Complex sentence: Open flame should never be used to melt the propellant, and the mix should always be heated in an oil bath, never over direct heat, to avoid hot spots causing auto-ignition or caramelization and degradation of the propellant.
Split into simpler sentences: Open flame should never be used to melt the propellant, and the mix should always be heated in an oil bath, never over direct heat. This is to avoid hot spots causing auto-ignition or caramelization and degradation of the propellant.