It is dangerous to try to light any flammable gas fueled device more than a few seconds after it has been turned on. This includes Bunsen burners, gas grills, gas stoves and ovens, gas powered lamps, basically any device fueled by propane or natural gas. The air does not actually become flammable, it is the spread of the gas fumes throughout the airspace around the appliance that are highly flammable and dangerous. Since gas fumes spread very quickly, an inadvertent flame or spark nearby could ignite the gas cloud and seriously burn someone. As a general rule, if a gas appliance doesn't light after about 5 seconds after the valve has been turned on, then the gas should be shut off. Wait for a couple of minutes for the escaped gas to clear before trying to light it again.