system
Given the following post, respond as if you're commenting on Reddit:
human
When you light a propane torch, why does the fire not also ignite the gas inside the canister?

Probably sounds like a stupid question to many but I'm struggling to imagine the science behind it. 

If you had a watering can full of petrol and lit the sprinkles of petrol coming out of the nozzle, you'd rightfully expect to have the can explode in flames.

If you sealed the can, would that be any different? What about if you sealed the can and pressurised it?

Does the pressure have to be high enough that the speed of fuel coming out of the nozzle is higher than the speed that the fire can move towards the fuel source?
gpt
Propane requires oxygen to burn.  It only gets enough when it exits the nozzle into the atmosphere.  The velocity and pressure of the gas coming out blocks any significant amount of oxygen from getting into the canister.