3.—(1) These Regulations shall apply to and in relation to the carriage of any dangerous substance, either in a road tanker or in a tank container carried on a vehicle, except where specified in Schedule 2.
(2) For the purposes of paragraph (1), a road tanker or a tank container carried on a vehicle shall be deemed to be engaged in the carriage of a dangerous substance throughout the period—
(a)in the case of a road tanker, from the commencement of loading it with the dangerous substance concerned for the purpose of carrying that substance on a road until the carrying tank of the road tanker and (where appropriate) any compartment of that carrying tank have been cleaned or purged so that any of the substance or its vapour which remains therein is not sufficient to create a risk to the health or safety of any person; or
(b)in the case of a tank container carried on a vehicle—
(i)(if the tank container has been loaded with the dangerous substance concerned before being placed on the vehicle) from the time when the tank container is placed on the vehicle for the purpose of carrying the dangerous substance on a road, or
(ii)(if the tank container has been placed on the vehicle before the commencement of loading) from the commencement of loading the tank container with the dangerous substance concerned for the purpose of carrying it by road,
until either—
(aa)the tank container is removed from the vehicle, or
(bb)the tank container and (where appropriate) any compartment of the tank container have been cleaned or purged so that any of the substance or its vapour which remains therein is not sufficient to create a risk to the health or safety of any person;
and, in either case, whether or not the vehicle is on a road at the material time.