Why does a flamethrower not explode?

To be more specific, why is it that when the flammable gas or liquid is pumped through the barrel and ignited at the end of the barrel, the flame does not spread backwards along the stream of liquid/gas into the fuel container and cause an explosion?

Is it simply because of the high pressure at which the fuel is pumped out? Or is there another reason, or a safety mechanism to prevent this from occurring?

Thanks!