This is known as a “flash-back”.
This is what you should do:
Turn the barbecue and gas cylinders OFF.
Allow the barbecue to cool and then check to see whether the burners have any obstructions such as spiders or insects.
Check that the Jetforce ignition is aligned properly with the neck of the burner and is not obstructed.
If the problem persists contact the local Garth Support Office in your region.