Since the invention and popular use of the gas fuelled BBQ, many urban myths have flourished popularised by rare, yet widely publicised, stories of explosions, fire and injuries. Every time my BBQ suffers a 'blow-back' my wife runs indoors convinced that the BBQ is about to explode and take half our apartment block with it.
Blow-back? For gas BBQs and many other gas stoves they operate with little or no noise and yet occasionally a loud 'pop' is heard before the sound of rushing gas like a blowtorch. If you look underneath your barbeque you will see that the flame from your gas burner has migrated from calmly and quietly burning from the correct apertures along or above the flame ring or 'burner' as some may call it; to a violent blowtorch like flame originating at the gas and air mixing chamber where the gas connection first connects to the flame ring or burner. This is the point where my wife makes her emergency exit and heads for the hills, despite my reassurances.
Here's the common misconception. The gas flame has for whatever reason, transferred to the mixing chamber and because it now resembles a flame thrower the natural and uninformed opinion is that the flame will now burn back down inside the LPG hose into the LPG cylinder causing a catastrophic explosion worthy of CNN news helicopter coverage and four fire trucks responding.
No it won't. Two things stop that from happening. Firstly, there is a net outflow of gas from your cylinder, which is why the incorrectly burning flame sounds so ferocious. Secondly, inside the gas hose is just gas (LPG); there is no air. LPG is flammable between 2% and 9% concentration in air. That's a very narrow flammability range. Have you ever tried to light your gas burner atop your stove and it seems like gas is pouring out at an alarming rate and your stove's piezo is clicking and sparking away but the gas still won't ignite?That's because the gas is too rich to burn. The same goes for your gas hose connecting your gas cylinder to your gas BBQ.
So what should you do? Calmly, determine which of your burners beneath your grill is the offending burner and switch it off. You'll hear the same 'pop' noise as the flame extinguishes now that the gas has ceased flowing. Then, turn the gas on again and ignite the burner in the usual fashion and continue cooking your lunch or dinner. Oh, you may also have to go and find your wife or friends from wherever they are hiding and reassure them that dinner is served.
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