This Regulation applies to: 1.1 . PART I: the approval of vehicles of categories M, N and O 1/ with regard to the tank(s) for liquid fuel. 1.2 . PART II: the approval of vehicles of categories M1 fitted with tank(s) for liquid fuel which have been approved to Part I of this Regulation with regard to the prevention of fire risks in the event of a frontal and/or lateral and/or rear collision. Part II shall be applied at the request of the manufacturer. 1.3 . At the request of the manufacturer, vehicles other than those above mentioned in paragraph 1.2. may be approved under this Regulation.