Exploding CNG driven buss!

[MT]

Tesla Lipo fires we all know is troublesome but whats probably more so is CNG tankers and CNG driven devices, today a buss driver in Stockholm drove one into a protection steel barrier infront a tunnel and buss went off. Driver was shipped to hospital. The argument could be that CNG is more dangerous then LIPO but both quite bad.


CNG gass off like Tesla Lipo but in much more dramatic way.


Another one who seams to gass of upwards.


And one in Greece rapidly going off!


This recent one firemen tries calm fire but the CNG cylinder starts to flame on both sides.


CNG car burn by Dutch Brandweer.


And of course the Chinese version...

[apis]

The last one from China isn't from a gas station, it was a warehouse full of explosive chemicals.

But I agree, gas is a pretty dangerous fuel for cars, weather it's hydrogen or natural gas. Would much prefer electric vehicles if it was up to me.

[IanMacdonald]

It's interesting that petrol/gasoline would seem from its chemical properties to be a very dangerous fuel, perhaps more so than CNG, but in practice it has a relatively good safety record when used in vehicles. Point to be learned here is that it's unwise to make assumptions about what will prove safe in practice.

[langwadt]

Hydrogen is better. They are stored compressed, but also absorbed by certain metal-hydride structures. They don't store at 30MPa.

some are high pressure: https://en.wikipedia.org/wiki/Hydrogen_tank

They thing with hydrogen is that it is flammable at almost any concentration

[nctnico]

Hydrogen is better. They are stored compressed, but also absorbed by certain metal-hydride structures. They don't store at 30MPa.

some are high pressure: https://en.wikipedia.org/wiki/Hydrogen_tank

They thing with hydrogen is that it is flammable at almost any concentration

Unfortunately the statistics are against you. Hydrogen is used a lot and it has a very good safety record. In the outside hydrogen will rise up quickly and mix with enough air not to stay combustible. In contrast most gasses and fuel vapors are heavier than air and tend to sink to the ground and are more likely to mix into explosive mixtures.

Note that the second video (from the top) shows that the safety vent valve on the CNG bus does it's job and allows for a controlled burn of the CNG instead of letting the fuel tank explode.

@blueskull: yes the energy content of hydrogen per kg is fantastic compared to everything else.

[dmills]

But the volumetric energy density of H2 at any pressure you would want to deal with is purely crap. 5kg of H2(g) is a BIG TANK!

Yea, cryogenic slush, I know, but then the energy needed for liquification and super cooling are so large as to make the overall cycle efficiency very poor.

The stuff is a naff road fuel even if you get away from the Carnot cycle as a means to convert it into useful work.

Most of those bus fires were fairly standard bus fires followed by the tank rupture disks working as designed.

Regards, Dan.

[nctnico]

But the volumetric energy density of H2 at any pressure you would want to deal with is purely crap. 5kg of H2(g) is a BIG TANK!

A 5kg tank seems to fit just fine in the Toyota Mirai in the place where normally the fuel tank is located. It is all about the pressure.

[Jr460]

Hydrogen is better. They are stored compressed, but also absorbed by certain metal-hydride structures. They don't store at 30MPa.

some are high pressure: https://en.wikipedia.org/wiki/Hydrogen_tank

They thing with hydrogen is that it is flammable at almost any concentration

Greater than 4% and less than 94%.   In many applications H2 used for it's good thermal properties and is kept above 98% pure.  The biggest problems I've seen has to do with sealing a system from leaks.  H2 being so small a light weight, it finds ways out that block other gases.   And then the detection of the leak is your next problem.  The normal soapy water and looking for bubbles doesn't find the smaller leaks.   The way we did it was to dope the system with a bit of helium and then use a portable mass spectrometer tuned for He.

[janoc]

Tesla Lipo fires we all know is troublesome but whats probably more so is CNG tankers and CNG driven devices, today a buss driver in Stockholm drove one into a protection steel barrier infront a tunnel and buss went off. Driver was shipped to hospital. The argument could be that CNG is more dangerous then LIPO but both quite bad.

The same sort of thing can happen even with regular diesel. If a fuel tank is ruptured on impact, an enormous fireball is very likely - just look at the recent train crash in Cairo where an engine ran into buffers. The fuel tank ruptured and KABOOM, over 20 dead and many injured in the resulting fireball. Another famous crash that resulted in diesel exploding was the Ladbroke Grove disaster:
https://en.wikipedia.org/wiki/Ladbroke_Grove_rail_crash

It happens quite often in truck crashes too but there it usually "only" starts a massive fire and doesn't explode.

CNG is a very safe tech routinely used on city buses and public transport because of both costs and much lower emissions than diesel. Furthermore existing buses can be relatively easily converted to CNG, that's what makes it attractive for the transportation companies because they don't need to replace buses (uber expensive) when faced with emission-based traffic restrictions in cities. Purely battery powered electric buses are not really an option yet - the battery capacity is insufficient to run large capacity vehicles for several hours that would be required.

Bus fires due to mechanical problems are quite common (regardless of fuel type) but these kinds of spectacular incidents are extremely rare. Let's not blow things out of proportion here, especially given that this was not caused by the fuel but by the bus crashing into an obstacle and rupturing the fuel tank.

[nctnico]

Well don't rule electric busses out yet. Where I live there are several electric busses driving around (made by BYD from China). It seems these have a range of 250km to 300km and get charged at night.

[langwadt]

Well don't rule electric busses out yet. Where I live there are several electric busses driving around (made by BYD from China). It seems these have a range of 250km to 300km and get charged at night.

there are places that use busses that charge via pantograph at the end station, only takes a few minutes to charge enough for more
than a round trip

[apis]

We have battery electric busses here as well in a few places, it is supposed to work well. Only problem is during winter in the far north where they need diesel space heaters during winter, but you can use biofuel for that so it's still renewable.

[janoc]

Well don't rule electric busses out yet. Where I live there are several electric busses driving around (made by BYD from China). It seems these have a range of 250km to 300km and get charged at night.

there are places that use busses that charge via pantograph at the end station, only takes a few minutes to charge enough for more
than a round trip

Yes but that's not usable everywhere. Trolleybuses also exist, as do hybrid diesel/electric buses. But each have their own issues, mostly the infrastructure (overhead wires being an eyesore and not cheap to put up + energy distribution is needed, it also severely limits where the buses can go). The diesel/electric hybrids are good only for short trips on electric power.

Heck, there were even buses that ran using flywheels - the flywheel was spun up at a stop using electric power and then powered the bus until the next stop. It didn't exactly take hold ... https://en.wikipedia.org/wiki/Gyrobus
 
And fully electric battery powered vehicles are still very expensive, compared to regular ones (almost 60% more). Not exactly a very appealing proposition to transport companies facing upgrades/replacements of large fleets.

I am not writing them off but purely electric buses being a widespread alternative to diesel or CNG is still quite a few years off except for small vehicles.

[langwadt]

Well don't rule electric busses out yet. Where I live there are several electric busses driving around (made by BYD from China). It seems these have a range of 250km to 300km and get charged at night.

there are places that use busses that charge via pantograph at the end station, only takes a few minutes to charge enough for more
than a round trip

Yes but that's not usable everywhere. Trolleybuses also exist, as do hybrid diesel/electric buses. But each have their own issues, mostly the infrastructure (overhead wires being an eyesore and not cheap to put up + energy distribution is needed, it also severely limits where the buses can go). The diesel/electric hybrids are good only for short trips on electric power.

I think most city busses here have a round trip of less than 30km, a pantograph super charger at the end could easily charge it for around trip in a few minutes. Only infrastructure needed is enough power at the charging station and it could be used for charging cars when the bus isn't there

[vk6zgo]

Tesla Lipo fires we all know is troublesome but whats probably more so is CNG tankers and CNG driven devices, today a buss driver in Stockholm drove one into a protection steel barrier infront a tunnel and buss went off. Driver was shipped to hospital. The argument could be that CNG is more dangerous then LIPO but both quite bad.

The same sort of thing can happen even with regular diesel. If a fuel tank is ruptured on impact, an enormous fireball is very likely - just look at the recent train crash in Cairo where an engine ran into buffers. The fuel tank ruptured and KABOOM, over 20 dead and many injured in the resulting fireball. Another famous crash that resulted in diesel exploding was the Ladbroke Grove disaster:
https://en.wikipedia.org/wiki/Ladbroke_Grove_rail_crash

It happens quite often in truck crashes too but there it usually "only" starts a massive fire and doesn't explode.

CNG is a very safe tech routinely used on city buses and public transport because of both costs and much lower emissions than diesel. Furthermore existing buses can be relatively easily converted to CNG, that's what makes it attractive for the transportation companies because they don't need to replace buses (uber expensive) when faced with emission-based traffic restrictions in cities. Purely battery powered electric buses are not really an option yet - the battery capacity is insufficient to run large capacity vehicles for several hours that would be required.

Bus fires due to mechanical problems are quite common (regardless of fuel type) but these kinds of spectacular incidents are extremely rare. Let's not blow things out of proportion here, especially given that this was not caused by the fuel but by the bus crashing into an obstacle and rupturing the fuel tank.

We've been running CNG buses in Perth WA for decades, & although there have been a few impressive "burn ups", these have been very rare, with no injuries, so considering the thousands of km covered, are a pretty good trade off.

We had a couple of "Eco-busses" running, using hydrogen & a fuel cell, but the cells tend to fail after a while.

[wraper]

Rear seats have nice passenger ejection system underneath  .

But the volumetric energy density of H2 at any pressure you would want to deal with is purely crap. 5kg of H2(g) is a BIG TANK!

A 5kg tank seems to fit just fine in the Toyota Mirai in the place where normally the fuel tank is located. It is all about the pressure.

[duak]

I remember seeing a newspaper headline "BARBEQUE EXPLODES, TWO LAND IN HOSPITAL".  Now there's a vivid thought.  Perhaps it could be trotted out and retooled in case the previous post come true.

[apis]

Well don't rule electric busses out yet. Where I live there are several electric busses driving around (made by BYD from China). It seems these have a range of 250km to 300km and get charged at night.

there are places that use busses that charge via pantograph at the end station, only takes a few minutes to charge enough for more
than a round trip

Yes but that's not usable everywhere. Trolleybuses also exist, as do hybrid diesel/electric buses. But each have their own issues, mostly the infrastructure (overhead wires being an eyesore and not cheap to put up + energy distribution is needed, it also severely limits where the buses can go). The diesel/electric hybrids are good only for short trips on electric power.

Heck, there were even buses that ran using flywheels - the flywheel was spun up at a stop using electric power and then powered the bus until the next stop. It didn't exactly take hold ... https://en.wikipedia.org/wiki/Gyrobus
 
And fully electric battery powered vehicles are still very expensive, compared to regular ones (almost 60% more). Not exactly a very appealing proposition to transport companies facing upgrades/replacements of large fleets.

I am not writing them off but purely electric buses being a widespread alternative to diesel or CNG is still quite a few years off except for small vehicles.

They began testing with 100% battery electric city busses in a nearby city in 2016, last year they began expanding to other cities. Found out now that they are planing to replace most city busses with battery electric by 2030.


These are also made by BYD.

There's also a battery hybrid ferry nearby:

[Mr. Scram]

You'd almost think that storing energy densely comes with some risks.

[MT]

The last one from China isn't from a gas station, it was a warehouse full of explosive chemicals.

Yes i know, i just felt for some exaggeration! Chinese the best at staging unexpected explosions!

Rear seats have nice passenger ejection system underneath  .

LPG, Russia.
https://youtu.be/5-nOPvXiIWQ?t=33

[wraper]

Rear seats have nice passenger ejection system underneath  .

LPG, Russia.

LPG has up to about 10 bar pressure when tank gets quite warm, in that case tank was placed inside the trunk. Toyota Mirai has tank sitting right under the rear seats.
https://ssl.toyota.com/mirai/assets/modules/carpagehowitworks/Docs/MY18_Mirai_eBrochure_FuelCellTech.pdf

MAXIMUM FILLING PRESSURE
87.5 MPa S
NORMAL OPERATIONAL PRESSURE
70 MPa

Very nice knowing there is a tank under 750 Bar placed beneath your ass. If it ruptures ejection is almost guaranteed.

[wraper]

Hydrogen fireball about 170 m/sec after tank rupture in Test 2 (cylinder installed under an SUV). (From Zalosh, R., Proceedings of the 5th International Seminar on Fire and Explosion Hazards, Edinburgh, UK, April 23–27, 2007. With permission from the School of Engineering, University of Edinburgh

[MT]

Toyota Rav4 flaming out, is it the petrol tank or the bat electrolyte or both or neither?!


This is supposedly the batt pack in the chassis.

[raptor1956]

It's interesting that petrol/gasoline would seem from its chemical properties to be a very dangerous fuel, perhaps more so than CNG, but in practice it has a relatively good safety record when used in vehicles. Point to be learned here is that it's unwise to make assumptions about what will prove safe in practice.

There have been many cases of cars going up in flames due to problems with the gasoline (petrol) tank.  Several models of car like the Ford Pinto were renowned for going up at the slightest provocation.  But, with time they've managed to improve safety so major problems are mostly a thing of the past.  With time electric cars will improve the fire risks and if CHG became a major fuel option I could see improvements made there to.  From a pure energy standpoint petrol and diesel are both very energy dense and petrol in particular can burst into flames explosively under the right conditions. 






Brian

[Berni]

Dang... over here these CNG fueled buses are getting more and more popular too.

My car is modified to run on LPG since the stuff is 50% the price of gasoline, but that stuff is much safer. The problem with CNG is that it has to be kept under a huge amount of pressure to be able to fit a reasonable amount of it into a tank. These large tanks typically operate at 25 bar! If they get hot (such as in a fire) these tanks can rise to many times that pressure. So when such a tank fails it is like a few sticks of dynamite going off from the pressure alone, let alone the gas then igniting.

On the other hang LPG is much safer because it only takes a few bar to liquefy it (Even a normal soda bottle can contain liquefied LPG, but don't do that for obvious reasons) and is popularly used to run gas stoves and gas grills all over the world. The tank is easily way overbuilt for these pressures and if a leak happens its just a loud hissing before the tank cools down rapidly and goes cryogenic, limiting the amount of output (If there is not a safety valve that stops the flow before that). However its still very dangerous if a LPG tank ends up in a fire, it can build pressure faster than a relief valve can cope and cause it to explode with a lot of energy.