How does a Blowtorch/BBQ/etc. work?

[speg]

How do these things work? You've got a flame, with a stream of gas coming out behind it. Why doesn't the flame ignite the gas coming out and explode the holding tank. I'm interested in the engineering of whatever doohickey (or plain physics) prevent this. Thanks!

http://www.nbcchicago.com/news/local-beat/Man-Dies-in-Blow-Torch-Explosion-91518664.html

 

[Eli]

Fuel requires oxygen to burn. There is no oxygen before the gas reaches the atmosphere.

The gas is under pressure. It's moving faster than the flame front does. Ever lit a spray of hair spray on fire? The flames stay like 6" away from the can.

The only two doohickeys are a gas pressure regulator and device that mixes oxygen with the gas - aka a burner.

 

[xSauronx]

Fuel requires oxygen to burn. There is no oxygen before the gas reaches the atmosphere.

The gas is under pressure. It's moving faster than the flame front does. Ever lit a spray of hair spray on fire? The flames stay like 6" away from the can.

wait wait wait....have you been to school or something?

 

[Mr. Pedantic]

Gas in tank. ==> Gas in tube. ==> Gas expelled from tube.

Gas expelled from tube meets spark meets oxygen. ==> combustion of gas.

Combustion of gas ==> heat

Heat ==> From gas expelled from tube towards gas in tube.

Cold gas in tube ==> hot gas out of tube.

Cold gas does not combust. Hot gas does.

Gas without oxygen does not combust. Gas with oxygen does.

Basically, that's it. The velocity of the gas itself could be sufficient to prevent the gas inside the tubing combusting, I don't know. I'm not an engineer. But the most important thing is that inside the tube there is no oxygen. There is no oxygen in the holding tank, there is no oxygen in the gas tube, even if you heated the whole thing up nothing would happen if you had a sufficiently strong container. It's only when the gas gets out of the tube, and into the presence of oxygen, that it gets oxidised.

 

[PottedMeat]

the gas pressure regulator keeps the fuel/o2 coming out at a constant rate



...that 'blowtorch' may have been a oxy-acetylene rig, maybe he didn't have a flashback arrestor in the torch.

 

[Colt45]

 

[Rubycon]

...that 'blowtorch' may have been a oxy-acetylene rig, maybe he didn't have a flashback arrestor in the torch.

Yes and acetylene can become unstable and dangerous if the bottle is damaged. Bottle (mis) handling causes lots of accidents when dealing with welding gases. Back in 2007 during drydock we had a scare when a fire broke out under the ship. It was caused by a bottle getting knocked over that was not secured properly. Operating without a flashback arrestor is dangerous too!

 

[speg]

So how does something like the link above happen? (guy's blowtorch exploded)