How is a bowser defined for the purposes of the regulations and what exemptions apply?

There is no definition of bowser. It is not a term recognised by ADR . For the purposes of this guidance a bowser is regarded as wheeled trailer fitted with a "tank" for carrying dangerous goods such as diesel or kerosene. They are commonly used for moving fuel to construction sites, forestry operations etc

Diesel and gas oil

Diesel and gas oil (UN 1202) are in scope up to flash point 100 deg C. Diesel/fuel oil is in TC 3, so up to 1000 litres may be carried in packages without application of much of the regulations (small load exemption).

Authorisation No 1 allows certain bowsers (carrying UN 1202 diesel /gas oil only) to be treated as if they are IBCs. The main conditions are

The bowser was made before 10th May 2004
The tank must not be "permanently fixed to a motor vehicle or trailer".
Maximum capacity 3000 litres
Designed for mechanical handling
It shall remain "safe and suitable"

The significance of this is that the bowser can be treated as a package and labelled accordingly, and that if it does not carry more than 1000 litres the small load exemptions apply.

There are many types of bowser which are certified as IBCs, and they may look like "tanks" so care needs to be taken in deciding what rules apply. If the bowser is a properly certified IBC it can be used to carry kerosene (inc jet fuel) and be treated as package.

In all other respects carriers of diesel are now subject to the standard ADR and CDG Regulations requirements.

Petrol

Bowsers are not commonly used for petrol, but they may be seen supporting aircraft operations or motor sports away from their usual bases. If the bowser is a tank vehicle meeting all the usual tank conditions there is no problem, but note the requirements for the towing vehicle to be FL certified. If the bowser is a certified IBC then packing provision IBC 02 applies. Note that special provision BB2 (part of IBC 02) requires that the actual vapour pressure of the petrol does not exceed the usual IBC criteria.

Towing vehicles

Bowsers are commonly towed by vans, 4 x 4s etc. Where the bowser is not an IBC (either conventionally or via authorisation no. 1), then the towing vehicle should meet the AT or FL standards as appropriate for the substance being carried (ADR 9.1.2.3)