In another thread the question of lorry fires was raised.
Here in Hereford/Worcester,as was, in the last three months there have been two major RTAs involving collisions between two heavy goods vehicles which resulted in four fatalities. There were fires in both cases.
It was suggested to me that the very high pressure diesel in modern common rail systems was as inflammable as petrol, would this be true?
Of course virtually all the newer diesel cars on the road have common rail systems but I haven't heard of any increased fire risk.
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I'd imagine that only the diesel in confined parts of the fuel system would be as explosive as petrol as there's less space for it to move to should that part of the system be crushed. I'd imagine the real difference in safety would be that petrol would continue to burn back into the fuel tank (given enough air) and would also burn on road surfaces, whereas spilled diesel would just be slippery when deprived of compression.
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Are these the lorries burning, or cars they have hit? Diesel needs to be heated quite a lot before something will ignite it, in fact, petrol has a much higher auto-ignition point than either diesel or cooking oil in a pan, it's the low flashpoint that make petrol vapours abundant which have a high risk of spark ignition. Well, I'm not convinced that high pressures are to blame, as any vehicle new enough to have these systems will also have intertia fuel cut off, and even the though the pressure is very very high, upon rupture, the volume released is miniscule, as liquid is not compressable, there is virtually nothing to force the liquid out, but with a petrol system, there is teh fuel pressure regulator, and the volume of the diagfram inside this will be displaced upon rupture.
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Lorry fuel tanks are very exposed at sides of vehicles. Any side impact is likely to puncture them including bad jacknifing. Hit a hot exhaust manifold or pipe plus add electrical/mechanical spark and there's your fire.
madf
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20 years ago I saw a RTA where one vehicle ran at high speed into the back of a stationary car. I didn't see the moment of impact, just the immediate aftermath, with the stationary car shunted right across the road and four people burning to death inside. Nasty.
Which was one (of several) reasons why I have driven nothing but diesels for the last 20 years.
Ian
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Saw a program some time ago I think on top gear where petrol was poured on a really hot exhaust pipe,it did not ignite just evaporated,they repeated the experiment with normal brake fluid,this ignited immediately,could this be the reason for many fires after collisions?.
I have noticed that many plastic brake fluid containers only appear to be held on top of the master cylinder by being a tight fit in the neoprene seal,the half pint or so of fluid would increase its weight many times in a frontal impact and could come loose spilling fluid over the exhaust manifold.
They also said there was a safer Glycol based alternative but I cannot remember the supplier.
ndbw
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The brake fluid problem is well known. In an impact the fluid can spray as a fine mist across hot components and ignite.
Normal Diesel has a flashpoint of 61 deg. C., but I know that it is common practice for farmers to use it when burning stubble because it burns steadily and reliably.
I also have heard that ethanol is now being added to Diesel as an oxygenating agent and to improve emissions - presumably this lowers the flashpoint?
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There was a picture in the evening standard earlier this week that shows what happens when a London bus goes up in smoke. There was a 30 yard ribbon of burning diesel running along the gutter, showing that once a diesel engine does go "pop" you still face the risk of burning fuel pouring out all over the place.
Their website doesn't show the pictures, but details of the blaze can be found here:
www.thisislondon.co.uk/news/londonnews/articles/11...d
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I recall that investigations into rail crashes have discovered that it is the presence of a fine mist of diesel fuel which ignites. Even powders, such as flour, can ignite explosively when in a mist form.
A sudden rupturing of a fuel line or tank under pressure would probably cause such a mist of diesel.
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I recall that investigations into rail crashes have discovered that it is the presence of a fine mist of diesel fuel which ignites.
Correct, indeed. There was a lot of research done after the Ladbroke Grove accident because the diesel burnt much more fiercly than would have been expected. It was found that the severity of the impact caused misting of the fuel, resulting in the subsequent fireball.
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This is not a common occurence, fires after a RTA are very rare indeed, in my 10 years as a wholetime firefighter I have only come across one.
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Yet in every movie you ever see the car bursts into flames as it plunges over the cliff or towards the innocent kiddies on the crossing...
There was a horrific 25 vehicle pile up on the Kent Surrey part of the M25 in fog a few years back and IIRC most of the deaths were people trapped in blazing cars and not as a result of the accident.
I know that the motorway had to be closed for resurfacing of the carriageway where it had melted - Not a nice way to die ( if there are any nice ways)
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Even humble custard powder in the right (wrong) proprtions suspended in air, plus a spark, can cause a very powerful explosion/fire, so diesel in the same circumstances can be at least as volatile as petrol.
Try not to sneeze when making custard.
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Wasn't the fire in the Mont Blanc tunnel the result of a collision between lorries carrying flour and margarine? Or should I shut my cakehole?
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And another carrying sugar & eggs. Alfred the Great was in there as well, which is why the cake was burnt.
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No milk though. Otherwise there'd have been no fire - only harmless blancmange.
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I don't think I've ever heard such a terrible joke as that. You should go to your room and think about what you've done. ;)
>>Not a nice way to die ( if there are any nice ways)<<
I can think of several nice ways to die, but they all seem to involve Jennie Agutter and a younger Ingrid Pitt.
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Can't I go to my room and think about Jennie Agutter and a younger Ingrid Pitt?
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