Gas flare. Waste gas flaring from a column in a petro-chemical plant. The gas flare is used to burn off small amounts of natural gas which are within the crude oil. This method is used where the volume of gas is not sufficient to justify extraction for commercial use. In an oil refinery, crude oil is heated and passed through catalytic cracking towers to break up the heavy hydrocarbon molecules into lighter fragments. The resulting components from heavy industrial oils to light fuels (such as petrol or kerosene) or gas are separated out. The components called fractions may then be processed.