Excise classification of petroleum bitumen: packaging determines tariff heading and no extra duty on blown grade from duty paid straight grade. Petroleum bitumen, whether straight grade or air blown, is classifiable under the petroleum bitumen tariff headings according to whether it is packed in drums or supplied in bulk; air modified bitumen remains within the same heading as un blown bitumen. Where blown grade bitumen is produced from duty paid straight grade bitumen, no additional excise duty is payable on the blown grade product.