ADR exempts completely private, non-work related carriage subject to some conditions (ADR 18.104.22.168(a)).
Work related carriage may be exempt or partially exempt in three ways:
Ancillary to main activity. ADR 22.214.171.124(c). This is a limited exemption which is discussed in Main Exemptions.
Up to 1 litre of petrol can be carried under the LQ provisions (see Main Exemptions).
The small load exemptions (Main Exemptions) will be applicable up to a total quantity of 333 litres (if other dangerous goods are carried the aggregation rules must be applied). The containers must be UN approved (see Packaging) and properly labelled (see Consignment Procedures). Typical 5 litre containers purchased from car accessory shops and garages may not be so approved.
A typical case would be the carriage of two or three jerricans in a van. Providing those cans are UN approved, marked UN 1203 and labelled with the flammable diamond, the only requirements are
Note: a typical steel jerry can might be marked 3A1/Y/170/**/GB/****
** is the year of manufacture and **** the packaging certificate number.
In this case no density figure is give after the "Y" which means it is suitable only for liquids with relative density ≤ 1.2 (petrol is typically 0.8 or less)