So, yes, compressed gas released toward a person can kill him.

A full CNG tank is roughly 2900-3600 PSI. Say the safety release valve fails, then you have to add in the factor of heat increasing the pressure. If you call the instantaneous release of 3600+ PSI a “no boom boom” then your absolutely right….

http://tinyurl.com/9yc6waf

While the vehicle in this article wasn’t on fire it still clearly points out that a ruptured tank WILL KILL YOU!

Which leads to the follow-up question: What happens if the pressure relief valve fails?

If the pressure doesn’t go up, nothing happens unless it fails by releasing early, in which case the fuel is gone.
If there is a fire which raises the pressure and it goes above the strength of the tank, the tank ruptures.

Does the gas in the tank explode? No, it has to be mixed with oxygen to burn. It has to be confined to explode. Until it ruptures, there is no oxygen. After it ruptures, it is not confined. Ergo, no boom boom.

If the tank ruptures, how much mechanical energy will be released? Roughly the product of pressure times volume released. Will it hit the people in the car? Probably not, the rupture is more likely to be where the fire impinges on it and that is most likely to be away from the body of the vehicle.

In fact, where is the fire most likely to be? Around the engine.
Is the fuel tank near the engine? Nope, not likely.

I’ve had oil fires on my engine. Well, okay AN oil fire on one engine. It didn’t ignite the gasoline and the car was not destroyed. I drove it several more years.

We are still left with the thought that fire is only supported by inflammable material. Gasoline would remain in the areas for a while; natural gas would not remain in the area very long. This shouldn’t be hard to see or accept.

David for keeping fuel from fire

The worse experience I ever had was a rare explosive backfire, which/that ignited a tiny fuel leak. I could see the fire through the hood cowling and reacted by switching off the electrict fuel pump and increasing throttle to full, in order to consume all the gas in the fuel bowls and to also help blow out the fire. Fire shields for fiberglass hoods (bonnets) are cheap insurance.

Inspect your engine compartment for wires and fuel lines that may be rubbing against other components. This condition can lead to an/a electrical short or leak and possibly fire.

I believe you’re still missing my original point. The majority of the fire is in the interior and engine compartment. Unless he was carrying several gallons of gas under his hood and in the interior then gasoline had nothing to do with this fire. It was clearly a mechanical issue that, as I previously stated, would have happened with a CNG vehicle as well. At most you would end up with a SLIGHTLY less burned total loss, with the possibility of explosion. As the article stated, safety relief valves can and do fail.

Agreed. For example liquid fuels will fall to the ground just as the pictures seem to show burning fuel under the back of the vehicle. In contrast, a compressed lighter than air gas will shoot out, disperse and rise — not stay near the vehicle, not be around to burn.

This disagrees with the conclusion given in the abstract of the article you cite. They could be right and I could be completely wrong. I can’t read the entire report to judge it. They may identify modes I haven’t considered. They mention they don’t have enough CNG fatalities to check their engineering assumptions and guesses. Assuming they are good engineers, their assumptions err on the side of caution — possibly deciding the unknown but safer system is more dangerous than the known but more dangerous system.

Also note we’re talking diesel buses, not gasoline cars, but I’m not backing down on CNG yet.

David the stubborn

You don’t SET your oil on fire. The only difference between this car and a CNG vehicle is the fuel. The same exact thing could have happened whether it was CNG or gasoline powered. You act as if its some magical thing that’s completely safe. While I can’t guarantee it, I’m pretty sure the gasoline in this persons vehicle didn’t just spontaneously combust and a mechanical problem caused the fire. My point, whatever happened to this vehicle would have happened whether it was gasoline powered or CNG powered.

BTW, like any mechanical device, these “pressure relief valves” you speak of can fail. Wanna guess what happens when they do? Accidents happen….

http://www.ncbi.nlm.nih.gov/pubmed/15876211 <—-The last 4 sentences is what you're going to want to read.