Electric F-150

[Italian Tow]

I think CNG makes for a poor explosion. Its more of a fireball then an explosion. And the rest of the story is? As far as safety, was something overlooked? Could terrorism have been a cause?

[Hilola]

Originally Posted by Italian Tow

I think CNG makes for a poor explosion. Its more of a fireball then an explosion. ha?

I beg to differ. Recently happened near us:

Explosion at Buttonwillow gas station injures 1 person – What’s Up Bakersfield

[Mike Lewis]

Originally Posted by cpaharley2008

But, but we carry 40 lbs of it on our Escape............

Yeah, propane is sort of a hazard as well, but we have to heat and cook with something.

Compressed natural gas is more dangerous than propane because:
- it is a compressed gas, not a liquid under pressure like propane.
- it is carried at a much higher pressure than propane (forgot the numbers).
- when released it expands into the air in all directions, whereas propane gas is heavier than air and will flow along the ground if there is a tank rupture. Granted, that isn't a great situation, either.

I think the above can be said for compressed hydrogen as well, though it will rise into the air as it burns. I don't like the idea of propane-powered vehicles, either, but they are probably safer than CNG or hydrogen-powered vehicles.

[sunrisetrucker]

Originally Posted by Mike Lewis

Yeah, propane is sort of a hazard as well, but we have to heat and cook with something.

Compressed natural gas is more dangerous than propane because:
- it is a compressed gas, not a liquid under pressure like propane.
- it is carried at a much higher pressure than propane (forgot the numbers).
- when released it expands into the air in all directions, whereas propane gas is heavier than air and will flow along the ground if there is a tank rupture. Granted, that isn't a great situation, either.

I think the above can be said for compressed hydrogen as well, though it will rise into the air as it burns. I don't like the idea of propane-powered vehicles, either, but they are probably safer than CNG or hydrogen-powered vehicles.

Some in the trucking industry are using CNG. The company I work for has 12 CNG trucks. We all had to attend a safety meeting to learn how fuel them and what sort of things to keep an eye on. When fully fueled, the pressure in the tanks is 3500psi and they are apparently able to withstand a 100 foot drop and still maintain their integrity.

[Brian B-P]

It seems to me that natural gas (piped in to a stationary location, or carried in compressed cylinders) is only an explosion hazard in a confined space. Occasionally a house blows up, but it's hard to imagine a natural gas fueled vehicle (outside of a garage, or perhaps a filling station canopy) exploding.

As the article about the Bangladesh fire said:

The United States Energy Department says that natural-gas-powered vehicles are generally as safe as or safer than those that use gasoline.

Of course, while great intelligence can solve almost any problem, greater stupidity can cause almost any imaginable problem.

[Italian Tow]

Brian I love your 3rd paragraph! Its every where!

[Mike Lewis]

This may end up being a perception problem. Truckers are trained professional drivers, and the CNG tanks are well-protected in big trucks. But suppose an average U.S. driver going down the road in a CNG-powered car collides with and incinerates a school bus full of kids. Yes, that sounds awful but it could happen. Even though the same thing can happen with gasoline-powered vehicles, the unfamiliarity of CNG will lead to a widespread fear of it and a possible ban of its use (and hydrogen for that matter) for passenger cars. It would be like how the Three Mile Island incident instilled a fear of nuclear power and ruined that industry.

[mizterwizard]

I used to fill dry cleaning bags with natural gas from my stove. I would tie off the bottom of the bag and attach a length of crumpled toilet paper to it. I would light the end of the toilet paper and then let it go. Natural gas is lighter than air and the bag of it would rise up in the night sky with it's burning tail. After a minute or so the tail would burn up to the bag and ignite it. There would be a big ball of fire in the sky that lasted a second or so while the gas mixed with air and burned but never any kind of explosion.

Now if you want a bang, you attach a condom filled with the mixture from and extinguished acetylene torch. When the natural gas burns it will melt the condom and ignite the perfectly mixed gasses within. BOOM. Fun Times! How did I ever survive?

When released into the air, CNG and hydrogen both float away and disperse rapidly. There needs to be a way to contain them for much of a hazard to develop.

No fuel can burn without an oxidizer. A few fuels, like explosives, have an oxidizer built in but natural gas, propane, butane, gasoline, diesel fuel, kerosene, jet-A, alcohols of all sorts, wood, coal, wheat dust, etc. all need to be mixed with air to burn. A few fuels, like dimethylether (starting fluid), have a pretty broad range of usable mixture ratios. Most fuels will only burn when mixed in a pretty narrow band of ratios. Gasoline for instance will not burn well if it is richer than 11:1 or leaner than 16:1 by weight when mixed with air.

If you search the world for troubles you will surely find some. The story of an explosion in Bangladesh isn't really very applicable here. In Bangladesh they do all sorts of things that would never pass here. Who knows what kind of engineering went into that event. Besides, the story made the news because it was unusual. If it was a common occurrence it would never have been reported.

Referencing the extreme possibility on a topic is hardly convincing either. Suppose a school bus full of children ran off a bridge? Would we then contemplate banning bridges? When it comes to school buses full of kids, I'm more concerned about snow and drunk drivers than fuel explosions.

By the way, the difference between combustion, deflagration and detonation is one of time. A log has a lot of energy available but it is hard to access it all at once. You would have to powder the wood and mix it with oxidizer before you could get anything more than normal combustion. In fact, in the building code, beam larger then 8 inches are considered non-combustible. Most fuels can be made to deflagrate if premixed with air. This kind of burning will produce a whoosh or even a small boom in the open or a decent bang if enclosed, like in a pipe bomb. Really big bangs need a fuel that will detonate. This is hard to achieve with air and most liquid and gaseous fuels. In an engine this kind of burning leads to knocking.

Explosion is a poorly defined word for most people. If a pan of cooking oil gets hot enough it can "blow up in your face" when in reality it just catches fire at a rate that you can see. On the other end, a nuclear bomb is all done exploding in a few millionths of a second. It takes very special cameras to catch it. I guess anything that startles you is an explosion, if you want to call it that.

[Brian B-P]

Originally Posted by Mike Lewis

This may end up being a perception problem. Truckers are trained professional drivers, and the CNG tanks are well-protected in big trucks.

I don't think they're deliberately protected so much as they are stacked where they can be fit in. Since about four times as much tank volume is needed as compared to diesel, and the tanks are cylindrical pressure vessels, they're don't fit well in the traditional saddle tank location (hung on each side of the frame between the wheels); they usually end up stacked behind the cab. The ends are unprotected and if the truck is T-boned by another large vehicle the compressed natural gas cylinders will be hit. And that's not a big concern to me.

But yes, perception is everything, unfortunately.

[Mike Lewis]

Originally Posted by mizterwizard

I used to fill dry cleaning bags with natural gas from my stove. I would tie off the bottom of the bag and attach a length of crumpled toilet paper to it. I would light the end of the toilet paper and then let it go. Natural gas is lighter than air and the bag of it would rise up in the night sky with it's burning tail. After a minute or so the tail would burn up to the bag and ignite it. There would be a big ball of fire in the sky that lasted a second or so while the gas mixed with air and burned but never any kind of explosion.

Wow! Dang these all-electric homes. I never have any fun.

Referencing the extreme possibility on a topic is hardly convincing either. Suppose a school bus full of children ran off a bridge? Would we then contemplate banning bridges?

No, because people are familiar with bridges. If one fails the public doesn't condemn all of them. It is the unfamiliarity of CNG-powered vehicles that is the risk to their acceptance, and a big, bad accident with one early on may put the kibosh on their acceptance. I think the analogy with nuclear power is apt.

Regarding DOE's determination that CNG-powered vehicles are no more dangerous than gasoline-powered vehicles, I simply don't believe it. It seems to me that a flammable gas under pressure is more dangerous than a liquid that produces flammable vapor, like gasoline. But again-- that is just my perception, based on nothing but intuition. I can see many people reaching the same conclusion, though, after a big accident involving a CNG-powered vehicle.

[Brian B-P]

Originally Posted by Mike Lewis

Regarding DOE's determination that CNG-powered vehicles are no more dangerous than gasoline-powered vehicles, I simply don't believe it. It seems to me that a flammable gas under pressure is more dangerous than a liquid that produces flammable vapor, like gasoline. But again-- that is just my perception, based on nothing but intuition.

I get the logic, but the DOE's statement is based on decades of actual experience with many thousands of CNG vehicles. They're a tiny fraction of the vehicles on the road, but there are still enough for a useful history.

On the other hand, gasoline seems like a disaster waiting to happen, because it is a liquid with a significant vapour pressure and high flammability. A common sentiment is that if gasoline were newly introduced today, into a world which had been using other existing fuels (especially diesel and other kerosene-like liquid fuels), gasoline would be rejected as unsafe.

[mizterwizard]

Actually gasoline isn't as bad as some people think. We have the movies and TV to thank for that. About 90% of Hollywood crashes either end up in a fire ball or a lake but according to the NHTSA, fewer than half of one percent of all accidents involve fire or water. Fiction rarely follows reality very closely.

The saving grace for gasoline is its narrow flammability range. It isn't easy to get it mixed with air in just the right quantities in the presence of an ignition source. Not that a puddle on the ground isn't dangerous. It just isn't a bomb waiting to go off.

Almost all gasoline engines these days use an electric fuel pump inside the gas tank. These things have brushes and throw sparks but they don't blow up the tank because even when the fuel level is too low to submerge the brushes, the mixture isn't even close to combustible.

Back to gaseous fuels. First of all you have to realize that fuel tanks are made of ductile and malleable materials. That means the bend rather than break when struck.

Now consider a propane tank that is 75% full of non-compressible liquid when it is crushed to half volume in a collision. It has to rupture or deform. It will most likely rupture because the tank isn't that ductile.

With CNG what will happen in the same scenario is that the gas pressure would rise to about 250% of rated pressure. This is more than you might calculate from strict pressure / volume numbers because the compression would also increase the temperature. Since the tank is built to burst at several times its rated working pressure, nothing happens.

Every technology has risks. The trick is to understand the risks and manage them. The worst natural gas incident I have ever seen is when they redid the road in front of my house and the grader got into the 6" steel gas main at 250 PSI. For 3 days it blew through a 1X2 hole in the side of the pipe. It sounded like a jet engine. The fear was that someone would ignore the signs and drive by, igniting the gas.

When the gas company got around to it they sent a guy out to patch the pipe. He parked his truck about 50 feet back, way to close for my comfort. He ran welding leads to the pipe and welded the patch in place. There is hardly a better ignition source than a welding rod but nothing happened except the roar went away. Natural gas is not all that dangerous if you understand it.

MythBusters did a segment on spy move stunts. One that they did was to reproduce the gas explosion from one of the Borne movies. They had a heck of a time getting the gas to ignite inside their purpose built building. They switched from the magazine in the toaster igniter to a neon light transformer. It still just kind of went poof.

[sunrisetrucker]

Originally Posted by Brian B-P

I don't think they're deliberately protected so much as they are stacked where they can be fit in. Since about four times as much tank volume is needed as compared to diesel, and the tanks are cylindrical pressure vessels, they're don't fit well in the traditional saddle tank location (hung on each side of the frame between the wheels); they usually end up stacked behind the cab. The ends are unprotected and if the truck is T-boned by another large vehicle the compressed natural gas cylinders will be hit. And that's not a big concern to me.

You can see the tanks in the picture, there's one on each side. I've often thought that if I was t-boned it would be game over. But we've been told that that is not the case, apparently there is enough of a safety factor build in. I just don't want to be the guy who gets to find out if that's true.


And just as a side note, they are so under powered and so frustrating to drive that all the drivers wish they would go back to diesel.

[Italian Tow]

All this reminds me of the GM saddle gas tanks where they were placed on the outside of the frame rails... they changed, they adapted, GM is still here today... I was stationed in Italy in the early 80s and drove a 1967 Alfa that was CNG powered... We (the US)could have dipped into that well as an alternative.

[gbaglo]

My favourite Simpsons segment shows a tanker truck careering down a mountain road and crashing, then exploding in a huge fireball. Pull back and the logo on the side of the the tanker says "MILK".

[Brian B-P]

Originally Posted by mizterwizard

Actually gasoline isn't as bad as some people think. We have the movies and TV to thank for that. About 90% of Hollywood crashes either end up in a fire ball or a lake but according to the NHTSA, fewer than half of one percent of all accidents involve fire or water. Fiction rarely follows reality very closely.

I agree. I participated in a training session, learning to put out a car fire, and the biggest problem was getting the scrap car to burn... even liberally splashed with gasoline.

I think the point is that every fuel has its hazards, and as Mike has suggested, it is the unfamiliar fuels that we are most concerned about.

Originally Posted by mizterwizard

Now consider a propane tank that is 75% full of non-compressible liquid when it is crushed to half volume in a collision. It has to rupture or deform. It will most likely rupture because the tank isn't that ductile.

If you could crush it, sure. Ever seen a photo of a crushed propane cylinder? I haven't. It can be done, of course, and is done (to unpressurized tanks without valves and thus much weaker) in the process of recycling them, but accidentally...? I found an online article about a company which built a cylinder-crushing machine for recycling - it takes two minutes for a 5-ton machine with a 38-horsepower engine running a hydraulic system to exert 85,000 pounds to crush a cylinder. I'm not worried about my propane cylinders getting crushed or ruptured in an accident.

Propane is not something to play with, and must be handled with care. The good news is that, as with any other fuel, the equipment used for it has been designed and built by people who know what they're doing.

Now, if only all of the do-it-yourself electric vehicle enthusiasts were as careful with high-voltage lithium-ion batteries as the vehicle manufacturers are. The ones who are not careful usually get away with it, but some have had dramatic fires.

[Brian B-P]

Originally Posted by Italian Tow

All this reminds me of the GM saddle gas tanks where they were placed on the outside of the frame rails... they changed, they adapted, GM is still here today...

We had one of those (a 1980 Chev C10 Silverado). The saddle tanks look like a stupid idea (in case of a side impact), but that's the standard configuration for heavy trucks, and no worse than the fuel tanks right in front of the rear bumper that were normal for cars for decades. School buses of the time all had their fuel tanks similarly mounted. The GM tanks never were a safety problem (despite the Dateline NBC stunt), but yes they were moved inboard later.

[Mike Lewis]

I remember pickups that had the fuel tank mounted vertically inside the cab, behind the seat. You could hear the gasoline slosh around as you drove down the road.

[Donna D.]

Originally Posted by Mike Lewis

I remember pickups that had the fuel tank mounted vertically inside the cab, behind the seat. You could hear the gasoline slosh around as you drove down the road.

Yeah, a 1956 Ford F-100 is one. The rubber hose between the outside filler and the tank would rot and then the fumes inside the cab were awful!

[rbryan4]

Originally Posted by Mike Lewis

I remember pickups that had the fuel tank mounted vertically inside the cab, behind the seat. You could hear the gasoline slosh around as you drove down the road.

Worse yet was the Pinto. While the bed of the truck offered "some" protection to the fuel tank in a rear end collision, the Pinto's tank was right behind the rear bumper, with a metal tube from the filler cap right into the center of the tank. Rear end collision could shove that filler pipe into the tank, and the whole thing would explode. My grandmother was almost killed many years ago when she was rear ended driving a Pinto.