel and therefore give a better chance of creating the correct mixture.

[andy hughes]

As my esteemed colleague pointed out, the massive explosions are the stuff of Hollywood legend - real life is always more mundane. File them alongside all the car chases where cars smash into walls / leap over obstacles, and so on, but any 'real life' car chase footage demonstrates how fragile production cars actually are. Next week - 'The Matrix', and how Keanu Reeves and Hugo Weaving would actually break their hands and limbs if they hit each other just once each like that!

[gazzawazza]

Esteemed colleague... I like that Andy! You've hit the nail on the head there though but... in fact when I was typing my answer, I was trying to remember which British programme I was watching years ago where a car had burst into flames and the inspector was puzzled by the fire officer's response which was something along the lines of "Something doesn't quite add up, he said they never go up Hollywood style!"

[darth vader]

The petrol tank does not explode - it has been designed not to. Actually this is one of those questions where i've not been able to find ANY evidence as to why, on the internet (which is not often). I do remember a website which was all about "impossible science" and explained various films such as the Schwarzenegger one where he pilots a harrier jumpjet above a building (forget the name) which just wouldn't happen for various aerodynamic reasons, also why you wouldn't hear spaceships blowing up in the starwars films, why going head first through a plate of glass and walking away from it is NOT possible etc. and also why a car does not blow up on impact. Unfortunately i can't find the blinking site any more but if i do i'll let you know. Suffice to say it just ain't possible. In fact this safety info. webpage explains how to survive in a forest fire by staying inside the car http://home.vicnet.net.au/~chfb/caught_out.html

[LeMarchand]

Cars in Hollywood movies are packed with petrol and explosive to make them blow up spectacularly. As for the other movies: The Matrix scenes are set in "The Matrix", so the laws of physics don't apply; there's no sound in space as it is (pretty much) a vacuum, so there is no air to carry the soundwaves (I can only think of "2001" and "Firefly" off the top of my head where space has been realistically silent), but it isn't as exciting to have silent space battles; don't know about the aerodynamics in "True Lies"; and it is possible to jump through a glass window and walk away - I have seen it done by a drunken friend, but there were curtains up that protected him from cuts - I suspect that jumping through a "naked" window would carry a high risk of severe lacerations though. On the other hand, movies would be kinda dull if they were totally realistic - as anyone who has been hit really hard will tell you, fights would be a lot shorter!

[gilf]

When I was a kid the guy who lived behind me fell through our back window he survived but he was cut to bits. There was a program on the BBC which discussed about movie stuff and they said that it was possible to go through a window but you would be cut to bits.

[gazzawazza]

I would imagine that the harrier in front of the building would need a clear path for the air intakes for the engines. Would the turbulence around a skyscraper be just too "lumpy" to hold the craft level?

[darth vader]

grin - sorry i wasn't expecting anyone to explain my examples, just using them in my response

[darth vader]

actually the harrier one was a pile of poo, if i remember rightly Arnie is piloting the harrier (unbelievable in it's own right) and he gets a kid to jump off a skyscraper and onto the nose cone of the jump jet. Rrrriiggghhhttt........

[treaclefight]

guys you're really shattering my illusions here, i thought all hollywood films were 100% real, i watch them only for their documantary value, it had not occured to me that they might be trying to entertain me. from my misspent youth i can confirm that cars dont blow up, but on a clear wintery night the fire is quite spectacular, as were the firemen.

[Symon]

The tank possibly got hot, excess pressure might have been relieved via burnt flexible pipes fueling fire elsewhere. There is always a danger we expect emergency servies to act, they have to be calm whatever, have they have been caught out. However would we be driving if cars went up this way so much in design we take for granted. Hollywood changes out prespective in so many ways and all too often gives us a flase perspective of surival and life !